• D.A. Zakaryan, D.K. Kalantaryan
  YSU, Yerevan
• E.D. Gazazyan, K.A. Ispirian, M.K. Ispirian
  YerPhI, Yerevan

• G.V. Stupakov
  SLAC, Menlo Park, California

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.

• F. Seyvet, J. Beauquis, E.D. Fernandez Cano, J.-B. Jeanneret, A. Poncet, D. Tommasini
  CERN, Geneva

• A.Y. Zelinsky, I.V. Drebot, Yu.N. Grigor'ev, O.D. Zvonarjova
  NSC/KIPT, Kharkov
• R. Tatchyn
  SLAC, Menlo Park, California

• M. Ferrario
  INFN/LNF, Frascati (Roma)

• 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

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.

• 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

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.

• 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

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.

• 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

• T. Ohkubo, M. Uesaka, G. Zhidkov
  UTNL, Ibaraki

• C. Kim, I.S. Ko
  POSTECH, Pohang, Kyungbuk
• N. Hafz, G.-H. Kim, H. Suk
  KERI, Changwon

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.

• A.A. Mikhailichenko
  Cornell University, Department of Physics, Ithaca, New York

• T. Plettner, S. Sinha, J. Wisdom
  Stanford University, Stanford, Califormia
• E.R. Colby
  SLAC, Menlo Park, California

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.

• T. Plettner, R.M. Gaume, J. Wisdom
  Stanford University, Stanford, Califormia
• J.E. Spencer
  SLAC, Menlo Park, California

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.

• 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

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.

• K.R. Samokhvalova, C. Chen
  MIT/PSFC, Cambridge, Massachusetts
• B.L. Qian
  National University of Defense Technology, Hunan

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.

• R. Siemann, A. Chao
  SLAC, Menlo Park, California

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.

• J.E. Spencer, Y.A. Hussein
  SLAC, Menlo Park, California

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.

• J.E. Spencer, E.R. Colby, R.J. Noble, D.T. Palmer, R. Siemann
  SLAC, Menlo Park, California

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.

• 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

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.

• Z. Zhang, R.D. Ruth, S.G. Tantawi
  SLAC, Menlo Park, California

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.

• 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

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 (≈λ_p) 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).

• 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

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.

• P. Schoessow
  Tech-X, Boulder, Colorado
• A. Kanareykin
  Euclid TechLabs, LLC, Solon, Ohio

• S. Deng, T.C. Katsouleas, X. Wang
  USC, Los Angeles, California
• W.B. Mori
  UCLA, Los Angeles, California

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.

• P. Piot
  Fermilab, Batavia, Illinois
• A.C. Melissinos, R. Tikhoplav
  Rochester University, Rochester, New York

• J.E. Ralