A   B   C   D   E   F   G   H   I   K   L   M   O   P   Q   R   S   T   U   V   W    

laser

Paper Title Other Keywords Page
MPPE080 Transversal Deflection of Electrons Moving in Parallel with Linearly Polarized Laser Beam and its Application electron, interaction-region, photon, polarization 4054
 
  • D.A. Zakaryan, D.K. Kalantaryan
    YSU, Yerevan
  • E.D. Gazazyan, K.A. Ispirian, M.K. Ispirian
    YerPhI, Yerevan
  The motion of electrons in linearly polarized laser beams in a finite length interaction region and after in a field free drift length is investigated. It is shown that in the interaction region the trajectory of the electrons is almost straight lines with very small oscillation weakly depending on the laser intensity. In the drift region the electrons acquire significant transversal deflection that allows to carry out the measurement of the length and longitudinal particle distribution of femtosecond bunches. The dependence of this deflection upon the electron energy, interaction region length, etc is studied. The principles of the construction of femtosecond oscilloscopes are discussed.  
 
MPPP046 Transient Resistive Wall Wake for Very Short Bunches vacuum, electron 2926
 
  • G.V. Stupakov
    SLAC, Menlo Park, California
  Funding: Work supported by U.S. Department of Energy, contract DE-AC03-76SF00515.

The catch up distance for the resistive wall wake in a round pipe is approximately equal to the square of the pipe radius divided by the bunch length. The standard formulae for this wake are applicable at distances much larger than the catch up distance. For extremely short bunches, considered recently by Zholents and Fawley in application for SASE (PRL, vol. 92, p. 224801), this formation length can be tens of meters. In this paper, we calculate the resistive wall wake for such a beam at distances compared with the catch up distance assuming a constant wall conductivity. We also discuss how the derivation can be modified to include the frequency dependence of the conductivity characteristic for very short wavelength.

 
 
MPPT041 Improvement of the Geometrical Stability of the LHC Cryodipoles when Blocking the Central Support Post dipole, vacuum, superconducting-magnet, alignment 2675
 
  • F. Seyvet, J. Beauquis, E.D. Fernandez Cano, J.-B. Jeanneret, A. Poncet, D. Tommasini
    CERN, Geneva
  The LHC will be composed of 1232 horizontally curved 16 meter long super-conducting dipole magnets cooled at 1.9K, supported within their vacuum vessel by three Glass Fiber Resin Epoxy (GFRE) support posts. The two support posts at the dipole extremities were initially designed free to slide longitudinally with respect to the vacuum vessel and the central support post was designed free to slide transversally. However the magnet shape did not retain the tight geometrical tolerances, of the order of fractions of mm, imposed by machine aperture and magnetic corrector centering requirements. Thereafter a modification to the supporting system, removing the initial transversal degree of freedom of the lower flange of the central support post with respect to the vacuum vessel, was designed and implemented. This paper describes the design of the magnet/cryostat interface with and without blockage of the central support post, analyzes the additional mechanical loads related to the modification and reviews the experimental results with respect to the requirements for beam aperture and magnetic corrector centering.  
 
MPPT077 Radiation of Electron in the Field of Plane Light Wave electron, radiation, scattering, photon 3997
 
  • A.Y. Zelinsky, I.V. Drebot, Yu.N. Grigor'ev, O.D. Zvonarjova
    NSC/KIPT, Kharkov
  • R. Tatchyn
    SLAC, Menlo Park, California
  In the work the process of electron interaction with field of oncoming light wave (Compton scattering) has been considered with methods of classical electrodynamics. As results of Lorenz equation integration the trajectories of electron motion in the wave field were derived. On the base of obtained results the expressions for electron radiation spectrum were produced.In the work dependences of spectrum shape on electron and photon beams parameters are analyzed.  
 
MOPB006 Frontiers of RF Photoinjectors emittance, gun, electron, cathode 530
 
  • M. Ferrario
    INFN/LNF, Frascati (Roma)
  New ideas have been recently proposed to achieve ultra-high brightness electron beams, as particularly needed in SASE-FEL experiments, and to produce flat beams, as required in linear colliders. Low emittance schemes already foreseen for split normal conducting photoinjectors have been applied to the superconducting case in order to produce high peak and high average beam brightness. RF compressor techniques have been partially confirmed by experimental results and more compact RF photoinjector designs including compression scheme are under development. Research and experiments in the flat beam production from a photoinjector as a possible alternative to damping rings are in progress. An overview of recent advancements and future perspectives in photoinjector beam physics is reported in this talk.  
 
MOPB008 Temporal E-Beam Shaping in an S-Band Accelerator electron, emittance, linac, diagnostics 642
 
  • H. Loos, D. Dowell, A. Gilevich, C. Limborg-Deprey
    SLAC, Menlo Park, California
  • M. Boscolo, M. Ferrario, M. Petrarca, C. Vicario
    INFN/LNF, Frascati (Roma)
  • J.B. Murphy, B. Sheehy, Y. Shen, T. Tsang, X.J. Wang, Z. Wu
    BNL, Upton, Long Island, New York
  • L. Serafini
    INFN-Milano, Milano
  Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contracts DE-AC02-98CH10886 and DE-AC03-76SF00515.

New short-wavelength SASE light sources will require very bright electron beams, brighter in some cases than is now possible. One method for improving brightness involves the careful shaping of the electron bunch to control the degrading effects of its space charge forces. We study this experimentally in an S-band system, by using an acousto-optical programmable dispersive filter to shape the photocathode laser pulse that drives the RF photoinjector. We report on the efficacy of shaping from the IR through the UV, and the effects of shaping on the electron beam dynamics.

 
 
MOPB010 Simulations and Experiments of Electron Beams Pre-Modulated at the Photocathode electron, simulation, radiation, space-charge 704
 
  • J.G. Neumann, R.B. Fiorito, P.G. O'Shea
    IREAP, College Park, Maryland
  • G.L. Carr, T.V. Shaftan, B. Sheehy, Y. Shen, Z. Wu
    BNL, Upton, Long Island, New York
  • W. Graves
    MIT, Middleton, Massachusetts
  • H. Loos
    SLAC, Menlo Park, California
  Funding: Work is supported by the Office of Naval Research, the Joint Technology Office, and the Department of Energy.

The University of Maryland and the Source Development Laboratory at Brookhaven National Laboratory have been collaborating on a project that explores the use of electron beam pre-modulation at the cathode to control the longitudinal structure of the electron beam. This technique could be applied to creating deliberate modulations which can lead to the generation of terahertz radiation, or creating a smooth profile in order to supress radiation. This paper focuses on simulations that explore some of the pre-modulated cases achieved experimentally.

 
 
TPAE001 Experiments on Wake Field Acceleration in Plasma and the Program of the Further Works in YerPhI electron, plasma, acceleration, vacuum 752
 
  • M.L. Petrosyan, M. Akopov, Y.A. Garibyan, E.M. Laziev, R.A. Melikian, Y. Nazaryan, M.K. Oganesyan, G.M. Petrosyan, L.M. Petrosyan, V.S. Pogosyan, G.K. Tovmasyan
    YerPhI, Yerevan
  Funding: ISTC, Project A-405.

The use of wake field acceleration basically is aimed to obtaining of high acceleration rate in comparison with traditional methods of acceleration. Meantime in the last years in YerPhI it was offered to use wake field acceleration for acceleration of high-current electron bunches on energy about 100 MeV. Experimental installation for research of formation of high-current electron bunches of the given configuration, necessary for wake field acceleration and acceleration of these bunches in plasma is created. The installation is intended for acceleration of electron bunches with a current of few tens amperes and up to energy 1-2 MeV. For excitation of wake waves in plasma the electron accelerator of direct action with use of high-voltage pulse transformer is used. Results of researches have revealed some properties of formation of high-current bunches, especially restrictions of a electron current because of space charge effects at sub-picoseconds duration of bunches. The basic parameters of the wake field acceleration project on energy about 100 MeV are given, taking into account results of researches on experimental installation.

 
 
TPAE002 The Project PLASMONX for Plasma Acceleration Experiments and a Thomson X-Ray Source at SPARC plasma, electron, acceleration, simulation 820
 
  • L. Serafini, F. Alessandria, A. Bacci, I. Boscolo, S. Cialdi, C. De Martinis, D. Giove, C. Maroli, M. Mauri, V. Petrillo, R. Pozzoli, M. Rome
    INFN-Milano, Milano
  • D. Alesini, M. Bellaveglia, S. Bertolucci, M.E. Biagini, R. Boni, M. Boscolo, M. Castellano, A. Clozza, G. Di Pirro, A. Drago, A. Esposito, M. Ferrario, L. Ficcadenti, D. Filippetto, V. Fusco, A. Gallo, G. Gatti, A. Ghigo, S. Guiducci, M. Incurvati, C. Ligi, F. Marcellini, M.  Migliorati, A. Mostacci, L. Palumbo, L. Pellegrino, M.A. Preger, R. Ricci, C. Sanelli, M. Serio, F. Sgamma, B. Spataro, A. Stecchi, A. Stella, F. Tazzioli, C. Vaccarezza, M. Vescovi, C. Vicario
    INFN/LNF, Frascati (Roma)
  • W. Baldeschi, A. Barbini, M. Galimberti, A. Giulietti, A. Gizzi, P. Koester, L. Labate, A. Rossi, P. Tommasini
    CNR/IPP, Pisa
  • R. Bonifacio, N. Piovella
    Universita' degli Studi di Milano, MILANO
  • U. Bottigli, B. Golosio, P.N. Oliva, A. Poggiu, S. Stumbo
    INFN-Cagliari, Monserrato (Cagliari)
  • F. Broggi
    INFN/LASA, Segrate (MI)
  • C.A. Cecchetti, D. Giulietti
    UNIPI, Pisa
  We present the status of the activity on the project PLASMONX, which foresees the installation of a multi-TW Ti:Sa laser system at the CNR-ILIL laboratory to conduct plasma acceleration experiments and the construction of an additional beam line at SPARC to develop a Thomson X-ray source at INFN-LNF. After pursuing self-injection experiments at ILIL, when the electron beam at SPARC will be available the SPARC laser system will be upgraded to TW power level in order to conduct either external injection plasma acceleration experiments and ultra-bright X-ray pulse generation with the Thomson source. Results of numerical simulations modeling the interaction of the SPARC electron beam and the counter-propagating laser beam are presented with detailed discussion of the monochromatic X-ray beam spectra generated by Compton backscattering: X-ray energies are tunable in the range 20 to 1000 keV, with pulse duration from 30 fs to 20 ps. Preliminary simulations of plasma acceleration with self-injection are illustrated, as well as external injection of the SPARC electron beam. The proposed time schedule for this initiative is finally shown, which is tightly correlated with the progress of the SPARC project.  
 
TPAE003 Numerical Study of Injection Mechanisms for Generation of Mono-Energetic Femtosecond Electron Bunch from the Plasma Cathode electron, plasma, injection, acceleration 859
 
  • T. Ohkubo, M. Uesaka, G. Zhidkov
    UTNL, Ibaraki
  Acceleration gradients of up to the order of 100GV/m and mono-energetic electron bunch up to 200MeV have recently been observed in several plasma cathode experiments. However, mechanisms of self-injection in plasma are not sufficiently clarified, presently. In this study, we carried out 2D PIC simulation to reveal the mechanisms of mono-energetic femtosecond electron bunch generation. We found two remarkable conditions for the generation: electron density gradient at vacuum-plasma interface and channel formation in plasma. Steep electron density gradient (~ plasma wave length) causes rapid injection and produces an electron bunch with rather high charge and less than 100fs duration. The channel formation guides an injected laser pulse and decreases the threshold of laser self-focusing, which leads to high electric field necessary for wave-breaking injection.  
 
TPAE005 Generation of Small Energy Spread Electron Beam from Self-Modulated Laser Wakefield Accelerator electron, plasma, ion, space-charge 976
 
  • C. Kim, I.S. Ko
    POSTECH, Pohang, Kyungbuk
  • N. Hafz, G.-H. Kim, H. Suk
    KERI, Changwon
  Funding: The authors are grateful for financial support from the Korean Ministry of Science and Technology through the Creative ResearchInitiatives Program.

Laser and plasma based accelerators have been studied for a next generation particle accelerator. Still, there are some problems to solve for real applications. For example, it has been observed that the accelerated electron beam from laser and plasma based accelerators has a 100% energy spread. Thus, the generation of small energy spread beam is an important issue in the laser and plasma based accelerator study. In this work, we introduce a method to control the energy spread. From a basic theory and simulation, it is found that the transverse electron distribution is changed from the Gaussian to a Maxwell-Boltzmann distribution and low energy electrons spread out more rapidly than high energy electrons as they propagate in vacuum. Thus, a small size collimator is installed to remove the small energy electrons and it is conformed that the small energy spread can be obtained from an experiment.

 
 
TPAE011 Fast Sweeping Device for Laser Bunch radiation, acceleration, focusing, electron 1219
 
  • A.A. Mikhailichenko
    Cornell University, Department of Physics, Ithaca, New York
  Electro-optical laser sweeping device deflects the head and tail of laser bunch into different frontal directions, so at some distance, the laser bunch becomes tilted with respect to forward direction. For sweeping of laser bunch having 300 ps duration up to 10 mrad, the voltage drop along the laser bunch must be ~10kV. Repetition rate desirable for this type of device used in laser acceleration or generation of secondary back-scattered electrons is up to 1 MHz. Details of the scheme described here.  
 
TPAE014 Optical Phase Locking of Modelocked Lasers for Particle Accelerators acceleration, vacuum, electron, controls 1389
 
  • T. Plettner, S. Sinha, J. Wisdom
    Stanford University, Stanford, Califormia
  • E.R. Colby
    SLAC, Menlo Park, California
  Funding: Department of Energy DE-FG03-97ER41043, DARPA DAAD19-02-1-0184.

Particle accelerators require precise phase control of the electric field through the entire accelerator structure. Thus a future laser driven particle accelerator will require optical synchronism between the high-peak power laser sources that power the accelerator. The precise laser architecture for a laser driven particle accelerator is not determined yet, however it is clear that the ability to phase-lock independent modelocked oscillators will be of crucial importance. We report the present status on our work to demonstrate long term phaselocking between two modelocked lasers to within one dregee of optical phase and describe the optical synchronization techniques that we employ.

 
 
TPAE015 Laser and Particle Guiding Micro-Elements for Particle Accelerators undulator, radiation, vacuum, focusing 1434
 
  • T. Plettner, R.M. Gaume, J. Wisdom
    Stanford University, Stanford, Califormia
  • J.E. Spencer
    SLAC, Menlo Park, California
  Funding: Department of Energy contract DE-AC02-76SF00515, DARPA contract DAAD19-02-1-0184.

Laser driven particle accelerators based on the current generation of lasers will require sub-micron control of the laser field as well as precise beam guiding. Hence the fabrication techniques that allow integrating both elements into an accelerator-on-chip format become critical for the success of such particle accelerators. Micromachining technology for silicon has been shown to be one such feasible technology in PAC2003 but with a variety of complications on the laser side. Fortunately, in recent years the fabrication of transparent ceramics has become an interesting technology that could be applied for laser-particle accelerators in several ways. We discuss this area, its advantages such as the range of materials it provides and various ways to implement it followed by some different test examples that have been considered. One important goal of this approach is an integrated system that could avoid the necessity of having to inject either laser or particle pulses into these structures.

 
 
TPAE016 The Argonne Wakefield Accelerator Facility: Status and Recent Activities electron, gun, klystron, cathode 1485
 
  • M.E. Conde, S.P. Antipov, W. Gai, C.-J. Jing, R. Konecny, W. Liu, J.G. Power, H. Wang, Z.M. Yusof
    ANL, Argonne, Illinois
  Funding: This work is supported by the U.S. Department of Energy, under contract No. W-31-109-ENG-38.

The Argonne Wakefield Accelerator Facility (AWA) is dedicated to the study of electron beam physics and the development of accelerating structures based on electron beam driven wakefields. In order to carry out these studies, the facility employs a photocathode RF gun capable of generating electron beams with high bunch charges (up to 100 nC) and short bunch lengths. This high intensity beam is used to excite wakefields in the structures under investigation. The wakefield structures presently under development are dielectric loaded cylindrical waveguides with operating frequencies of 7.8 or 15.6 GHz. The facility is also used to investigate the generation and propagation of high brightness electron beams. Presently under investigation, is the use of photons with energies lower than the work function of the cathode surface (Schottky-enabled photoemission), aimed at generating electron beams with low thermal emittance. Novel electron beam diagnostics are also developed and tested at the facility. The AWA electron beam is also used in laboratory-based astrophysics experiments; namely, measurements of microwave Cherenkov radiation and fluorescence of air. We report on the current status of the facility and present recent results.

 
 
TPAE022 Analytical and Numerical Calculations of Two-Dimensional Dielectric Photonic Band Gap Structures and Cavities for Laser Acceleration simulation, lattice, acceleration, plasma 1793
 
  • K.R. Samokhvalova, C. Chen
    MIT/PSFC, Cambridge, Massachusetts
  • B.L. Qian
    National University of Defense Technology, Hunan
  Funding: Research supported in part by Department of Energy, Office of High Energy Physics, Grant No. DE-FG02-95ER40919 and in part by Department of Defense, Joint Technology Office, under a subcontract with University of Arizona.

Dielectric photonic band gap (PBG) structures have many promising applications in laser acceleration. For these applications, accurate determination of fundamental and high order band gaps is critical. We present the results of our recent work on analytical calculations of two-dimensional (2D) PBG structures in rectangular geometry. We compare the analytical results with computer simulation results from the MIT Photonic Band Gap Structure Simulator (PBGSS) code, and discuss the convergence of the computer simulation results to the analytical results. Using the accurate analytical results, we design a mode-selective 2D dielectric cylindrical PBG cavity with the first global band gap in the frequency range of 8.8812 THz to 9.2654 THz. In this frequency range, the TM01-like mode is shown to be well confined.

 
 
TPAE026 Wakefields in a Dielectric Tube with Frequency Dependent Dielectric Constant resonance, impedance, plasma, damping 1916
 
  • R. Siemann, A. Chao
    SLAC, Menlo Park, California
  Funding: U.S. Department of Energy.

Dielectric laser driven accelerators could operate at a fundamental mode frequency where consideration must be given to the frequency dependence of the dielectric constant when calculating wakefields. Wakefields are calculated for a frequency dependence that arises from a single atomic resonance. Causality is considered, and the effect on the short range wakefield is calculated.

 
 
TPAE027 Calculations for Tera-Hertz (THz) Radiation Sources radiation, electron, simulation, scattering 1994
 
  • J.E. Spencer, Y.A. Hussein
    SLAC, Menlo Park, California
  Funding: This work was supported by the U.S. Department of Energy under contract DE-2-76SF00515.

We explore possibilities for THz sources from 0.3 - 30 THz. While still inaccessible, this broad gap is even wider for advanced acceleration schemes extending from X or, at most, W band RF at the low end up to CO2 lasers. While the physical implementations of these two approaches are quite different, both are proving difficult to develop so that even lower frequency, superconducting RF seems to be the currently preferred means. Similarly, the validity of modelling techniques varies greatly over this range of frequencies but generally mandates coupling Maxwell’s equations to the appropriate device transport physics for which there are many options. Here we calculate radiation from shaped transmission lines using finite-difference, time-domain (FDTD) simulations of Maxwell’s equations coupled to Monte-Carlo techniques for both the production and transport physics of short electron pulses. Examples of THz sources that demonstrate coherent interference effects will be discussed with the goal of optimizing on-chip THz radiators for different applications - ultimately including improved electron sources and accelerators.

 
 
TPAE028 Beam Dynamics Studies for a Laser Acceleration Experiment linac, gun, space-charge, emittance 2024
 
  • J.E. Spencer, E.R. Colby, R.J. Noble, D.T. Palmer, R. Siemann
    SLAC, Menlo Park, California
  Funding: Support of this work was under U.S. Dept. of Energy contract DE-AC02-76SF00515.

The NLC Test Accelerator at SLAC was built to address various beam dynamics issues for the Next Linear Collider. An S-Band RF gun, originally proposed for the NLCTA, is being installed together with a large-angle extraction line at 60 MeV. This is followed by a matching section, final focus and buncher for the laser acceleration experiment, E163. The laser-electron interaction area is followed by a broad range, high resolution spectrometer (HES) for electron bunch analysis. The RF gun is discussed in another paper. We discuss only the beam dynamics and high resolution analysis system at 6 MeV based on using Parmela and high-order Transport for bunch charges from 50 pC to 1 nC. Beyond the diagnostics, this system uses the emittance compensating solenoids and a low energy, high resolution spectrometer (LES) to help tune for best operating point and match to the linac. Optical symmetries in the design of the 25.5° extraction line provide 1:1 phase space transfer without linear dispersion or use of sextupoles for a large, 6D phase space volume and range of input conditions. Tolerances and tuning sensitivities (knobs) for certain parts of the system are discussed.

 
 
TPAE029 High-Harmonic Inverse Free-Electron-Laser Interaction at 800 nm electron, simulation, undulator, resonance 2113
 
  • C.M.S. Sears, E.R. Colby, B.M. Cowan, R. Siemann, J.E. Spencer
    SLAC, Menlo Park, California
  • R.L. Byer, T. Plettner
    Stanford University, Stanford, Califormia
  Funding: This work supported by Department of Energy contracts DE-AC03-76SF00515 (SLAC) and DE-FG03-97ER41043-II (Stanford).

The inverse Free Electron Laser (IFEL) interaction has recently been proposed and used as a short wavelength modulator forμbunching of beams for laser acceleration experiments*,**. These experiments utilized the fundamental of the interaction between the laser field and electron bunch. In the current experiment, we explore the higher order resonances of the IFEL interaction from a 3 period, 1.8 centimeter wavelength undulator with a picosecond, 0.25 mJ/pulse laser at 800 nm. The resonances are observed by adjusting the gap of the undulator while keeping the beam energy constant. We will also discuss diagnostics for obtaining beam overlap and statistical techniques used to account for machine drifts and analyze the data.

*W. D. Kimura, et. al., Phys. Rev. S.T. Acc. & Beams 4 101301 (2001). ** P. Musumeci, et. al., AAC 2004 Proceedings. Pg 170.

 
 
TPAE030 Distributed Bragg Coupler for Optical All-Dielectric Electron Accelerator coupling, electron, vacuum, radiation 2125
 
  • Z. Zhang, R.D. Ruth, S.G. Tantawi
    SLAC, Menlo Park, California
  Funding: Department of Energy.

A Bragg waveguide consisting of multiple dielectric layers with alternating index of refraction becomes an excellent option to form electron accelerating structure powered by high power laser sources. It provides confinement of a synchronous speed-of-light mode with extremely low loss. However, laser field can not be coupled into the structure collinearly with the electron beam. There are three requirements in designing input coupler for a Bragg electron accelerator: side-coupling, selective mode excitation, and high coupling efficiency. We present a side coupling scheme using a Bragg-grating-assisted input coupler to inject the laser into the waveguide. Side coupling is achieved by a second order Bragg grating with a period on the order of an optical wavelength. The phase matching condition results in resonance coupling thus providing selective mode excitation capability. The coupling efficiency is limited by profile mismatch between the outgoing beam and the incoming beam, which has normally, a Gaussian profile. We demonstrate a non-uniform distributed grating structure generating an outgoing beam with a Gaussian profile, therefore, increasing the coupling efficiency.

 
 
TPAE031 Simulations of Laser Pulse Coupling and Transmission Efficiency in Plasma Channels plasma, simulation, diagnostics, coupling 2179
 
  • R. Giacone, D.L. Bruhwiler, J.R. Cary, D.A. Dimitrov, P. Messmer
    Tech-X, Boulder, Colorado
  • E. Esarey, C.G.R. Geddes, W. Leemans
    LBNL, Berkeley, California
  Funding: Work supported by U.S. DOE under contracts DE-FG03-02ER83557, DE-FC02-01ER41178, DE-AC03-76SF00098, DE-FG03-95ER40926 and use of NERC supercomputer facilities.

Optical guiding of the laser pulse in a laser wakefield accelerator (LWFA) via plasma channels can greatly increase the interaction length and, hence, the maximun energy of trapped electrons.* Energy efficient coupling of laser pulses from vacuum into plasma channels is very important for optimal LWFA performance. We present 2D particle-in-cell simulations of this problem using the VORPAL code.** Some of the mechanisms considered are enhanced leakage of laser energy transversely through the channel walls, enhanced refraction due to tunneling ionization of neutral gas on the periphery of the gas jet, ionization of neutral gas by transverse wings of the laser pulse and effect of the pulse being off axis of the channel. Using power spectral diagnostics,*** we are able to differentiate between pump depletion and leakage from the channel. The results from our simulations show that for short (≈λp) plasma ramp, very little leakage and pump depletion is seen. For narrow channel walls and long ramps, leakage increases significantly.

*C. G. R. Gedes et al., Nature 431 (2004), p. 538. **C. Nieter and J. R. Cary, J. Comp. Phys. 196 (2004), p. 448.***D. A. Dimitrov et al., Proc. Advanced Accel. Concepts Workshop (2004).

 
 
TPAE032 Particle-in-Cell Simulations of Lower-Density CM-Scale Capillary Channels plasma, simulation, electron, vacuum 2248
 
  • P. Messmer, D.L. Bruhwiler, D.A. Dimitrov, P. Stoltz
    Tech-X, Boulder, Colorado
  • E. Esarey, C.G.R. Geddes, W. Leemans
    LBNL, Berkeley, California
  Funding: This work is funded by DOE under contracts DE-FC02-01ER41178, DE-FG02-04ER84097, DE-AC03-76SF00098 and DE-FG03-95ER40926, including the SciDAC Accelerator Project and use of NERSC.

Capillary channels of cm-length and at plasma density low compared to gas jets are promising setups for low noise laser wakefield acceleration. Computationally, however, the large discrepancy of the length scales of the plasma and the laser are a big challenge. Methods are therefore sought that relax the need to concurrently resolve both length scales. Moving windows allow to reduce the size of the computational box to a few plasma wave-lengths, which can already be a big gain compared to the full length of the capillary. On the other hand, average methods allow to relax the constraint to resolve the laser wavelength. These methods split the laser induced current into a fast varying part and a slowly varying envelope. The average over the fast timescales is performed in a semi analytic way, leaving the evolution of the envelope to be modeled. Such an envelope model is currently being incorporated into the VORPAL code.* Preliminary results show considerable time savings compared to fully resolved simulations. The status of this ongoing work will be presented.

*C. Nieter and J. R. Cary, J. Comp. Phys. 196 (2004), p. 448.

 
 
TPAE033 Experimental and Numerical Studies of Particle Acceleration by an Active Microwave Medium acceleration, simulation, resonance, radiation 2275
 
  • P. Schoessow
    Tech-X, Boulder, Colorado
  • A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio
  There has been considerable theoretical work on the so-called PASER concept, in which a particle beam is accelerated directly by absorbing energy from an active medium, analogous to the amplification of an optical signal in a laser. Use of an active microwave (maser) medium would have the advantage of requiring relaxed beam quality (mm vs. nm characteristic beam dimensions). Recent work using electron paramagnetic resonance (EPR) techniques has demonstrated activity in the microwave regime (i.e. negative imaginary part of the magnetic susceptibility) for a class of organic compounds. A solution of fullerene (C60) in a liquid crystal solvent has been reported in the literature to possess a maser transition in the X-band region. An external DC magnetic field is required to obtain the effect; the frequency of the maser transition is adjustable by varying the magnetic field strength. We will report on the development of numerical and laboratory tools to evaluate the use of this material for accelerator applications, and evaluate the feasibility of an accelerating structure based on an active microwave medium.  
 
TPAE034 Developing a Multi-Timescale PIC Code for Plasma Accelerators plasma, simulation, betatron 2324
 
  • S. Deng, T.C. Katsouleas, X. Wang
    USC, Los Angeles, California
  • W.B. Mori
    UCLA, Los Angeles, California
  Funding: DOE: DE-FG02-92ER40745, DOE-SCIDAC: DE-FC02-01ER41192.

An idea for advancing beam and plasma particles with different time scales in a full PIC model of plasma accelerators is proposed. Because beam particles usually respond much slower than plasma particles, large time steps can be used to update beam particles to save computation time. In this paper, we will describe how to apply this multi-timescale method in a particle-in-cell (PIC) [1] code OSIRIS [2]. Simulation results for SLAC E164 [3] experimental parameters are given and show a high degree of accuracy while gaining a factor of 4-6 in computing time. The limitations of this method are also studied. The maximum time saving is determined by driver beam energy and size of simulation box.

 
 
TPAE037 Simulation of the Laser Acceleration Experiment at the Femilab/NICADD Photoinjector Laboratory acceleration, electron, vacuum, interaction-region 2503
 
  • P. Piot
    Fermilab, Batavia, Illinois
  • A.C. Melissinos, R. Tikhoplav
    Rochester University, Rochester, New York
  The possibility of using a laser to accelerate electrons in a waveguide structure with dimension much larger than the laser wavelength was first proposed by Pantell [NIM A 393 pg 1-5 (1997)] and investigated analytically by M. Xie [reports LBNL-40558 (1997) and LBNL-42055 (1998) available from LBNL Berkeley]. In the present paper we present the status of our experimental plan to demonstrate the laser interaction on an electron beam with initial momentum of 40-50 MeV/c. A laser (λ=1.06 micron) operating on the TM*01 mode has been developed. The large wavenumber (k~6x106 m-1) together with the initial low electron momentum poses a serious problem for efficient acceleration. In the present paper, we present start-to-end simulations of the laser acceleration experiment as foreseen to be installed in the upgraded Femilab/NICADD photoinjector laboratory.  
 
TPAE043 Production of Terahertz Seed Radiation for FEL/IFEL Microbunchers for Second Generation Plasma Beatwave Experiments at Neptune radiation, electron, plasma, beat-wave 2780
 
  • J.E. Ralph, C. Joshi, J.B. Rosenzweig, C. Sung, S. Tochitsky
    UCLA, Los Angeles, California
  Funding: This work was supported by the DOE Contract No. DE-FG03-92ER40727.

To achieve phase locked injection of short electron bunches in a plasma beatwave accelerator, the Neptune Laboratory will utilize microbunching in an FEL or IFEL system. These systems require terahertz (THz) seed radiation on the order of 10 kW for the FEL and 10 MW for the IFEL bunchers. We report results of experiments on THz generation using nonlinear frequency mixing of CO2 laser lines in GaAs. A two-wavelength laser beam was split and sent onto a 2.5 cm long GaAs crystal cut for noncollinear phase matching. Low power measurements achieved ~1 W of 340 ?m radiation using 200 ns CO2 pump pulses with wavelengths 10.3?m and 10.6?m. We also demonstrated tunability of difference frequency radiation, producing 240?m by mixing two different CO2 laser lines. By going to shorter laser pulses and higher intensities, we were able to increase the conversion efficiency while decreasing the surface damage threshold. Using 200ps pulses we produced ~2 MW of 340 ?m radiation. Future studies in this area will focus on developing large diameter Quasi-Phase matched structures for production of high power THz radiation.

 
 
TPAE044 Terahertz IFEL/FEL Microbunching for Plasma Beatwave Accelerators electron, undulator, radiation, plasma 2812
 
  • C. Sung, C.E. Clayton, C. Joshi, P. Musumeci, C. Pellegrini, J.E. Ralph, S. Reiche, J.B. Rosenzweig, S. Tochitsky
    UCLA, Los Angeles, California
  Funding: Work supported by the U.S. Department of Energy under Contract No. DE-FG03-92ER40727.

In order to obtain monoenergetic acceleration of electrons, phase-locked injection using electron microbunches shorter than the accelerating structure is necessary. For a laser-driven plasma beatwave accelerator experiment, we propose to microbunch the electrons by interaction with terahertz (THz) radiation in an undulator via two mechanisms– free electron laser (FEL) and inverse free electron laser (IFEL). Since the high power FIR radiation will be generated via difference frequency mixing in GaAs by the same CO2 beatwave used to drive the plasma wave, electrons could be phase-locked and pre-bunched into a series of microbunches separated with the same periodicity. Here we examine the criteria for undulator design and present simulation results for both IFEL and FEL approaches. Using different CO2 laser lines, electrons can be microbunched with different periodicity 300 – 100 mm suitable for injection into plasma densities in the range 1016 – 1017 cm-3, respectively. The requirement on the THz radiation power and the electron beam qualities are also discussed.

 
 
TPAE047 Parameters Optimization for a Novel Vacuum Laser Acceleration Test at BNL-ATF electron, acceleration, vacuum, simulation 2959
 
  • L.H. Shao, D. Cline, F. Zhou
    UCLA, Los Angeles, California
  Funding: U.S. DOE.

This paper presents a new VLA theory model which has revealed that the injection electrons with low energy and small incident angle relative to the laser beam are captured and significantly accelerated in a strong laser field. For the further step for verifying the novel-VLA mechanics, we propose to use the BNL-ATF Terawatt CO2 laser and a high-brightness electron beam to carry out a proof-of-principle beam experiment. Experiment setup including the laser injection optics and electron extraction system and beam diagnostics is presented. Extensive optimized simulation results with ATF practical parameters are also presented, which shows that even when the laser intensity is not very high, the net energy gain still can be seen obviously. This could be prospect for a new revolution of vacuum laser acceleration.

 
 
TPAE049 The UCLA/SLAC Ultra-High Gradient Cerenkov Wakefield Accelerator Experiment electron, radiation, simulation, photon 3067
 
  • M.C. Thompson, H. Badakov, J.B. Rosenzweig, G. Travish
    UCLA, Los Angeles, California
  • M.J. Hogan, R. Ischebeck, R. Siemann, D.R. Walz
    SLAC, Menlo Park, California
  • P. Muggli
    USC, Los Angeles, California
  • A. Scott
    UCSB, Santa Barbara, California
  • R.B. Yoder
    ,
  Funding: Work Supported by U.S. Dept. of Energy grant DE-FG03-92ER40693.

An experiment is planned to study the performance of dielectric Cerenkov wakefield accelerating structures at extremely high gradients in the GV/m range. This new UCLA/SLAC collaboration will take advantage of the unique SLAC FFTB electron beam and its demonstrated ultra-short pulse lengths and high currents (e.g., sz = 20 μm at Q = 3 nC). The electron beam will be focused down and sent through varying lengths of fused silica capillary tubing with two different sizes: ID = 200 μm / OD = 325 μm and ID = 100 μm / OD = 325 μm. The pulse length of the electron beam will be varied in order to alter the accelerating gradient and probe the breakdown threshold of the dielectric structures. In addition to breakdown studies, we plan to collect and measure coherent Cerenkov radiation emitted from the capillary tube to gain information about the strength of the accelerating fields. Status and progress on the experiment are reported.

 
 
TPAE053 Near-GeV Electron Beams from the Laser Wakefield Accelerator in the “Bubble” Regime electron, plasma, simulation, vacuum
 
  • N. Hafz, H. Suk
    KERI, Changwon
  • D.-K. Ko, J. Lee
    APRI-GIST, Gwangju
  Funding: This research was funded by the Korean Ministry Science and Technology through the Creative Research Initiative (CRI) Program.

This Communication describes a 2D-PIC simulation of a laser wakefield accelerator in which an ultrashort, petawatt-class laser is focused and propagated through an underdense preformed plasma. We are looking at the phase-spaces of a large number of background plasma electrons that are accelerated to very high energies by the laser-induced plasma bubble. The result shows the possibility of generating a GeV-level electron beam in a few millimeters plasma size. As a future work, we will use a 500 TW laser system, that is under construction at APRI-GIST in Korea, for laser-plasma based accelerator researches to which the current simulation is relevant.

 
 
TPAE054 Ultraintense and Ultrashort Laser Pulses from Raman Amplification in Plasma for Laser-Plasma Accelerators simulation, plasma, electron, resonance 3274
 
  • M.S. Hur, G.-H. Kim, H. Suk
    KERI, Changwon
  • A.E. Charman, R.R. Lindberg, J.S. Wurtele
    LBNL, Berkeley, California
  Funding: Korea Electrotechnology Research Institute, Korea; Creative Research Initiatives, Korea.

We present analysis and simulations of kinetic effects in the Raman pulse amplification in plasma. An ultraintense and ultrashort laser pulse is a very essential part in an advanced acceleration scheme using laser and plasma. To make strong pulses, a noble scheme of using Raman backscatter in plasma was proposed and has been studied intensively.* The Raman amplification in plasma does not have a restriction in material damage threshold. However, for the new amplifier to be a promising alternative of the CPA technique, more extensive studies on various issues are required. One of the fundamental issues is the electron kinetic effect such as particle trapping or wavebreaking. We present a theoretical analysis of the kinetic effect; a new kinetic term is derived to be added to the fluid model and the effect of the new term is verified by averaged-PIC (aPIC)** simulations. Various one dimensional and semi-two dimensional aPIC simulations of pulse amplification are presented. We discuss the future application of the Raman scheme to upgrading the laser pulse of the Center of Advanced Accelerator in KERI, which are currently 2 TW and 700 fs, into a few more TW and less than 100 fs.

*V. M. Malkin, G. Shvets, and N. J. Fisch, Phys. Rev. Lett. vol. 82, 4448 (1999).**M. S. Hur, G. Penn, J. S. Wurtele, and R. Lindberg, Phys. Plasmas vol. 11, 5204 (2004).

 
 
TPAE056 Acceleration of Charged Particles by High Intensity Few-Cycle Laser Pulses electron, acceleration, plasma, undulator 3337
 
  • U. Schramm, F. Gruener, D. Habs, J. Schreiber
    LMU, München
  • S. Becker, M. Geissler, S. Karsch, F. Krausz, J. Meyer-ter-Vehn, K. Schmid, G. Tsakiris, L. Veisz, K. Witte
    MPQ, Garching, Munich
  Funding: Funded by the german DFG (TR18) and BMBF (06ML184).

Only recently a breakthrough in laser plasma acceleration has been achieved with the observation of intense (nC) mono-energetic (10% relative width) electron beams in the 100MeV energy range.* Above the wave-breaking threshold the electrons are trapped and accelerated in a single wake of the laser pulse, called bubble, according to PIC simulations.** However, pulse energis varied from shot-to-shot in the experiments. At the MPQ Garching we prepare the stable acceleration of electrons by this bubble regime by the use of 10TW few-cycle laser pulse. As the pulse lenght of 5-10fs remains below the plasma period also at higher plama densities, we expect the scheme to be more stable and efficient. The status of the experiment will be reported. Further, we exploit a colliding beam setup existing at the Jena multi TW laser system for the investigation of the positron generation in the electron-electron collision or in the collision of hard X-rays resulting from Thomson backscattering. The presentation of results on heavy ion acceleration from laser-irradiated thin foils will round up this summary of the Munich activities.

*See ‘dream beams' in Nature 431 (2004).**A. Pukhov, J. Meyer-ter-Vehn, Appl. Phys. B 74, 355 (2002).

 
 
TPAE057 A Multibunch Plasma Wakefield Accelerator plasma, electron, simulation, background 3384
 
  • E.K. Kallos, T.C. Katsouleas, P. Muggli
    USC, Los Angeles, California
  • M. Babzien, I. Ben-Zvi, K. Kusche, P.I. Pavlishin, I. Pogorelsky, V. Yakimenko
    BNL, Upton, Long Island, New York
  • W.D. Kimura
    STI, Washington
  • F. Zhou
    UCLA, Los Angeles, California
  We investigate a plasma wakefield acceleration scheme where a train of electron microbunches feeds into a high density plasma. When the microbunch train enters such a plasma that has a corresponding plasma wavelength equal to the microbunch separation distance, a strong wakefield is expected to be resonantly driven to an amplitude that is at least one order of magnitude higher than that using an unbunched beam. PIC simulations have been performed using the beamline parameters of the Brookhaven National Laboratory Accelerator Test Facility operating in the configuration of the STELLA inverse free electron laser (IFEL) experiment. A 65 MeV electron beam is modulated by a 10.6 um CO2 laser beam via an IFEL interaction. This produces a train of ~90 microbunches separated by the laser wavelength. In this paper, we present both a simple theoretical treatment and simulation results that demonstrate promising results for the multibunch technique as a plasma-based accelerator.  
 
TPAE060 Planned Enhanced Wakefield Transformer Ratio Experiment at Argonne Wakefield Accelerator simulation, electron, linac, pick-up 3487
 
  • A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio
  • P.A. Avrakhov
    LPI, Moscow
  • W. Gai, C.-J. Jing, R. Konecny, J.G. Power
    ANL, Argonne, Illinois
  Funding: U.S. Department of Energy.

In this paper, we present a preliminary experimental study of a wakefield accelerating scheme that uses a carefully spaced and current ramped electron pulse train to produce wakefields that increases the transformer ratio much higher than 2. A dielectric structure was designed and fabricated to operate at 13.625 GHz with dielectric constant of 15.7. The structure will be initially excited by two beams with first and second beam charge ratio of 1:3. The expected transformer ratio is 3 and the setup can be easily extend to 4 pulses which leads to a transformer ratio of more than 6. The dielectric structure cold test results show the tube is within the specification. A set of laser splitters was also tested to produce ramped bunch train of 2 - 4 pulses. Overall design of the experiment and initial results will be presented.

 
 
TPAE063 Observation of Superposition of Wake Fields Generated by Electron Bunches in a Dielectric-Lined Waveguide electron, acceleration, gun, vacuum 3609
 
  • S.V. Shchelkunov, T.C. Marshall
    Columbia University, New York
  • M. Babzien
    BNL, Upton, Long Island, New York
  • J.L. Hirshfield, M.A. LaPointe
    Yale University, Physics Department, New Haven, CT
  Funding: Research supported by the Department of Energy, Division of High Energy Physics.

We report results from an experiment, done at the Accelerator Test Facility, Brookhaven National Laboratory, which demonstrates the successful superposition of wake fields excited by 50MeV bunches which travel ~50cm along the axis of a cylindrical waveguide which is lined with alumina. Wake fields from two short (5-6psec) 0.15-0.35nC bunches are superimposed and the energy losses of each bunch are measured as the separation between the bunches is varied so as to encompass approximately one wake field period (~21cm). A spectrum of 40 TM0m eigenmodes is excited by the bunch. A substantial retarding wake field (2.65MV/m×nC for just the first bunch) is developed because of the short bunches and the narrow vacuum channel diameter (3mm) through which they move. The energy loss of the second bunch exhibits a narrow resonance with a 4mm (13.5psec) footprint. This experiment may be compared with a related experiment reported by a group at the Argonne National Laboratory where a much weaker wake field (~0.1MV/m×nC for the first bunch) having ~10 eigenmodes was excited by a train of much longer bunches,* and the bunch spacing was not varied.

*J. G. Power, M. E. Conde, W. Gai, R. Konecny, and P. Schoessow, Phys. Rev. ST Accel. Beams 3, 101302 (2000).

 
 
TPAE064 Externally Controlled Injection of Electrons by a Laser Pulse in a Laser Wakefield Electron Accelerator electron, injection, plasma, scattering 3644
 
  • S.-Y. Chen, C.-L. Chang, W.-T. Chen, T.-Y. Chien, C.-H. Lee, J.-Y. Lin, J. Wang
    IAMS, Taipei
  Funding: National Science Council, Taiwan

Spatially and temporally localized injection of electrons is a key element for development of plasma-wave electron accelerator. Here we report the demonstration of two different schemes for electron injection in a self-modulated laser wakefield accelerator (SM-LWFA) by using a laser pulse. In the first scheme, by implementing a copropagating laser prepulse with proper timing, we are able to control the growth of Raman forward scattering and the production of accelerated electrons. We found that the stimulated Raman backward scattering of the prepulse plays the essential role of injecting hot electrons into the fast plasma wave driven by the pump pulse. In the second scheme, by using a transient density ramp we achieve self-injection of electrons in a SM-LWFA with spatial localization. The transient density ramp is produced by a prepulse propagating transversely to drill a density depression channel via ionization and expansion. The same mechanism of injection with comparable efficiency is also demonstrated with a transverse plasma waveguide driven by Coulomb explosion.

 
 
TPAE066 Robust Autoresonant Excitation in the Plasma Beat-Wave Accelerator: A Theoretical Study plasma, resonance, electron, beat-wave 3688
 
  • A.E. Charman, R.R. Lindberg, J.S. Wurtele
    UCB, Berkeley, California
  • L. Friedland
    The Hebrew University of Jerusalem, The Racah Institute of Physics, Jerusalem
  Funding: Division of High Energy Physics, U.S. Department of Energy, DARPA, U.S. Department of Defense.

A modified version of the Plasma Beat-Wave Accelerator scheme is introduced and analyzed, which is based on autoresonant phase-locking of the nonlinear Langmuir wave to the slowly chirped beat frequency of the driving lasers via adiabatic passage through resonance. This new scheme is designed to overcome some of the limitations of previous approaches, namely relativistic detuning and nonlinear modulations in the driven Langmuir wave amplitude, and sensitivity to frequency mismatch from density fluctuations. As in previous schemes, instabilities of the ionic background ultimately limit the useful interaction time, but nevertheless peak electric fields approaching the wave-breaking limit seem readily attainable. Compared to traditional approaches, the autoresonant scheme achieves larger accelerating electric fields for given laser intensity; the plasma wave excitation is more robust to variations in plasma density; it is largely insensitive to the choice of chirp rate, provided that chirping is sufficiently slow; and the quality and uniformity of the resulting plasma wave and its suitability for accelerator applications may be superior.

 
 
TPAE067 Femtosecond Electron Diffraction and its Application for Beam Characterization at the PAL electron, gun, emittance, space-charge 3721
 
  • D. Xiang
    TUB, Beijing
  • H. Ihee
    KAIST, Daejeon
  • I.S. Ko, S.J. Park
    PAL, Pohang, Kyungbuk
  • X.J. Wang
    BNL, Upton, Long Island, New York
  Electron diffraction is widely used in electron microscopy to obtain ultrahigh magnification factor, or crystallography to determine the internal structure of the molecule. High energy electron (MeV) has been used to probe the solid state thick sample, now being explored for femto-second electron diffraction (FED) to determine the transient structure of the molecule. We are proposing to perform FED using a photocathode RF gun at the Pohang Accelerator Laboratory (PAL), and develop an advanced electron beam diagnostic tool based on the electron diffraction. In this paper we will study how the diffraction pattern can be used to extract the information on the beam’s divergence. With a well-known sample, such as aluminum foil, whose internal structure is predetermined, the diffraction pattern for both single electron and the electron beam with a given divergence distribution can be calculated. Our proposed technique shows great potential of electron diffraction in beam divergence characterization. An experiment to verify the practicality of this method is under preparation and will be carried out at the proposed high brightness R&D facility at the PAL) in the near future.  
 
TPAP030 Tevatron Alignment Issues 2003-2004 dipole, quadrupole, alignment, closed-orbit 2146
 
  • J.T. Volk, J. Annala, L. Elementi, N.M. Gelfand, K. Gollwitzer, J.A. Greenwood, M.A. Martens, C.D. Moore, A. Nobrega, A.D. Russell, T. Sager, V.D. Shiltsev, R. Stefanski, M.J. Syphers, G. Wojcik
    Fermilab, Batavia, Illinois
  Funding: U.S. Department of Energy under contract No. DE-AC02-76CH03000.

It was observed during the early part of Run II that dipole corrector currents in the Tevatron were changing over time. Measurement of the roll for dipoles and quadrupoles confirmed that there was a slow and systematic movement of the magnets from their ideal position. A simple system using a digital protractor and laptop computer was developed to allow roll measurements of all dipoles and quadrupoles. These measurements showed that many magnets in the Tevatron had rolled more than 1 milli-radian. To aid in magnet alignment a new survey network was built in the Tevatron tunnel. This network is based on the use of free centering laser tracker. During the measurement of the network coordinates for all dipole, quadrupole and corrector magnets were obtained. This paper discusses roll measurement techniques and data, the old and new Tevatron alignment network.

 
 
TPAT001 An Ultra-Bright Pulsed Electron Beam with Low Longitudinal Emittance electron, brightness, emittance, ion 770
 
  • M.S. Zolotorev, E. D. Commins, P. Denes, Z. Hussain, G.V. Lebedev, S.M. Lidia, D. Robin, F. Sannibale, R.W. Schoenlein, R. A. Vogel, W. Wan
    LBNL, Berkeley, California
  • S.A. Heifets
    SLAC, Menlo Park, California
  Funding: Work supported by the U.S. Department of Energy under Contract No. DE-AC03-76SF00098.

We describe a novel scheme for an electron source in the 10 - 100 eV range with the capability of approaching the brightness quantum-limit and of lowering the effective temperature of the electrons orders of magnitude with respect to existing sources. Such a device can open the way for a wide range of novel applications that utilize angstrom-scale spatial resolution and ?eV-scale energy resolution. Possible examples include electron microscopy, electron holography, and investigations of dynamics on a picosecond time scale using pump-probe techniques. In this paper we describe the concepts for such a source including a complete and consistent set of parameters for the construction of a real device based on the presented scheme.

 
 
TPAT034 Manipulations of Double Electron Beams within One RF Period for Seeded SM-LWFA Experiment electron, emittance, plasma, linac 2312
 
  • F. Zhou, D. Cline
    UCLA, Los Angeles, California
  • M. Babzien, V. Yakimenko
    BNL, Upton, Long Island, New York
  • W.D. Kimura
    STI, Washington
  Funding: Work supported by U.S. DOE.

Although seeded SM-LWFA only requires one electron beam to initiate the laser wakefield, it would be highly desirable to have a second electron beam traveling after the first one to probe the accelerated electrons. To create and preserve significant amount of wakefield in the STELLA SM-LWFA experiment, the first e-beam needs to be tiny (<40 microns FWHM) in size and short in length within the plasma. To probe the wakefield which is damped within 10 ps for certain plasma density, the separation between the first and second beams needs to be within one RF period and the second e-beam must have smaller energy spread and smaller size. Design of double beams in one RF period to meet the strict requirements and the preliminary beam study at BNL-ATF facility are presented. The scheme of double beams with ATF bunch compressor is also discussed.

 
 
TOAB005 4GLS and the Energy Recovery Linac Prototype Project at Daresbury Laboratory linac, gun, beam-transport, undulator 431
 
  • E.A. Seddon, M.W. Poole
    CCLRC/DL, Daresbury, Warrington, Cheshire
  4GLS is a novel next generation proposal for a UK national light source to be sited at Daresbury Laboratory. It is based on a superconducting energy recovery linac (ERL) with capabilities for both high average current spontaneous photon sources (undulators and bending magnets) and high peak current free electron lasers. Key features of the proposal are a high gain, seeded FEL amplifier to generate XUV radiation and the prospect of advanced dynamics work arising from its unique combinations of sources and its femtosecond pulse structure. To meet the challenging accelerator technology involved, a significant R&D programme has commenced and a major part of this is a 35 MeV demonstrator, the ERL Prototype (ERLP), currently under construction. This paper summarises the 4GLS design activities, describes the ERLP in detail and explains the 4GLS project status and plans.  
 
TOAB007 Femtoslicing in Storage Rings electron, radiation, photon, undulator 590
 
  • S. Khan
    BESSY GmbH, Berlin
  Funding: Funded by the Bundesministerium für Bildung und Forschung and by the Land Berlin.

The generation of ultrashort synchrotron radiation pulses by laser-induced energy modulation of electrons and their subsequent transverse displacement, now dubbed "femtoslicing," was demonstrated at the Advanced Light Source in Berkeley. More recently, a femtoslicing user facility was commissioned at the BESSY storage ring in Berlin, and another project is in progress at the Swiss Light Source. The paper reviews the principle of femtoslicing, its merits and shortcomings, as well as the variations of its technical implementation. Various diagnostics techniques to detect successful laser-electron interaction are discussed and experimental results are presented.

 
 
TOAD001 Techniques for Pump-Probe Synchronisation of Fsec Radiation Pulses electron, photon, booster, undulator 59
 
  • H. Schlarb
    DESY, Hamburg
  The increasing interest on the production of ultra-short photon pulses in future generations of Free-Electron Lasers operating in the UV, VUV or X-ray regime demands new techniques to reliably measure and control the arrival time of the FEL-pulses at the experiment. For pump-probe experiments using external optical lasers the desired synchronisation is in the order of tens of femtoseconds, the typical duration of the FEL pulse. Since, the accelerators are large scale facilities of the length of several hundred meters or even kilometers, the problem of synchronisation has to be attacked twofold. First, the RF acceleration sections upstream of the magnetic bunch compressors need to be stabilised in amplitude and phase to high precision. Second, the remain electron beam timing jitter needs to be determined with femtosecond accuracy for off-line analysis. In this talk, several techniques using the electron or the FEL beam to monitor the arrival time are presented, and the proposed layout of the synchronisation system for the European XFEL towards the 10 fsec regime.  
 
TOPB001 Methods of Attosecond X-Ray Pulse Generation electron, undulator, wiggler, radiation 39
 
  • A. Zholents
    LBNL, Berkeley, California
  Funding: This work was supported by the Director, Office of Science of the U. S. Department of Energy under Contract No. DE-AC03-76SF00098.

Our attitude towards attosecond x-ray pulses has changed dramatically over the past several years. Not long ago x-ray pulses with a duration of a few hundred attoseconds were just science fiction for most of us, but they are already a tool for some researchers in present days. Breakthrough progress in the generation of solitary soft x-ray pulses of attosecond duration has been made by the laser community. Following this lead, people in the free electron laser community have begun to develop new ideas on how to generate attosecond x-ray pulses in the hard x-ray energy range. In this report I will review some of these ideas.

 
 
TOPB003 Progress in Large-Scale Femtosecond Timing Distribution and RF-Synchronization polarization, space-charge, electron, feedback 284
 
  • F.X. Kaertner, H. Byun, J. Chen, F J. Grawert, F.O. Ilday, J. Kim, A. Winter
    MIT, Cambridge, Massachusetts
  For future advances in accelerator physics in general and seeding of free electron lasers (FELs) in particular, precise synchronization between low-level RF-system, photo-injector laser, seed radiation as well as potential probe lasers at the FEL output is required. We propose a modular system based on optical pulse trains from mode-locked lasers for timing distribution and timing information transfer in the optical domain to avoid detrimental effects due to amplitude to phase conversion in photo detectors. Synchronization of various RF- and optical sub-systems with femtosecond precision over distances of several hundred meters can be achieved. First experimental results and limitations of the proposed scheme for timing distribution are discussed.  
 
TPPE019 Laser Ion Source Development for ISOL Systems at RIA ion, ion-source, target, radiation 1640
 
  • Y. Liu, C. Baktash, J.R. Beene, H. Z. Bilheux, C.C. Havener, H.F. Krause, D.R. Schultz, D.W. Stracener, C.R. Vane
    ORNL, Oak Ridge, Tennessee
  • K. Brueck, Ch. Geppert, T. Kessler, K. Wendt
    Johannes Gutenberg University Mainz, Mainz
  Funding: Managed by UT-Battelle, LLC, for the U.S. DOE under contract DE-AC05-00OR22725.

The isobaric purity of radioactive ion beams (RIBs) is of crucial importance to many experiments. Laser ion sources based on resonant photoionization have already proved to be of great value at existing ISOL RIB facilities. In these ion sources, ions of a selected isotope are produced by laser radiation via stepwise atomic resonant excitations followed by ionization in the last transition. Because each element has its own unique atomic energy levels, the resonant photoionization process can provide elemental selectivity of nearly 100%. We have initiated a research effort to develop a prototype laser ion source with the potential to achieve the high selectivity and high efficiency required for research with ISOL-generated RIBs at the Rare Isotope Accelerator (RIA). A pilot experiment has been conducted to demonstrate resonant photoionization of three atomic species using all-solid-state tunable Ti:Sapphire lasers. Three Ti:Sapphire lasers were provided by the University of Mainz and used in the experiment for three-photon resonant ionization of the elements. Laser generated Sn, Ni, and Ge ions have been successfully obtained in a hot-cavity laser ion source with overall efficiencies of 22%, 2.7%, and 3.3%, respectively.

 
 
TPPE027 Properties of Laser-Produced Highly Charged Heavy Ions for Direct Injection Scheme plasma, ion, target, rfq 1976
 
  • K. Sakakibara, T. Hattori, N. Hayashizaki, T. Ito
    RLNR, Tokyo
  • H. Kashiwagi
    JAERI/ARTC, Gunma-ken
  • M. Okamura
    RIKEN, Saitama
  To accelerate highly charged intense ion beam, we have developed the Direct Plasma Injection Scheme (DPIS) with laser ion source. In this scheme an ion beam from a laser ion source is injected directly to a RFQ linac without a low energy beam transport (LEBT) and the beam loss in the LEBT can be avoided. We achieved high current acceleration of carbon ions (60mA) by DPIS with the high current optimized RFQ. As the next setp we will use heavier elements like Ag, Pb, Al and Cu as target in LIS (using CO2, Nd-YAG or other laser) for DPIS and will examine properties of laser-produced plasma (the relationship of between charge state and laser power density, the current dependence of the distance from the target, etc).  
 
TPPE031 60 mA Carbon Beam Acceleration with DPIS rfq, ion, plasma, injection 2206
 
  • M. Okamura, R.A. Jameson, K. Sakakibara, J. Takano
    RIKEN, Saitama
  • T. Fujimoto, S. Shibuya, T. Takeuchi
    AEC, Chiba
  • Y. Iwata, K. Yamamoto
    NIRS, Chiba-shi
  • H. Kashiwagi
    JAERI/ARTC, Gunma-ken
  • A. Schempp
    IAP, Frankfurt-am-Main
  We have studied "direct plasma injection scheme (DPIS)" since 2000. This new scheme is for producing very intense heavy ions using a combination of an RFQ and a laser ion source. An induced laser plasma goes directly into the RFQ without an extraction electrode nor any focusing devices. Obtained maximum peak current of Carbon 4+ beam reached 60 mA with this extremely simple configuration. The details of the experimental result will be presented.  
 
TPPE039 Development of Advanced Models for 3D Photocathode PIC Simulations simulation, electron, cathode, gun 2583
 
  • D.A. Dimitrov, D.L. Bruhwiler, J.R. Cary, P. Messmer, P. Stoltz
    Tech-X, Boulder, Colorado
  • D.W. Feldman, P.G. O'Shea
    IREAP, College Park, Maryland
  • K. Jensen
    NRL, Washington, DC
  Funding: This work is supported by the U.S. DOE, use of NERSC supercomputer facilities, and the Joint Technology office (JTO).

Codes for simulating photocathode electron guns invariably assume the emission of an idealized electron distribution from the cathode, regardless of the particular particle emission model that is implemented. The output of such simulations, a relatively clean and smooth distribution with very little variation as a function of the azimuthal angle, is inconsistent with the highly irregular and asymmetric electron bunches seen in experimental diagnostics. To address this problem, we have implemented a recently proposed theoretical model* that takes into account detailed solid-state physics of photocathode materials in the VORPAL particle-in-cell code.** Initial results from 3D simulations with this model and future research directions will be presented and discussed.

*K.L. Jensen, D.W. Feldman, M. Virgo, and P.G. O'Shea, Phys. Rev. ST Accel. Beams, 6:083501, 2003. **C. Nieter and J.R. Cary, J. Comp. Phys. 196 (2004), p. 448.

 
 
TPPE041 Multi-Alkali Photocathode Development at Brookhaven National Lab for Application in Superconducting Photoinjectors cathode, electron, vacuum, gun 2672
 
  • A. Burrill, I. Ben-Zvi, D. Pate, T. Rao, Z. Segalov
    BNL, Upton, Long Island, New York
  • D. Dowell
    SLAC, Menlo Park, California
  In this paper we will report our progress on the development of cesium potassium antimonide photocathodes and their application in superconducting photoinjectors. Quantum efficiencies of 2-3 % at 545 nm, and 10% at 365 nm have been routinely obtained in the test stand, and electron emission uniformity, quantum efficiency at a variety of wavelengths, and lifetime under different vacuum conditions has been well characterized. The extraction of high charge per laser pulse will also be addressed in addition to the comparison of results from two different deposition techniques.  
 
TPPE044 Upgrade of the Fermilab/NICADD Photoinjector Laboratory emittance, quadrupole, linac, electron 2848
 
  • P. Piot, H. Edwards
    Fermilab, Batavia, Illinois
  • M. Huening
    DESY, Hamburg
  • T. W. Koeth
    Rutgers University, The State University of New Jersey, Piscataway, New Jersey
  • J.L. Li, R. Tikhoplav
    Rochester University, Rochester, New York
  Funding: This work was supported by Universities Research Association Inc. under contract DE-AC02-76CH00300 with the U.S. DOE, and by NICADD.

The Femilab/NICADD photoinjector laboratory (FNPL) is a 16 MeV electron accelerator dedicated to beam dynamics and advanced accelerator studies. FNPL will soon be capable of operating at 50 MeV, after the installation of a high gradient TESLA cavity. In this paper we present the foreseen design for the upgraded facility along with its performance. We discuss the possible application of 50 MeV beam including the possible use of FNPL as an injector for the superconducting module and test facility (SM&TF).

 
 
TPPE047 Fabrication and Measurement of Low Work Function Cesiated Dispenser Photocathodes cathode, electron, dipole, photon 2953
 
  • N.A. Moody, D.W. Feldman, P.G. O'Shea
    IREAP, College Park, Maryland
  • K. Jensen
    NRL, Washington, DC
  Funding: We gratefully acknowledge our funding agencies, the Joint Technology Office and the Office of Naval Research for their support.

Photoinjector performance is a limiting factor in the continued development of high powered FELs and electron beam-based accelerators. Presently available photocathodes are plagued with limited efficiency and short lifetime in an RF-gun environment, due to contamination or evaporation of a photosensitive surface layer. An ideal photocathode should have high efficiency at long wavelengths, long lifetime in practical vacuum environments, and prompt emission. Cathodes with high efficiency typically have limited lifetime, and vice versa, and the needs of the photocathode are generally at odds with those of the drive laser. A potential solution is the low work function dispenser cathode, where lifetime issues are overcome by periodic in situ regeneration that restores the photosensitive surface layer, analogous to those used in the microwave power tube industry. This work reports on the fabrication techniques and performance of cesiated metal photocathodes and cesiated dispenser cathodes, with a focus on understanding and improving quantum efficiency and lifetime, and analyzing issues of emission uniformity. The efficiency versus coverage behavior of cesiated metals is discussed and closely matches that predicted by recent theory.*

*K. L. Jensen, et al., "Photoemission from Low Work Function Coated Metal Surfaces: A Comparison of Theory to Experiment" (this conference).

 
 
TPPE049 Synchronizaiton Between Laser and Electron Beam at Photocathode RF Gun electron, gun, cathode, linac 3079
 
  • A. Sakumi, A. Fukasawa, Y. Muroya, T. Ueda, M. Uesaka, K. Yoshii
    UTNL, Ibaraki
  • K. Dobashi
    NIRS, Chiba-shi
  • N. Kumagai, H. Tomizawa
    JASRI/SPring-8, Hyogo
  • J.U. Urakawa
    KEK, Ibaraki
  The chemical reactions of hot, room temperature and critical water in a time-range of picosecond and sub-picosecond have been carried out by the 18 MeV S-band linac and a Mg photocathode RF gun with the irradiation of third harmonic Ti: Sapphire laser, at Nuclear Engineering Research Laboratory (NERL), the University of Tokyo. Although this short bunch and 100 fs laser light are enough to perform the experiment of radiation chemistry in the time-range of sub-picosecond, the total time-resolution become worse by the instability of synchronization between laser and radio frequency of linac. We found that the fluctuation of room temperature causes the instability, particularly the cycle of turning on/off of the air-conditioner. It is shown that 0.3 °C (peak-to-peak) fluctuation of the laser-room temperature have approximately corresponded to the instability of 6 ps. We are trying to decrease the fluctuation of the room temperature, together with the local temperature stability of the Ti: Sapphire crystal, the pumping laser. Furthermore, we will develop the feed back system for reducing the instability of the synchronization.  
 
TPPE055 DC-SC Photoinjector with Low Emittance at Peking University emittance, gun, electron, cathode 3325
 
  • R. Xiang, Y.T. Ding, J. Hao, S.L. Huang, X.Y. Lu, S.W. Quan, B.C. Zhang, K. Zhao
    PKU/IHIP, Beijing
  High average power Free Electron Lasers require the high quality electron beams with the low emittance and the sub-picosecond bunches. The design of DC-SC photoinjector, directly combining a DC photoinjector with an SRF cavity, can produce high average current beam with moderate bunch charge and high duty factor. Because of the DC gun, the emittance increases quickly at the beginning, so a carefully design is needed to control that. In this paper, the simulation of an upgraded design has been done to lower the normalized emittance below 1.5mm·mrad. The photoinjector consists of a DC gap and a 2+1/2-cell SRF cavity, and it is designed to produce 4.2 MeV electron beams at 100pC bunch charge and 81.25MHz repetition rate (8 mA average current).  
 
TPPE056 Emittance Measurement with Upgraded RF Gun System at SPring-8 emittance, quadrupole, gun, simulation 3348
 
  • A. Mizuno, H. Dewa, H. Hanaki, T. Taniuchi, H. Tomizawa
    JASRI/SPring-8, Hyogo
  • M. Uesaka
    UTNL, Ibaraki
  A single cell S-band RFgun has been developed at the SPring-8 since 1996. The minimum normalized beam emittance, measured with double slits' scanning method in 2002, was 2.3 pi mm mrad at the exit of the gun cavity with charge of 0.1 nC/bunch. In 2004, we installed a following accelerator structure to investigate beam behavior of the whole injector system. In this paper, we report emittance measurement results of upgraded system, using variable quadrupole magnet method. The minimum emittance of 2.0 pi mm mrad with a net charge of 0.14 nC/bunch were able to be measured.  
 
TPPE058 Dual Feed RF Gun Design for the LCLS gun, coupling, quadrupole, dipole 3432
 
  • L. Xiao, R.F. Boyce, D. Dowell, Z. Li, C. Limborg-Deprey, J.F. Schmerge
    SLAC, Menlo Park, California
  Funding: Work supported by the U.S. DOE under contract DE-AC03-76SF00515.

In order to remove the dipole field introduced by the coupler in existing S-band BNL/SLAC/UCLA 1.6 cell rf gun, a dual feed design for the LCLS RF gun is proposed together with several significant changes. The improvements include adopting Z-coupling instead of ?-coupling for easier machining and reducing heating, increasing the 0-and ?-mode separation from 3.4 to 15 MHz to reduce the amplitude of the 0 mode, incorporating race-track cavity shape to minimize the quadruple fields, increased cooling for operation at 120Hz and other small changes to improve performance and diagnostic capabilities. The new design has been modeled with the parallel finite element eigenmode solver Omega3P to provide the desired RF parameters and to generate the gun cavity dimensions needed for fabrication.

 
 
TPPE063 Improved Electron Yield and Spin-Polarization from III-V Photocathodes Via Bias Enhanced Carrier Drift electron, cathode, polarization, vacuum 3603
 
  • G.A. Mulhollan, J.C.B. Bierman
    Saxet, Austin, Texas
  • A. Brachmann, J.E. Clendenin, E.G. Garwin, R.E. Kirby, D.-A.L. Luh, T.V.M. Maruyama
    SLAC, Menlo Park, California
  • R.X.P. Prepost
    UW-Madison/PD, Madison, Wisconsin
  Funding: Work at Saxet Surface Science, SLAC and the University of Wisconson is supported by the following U.S. DOE grants respectively: DE-FG02-04ER86231, DE-AC02-76SF00515 and DE-AC02-76ER00881.

Spin-polarized electrons are commonly used in high energy physics. Future work will benefit from greater polarization. Polarizations approaching 90% have been achieved at the expense of yield. The primary paths to higher polarization are material design and electron transport. Our work addresses the latter. Photoexcited electrons may be preferentially emitted or suppressed by an electric field applied across the active region. We are tuning this forward bias for maximum polarization and yield, together with other parameters, e.g., doping profile Preliminary measurements have been carried out on bulk GaAs. As expected, the yield change far from the bandgap is quite large. The bias is applied to the bottom (non-activated) side of the cathode so that the accelerating potential as measured with respect to the ground potential chamber walls is unchanged for different front-to-back cathode bias values. For a bias which enhances emission, the yield nearly doubles. For a bias which diminishes emission, the yield is approximately one half of the zero bias case. The size of the bias to cause an appreciable effect is rather small reflecting the low drift kinetic energy in the zero bias case.

 
 
TPPE064 Space-Charge Effects Near a Cathode cathode, electron, simulation, space-charge 3629
 
  • V. Gorgadze
    UCB, Berkeley, California
  • J.S. Wurtele
    LBNL, Berkeley, California
  Funding: This work was supported by the Director, Office of Science of the U.S. DOE under Contract No. DE-AC03-76SF00098.

RF photocathode guns are excellent sources of high brightness electron bunches. In the limit of high-current short bunches the electron are complicated space-charge fields. To mitigate space charge effect downstream of the gun it is often desirable to produce electorn bunches with uniform distribution. Our goal is to understand to what extent the non-uniformity of the laser pulse intensity is responsible for a non-uniform electron distribution and to what extent this is due to the electron beam dynamics near to the cathode. We investigate these effects with particle-in-cell simulations and simple theory. These studies are focused on the regime where the peak current as well as the temporal current profile are influenced by the self-fields of the bunch. The simulation code XOOPIC has been employed. The critical current limitation for virtual cathode formation and current density profile at the exit of the injector have been found.

 
 
TPPT086 Elliptical Cavity Shape Optimization for Acceleration and HOM Damping damping, resonance, single-bunch, impedance 4191
 
  • H. Wang, R.A. Rimmer, G. Wu
    Jefferson Lab, Newport News, Virginia
  Funding: Supported by the Office of Naval Research, the Joint Technology Office, the Commonwealth of Virginia, the Air Force Research Laboratory, and by DOE Contract DE-AC05-84ER40150.

A normal design process for a superconducting cavity shape is to maximize the R/Q (shunt impedance/intrinsic quality factor) and geometry factor G for a given RF field limit of Bpeak/Eacc or Epeak/Eacc. For the application of an Ampere-class, high current energy recovery linac or storage ring, heavy HOM damping is required. This paper reports on a survey of single cell shapes developed for multi-cell cavities for different projects. Using a set of normalized parameters, we compare the designs for different frequencies and ß structures for the fundamental mode. Using dispersion curve (frequency verse phase advance) calculated by MAFIA for a single cell, we explore further how to optimize the cavity shape to avoid a light cone line crossing at the dangerous resonance frequencies determined by the beam bunch structure or the dangerous (trapped or high R/Q) modes with a low group velocity. We expect such a formulation to inform our development of a 5-cell, optimized cavity shape, with good real estate accelerating gradient and strong HOM damping waveguide structure for the JLab 1MW ERL-FEL project.

 
 
TPPT088 Power Dependence of the RF Surface Resistance of MgB2 Superconductor superconductivity, target, vacuum, superconducting-RF 4215
 
  • T. Tajima, A. Findikoglu, A.J. Jason, F.L. Krawczyk, F. M. Mueller, A. H. Shapiro
    LANL, Los Alamos, New Mexico
  • R.L. Geng, H. Padamsee, A.S. Romanenko
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  • B. Moeckly
    STI, Santa Barbara, California
  MgB2 is a superconducting material that has a transition temperature (Tc) of ~40 K. Recently, it has been shown at 4 K, liquid helium temperature, that the surface RF resistance can be lower than Nb that has the Tc of 9.2 K and has been used for most superconducting RF cavities in the past decades. One of the problems with other high-Tc materials such as YBCO was its rapid increase in RF surface resistance with higher surface magnetic fields. Recently, we have shown that MgB2 shows little increase up to about 120 Oe, equivalent of an accelerating field of about 3 MV/m. The highest field tested was limited by available power. This result is encouraging and has made us consider fabricating a cavity coated with MgB2 and test it. Also, there might be a potential that this material has a higher critical magnetic field that enables the cavity to run at a higher gradient than Nb cavities.  
 
TOPA001 Mono Energetic Beams from Laser Plasma Interactions electron, plasma, injection, simulation 69
 
  • C.G.R. Geddes, E. Esarey, W. Leemans, C.B. Schroeder, C. Toth
    LBNL, Berkeley, California
  • J.R. Cary, C. Nieter
    Tech-X, Boulder, Colorado
  • J. Van Tilborg
    TUE, Eindhoven
  Funding: Supported by U.S. Dept. of Energy contracts DE-AC03-76SF00098, DE-FG03-95ER40926, DE-FG02-01ER41178, DE-FG02-03ER83857, SciDAC, and NSF 0113907. C. Geddes is also supported by the Hertz foundation.

A laser driven wakefield accelerator has been tuned to produce high energy electron bunches with low emittance and energy spread by extending the interaction length using a plasma channel. Wakefield accelerators support gradients thousands of times those achievable in RF accelerators, but short acceleration distance, limited by diffraction, has resulted in low energy beams with 100% electron energy spread. In the present experiments on the L’OASIS laser,* the relativistically intense drive pulse was guided over 10 diffraction ranges by a plasma channel. At a drive pulse power of 9 TW, electrons were trapped from the plasma and beams of percent energy spread containing >200pC charge above 80 MeV and with normalized emittance estimated at < 2 pi -mm-mrad were produced.** Data and simulations (VORPAL***) show the high quality bunch was formed when beam loading turned off injection after initial trapping, and when the particles were extracted as they dephased from the wake. Up to 4TW was guided without trapping, potentially providing a platform for controlled injection. The plasma channel technique forms the basis of a new class of accelerators, with high gradients and high beam quality.

*W.P. Leemans et al., Phys. Plasmas 5, 1615-23 (1998). **C.G.R. Geddes et al., Nature 431, 538-41 (2004). ***C. Nieter et al., J. Comp. Phys. 196, 448-73 (2004).

 
 
TOPA006 High Energy Gain IFEL at UCLA Neptune Laboratory undulator, electron, acceleration, simulation 500
 
  • P. Musumeci, S. Boucher, C.E. Clayton, A. Doyuran, R.J. England, C. Joshi, C. Pellegrini, J.E. Ralph, J.B. Rosenzweig, C. Sung, S. Tochitsky, G. Travish, R.B. Yoder
    UCLA, Los Angeles, California
  • S.V. Tolmachev, A. Varfolomeev, A. Varfolomeev, T.V. Yarovoi
    RRC Kurchatov Institute, Moscow
  We report the observation of energy gain in excess of 20 MeV at the Inverse Free Electron Laser Accelerator experiment at the Neptune Laboratory at UCLA. A 14.5 MeV electron beam is injected in an undulator strongly tapered in period and field amplitude. The IFEL driver is a CO2 10.6 mkm laser with power larger than 400 GW. The Rayleigh range of the laser, ~ 1.8 cm, is much shorter than the undulator length so that the interaction is diffraction dominated. A few per cent of the injected particles are trapped in a stable accelerating bucket. Electrons with energies up to 35 MeV are measured by a magnetic spectrometer. Simulations, in good agreement with the experimental data, show that most of the energy gain occurs in the first half of the undulator at a gradient of 70 MeV/m and that the structure in the measured energy spectrum arises because of higher harmonic IFEL interaction in the second half of the undulator.  
 
TOPA008 First Observation of Laser-Driven Acceleration of Relativistic Electrons in a Semi-Infinite Vacuum Space electron, acceleration, polarization, vacuum 650
 
  • T. Plettner, R.L. Byer, T.I. Smith
    Stanford University, Stanford, Califormia
  • E.R. Colby, B.M. Cowan, C.M.S. Sears, R. Siemann, J.E. Spencer
    SLAC, Menlo Park, California
  Funding: Department of Energy DE-FG03-97ER41043.

We have observed acceleration of relativistic electrons in vacuum driven by a linearly polarized laser beam incident on a thin gold-coated reflective boundary. The observed energy modulation effect follows all the characteristics expected for linear acceleration caused by a longitudinal electric field. As predicted by the Lawson-Woodward theorem the laser driven modulation only appears in the presence of the boundary. It shows a linear dependence with the strength of the electric field of the laser beam and also it is critically dependent on the laser polarization. Finally, it appears to follow the expected angular dependence of the inverse transition radiation process.

 
 
TOPA010 Photonic Crystal Laser-Driven Accelerator Structures lattice, focusing, dynamic-aperture, simulation 731
 
  • B.M. Cowan
    SLAC, Menlo Park, California
  Funding: Work supported by Department of Energy contract DE-AC03-76SF00515 (SLAC).

We discuss simulated photonic crystal structure designs, including two- and three-dimensional planar structures and fibers. The discussion of 2D structures demonstrates guiding of a speed-of-light accelerating mode by a defect in a photonic crystal lattice and reveals design considerations and trade-offs. With a three-dimensional lattice, we introduce a candidate geometry and discuss beam dynamics, coupling, and manufacturing techniques for that structure. In addition we discuss W-band scale tests of photonic crystal structures. The computational methods are also discussed.

 
 
TOPA011 Self Consistent Scheme for Obtaining Electron-Positron Collisions with Multi-TeV Energy acceleration, radiation, photon, damping 740
 
  • A.A. Mikhailichenko
    Cornell University, Department of Physics, Ithaca, New York
  We describe here a self-consistent scheme for arrangement of multi-TeV collisions of electrons and positrons by using laser burst swept along microstructures with stable rate of acceleration ~10GeV/m. Shown that all component of the scheme are within present day technology. For energy ~1TeV luminosity could reach 1035 /cm2/s with wall-plug power of few tens of kW only.  
 
TOPE003 Results from DR and Instrumentation Test Facilities damping, emittance, coupling, quadrupole 305
 
  • J.U. Urakawa
    KEK, Ibaraki
  The KEK Accelerator Test Facility (ATF) is a 1.3GeV storage ring capable of producing ultra-low emittance electron beams and has a beam extraction line for ILC R&D. The ATF has proven to be an ideal place for researches with small, stable beams. 2x1010 single bunch and low current 20 bunch-train with 2.8nsec bunch spacing have been extracted to develop Nano-Cavity BPM’s, FONT, Nano Beam Orbit handling (FEATHER), Optical Diffraction Radiation (ODR) monitor, a precision multi-bunch laser-based beam profile monitor and polarized positron beam generation via backward-Compton scattering by the international collaboration. A set of three cavity BPM's is installed in the ATF extraction line on a set of extremely stiff supports. The KEK group installed another set of three BPM's, with their own support mechanism. The full set of 6 will prove extremely useful. In the DR (Damping Ring), we are researching the fast ion instability, micro-wave instability with four sets of damping wiggler and developing pulsed laser wire monitor, X-ray SR monitor, very fast kicker with about 1nsec rise/fall time to make ILC beam. I will report the recent results on above R&D’s.  
 
WPAE019 How to Fill a Narrow 27 km Long Tube with a Huge Number of Accelerator Components? site, injection, civil-engineering, extraction 1634
 
  • Y. Muttoni, J.-P. Corso, R. V. Valbuena
    CERN, Geneva
  As in large scale industrial projects, research projects, such as giant and complex particle accelerators, require intensive spatial integration studies using 3D CAD models, from the design to the installation phases. The future management of the LHC machine configuration during its operation will rely on the quality of the information, produced during these studies.This paper presents the powerful data-processing tools used in the project to ensure the spatial integration of several thousand different components in the limited space available.It describes how the documentation and information generated have been made available to a great number of users through a dedicated Web site and how installation nonconformities were handled.  
 
WPAE036 Harmonic Analysis of Linac Alignment alignment, linac, focusing, lattice 2431
 
  • R.C. McCrady
    LANL, Los Alamos, New Mexico
  Funding: Work conducted at Los Alamos National Laboratory, which is operated by the University of California for the United States Department of Energy under contract W-7405-ENG-36.

We have analyzed the requirements on alignment of the focusing elements (quadrupole doublets) in the Los Alamos Neutron Science Center (LANSCE) side coupled linac. The analysis is performed in terms of harmonics of the quardrupole spacing. This allows us to determine the effect of intentional deviations from a straight line, such as following the curvature of the Earth, and of unintentional deviations introduced by measurement and alignment errors. Results are compared to measured positions of the doublets.

 
 
WPAE039 Optical Tooling and its Uses at the Spallation Neutron Source (SNS) target, alignment, SNS, instrumentation 2577
 
  • S.A. Helus, D.R. Bruce, J.J. Error, J.J. Fazekas, J.R. Maines
    ORNL, Oak Ridge, Tennessee
  Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.

Optical tooling has been a mainstay of the accelerator alignment community for decades. Even now in the age of electronic survey equipment, optical tooling remains a viable alternative, and at times the only alternative. At SNS, we combine traditional optical tooling alignment methods, instrumentation, and techniques, with the more modern electronic techniques. This paper deals with the integration of optical tooling into the electronic survey world.

 
 
WPAE041 Development of a New Beam Diagnostics Platform diagnostics, vacuum, SNS, ion 2669
 
  • R.T. Roseberry, S. Assadi, G.R. Murdoch
    ORNL, Oak Ridge, Tennessee
  Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. SNS is a partnership of six national laboratories: Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos, and Oak Ridge.

The Spallation Neutron Source Project (SNS) is an accelerator-based neutron source currently under construction at Oak Ridge National Laboratory (ORNL). The availability of space along completed portions of the accelerator for the addition of beam diagnostic is limited. A new platform for mounting a variety of instruments has been created by replacing part of the Medium Energy Beam Transport (MEBT) section of the accelerator developed by Lawrence Berkeley National Laboratory. The design and current capabilities of this instrument platform will be presented along with plans for future enhancements.

 
 
WPAE043 Alignment of the Booster Injector for the Duke Free Electron Laser Storage Ring alignment, booster, storage-ring, dipole 2786
 
  • M. Emamian, M.D. Busch, S. Mikhailov
    DU/FEL, Durham, North Carolina
  • N. Gavrilov
    BINP SB RAS, Novosibirsk
  Funding: This work is supported by U.S. Department of Energy grant DE-FG02-01ER41175 and by U.S. AFOSR MFEL grant F49620-001-0370.

This paper presents the methodology and initial results for mechanical alignment of the booster synchrotron for the Duke FEL storage ring. The booster is a compact design and requires special considerations for alignment. The magnetic and vacuum elements of the arcs have been designed for alignment by a laser tracker system. A parametric 3D design package has been used to determine target coordinates. These target coordinates evolve from design goals to physically verified dimensions by modifying the parametric model to match mechanical measurement data after fabrication. By utilizing the functionality of the laser tracker system and a parametric 3D modeler, a direct and efficient measurement and alignment technique has been developed for a complex geometry.

 
 
WPAE082 Design of a Precision Positioning System for the Undulators of the Linac Coherent Light Source undulator, alignment, quadrupole, vacuum 4099
 
  • E. Trakhtenberg, J.T. Collins, P.K. Den Hartog, M. White
    ANL, Argonne, Illinois
  A precision positioning system has been designed for the Linac Coherent Light Source (LCLS) and a prototype system is being fabricated. The LCLS will use a beam based alignment technique to precisely align all of the segments of the 130-m long undulator line. The requirement for overlap between the electron beam and the x-ray beam, in order to develop and maintain lasing, demands that each of the quadrupoles be aligned within a tolerance of ± 2 μm and that the undulator axis be positioned within ± 10 μm vertically and horizontally. Five cam movers, each with an eccentricity of 1.5 mm, will allow adjustment of a cradle supporting the undulator, its vacuum chamber, a quadrupole, and a beam position monitor. An additional motion transverse to the beam axis allows removal of individual undulators from the beam path. Positioning feedback will be provided by a wire position monitor system and a hydrostatic leveling system.  
 
WPAP003 Emission Mechanisms in a Photocathode RF Gun electron, emittance, cathode, gun 856
 
  • J.H. Han, J.W. Baehr, H.-J. Grabosch, M. Krasilnikov, V. Miltchev, A. Oppelt, B. Petrosyan, S. Riemann, L. Staykov, F. Stephan
    DESY Zeuthen, Zeuthen
  • K. Floettmann, S. Schreiber
    DESY, Hamburg
  • M.V. Hartrott
    BESSY GmbH, Berlin
  • P. Michelato, L. Monaco, D. Sertore
    INFN/LASA, Segrate (MI)
  • J.R. Roensch
    Uni HH, Hamburg
  In photocathode rf guns, emission mechanisms at the photocathode play a crucial role in the overall beam dynamics. A low bunch charge as well as a short Gaussian bunch profile allow us to study the beam dynamics depending on emission phase without space charge force. This paper presents experimental and simulation studies toward detailed understanding of the photo emission and secondary emission processes at the cathode.  
 
WPAP004 Dark Current and Multipacting in the Photocathode RF Guns at PITZ cathode, electron, gun, simulation 895
 
  • J.H. Han, J.W. Baehr, H.-J. Grabosch, M. Krasilnikov, V. Miltchev, A. Oppelt, B. Petrosyan, S. Riemann, L. Staykov, F. Stephan
    DESY Zeuthen, Zeuthen
  • K. Floettmann, S. Schreiber
    DESY, Hamburg
  • M.V. Hartrott
    BESSY GmbH, Berlin
  • P. Michelato, L. Monaco, D. Sertore
    INFN/LASA, Segrate (MI)
  • J.R. Roensch
    Uni HH, Hamburg
  For photocathode rf guns, the amount of dark current depends on the cavity surface and the photocathodes. Smooth conditioning reduces the amount of dark current. Mechanical damages of the cathodes induce high dark current and chemical pollution changes emission properties of the cathode. Multipacting in the gun cavity changes the surface status of the cathodes and sometimes makes the gun operation impossible due to vacuum interlocks. In this paper, dark current and multipacting features of the rf gun are presented including experimental and simulation studies.  
 
WPAP005 Beam-Based Procedures for RF Guns gun, cathode, electron, alignment 967
 
  • M. Krasilnikov, J.W. Baehr, H.-J. Grabosch, J.H. Han, V. Miltchev, A. Oppelt, B. Petrosyan, L. Staykov, F. Stephan
    DESY Zeuthen, Zeuthen
  • M.V. Hartrott
    BESSY GmbH, Berlin
  A wide range of rf photo injector parameters has to be optimized in order to achieve an electron source performance as required for linac based high gain FELs. Some of the machine parameters can not be precisely controlled by direct measurements, whereas the tolerance on them is extremely tight. Therefore, this should be met with beam-based techniques. Procedures for beam-based alignment (BBA) of the laser on the photo cathode as well as solenoid alignment have been developed. They were applied at the Photo Injector Test facility at DESY Zeuthen (PITZ) and at the photo injector of the VUV-FEL at DESY Hamburg. A field balance of the accelerating mode in the 1 cell gun cavity is one of the key beam dynamics issues of the rf gun. Since no direct field measurement in the half and full cell of the cavity is available for the PITZ gun, a beam-based technique to determine the field balance has been proposed. A beam-based rf phase monitoring procedure has been developed as well.  
 
WPAP006 Recent Developments at PITZ emittance, booster, gun, electron 1012
 
  • M. Krasilnikov, K. Abrahamyan, G. Asova, J.W. Baehr, G. Dimitrov, U. Gensch, H.-J. Grabosch, J.H. Han, S. Khodyachykh, S. Liu, V. Miltchev, A. Oppelt, B. Petrosyan, S. Riemann, L. Staykov, F. Stephan
    DESY Zeuthen, Zeuthen
  • W. Ackermann, W.F.O. Müller, S. Schnepp, T. Weiland
    TEMF, Darmstadt
  • J.-P. Carneiro, K. Floettmann, S. Schreiber
    DESY, Hamburg
  • M.V. Hartrott, E. Jaeschke, D. Kraemer, D. Lipka, R. Richter
    BESSY GmbH, Berlin
  • P. Michelato, L. Monaco, C. Pagani, D. Sertore
    INFN/LASA, Segrate (MI)
  • J.R. Roensch, J. Rossbach
    Uni HH, Hamburg
  • W. Sandner, I. Will
    MBI, Berlin
  • I. Tsakov
    INRNE, Sofia
  The ability to produce high brightness electron beams as required for modern Free Electron Lasers (FELs) has been demonstrated during the first stage of the Photo Injector Test Facility at DESY Zeuthen (PITZ1). The electron source optimization at PITZ1 was successfully completed, resulting in the installation of the PITZ rf gun at the VUV-FEL (DESY, Hamburg). One of the main goals of the second stage of PITZ (PITZ2) is to apply higher gradients in the rf gun cavity in order to obtain smaller beam emittance by faster acceleration of the space charge dominated beams. In order to reach the required gradients a 10 MW klystron has to be installed and the gun cavity has to be conditioned for higher peak power. Another important goal of PITZ2 is a detailed study of the emittance conservation principle by using proper electron beam acceleration with a booster. Further photo injector optimization, including update of the photocathode laser and diagnostic tools, is foreseen as well. Recent progress on the PITZ developments will be reported.  
 
WPAP007 Status of the 3 Cell Superconducting RF Gun Project in Rossendorf gun, cathode, electron, pick-up 1081
 
  • R. Xiang, H. Buettig, P. Evtushenko, D. Janssen, U. Lehnert, P. Michel, K. Moeller, Ch. Schneider, R. Schurig, F. Staufenbiel, J. Teichert
    FZR, Dresden
  • T.  Kamps, D. Lipka
    BESSY GmbH, Berlin
  • W.-D. Lehmann
    IfE, Dresden
  • J. Stephan
    IKST, Drsden
  • V. Volkov
    BINP SB RAS, Novosibirsk
  • I. Will
    MBI, Berlin
  In the paper, we report on the status and progress of the superconducting rf gun project in Rossendorf. The gun is designed for cw operation mode with 1mA current and 10 MeV electron energy. The gun will be installed at the ELBE superconducting electron linear accelerator. It will have a 3 cell niobium cavity operating at 1.3 GHz. The cavity consists of three cells with TESLA geometry and a specially designed half-cell in which the photocathode will be placed. Two Nb cavities, with RRR 300 and 40 respectively, will be finished at the beginning of 2005. After delivery, the rf tests will be performed and the treatment of the cavities will be started. At the same time, the design of the cryostat is finished and the fabrication of its components is under way. Further activities are the design of the diagnostic beam line, the assembling of the new photocathode preparation system, and the upgrade of the 262 nm driver laser system.  
 
WPAP012 Preliminary Results on Beam Dynamics of Laser Pulse Shaping Effects in SPARC emittance, electron, simulation, target 1315
 
  • M. Boscolo, M. Ferrario, M.  Migliorati
    INFN/LNF, Frascati (Roma)
  • F. Castelli, S. Cialdi, A.F. Flacco
    INFN-Milano, Milano
  In a photoinjector system the role played by the laser pulse shaping in achieving high quality electron beam is crucial, as it determines the distribution dependent space charge effects in the early stages of the acceleration. A dedicated code to simulate pulse shaping in a laser system and able to generate the corresponding initial electron beam distribution has been developed. Realistic deviations from the ideal flat top pulse give for example a ramp or multi-peaks shape with a raletive rise time, plateau deformation and ripples. The beam dynamics of electron beams with different initial temporal pulse characteristics along the SPARC photoinjector has also been studied with the code PARMELA. More exotic pulse shaping are also discussed. The study presented here gives some indications on the tolerances of the laser beam characteristics for the electron beam quality preservation.  
 
WPAP013 Magnesium Film Photocathodes for High Brilliance Electron Injectors cathode, target, gun, electron 1350
 
  • F. Tazzioli, G. Gatti, C. Vicario
    INFN/LNF, Frascati (Roma)
  • I. Boscolo, S. Cialdi
    INFN-Milano, Milano
  • L. Cultrera, A. Perrone
    Lecce University, Lecce
  • S. Orlanducci, M.L. Terranova
    Università di Roma II Tor Vergata, Roma
  • M. Rossi
    Rome University La Sapienza, Roma
  Advanced high brilliance electron injectors require photocathodes having low thermal emittance, high quantum efficiency (QE) and prompt response. They should be easy to handle and capable of working in the very high electric fileds of a RF gun. Magnesium films deposited by laser ablation and sputtering techniques are discussed and QE measurements are presented.  
 
WPAP018 Generation of Double-Decker Femtosecond Electron Beams in a Photoinjector electron, linac, gun, emittance 1604
 
  • J. Yang, K. Kan, T. Kondoh, T. Kozawa, Y. Kuroda, S. Tagawa, Y. Yoshida
    ISIR, Osaka
  The femtosecond electron beam is a practical source in the pump-probe experiment for studies of ultrafast physical/chemical reactions in materials, in which a mode-locked ultrashort laser light is used as a probe source. The synchronized time jitter between the electron beam and the laser light limits the time resolution in the experiment. In order to reduce the time jitter, a new concept of synchronized double-decker electron beam generation in a photoinjector was proposed. The double electron beams were observed in an S-band photocathode RF gun by injecting two laser beams which produced with a picosecond laser. The double electron beams were compressed into 400fs(rms) with a phase-space rotation technique in magnetic fields. The beams, which one is used as a pump source and another is used as a probe source, are expected for ultrafast reaction studies in femtosecond resolution.  
 
WPAP021 Status of PPI (Pohang Photo-Injector) for PAL XFEL emittance, gun, cathode, electron 1733
 
  • S.J. Park, C. Kim, I.S. Ko, J.-S. Oh, Y.W. Parc, P.C.D. Park, J.H. Park
    PAL, Pohang, Kyungbuk
  • X.J. Wang
    BNL, Upton, Long Island, New York
  Funding: Supported by the POSCO and the MOST, Korea.

A X-Ray Free Electron Laser (XFEL) project based on the Self-Amplified Spontaneous Emission (SASE) is under progress at the Pohang Accelerator Laboratory (PAL). One of the critical R&D for the PAL XFEL* is to develop the Pohang Photo-Injector (PPI) which is required to deliver electron beams with normalized emittance < 1.5 mm-mrad. In order to achieve the required beam quality with high stability and reliability, we will use photocathode with quantum efficiency > 0.1 % and long lifetime. This will greatly lessen the laser energy requirement for producing flat-top UV pulses, and open the possibility of using only regenerative amplifiers (RGAs) to drive the photocathode RF gun. The RGAs can produce mJs output with much better stability than multi-pass amplifiers. Both the Cs2Te and Mg are under consideration for the possible photo-cathode. To demonstrate the suitability of the Mg and Cs2Te for the future 4th generation light source application, an improved BNL-type S-band RF gun with a high-performance load-lock system will be developed for the PPI. In this article, we present the design concept of the PPI, the expected performance, and report on its development status.

*J.S. Oh, S.J. Park et al., "0.3-nm SASE-FEL at PAL," NIM A528, 582 (2004); S.J. Park, J.S. Oh et al., "Design Study of Low-Emittance Injector for SASE XFEL at Pohang Accelerator Laboratory," FEL2004, Italy, 2004.

 
 
WPAP022 Measurements of Transverse Emittance for RF Photocathode Gun at the PAL emittance, gun, booster, cathode 1760
 
  • J.H. Park, I.S. Ko, J.-S. Oh, Y.W. Parc, S.J. Park
    PAL, Pohang, Kyungbuk
  • X.J. Wang
    BNL, Upton, Long Island, New York
  • D. Xiang
    TUB, Beijing
  Funding: Supported by the POSCO and the MOST, Korea.

A BNL GUN-IV type RF photo-cathode gun is under fabrication for use in the FIR (Far Infra-Red) facility being built at the Pohang Accelerator Laboratory (PAL). Performance test of the gun will include the measurement of transverse emittance profile along the longitudinal direction. Successful measurement of the emittance profile will provide powerful tool for the commissioning of the 4GLS (4th generation light source) injectors based on the emittance compensation principle. We are going to achieve this withthe use of pepper-pot based emittance meters that can be moved along the longitudinal direction. In this article, we present design considerations on the emittance meter with the resolution of 1 mm mrad.

 
 
WPAP031 Use of Multiobjective Evolutionary Algorithms in High Brightness Electron Source Design gun, emittance, electron, cathode 2188
 
  • I.V. Bazarov, C.K. Sinclair
    Cornell University, Department of Physics, Ithaca, New York
  • I. Senderovich
    Cornell University, Ithaca, New York
  Funding: Supported by Cornell University.

We describe the use of multiobjective evolutionary algorithms (MOEAs) for the design and optimization of a high average current, high brightness electron injector for an Energy Recovery Linac (ERL). By combining MOEAs with particle tracking, including space charge effects, and by employing parallel computing resources, we explored a multidimensional parameter space with 22 independent variables for a DC gun based injector which is being constructed at Cornell University. The simulated performance of the optimized injector is found to be excellent, with normalized rms emittances as low as 0.1 mm-mrad for a 77 pC bunch, and 0.7 mm-mrad for a 1 nC bunch. We detail the advantages and flexibility of MOEAs as a powerful tool well suited for wide application in solving various problems in the accelerator field.

 
 
WPAP036 Determination of the Field Enhancement Factor on Photocathode Surface Via the Schottky Effect cathode, photon, electron, emittance 2425
 
  • Z.M. Yusof, M.E. Conde, W. Gai
    ANL, Argonne, Illinois
  Funding: U.S. Department of Energy.

Using photons with energy that is less than the work function, we employ the Schottky effect to determine the field enhancement factor on the surface of a Mg photocathode. The Schottky effect is manifested via a shift in the threshold for photoemission as the amplitude of the RF in the photoinjector gun is varied. From the threshold condition, we can directly determine the field enhancement factor on the cathode surface. This is a viable technique to obtain the field enhancement factor of surfaces of other materials such as Nb and Cu.

 
 
WPAP038 Photoemission Studies on BNL/AES/JLab all Niobium, Superconducting RF Injector cathode, electron, space-charge, gun 2556
 
  • T. Rao, I. Ben-Zvi, A. Burrill, H. Hahn, D. Kayran, Y. Zhao
    BNL, Upton, Long Island, New York
  • M.D. Cole
    AES, Medford, NY
  • P. Kneisel
    Jefferson Lab, Newport News, Virginia
  Funding: Under contract with the U.S. DOE, Contract No. DE-AC02-98CH10886.

Photoemission from all niobium superconducting injector is of considerable interest for the development of higher average current electron sources. In the past year, we have generated photocurrent from such an injector by irradiating the back wall of the 1/2 cell cavity with 248 nm and 266 nm laser beams. In this paper, we present the results of these measurements including the quantum efficiency, and its dependence on the field and wavelength. Issues related to the quenching of the cavity by the laser radiation will also be addressed.

 
 
WPAP039 Progress on Lead Photocathodes for Superconducting Injectors cathode, vacuum, photon, gun 2598
 
  • J. Smedley, T. Rao
    BNL, Upton, Long Island, New York
  • P. Kneisel
    Jefferson Lab, Newport News, Virginia
  • J.L. Langner, P. Strzyzewski
    The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock
  • R.S. Lefferts, A.R. Lipski
    SBUNSL, Stony Brook, New York
  • J.S. Sekutowicz
    DESY, Hamburg
  Funding: This work was supported by DOE contracts DE-AC02-98CH10886, DE-AC03-76SF00515 and DE-FG02-97ER82336.

We present the results of our investigation of bulk, electroplated and vacuum deposited lead as suitable photocathode materials for superconducting RF injectors. The quantum efficiency of each sample is presented as a function of the wavelength of the incident light, from 310 nm to 190 nm. Quantum efficiencies of 0.3% have been obtained. Production of a niobium cavity with a lead-plated cathode is underway.

 
 
WPAP041 Time Dependent Quantum Efficiency and Dark Current Measurements in an RF Photocathode Injector with a High Quantum Efficiency Cathode gun, cathode, electron, linac 2681
 
  • R.P. Fliller, H. Edwards
    Fermilab, Batavia, Illinois
  • W. Hartung
    NSCL, East Lansing, Michigan
  Funding: This work was supported by Universities Research Association Inc. under contract DE-AC02-76CH00300 with the U.S. DOE and by NICADD.

A system was developed at INFN Milano for preparing cesium telluride photo-cathodes and transferring them into an RF gun under ultra-high vacuum. This system has been in use at the Fermilab NICADD Photo-Injector Laboratory (FNPL) since 1997. A similar load-lock system is used at the TeSLA Test Facility at DESY-Hamburg. Two 1.625-cell high duty cycle RF guns have been fabricated for the project. Studies of the photo-emission and field emission ("dark current") behavior of both RF guns have been carried out. Unexpected phenomena were observed in one of the RF guns. In situ changes in the cathode's quantum efficiency and dark current with time were seen during operation of the photo-injector. These changes were correlated with the magnetostatic field at the cathode.* In addition, multipacting is observed in the RF guns under certain conditions. Recent measurements indicate a correlation between multipacting, anomalous photo-emission behavior, and anomalous field emission behavior. Results will be presented.

*W. Hartung, J.-P. Carneiro, H. Edwards, M. Fitch, M. Kuchnir, P. Michelato, D. Sertore, in Proceedings of the 2001 Particle Accelerator Conference, p. 2239-2241.

 
 
WPAP043 Production of Transverse Controllable Laser Density Distribution in Fermilab/NICADD Photoinjector electron, simulation, emittance, space-charge 2783
 
  • J.L. Li, J.L. Li
    Rochester University, Rochester, New York
  • P. Piot, R. Tikhoplav
    Fermilab, Batavia, Illinois
  The Fermilab/NICADD photoinjector laboratory consist of a photoemission electron source based on an L band rf-gun. The CsTe photocathode is illuminated by an ultrashort UV laser. The transport line from the laser to the photocathode was recently upgraded to allow imaging of an object plane located ~20 m from the photocathode. This upgrade allows the generation of transverse laser distributions with controlled nonuniformity, yielding the production of an electron beam with various transverse densities patterns. Measuring the evolution of the artificial pattern on the electron bunch provides information that can be used to benchmark numerical simulations and investigate the impact of space charge. Preliminary data on these investigations are presented in the present paper.  
 
WPAP045 Ion Back-Bombardment of GaAs Photocathodes Inside DC High Voltage Electron Guns vacuum, electron, gun, ion 2875
 
  • J.M. Grames, P. Adderley, J. Brittian, D. Charles, J. Clark, J. Hansknecht, M. Poelker, M.L. Stutzman, K.E.L. Surles-Law
    Jefferson Lab, Newport News, Virginia
  Funding: This work was supported by U.S. DOE Contract No. DE-ACO5-84-ER40150.

The primary limitation for sustained high quantum efficiency operation of GaAs photocathodes inside DC high voltage electron guns is ion back-bombardment of the photocathode. This process results from ionization of residual gas within the cathode/anode gap by the extracted electron beam, which is subsequently accelerated backwards to the photocathode. The damage mechanism is believed to be either destruction of the negative electron affinity condition at the surface of the photocathode or damage to the crystal structure by implantation of the bombarding ions. This work characterizes ion formation within the anode/cathode gap for gas species typical of UHV vacuum chambers (i.e., hydrogen, carbon monoxide and methane). Calculations and simulations are performed to determine the ion trajectories and stopping distance within the photocathode material. The results of the simulations are compared with test results obtained using a 100 keV DC high voltage GaAs photoemission gun and beamline at currents up to 10 mA DC.

 
 
WPAP050 A High Average Current DC GaAs Photocathode Gun for ERLs and FELs gun, vacuum, cathode, electron 3117
 
  • C. Hernandez-Garcia, S.V. Benson, D.B. Bullard, H.F.D. Dylla, K. Jordan, C. M. Murray, G. Neil, M.D. Shinn, T. Siggins, R.L. Walker
    Jefferson Lab, Newport News, Virginia
  Funding: This work supported by The Office of Naval Research under contract to the Dept. of Energy, the Air Force Research Lab, and the Commonwealth of Virginia.

The Jefferson Lab (JLab) 10 kW IR Upgrade FEL DC GaAs photocathode gun is presently the highest average current electron source operational in the U.S., delivering a record 9.1 mA CW, 350 kV electron beam with 122 pC/bunch at 75 MHz rep rate. Pulsed operation has also been demonstrated with 8 mA per pulse (110 pC/bunch) in 16 ms-long pulses at 2 Hz rep rate. Routinely the gun delivers 5 mA CW and pulse current at 135 pC/bunch for FEL operations. The Upgrade DC photocathode gun is a direct evolution of the DC photocathode gun used in the previous JLab 1 kW IR Demo FEL. Improvements in the vacuum conditions, incorporation of two UHV motion mechanisms (a retractable cathode and a photocathode shield door) and a new way to add cesium to the GaAs photocathode surface have extended its lifetime to over 500 Coulombs delivered between re-cesiations (quantum efficiency replenishment). With each photocathode activation quantum efficiencies above 6% are routinely achieved. The photocathode activation and performance will be described in detail.

 
 
WPAP058 The ILC Polarized Electron Source electron, cathode, gun, polarization 3420
 
  • A. Brachmann, J.E. Clendenin, E.G. Garwin, R.E. Kirby, D.-A.L. Luh, T.V.M. Maruyama, D.C. Schultz, J. Sheppard
    SLAC, Menlo Park, California
  • R.X.P. Prepost
    UW-Madison/PD, Madison, Wisconsin
  Funding: This work is supported by U.S. DOE contracts DE-AC02-76SF00515 (SLAC) and DE-AC02-76ER00881 (UW).

The SLC polarized electron source (PES) can meet the expected requirements of the International Linear Collider (ILC) for polarization, charge and lifetime. However, experience with newer and successful PES designs at JLAB, Mainz and elsewhere can be incorporated into a first-generation ILC source that will emphasize reliability and stability without compromising the photocathode performance. The long pulse train for the ILC may introduce new challenges for the PES, and in addition more reliable and stable operation of the PES may be achievable if appropriate R&D is carried out for higher voltage operation and for a simpler load-lock system. The outline of the R&D program currently taking shape at SLAC and elsewhere is discussed. The principal components of the proposed ILC PES, including the laser system necessary for operational tests, are described.

 
 
WPAT006 The SPARC RF Synchronization System gun, feedback, linac, klystron 1024
 
  • A. Gallo, D. Alesini, M. Bellaveglia, R. Boni, G. Di Pirro, F. Tazzioli
    INFN/LNF, Frascati (Roma)
  The SPARC project consists in a 150 MeV Linac aimed at driving an ondulator for the production of 530 nm SASE FEL radiation. A bunch transverse emittance as low as 1mm mrad and a bunch peak current of about 100 A are required for this task. The RF voltages in the RF gun and in the 3 S-band accelerating sections have to be kept phase locked within 3 ps to the arrival time of the laser pulse on the photocathode to guarantee the required performances. This specification will be reduced to 0.5 ps in the phas·10-2 of the project when the rectilinear RF compression of the bunch will be tested. The general architecture of the SPARC RF control system together with some bench qualification measurements of the basic components is presented in this paper.  
 
WPAT022 Low Level RF System for the Energy Recovery Linac Prototype linac, gun, feedback, pick-up 1781
 
  • A.J. Moss
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
  Funding: ASTeC Department, CCLRC Daresbury Laboratory.

The Low Level RF system is described for the Energy Recovery Linac Prototype (ERLP) being constructed at Daresbury Laboratory. An analogue based feedback system, built around low cost proprietary components, has been designed to control the 1.3GHz RF system for this project. The system is scaleable, has digital control and can be easily upgraded as greater understanding of the accelerator becomes known. The design of the system is based around the central core of a very low phase noise master oscillator, which can provide, multiple outputs and timing pulses at all the required frequencies for the RF, laser and accelerator sub-systems.

 
 
WPAT049 The Penetrability of a Thin Metallic Film Inside the RF Field cathode, electron, pick-up, impedance 3073
 
  • Y. Zhao, I. Ben-Zvi, R.H. Beuttenmuller, X.Y. Chang, C. Chen, R. Di Nardo, T. Rao
    BNL, Upton, Long Island, New York
  Funding: Under contract with the U.S. Department of Energy, Contract Number DE-AC02-98CH10886.

Thin metallic film was widely applied in varies area. Especially, recently we are planning to apply it in a "Secondary emission enhanced photo-injector," of which a diamond cathode is coated with a golden film or so on its back to serve as a current path. The thickness of the film is originally considered to be in the order of 10 nm, which is much less than the skin depth, say 1/200. Since it is so thin, that intuitively the RF filed is penetrable. However, we found it is not true. The film will block most of the field. This paper addresses theoretic analysis as well as the experimental results. All demonstrated that the penetrability of a thin film is very poor. Consequently, most of the RF current will flow on the thin film causing a serous heating problem.

 
 
RPAE013 Laser System for Photoelectron and X-Ray Production in the PLEIADES Compton Light Source scattering, electron, photon, linac 1347
 
  • D.J. Gibson, C.P.J. Barty, S.M. Betts, K. Crane, I. Jovanovic
    LLNL, Livermore, California
  Funding: This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.

The PLEIADES (Picosecond Laser-Electron Interaction for the Dynamic Evaluation of Structures) facility provides tunable short x-ray pulses with energies of 30-140 keV and pulse durations of 0.3 – 5 ps by scattering an intense, ultrashort laser pulse off a 35-75 MeV electron beam. Synchronization of the laser and electron beam is obtained by using a photoinjector gun, and using the same laser system to generate the electrons and the scattering laser. The Ti:Sapphire, chirped pulse amplification based 500 mJ, 50 fs, 810 nm scattering laser and the similar 300 μJ, 5 ps, 266 nm photoinjector laser systems are detailed. Additionally, an optical parametric chirped pulse amplification (OPCPA) system is studied as a replacement for part of the scattering laser front end. Such a change would significantly simplify the set-up the laser system by removing the need for active switching optics, as well as increase the pre-pulse contrast ratio which will be important when part of the scattering laser is used as a pump beam in pump-probe diffraction experiments using the ultrashort tunable x-rays generated as the probe.

 
 
RPAE015 High Energy, High Brightness X-Rays Produced by Compton Back Scattering at the Livermore PLEIADES facility electron, brightness, lattice, linac 1464
 
  • A.M. Tremaine, S.G. Anderson, S.M. Betts, K. Crane, D.J. Gibson, F.V. Hartemann, J.S. Jacob
    LLNL, Livermore, California
  • P. Frigola, J. Lim, J.B. Rosenzweig, G. Travish
    UCLA, Los Angeles, California
  Funding: This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract no. W-7405-Eng-48.

PLEIADES (Picosecond Laser Electron Interaction for the Dynamic Evaluation of Structures) produces tunable 30-140 keV x-rays with 0.3-5 ps pulse lengths and 107 photons/pulse by colliding a high brightness electron beam with a high power laser. The electron beam is created by an rf photo-injector system, accelerated by a 120 MeV linac, and focused to 20 mm with novel permanent magnet quadrupoles. To produce Compton back scattered x-rays, the electron bunch is overlapped with a Ti:Sapphire laser that delivers 500 mJ, 80 fs, pulses to the interaction point. K-edge radiography at 115 keV on Uranium has verified the angle correlated energy spectrum inherent in Compton scattering and high-energy tunability of the Livermore source. Current upgrades to the facility will allow laser pumping of targets synchronized to the x-ray source enabling dynamic diffraction and time-resolved studies of high Z materials. Near future plans include extending the radiation energies to >400 keV, allowing for nuclear fluorescence studies of materials.

 
 
RPAE020 Production of High Harmonic X-Ray Radiation from Non-linear Thomson at LLNL PLEIADES electron, scattering, radiation, focusing 1673
 
  • J. Lim, A. Doyuran, P. Frigola, J.B. Rosenzweig, G. Travish
    UCLA, Los Angeles, California
  • S.G. Anderson, M. Betts, K. Crane, D.J. Gibson, F.V. Hartemann, A.M. Tremaine
    LLNL, Livermore, California
  Funding: US-DOE under contract no. DE-FG-98ER45693 and DE-FG03-92ER40693, and by LLNL under contract no. W-7405-Eng-48 and the LLNL ILSA program under contract LS04-001-B.

We describe an experiment for production of high harmonic x-ray radiation from Thomson backscattering of an ultra-short high power density laser by a relativistic electron beam at the PLEIADES facility at LLNL. In this scenario, electrons execute a “figure-8” motion under the influence of the high-intensity laser field, where the constant characterizing the field strength is expected to exceed unity: $aL=e*EL/m*c*ωL ≥ 1$. With large $aL$ this motion produces high harmonic x-ray radiation and significant broadening of the spectral peaks. This paper is intended to give a layout of the PLEIADES experiment, along with progress towards experimental goals.

 
 
RPAE021 Feasibility Study of a Laser Beat-Wave Seeded THz FEL at the Neptune Laboratory electron, undulator, radiation, beat-wave 1721
 
  • S. Reiche, C. Joshi, C. Pellegrini, J.B. Rosenzweig, S. Tochitsky
    UCLA, Los Angeles, California
  • G. Shvets
    The University of Texas at Austin, Austin, Texas
  Funding: The work was supported by the DOE Contract No. DE-FG03-92ER40727.

Free-Electron Laser in the THz range can be used to generate high output power radiation or to modulate the electron beam longitudinally on the radiation wavelength scale. Microbunching on the scale of 1-5 THz is of particular importance for potential phase-locking of a modulated electron beam to a laser-driven plasma accelerating structure. However the lack of a seeding source for the FEL at this spectral range limits operation to a SASE FEL only, which denies a subpicosecond synchronization of the current modulation or radiation with an external laser source. One possibility to overcome this problem is to seed the FEL with two external laser beams, which difference (beat-wave) frequency is matched to the resonant FEL frequency in the THz range. In this presentation we study feasibility of an experiment on laser beat-wave injection in the THz FEL considered at the UCLA Neptune Laboratory, where both a high brightness photoinjector and a two-wavelength, TW-class CO2 laser system exist. By incorporating the energy modulation of the electron beam by the ponderomotive force of the beat-wave in a modified version of the time-dependent FEL code Genesis 1.3, the performance of a FEL at Neptune is simulated and analyzed.

 
 
RPAE022 Improved Long Radius of Curvature Measurement System for FEL Mirrors wiggler, electron, optics, radiation 1787
 
  • J. Li, C. Sun, Y.K. Wu
    DU/FEL, Durham, North Carolina
  Funding: This work is supported by the U.S. AFOSR MFEL grant F49620-001-0370.

The 53.73 meter long Duke free electron laser (FEL) cavity consists of two concave mirrors with radius of curvature longer than 27 meters. A proper radius of curvature is designed to achieve an optimal and stable operation of the FEL. This requires accurate measurements of the cavity mirror's radius of curvature before its initial installation. Subsequent radius of curvature measurements are performed to ensure no significant deformation of the mirror occurs after a period of extensive use. A direct measurement based upon the geometric optics principles has been used at DFELL for years. Recently, we have significantly upgraded this measurement apparatus by utilizing a HeNe laser as the light source and a straight wire with a proper size as the object. In this paper we describe the details of the measurement setup and report the benefits of the recent upgrades. In addition, we report the improved data analysis technique and results of recent long radius of curvature measurements.

 
 
RPAE032 Femtosecond Laser-Electron Interaction in a Storage Ring Studied by Terahertz Radiation electron, radiation, dipole, storage-ring 2239
 
  • K. Holldack, S. Khan, T. Quast
    BESSY GmbH, Berlin
  • R. Mitzner
    Universität Muenster, Physikalisches Institut, Muenster
  Funding: This work was supported by the german Bundesministerium für Bildung und Forschung (BMBF).

The laser-induced energy modulation of relativistic electrons in the BESSY II storage ring was studied by temporal and spectral characterization of femtosecond far infrared (THz) pulses being emitted due to the fact that dispersive elements convert the energy modulation into a longitudinal density modulation. Bunch shapes down to 3 ps and phase noise effects as well as the length of the femtosecond density modulation and its temporal decay were measured. The THz diagnostics is crucial for the operation of the recently commissioned undulator based "femtosecond slicing" source at BESSY.

 
 
RPAE033 Commissioning Results from the BESSY II Femtoslicing Source electron, polarization, radiation, background 2309
 
  • S. Khan, K. Holldack, T. Kachel, T. Quast
    BESSY GmbH, Berlin
  • R. Mitzner
    Universität Muenster, Physikalisches Institut, Muenster
  Funding: Funded by the Bundesministerium für Bildung und Forschung and by the Land Berlin.

At the BESSY II storage ring, a source of sub-100 fs x-ray pulses with tunable polarization and excellent signal-to-background ratio has been constructed in 2004. This source is based on laser-induced energy modulation ("femtoslicing") and subsequent angular separation of the short-pulse x-rays emitted by an elliptical undulator. The paper reviews the layout of the source and reports on new insights and experimental results obtained while commissioning the source for user operation.

 
 
RPAE034 Storage Ring Fill Patterns for Femtoslicing Applications electron, radiation, injection, single-bunch 2327
 
  • S. Khan
    BESSY GmbH, Berlin
  Funding: Funded by the Bundesministerium für Bildung und Forschung and by the Land Berlin.

The generation of laser-induced ultrashort synchrotron radiation pulses ("femtoslicing") during user operation at the BESSY II storage ring requires to add several bunches with enhanced charge to the routinely used multibunch fill. The paper addresses these specialized fill patterns in view of beam stability against multibunch oscillations and ion effects, beam lifetime, and the effect of beam loading on the synchronous phase angles.

 
 
RPAE066 Terahertz Coherent Synchrotron Radiation from Femtosecond Laser Modulation of the Electron Beam at the Advanced Light Source radiation, lattice, synchrotron, electron 3682
 
  • J.M. Byrd, Z. Hao, M.C. Martin, D. Robin, F. Sannibale, R.W. Schoenlein, A. Zholents, M.S. Zolotorev
    LBNL, Berkeley, California
  Funding: Work supported by the U.S. Department of Energy under Contract No. DE-AC03-76SF00098.

At the Advanced Light Source (ALS), the "femtoslicing" beamline is in operation since 1999 for the production of x-ray synchrotron radiation pulses with femtosecond duration. The mechanism used for generating the short x-ray pulses induces at the same time temporary structures in the electron bunch longitudinal distribution with very short characteristic length. Such structures emit intense coherent synchrotron radiation (CSR) in the terahertz frequency range. This CSR, whose measured intensity is routinely used as a diagnostics for the tune-up of the femtoslicing experiments, represents a potential source of terahertz radiation with very interesting features. Several measurements have been performed for its characterization and in this paper an updated description of the experimental results and of their interpretation is presented.

 
 
RPAE069 Terahertz Coherent Synchrotron Radiation in the MIT-Bates South Hall Ring lattice, synchrotron, storage-ring, electron 3783
 
  • F. Wang, dc. Cheever, M. Farkhondeh, W.A. Franklin, W. Graves, E. Ihloff, C. Tschalaer, D. Wang, D. Wang, T. Zwart, J. van der Laan
    MIT, Middleton, Massachusetts
  • G.L. Carr, B. Podobedov
    BNL, Upton, Long Island, New York
  • F. Sannibale
    LBNL, Berkeley, California
  We investigate the terahertz coherent synchrotron radiation (CSR) potential of the South Hall Ring (SHR) at MIT-Bates Linear Accelerator Center. The SHR is equipped with a unique single cavity, 2.856 GHz RF system. The high RF frequency is advantageous for producing short bunch length and for having higher bunch current threshold to generate stable CSR. Combining with other techniques such as external pulse stacking cavity, femtosecond laser slicing, the potential for generating ultra-stable, high power, broadband terahertz CSR is very attractive. Beam dynamics issues related to short bunch length operation, and may associated with the high frequency RF system, such as multi-bunch instability are concerned. They could affect bunch length, bunch intensity and beam stability. The SHR is ideal for experimental exploration of these problems. Results of initial test of low momentum compaction lattice and bunch length measurements are presented and compared to expectations.  
 
RPAE082 The New Undulator Based fs-Slicing Beamline at the ALS undulator, insertion, insertion-device, wiggler 4096
 
  • C. Steier, D. Robin, F. Sannibale, R.W. Schoenlein, W. Wan, W. Wittmer, A. Zholents
    LBNL, Berkeley, California
  Funding: This work was supported by the U.S. Department of Energy, under Contract No. DE-AC03-76SF00098.

The existing Femtoslicing beamline at the ALS employs a femtosecond laser beam interacting resonantly with the electron beam in a wiggler (modulator). The induced energy spread over the femtosecond duration is converted to a transverse displacement by exploiting the storage ring dispersion. The displaced femtosecond pulse radiates and produces femtosecond synchrotron radiation. Up to now a regular bending magnet was used as radiator. To improve the flux, a significant upgrade was implemented, replacing the modulator, installing an in-vacuum undulator as new radiator, and installing a higher repeptition rate laser system. The new beamline will provide 100-200 fs long pulses of soft and hard x-rays with moderate flux and with a repetion rate of 10-40 kHz for experiments concerning ultrafast dynamics in solid state physics, chemistry and biology. To achieve the necessary spatial separation of the energy modulated slice from the rest of the bunch, a sizeable local vertical dispersion bump in the radiator is required. All accelerator physics aspects of the upgrade including challenging issues like the impact on the transverse single particle dynamics will be discussed together with initial results of the commissioning.

 
 
RPAP006 X-Band Linac Beam-Line for Medical Compton Scattering X-Ray Source photon, electron, linac, scattering 994
 
  • K. Dobashi
    NIRS, Chiba-shi
  • M. Akemoto, H. Hayano, T. Higo, J.U. Urakawa
    KEK, Ibaraki
  • F. Ebina, A. Fukasawa, T. Kaneyasu, H. Ogino, F. Sakamoto, M. Uesaka, Y. Yamamoto
    UTNL, Ibaraki
  Compton scattering hard X-ray source for 10~80 keV are under construction using the X-band (11.424 GHz) electron linear accelerator and YAG laser at Nuclear Engineering Research laboratory, University of Tokyo. This work is a part of the national project on the development of advanced compact medical accelerators in Japan. National Institute for Radiological Science is the host institute and U. Tokyo and KEK are working for the X-ray source. Main advantage is to produce tunable monochromatic hard ( 10-80 keV) X-rays with the intensities of 108-10 photons/s (at several stages) and the table-top size. Second important aspect is to reduce noise radiation at the beam dump by adopting the deceleration of electrons after the Compton scattering. The X-ray yield by the electron beam and Q-switch Nd:YAG laser of 2.5 J/10 ns is 107 photons/RF-pulse (108 photons/sec in 10 pps). X-band beam line for the demonstration is under commissioning. We also design to adopt a technique of laser circulation to increase the X-ray yield up to 109 photons/pulse (1010 photons/s). The construction of the whole system starts. X-ray generation and medical application will be performed in this year.  
 
RPAP010 Development of Femtosecond and Attosecond Pulse Radiolysis by Using Laser Photocathode RF Gun S-Band Electron Linac electron, linac, gun, cathode 1198
 
  • Y. Yoshida, T. Kondo, J. Yang
    ISIR, Osaka
  Funding: Grant-in-Aid for Scientific Research, Japan Society for the Promotion of Science.

Femtosecond pulse radiolysis system based on linear accelerator was developed in Osaka University for study of radiation-induced ultra fast physical and chemical reactions. 35 MeV single electron pulse with pulse width of 100 fs was generated by using a laser photocathode rf gun s-band linac with a magnet pulse compression system. Femtosecond laser synchronized with the linac was used as analyzing light. Transient absorption was measured by the equivalent velocity spectroscopy which was a new method to get high time-resolution. Also, we have started the preliminary experiment on atosecond pulse radiolysis The double decker beam which is a new concept to realize the twin linac by using one linac will be used.

 
 
RPAP011 Technical Development of Profile Measurement for the Soft X-Ray Via Compton Backward Scattering electron, scattering, background, quadrupole 1260
 
  • T. Saito, Y. Hama, K. Hidume, S. Minamiguchi, A. Oshima, D. Ueyama, M. Washio
    RISE, Tokyo
  • H. Hayano, J.U. Urakawa
    KEK, Ibaraki
  • S. Kashiwagi
    ISIR, Osaka
  • R. Kuroda
    AIST, Tsukuba, Ibaraki
  A compact X-ray source is called for such various fields as material development, biological science, and medical treatment. At Waseda University, we have already succeeded to generate the soft X-ray of the wavelength within so-called water window region (250-500eV) via Compton backward scattering between 1047nm Nd:YLF laser and 4.2MeV high quality electron beam. Although this method equips some useful characters, e.g. high intensity, short pulse, energy variableness, etc, the X-ray generating system is compact enough to fit in tabletop size. In the next step, there rises two principal tasks, that is, to make the soft X-ray intensity higher, and to progress X-ray profile measurement techniques as preliminary experiments for biomicroscopy. Specifically, we utilize two-pass amp for the former, and irradiate X-ray to a resist film which is previously exposed by UV lamp or get images with X-ray CCD for the latter. In this conference, we will show the experimental results and some future plans.  
 
RPAP033 Investigation of X-Ray Harmonics of the Polarized Inverse Compton Scattering Experiment at UCLA electron, photon, scattering, permanent-magnet 2303
 
  • A. Doyuran, R.J. England, C. Joshi, J. Lim, J.B. Rosenzweig, S. Tochitsky, G. Travish, O. Williams
    UCLA, Los Angeles, California
  Funding: U.S. Dept. of Energy grant DE-FG03-92ER40693.

An Inverse Compton Scattering (ICS) experiment, which will investigate nonlinear properties of scattering utilizing a terawatt CO2 laser system with various polarizations, is ongoing at the UCLA Neptune Laboratory. When the normalized amplitude of the incident laser’s vector potential a0 is larger than unity the scattering occurs in the nonlinear region; therefore, higher harmonics are also produced. ICS can be used, e.g., for a polarized positron source by striking a thin target (such as tungsten) with the polarized X-rays. As such, it is critical to demonstrate the production of polarized scattered photons and to investigate the ICS process as it enters the nonlinear regime. We present the description of the experimental set up and equipment utilized, including diagnostics for electron and photon beam detection. We present the current status of the experiment.

 
 
RPAP038 An Advantage of the Equivalent Velocity Spectroscopy for Femtsecond Pulse Radiolysis electron, gun, linac, emittance 2533
 
  • T. Kondoh, T. Kozawa, S. Tagawa, T. Tomosada, J. Yang, Y. Yoshida
    ISIR, Osaka
  Funding: Grant-in-Aid for Scientific Research, Japan Society for the Promotion of Science.

For studies of electron beam induced ultra-fast reaction process, femtosecond(fs) pulse radiolysis is under construction. To realize fs time resolution, fs electron and analyzing light pulses and their jitter compensation system are needed. About a 100fs electron pulse was generated by a photocathode RF gun linac and a magnetic pulse compressor. Synchronized Ti: Sapphire laser have a puleswidth about 160fs. And, it is significant to avoid degradation of time resolution caused by velocity difference between electron and analyzing light in a sample. In the ‘Equivalent velocity spectroscopy’ method, incident analyzing light is slant toward electron beam with an angle associated with refractive index of sample. Then, to overlap light wave front and electron pulse shape, electron pulse shape is slanted toward the direction of travel. As a result of the equivalent velocity spectroscopy for hydrated electrons, using slanted electron pulse shape, optical absorption rise time was about 1.4ps faster than normal electron pulse shape. Thus, the 'Equivalent velocity spectroscopy’ is effective for femtosecond pulse radiolysis.

 
 
RPAP045 Development of Laser-Induced Fluorescence Diagnostic for the Paul Trap Simulator Experiment ion, ion-source, diagnostics, background 2878
 
  • M. Chung, R.C. Davidson, P. Efthimion, E.P. Gilson, R. M. Majeski, E. Startsev
    PPPL, Princeton, New Jersey
  Funding: Research Supported by the U.S. Department of Energy.

The Paul Trap Simulator Experiment (PTSX) is a cylindrical Paul trap whose purpose is to simulate the nonlinear dynamics of intense charged particle beam propagation in alternating-gradient magnetic transport systems. For the in-situ measurement of the transverse ion density profile in the PTSX device, which is essential for the study of beam mismatch and halo particle production, a laser-induced fluorescence diagnostic system is being developed. Instead of cesium, which has been used in the initial phase of the PTSX experiment, barium has been selected as the preferred ion for the laser-induced fluorescence diagnostic. The installation of the barium ion source and the characterization of the tunable dye laser system are discussed. The design of the collection optics with an intensified CCD camera system is also discussed. Finally, initial test results using the laser-induced fluorescence diagnostic will be presented.

 
 
RPAT001 Experimental Results of a Non-Destructive Emittance Measurement Device for H- Beams ion, emittance, simulation, dipole 782
 
  • C. Gabor, H. Klein, O. Meusel, U. Ratzinger
    IAP, Frankfurt-am-Main
  • J. Pozimski
    Imperial College of Science and Technology, Department of Physics, London
  For the diagnostic of high power ion beams, non-destructive measurement devices should not only provide minimum influence on the beam itself, but also avoid various problems that occur when the high power density of the beam penetrates surfaces like slit- or pinhole plates. On the other hand, measurements of resolution should be comperable with destructive methods. Beams of negative ions offer the use of a non-destructive Emittance Measurement Instrument (EMI) based on the principle of photo detachment. Interaction of laser photons with the negative ions causes electron detachment. Due to moving the postion of the well collimated laser beam acros the ion beam the produced neutral atoms are well suited to detect the transverse beam emittance like a classical slit-grid device. After separation in a magnetic dipole, the neutrals can be viewed on a scintillator screen with a CCD camera. To investigate the use of such a photo detachment EMI and to study the transport of negative ions an experiment consisting of H minus ion source, electrostatic LEBT and EMI was constructed. The paper will present the setup of the experimental hardware and first results of measurements.  
 
RPAT047 Preliminary Design of a Femtosecond Oscilloscope electron, photon, interaction-region, electromagnetic-fields 2944
 
  • E.D. Gazazyan, K.A. Ispirian, A.T. Margaryan
    YerPhI, Yerevan
  • D.K. Kalantaryan
    YSU, Yerevan
  • E.M. Laziev
    CANDLE, Yerevan
  The calculations on motion of electrons in a finite length electromagnetic field of linearly and circularly polarized laser beams have shown that one can use the transversal deflection of electrons on a screen at a certain distance after the interaction region for the measurement of the length and longitudinal particle distribution of femtosecond bunches. In this work the construction and preliminary parameters of various parts of a device that may be called femtosecond oscilloscope are considered. The influence of various factors, such as the energy spread and size of the electron bunches, are taken into account. For CO2 laser intensity 1016 W/cm2 and field free drift length 1m the deflection is 5.3 and 0.06 cm, while the few centimeters long interaction length between 2 mirrors requires assembling accuracy 6 mm and 1.3 micron for 20 MeV to 50 keV, respectively.  
 
RPAT049 Numerical Studies on the Electro-Optic Sampling of Relativistic Electron Bunches electron, resonance, lattice, simulation 3070
 
  • S. Casalbuoni, H. Schlarb, B. Schmidt, B. Steffen
    DESY, Hamburg
  • P. Schmüser, A. Winter
    Uni HH, Hamburg
  Ultraviolet and X ray free electron lasers require sub-picosecond electron bunches of high charge density. Electro-optic sampling (EOS) is a suitable diagnostic tool for resolving the time structure of these ultrashort bunches. The transient electric field of the relativistic bunch induces a polarization anisotropy in a nonlinear crystal which is sampled by femtosecond laser pulses. In this paper, the EOS process is studied in detailed numerical calculations. The THz and the laser pulses are treated as wave packets which are propagated through the zinc telluride resp. gallium phosphide crystals. The effects of signal broadening and distortion are taken into account. The time resolution is limited by the lowest lattice oscillation frequency which amounts to 5.3 THz in ZnTe and 11 THz in GaP. The shortest bunch length which can be resolved with moderate distortion is about 200 fs (FWHM) in ZnTe and 100 fs in GaP.  
 
RPAT050 Electro Optic Bunch Length Measurements at the VUV-FEL at DESY linac, electron, polarization, free-electron-laser 3111
 
  • B. Steffen, S. Casalbuoni, E.-A. Knabbe, H. Schlarb, B. Schmidt
    DESY, Hamburg
  • P. Schmüser, A. Winter
    Uni HH, Hamburg
  For the operation of a SASE FEL, the longitudinal bunch length is one of the most critical parameters. At the superconducting linac of the VUV-FEL at DESY, we have installed an electro optic sampling (EOS) experiment to probe the time structure of the electric field of the bunches to better than 100 fs rms. The field-induced birefringence of a ZnTe crystal is detected by a femtosecond laser pulse (TiSa) and the time structure is measured by scanning the relative timing of the electron bunch and the TiSa pulse. A synchronization stability of better than 50 fs between laser and accelerator RF has been achieved. First results on the synchronization measurements and for the bunch length as function of the linac parameters are presented.  
 
RPAT075 Optical Synchronization Systems for Femtosecond X-Ray Sources polarization, linac, synchrotron, scattering 3958
 
  • R.B. Wilcox, J.W.  Staples
    LBNL, Berkeley, California
  • R. Holzwarth
    Menlo Systems GmbH, Martinsried
  Funding: This work was supported by the Laboratory Directed Research and Development Program of Lawrence Berkeley National Laboratory under the Department of Energy Contract No. DE-AC03-76SF00098.

In femtosecond pump/probe experiments using short x-ray and optical pulses, precise synchronization must be maintained between widely separated lasers in a synchrotron or FEL facility. We are developing synchronization systems using optical signals for applications requiring different ranges of timing error. For the sub-100fs range we use an amplitude modulated CW laser at 1GHz to transmit RF phase information, and control the delay through a 100m fiber by observing the retroreflected signal. Initial results show 40fs peak-to-peak error above 10Hz, and 200fs long term drift, mainly due to amplitude sensitivity in the analog mixers. For the sub-10fs range we will lock two single-frequency lasers separated by several teraHertz to a master modelocked fiber laser, transmit the two frequencies over fiber, and lock two comb lines of a slave laser to these frequencies, thus synchronizing the two modelocked laser envelopes. For attosecond synchronization we propose a stabilized, free space link using bulk lens waveguides and high peak power ultrashort pulses.

 
 
RPAT082 Coherent Transition Radiation To Measure the SLAC Electron Bunch Length electron, radiation, background, alignment 4102
 
  • P. Muggli
    USC, Los Angeles, California
  • C.D. Barnes, M.J. Hogan, P. Krejcik, R. Siemann, D.R. Walz
    SLAC, Menlo Park, California
  • R. Ischebeck, H. Schlarb
    DESY, Hamburg
  Funding: Work supported by U.S. DOE.

Ultrashort electron bunches are now available at Stanford Linear Accelerator Center and are use mainly to produce short bursts of x-rays in a magnetic undulator and for plasma wakefield acceleration experiments. The shortest bunches have an rms longitudinal width of 10 microns, and a peak current of about 30 kA. Methods to measure such short bunch lengths include electro-optic modulation of a short laser pulse in a nonlinear crystal and coherent transition (CTR) autocorrelation. The transition radiation spectrum emitted by the bunches when traversing a 1 micron thin titanium foil is coherent for wavelengths longer that the bunch length and extends into the millimeter wavelength range. A CTR far-infrared autocorrelator was used to measure the bunch length as a function of the accelerator. The results obtained with this autocorrelator are the only measurements of the SLAC ultra-short bunches to date. Experimental results, as well as the limitations of the measurements and the future improvements to the autocorrelator will be presented.

 
 
RPAT083 Beam Profile Measurements and Simulations of the PETRA Laser-Wire electron, photon, simulation, collider 4123
 
  • J. Carter, I.V. Agapov, G.A. Blair, G.E. Boorman, C.D. Driouichi, F. Poirier, M.T. Price
    Royal Holloway, University of London, Surrey
  • K. Balewski, H.-C. Lewin, S. Schreiber, K. Wittenburg
    DESY, Hamburg
  • S.T. Boogert, S. Malton
    UCL, London
  • N. Delerue, D.F. Howell
    OXFORDphysics, Oxford, Oxon
  • T.  Kamps
    BESSY GmbH, Berlin
  The laser-wire will be an essential diagnostic tool at the International Linear Collider and advanced light sources. It uses a finely focussed laser beam to measure the transverse profile of electron bunches by detecting the Compton-scattered photons (or electrons) downstream of where the laser beam intersects the electron beam. Such a system has been installed at the PETRA storage ring at DESY, which uses a piezo-driven mirror to scan the laser light across the electron beam. Latest experimental results are presented and compared to detailed simulations using Geant4.  
 
RPAT091 Longitudinal Electron Bunch Diagnostics Using Coherent Transition Radiation electron, radiation, simulation, linac 4254
 
  • D. Mihalcea, C.L. Bohn
    Northern Illinois University, DeKalb, Illinois
  • U. Happek
    UGA, Athens, Georgia
  • P. Piot
    Fermilab, Batavia, Illinois
  The longitudinal charge distribution of electron bunches in the Fermilab A0 photo-injector was determined by using the coherent transition radiation produced by electrons passing through a thin metallic foil. The auto-correlation of the transition radiation signal was measured with a Michelson type interferometer. The response function of the interferometer was determined from measured and simulated power spectra for low electron bunch charge and maximum longitudinal compression. Kramers-Kroning technique was used to determine longitudinal charge distribution. Measurements were performed for electron bunch lengths in the range from 0.3 to 2 ps (rms).  
 
RPAT094 Femtosecond Synchronisation of Ultrashort Pulse Lasers to a Microwave RF Clock linac, monitoring, resonance, feedback 4299
 
  • A. Winter
    Uni HH, Hamburg
  • N. Ignashin, A. Simonov, S. Sytov
    IHEP Protvino, Protvino, Moscow Region
  • E.-A. Knabbe, S. Simrock, B. Steffen
    DESY, Hamburg
  A precise synchronization between the laser repetition rate and the linac-RF is mandatory for electro-optic sampling or pump-probe experiments. The level of stability is usually determined by measuring of the spectral noise power density of the feedback signal when the system is locked. However, an independent measurement is needed to confirm this. In this paper, we present an approach exploiting electronic techniques to synchronize a TiSa laser to the RF of the DESY VUVFEL with sub-50 fs stability. The remaining time jitter is measured by an RF monitoring system independent of the locking PLL.  
 
ROAB010 Development of a Compact Radiography Accelerator Using Dielectric Wall Accelerator Technology cathode, vacuum, pulsed-power, acceleration 716
 
  • S. Sampayan, G.J. Caporaso, Y.-J. Chen, S.A. Hawkins, L. Holmes, J.F. McCarrick, S.D. Nelson, C. Nunnally, B.R. Poole, A. Rhodes, M. Sanders, S. Sullivan, L. Wang, J.A. Watson
    LLNL, Livermore, California
  Funding: This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

We are developing of a compact accelerator system primarily intended for pulsed radiography. Design characteristics are an 8 MeV endpoint energy, 2 kA beam current and a cell gradient of approximately 3 MV/m. Overall length of the device is below 3 m. Such compact designs have been made possible with the development of high specific energy dielectrics (> 10 J/cc), specialized transmission line designs and multi-gap laser-triggered low jitter (<1 ns) gas switches. In this geometry, the pulse forming lines, switches and insulator/beam pipe are fully integrated within each cell to form a compact stand-alone stackable unit. We detail our research and modeling to date, recent high voltage test results, and the integration concept of the cells into a radiographic system.

 
 
RPPE010 Beam Transport Devices for the 10kW Free Electron Laser at Thomas Jefferson National Accelerator Facility electron, vacuum, beam-transport, photon 1210
 
  • L.A. Dillon-Townes, C.P. Behre, M.E. Bevins, G.H. Biallas, D. Douglas, C.W. Gould, J.G. Gubeli, D.H. Kashy, R. Lassiter, L. Munk, G. Neil, M.D. Shinn, S. Slachtouski, D. Waldman
    Jefferson Lab, Newport News, Virginia
  Funding: Department of Energy

The beam transport vacuum components for the 10 kW Free Electron Laser (FEL) at Thomas Jefferson National Accelerator Facility (TJNAF) were designed to address 10 MeV electron beam characteristics and maintain an accelerator transport vacuum of 10-9 torr. The components discussed include a novel zero length beam clipper, novel shielded bellows, one decade differential pumping stations with a 7.62 cm (3.0”) aperture, and a 50 kW beam dump. Incorporation of these accelerator transport components assist in establishing the environment needed for the electron beam to produce the optical light required to lase at 10 kW.

 
 
RPPE045 Vacuum Pumping Performance Comparison of Non-Evaporable Getter Thin Films Deposited Using Argon and Krypton as Sputtering Gases vacuum, cathode, target, linac 2860
 
  • X. Liu, Y. He, Y. Li
    Cornell University, Department of Physics, Ithaca, New York
  • M.R. Adams
    Cornell University, Ithaca, New York
  Funding: Work Supported by the National Science Foundation.

Owing to the outstanding vacuum performance and the low secondary electron yield, non-evaporable getter (NEG) thin film deposited onto interior walls has gained widespread acceptance and has been incorporated into many accelerator vacuum system designs. The titanium-zirconium-vanadium (T-Zr-V) NEG thin films were deposited onto the interior wall of stainless steel pipes via DC magnetron sputtering method using either argon or krypton gas as sputtering gas. Vacuum pumping evaluation tests were carried out to compare vacuum pumping performances of the Ti-Zr-V NEG thin films deposited using argon or krypton. The results showed much higher initial pumping speed for the Kr-sputtered NEG film than the Ar-sputtered film, though both films have similar activation behavior. The compositions and textures of both thin films were measured to correlate to the pumping performances.

 
 
RPPT013 Status of the SPARC Project gun, emittance, undulator, klystron 1327
 
  • L. Serafini, F. Alessandria, A. Bacci, S. Cialdi, C. De Martinis, D. Giove, M. Mauri, M. Rome, L. Serafini
    INFN-Milano, Milano
  • D. Alesini, M. Bellaveglia, S. Bertolucci, M.E. Biagini, R. Boni, M. Boscolo, M. Castellano, A. Clozza, G. Di Pirro, A. Drago, A. Esposito, M. Ferrario, L. Ficcadenti, D. Filippetto, V. Fusco, A. Gallo, G. Gatti, A. Ghigo, S. Guiducci, M. Incurvati, C. Ligi, F. Marcellini, M.  Migliorati, A. Mostacci, L. Palumbo, L. Pellegrino, M.A. Preger, R. Ricci, C. Sanelli, M. Serio, F. Sgamma, B. Spataro, A. Stecchi, A. Stella, F. Tazzioli, C. Vaccarezza, M. Vescovi, C. Vicario
    INFN/LNF, Frascati (Roma)
  • I. Boscolo, C. Maroli, V. Petrillo
    Universita' degli Studi di Milano, MILANO
  • F. Broggi
    INFN/LASA, Segrate (MI)
  • L. Catani, E. Chiadroni, A. Cianchi, E. Gabrielli, S. Tazzari
    INFN-Roma II, Roma
  • F. Ciocci, G. Dattoli, A. Dipace, A. Doria, F. Flora, G.P. Gallerano, L. Giannessi, E. Giovenale, G. Messina, P.L. Ottaviani, S. Pagnutti, G. Parisi, L. Picardi, M. Quattromini, A. Renieri, G. Ronci, C. Ronsivalle, M. Rosetti, E. Sabia, M. Sassi, A. Torre, A. Zucchini
    ENEA C.R. Frascati, Frascati (Roma)
  • D. Dowell, P. Emma, C. Limborg-Deprey, D.T. Palmer
    SLAC, Menlo Park, California
  • D. Levi, M. Mattioli, G. Medici, P. Musumeci, D. Pelliccia
    Università di Roma I La Sapienza, Roma
  • M. Nisoli, S. Stagira, S. de Silvestri
    Politecnico/Milano, Milano
  • M. Petrarca
    INFN-Roma, Roma
  • J.B. Rosenzweig
    UCLA, Los Angeles, California
  The SPARC project has entered its installation phase at INFN-LNF: its main goal is the promotion of an R&D activity oriented to the development of a high brightness photoinjector to drive SASE-FEL experiments. The design of the 150 MeV photoinjector has been completed and the construction of its main components is in progress, as well as the design of the 12 m undulator. In this paper we will report on the installation and test of some major components, like the Ti:Sa laser system to drive the photo-cathode, the RF gun, the RF power system, as well as some test results on the RF deflector and 4th harmonic X-band cavity prototypes. Advancements in the control and beam diagnostics systems will also be reported, in particular on the emittance-meter device for beam emittance measurements in the drift space downstream the RF gun. Recent results on laser pulse shaping, obtained with two alternative techniques (DAZZLER and Liquid Crystal Mask), show the feasibility of producing 10 ps flat-top laser pulses in the UV with rise time below 1 ps, as needed to maximize the achievable beam brightness. First FEL experiments have been proposed, using SASE, seeding and non-linear resonant harmonics: these will be briefly described.  
 
RPPT027 Considerations on Beam Quality Control in MIT X-Ray FEL linac, electron, feedback, emittance 1961
 
  • D. Wang, W. Graves, D. Wang, T. Zwart
    MIT, Middleton, Massachusetts
  • P. Emma, J. Wu
    SLAC, Menlo Park, California
  • G. Huang
    LBNL, Berkeley, California
  Funding: U.S. Department of Energy.

The next generation of x-ray FEL requires very high quality electron beams for producing unprecedented x-ray radiations. In proposed x-ray FEL facilities, especially those that use multi-stage high gain high harmonic (HGHG) principle to obtain coherence in both transverse and longitudinal dimensions, the arrival timing of electron bunches must be very precise to ensure the seed laser overlap the desired sections of the electron bunch. A scheme is proposed to achieve 10s fs level of arrival timing control level.

 
 
RPPT030 Alternate Tunings for the Linac Coherent Light Source Photoinjector emittance, cathode, space-charge, injection 2140
 
  • C. Limborg-Deprey, P. Emma
    SLAC, Menlo Park, California
  Funding: This work was supported by US Department of Energy, contract No. DE-AC03-76SF00515A06.

The Linac Coherent Light Source (LCLS) is an x-ray free-electron laser (FEL) project based on the SLAC linac. The LCLS Photoinjector beamline has been designed to deliver 10 ps long electron bunches of 1nC with a normalized transverse emittance of less than 1 mm.mrad for 80% of the slices constituting the core of the bunch at 135 MeV. Tolerances and regulation requirements are tight for this tuning. The main contribution to emittance is the "cathode emittance which counts for 0.72 mm.mrad for the nominal tuning. As the "cathode emittance" scales linearly with laser spot radius, the emittance will be dramatically reduced for smaller radius, but this is only possible at lower charge. In particular, for a 0.2nC, we believe we can achieve an emittance closer to 0.4 mm.mrad. This working point will be easier to tune and the beam quality should be much easier to maintain than for the nominal one. In this paper, we also discuss how emittance could be further reduced by using the appropriate laser pulse shaping.

 
 
RPPT037 Technique for the Generation of Attosecond X-Ray Pulses Using an FEL electron, undulator, radiation, background 2506
 
  • G. Penn, A. Zholents
    LBNL, Berkeley, California
  Funding: This work was supported by the Office of Science, High Energy Physics, U.S. Department of Energy under Contract No. DE-AC03-76SF00098.

We describe a technique for the generation of an isolated burst of X-ray radiation with a duration of ~100 attoseconds in a free electron laser (FEL) employing self-amplified spontaneous emission. Our scheme relies on an initial interaction of the electron beam with an ultra-short laser pulse in a one-period wiggler followed by compression in a dispersive section. The result of this interaction is to create a sub-femtosecond slice of the electron beam with enhanced growth rates for FEL amplification. After many gain lengths through the FEL undulator, the X-ray output from this slice dominates the radiation of the entire bunch. We consider the impact of various effects on the efficiency of this technique. Different configurations are considered in order to realize various timing structures for the resulting radiation.

 
 
RPPT038 Phase Noise Characteristics of Fiber Lasers as Potential Ultra-Stable Master Oscillators electron, booster, radio-frequency, feedback 2521
 
  • A. Winter, P. Schmüser
    Uni HH, Hamburg
  • J. Chen, F.O. Ilday, F.X. Kaertner, J. Kim
    MIT, Cambridge, Massachusetts
  • H. Schlarb
    DESY, Hamburg
  Fourth-generation light sources, such as the European X-Ray free electron laser facility (XFEL) require timing signals distributed over distances of the order of kilometers with a timing jitter in the order of femtoseconds. The master clock for the proposed optical distribution system must operate with exceptionally low timing jitter. A promising approach is the use of a mode-locked laser that generates ultrastable pulses which are distributed via timing stabilized fiber links. Candidates for the pulse source are mode-locked Erbium doped fiber lasers, featuring very low high frequency noise. In this paper, we present a study of the phase noise of various fiber lasers in view of their applicability as laser-based master oscillators for femtosecond timing distributions.  
 
RPPT039 Stabilized Optical Fiber Links for the XFEL feedback, resonance, polarization, electron 2589
 
  • A. Winter
    Uni HH, Hamburg
  • J. Chen, F J. Grawert, F.O. Ilday, F.X. Kaertner, J. Kim
    MIT, Cambridge, Massachusetts
  • H. Schlarb, B. Schmidt
    DESY, Hamburg
  The timing synchronization scheme for the European X-Ray free electron laser facility (XFEL) is based on the generation and distribution of sub-picosecond laser pulses with actively stabilized repetition rate which are used to synchronize local RF oscillators. An integral part of the scheme is the distribution of the optical pulse stream to parts of the facility via optical fiber links. The optical path length of the fiber has to be stabilized against short-term and long-term timing jitter due to environmental effects, such as temperature drifts and acoustic vibrations, to better than 10 fs for distances ranging from tens of meters to several kilometers. In this paper, we present first experimental results for signal transmission through a km-long fiber link with femtosecond stability.  
 
RPPT040 Weak FEL Gain Detection with a Modulated Laser-Based Beam Heater undulator, radiation, electron, emittance 2636
 
  • P. Emma, Z. Huang, J. Wu
    SLAC, Menlo Park, California
  For an x-ray free-electron laser (FEL) such as the LCLS, the FEL gain signal is accompanied by spontaneous radiation with a significant power level. Detecting the weak FEL gain among the large spontaneous background in the early stage of the exponential growth or for a low quality electron beam is important in commissioning the FEL. In this paper, we describe a simple "lock-in" method of weak FEL gain detection by slowly modulating the laser power of a designated beam heater that controls the local energy spread of the electron beam. We present numerical modeling that shows the effectiveness of this method and discuss its implementation in the LCLS.  
 
FPAE053 Isobar Suppression by Photodetachment in a Gas-Filled RF Quadrupole Ion Guide ion, rfq, quadrupole, photon 3250
 
  • Y. Liu, J.R. Beene, C.C. Havener, J. F. Liang
    ORNL, Oak Ridge, Tennessee
  • A.C. Havener
    University of Tennessee, Knoxville, Tennessee
  Funding: Managed by UT-Battelle, LLC, for the U.S. DOE under contract DE-AC05-00OR22725. Co-author Aaron Havener was under a U.S. DOE Science Undergraduate Laboratory Internship.

A novel method is described for selective suppression of isobar contaminants in negative radioactive ion beams. Negative ion beams extracted from an ion source were decelerated to low energies and injected into a gas-filled radio-frequency quadrupole (RFQ) ion guide where the ions were cooled and unwanted ions were selectively removed by non-resonant photodetachment with photons of sufficient energy. Simulation studies show that the laser-ion interaction time in a 40 cm long RFQ ion guide can be on the order of milliseconds, thus, high efficiency photodetachment is possible with commercially available CW lasers. There are a number of adjacent-Z species whose negative ions are such that photodetachment can be used to suppress the unwanted negative ion species while leaving the species of interest intact. Examples of particular interest include suppressing the 56Co- component in a mixed 56Ni- + 56Co- beam and the 17O- component in a mixed 17O- + 17F- beam. In a proof–of-principle experiment a CW Nd:YAG laser at 1064 nm wavelength was used to selectively remove Co- ions in the (Ni, Co) pair. With laser power on the order of 3 W, 95% of Co- beams were suppressed while only 10% of Ni- beams were neutralized in a He-filled RFQ guide.

 
 
FPAE073 A Free Hg Jet System for Use in a High-Power Target Experiment target, proton, diagnostics, collider 3895
 
  • P.T. Spampinato, T.A. Gabriel, V.B. Graves, M.J. Rennich
    ORNL, Oak Ridge, Tennessee
  • A. Fabich, H. Haseroth, J. Lettry
    CERN, Geneva
  • H.G. Kirk, N. Simos, T. Tsang
    BNL, Upton, Long Island, New York
  • K.T. McDonald
    PU, Princeton, New Jersey
  • P. Titus
    MIT/PSFC, Cambridge, Massachusetts
  Funding: Work funded by the U.S. Department Of Energy.

We describe a mercury jet system that is suitable for insertion into the 15cm diameter bore of a high-field solenoid magnet. The device features a hermetically sealed primary containment volume which is enclosed in a secondary containment system to insure isolation of mercury vapors from the remaining experimental environment. The jet diameter is 1-cm while the jet velocity will be up to 20 m/s. Optical diagnostics is incorporated into the target design to allow observation of the dispersal of the mercury as a result of interaction with a 24 GeV proton beam with up to 20 x 1012 ppp.

 
 
FOAB010 Present Status of Photo-Cathode RF Gun System and Its Applications electron, injection, gun, emittance 710
 
  • R. Kuroda, Y. Hama, K. Hidume, M. Kawaguchi, R. Moriyama, T. Saito, K. Sakaue, M. Washio
    RISE, Tokyo
  • H. Hayano, J.U. Urakawa
    KEK, Ibaraki
  • S. Kashiwagi
    ISIR, Osaka
  High quality electron beam generation using photo-cathode rf gun system and its applications have been developed at Waseda University. This system can generate up to 4.6 MeV low emittance electron beam. It is applied for soft X-ray generation using laser Compton scattering and pulse radiolysis experiments based on the pump-probe technique. In the former, Compton scattering experiments between about 4.6 MeV electron beam and 1047 nm laser beam is performed at 20 degrees interaction angle, so that about 370 eV soft X-ray is generated. In the latter, the electron beam is used for the pump beam and the probe beam is generated as white light by concentrating laser beam on the water cell, so that the measurement with about 30 ps (FWHM) time resolution of the pulse radiolysis system is demonstrated for the absorption of hydrated electrons. In this conference, we will present the experimental results, status of this system and future applications.  
 
FOAD001 Frozen Beams storage-ring, lattice, ion, resonance 4
 
  • H. Okamoto
    HU/AdSM, Higashi-Hiroshima
  In general, the temperature of a charged particle beam traveling in an accelerator is very high. Seen from the rest frame of the beam, individual particles randomly oscillate about the reference orbit at high speed. This internal kinetic energy can, however, be removed by introducing dissipative interactions into the system. As a dissipative process advances, the beam becomes denser in phase space or, in other words, the emittance is more diminished. Ideally, it is possible to reach a "zero-emittance" state where the beam is Coulomb crystallized. The space-charge repulsion of a crystalline beam just balances the external restoring force provided by artificial electromagnetic elements. In this talk, general discussion is made of coasting and bunched crystalline beams circulating in a storage ring. Results of molecular dynamics simulations are presented to demonstrate the dynamic nature of various crystalline states. A possible method to approach such an ultimate state of matter is also discussed.  
 
FOAD004 Laser Cooling of Relativistic Heavy Ion Beams ion, synchrotron, electron, heavy-ion 401
 
  • U. Schramm, M.H. Bussmann, D. Habs
    LMU, München
  • K. Beckert, P. Beller, B.  Franzke, T. Kuehl, F. Nolden, M. Steck
    GSI, Darmstadt
  • S. Karpuk
    Johannes Gutenberg University Mainz, Mainz
  • S. Reinhardt, G. Saathoff
    MPI-K, Heidelberg
  Funding: Partially funded by the german BMBF (06ML183).

We report on the first laser cooling of a bunched beam of multiply charged C3+ ions performed at the ESR (GSI) at a beam energy of E=1.47GeV. Moderate bunching provided a force counteracting the decelerating laser force of one counterpropagating UV laser beam. This versatile type of laser cooling lead to longitudinally space-charge dominated beams with an unprecedented relative momentum spread of 10-7. Concerning the beam energy and charge state of the ion, the experiment depicts an important intermediate step from the established field of laser cooling of ion beams at low energies toward the laser cooling scheme proposed for relativistic beams of highly charged heavy ions at the future GSI facility FAIR.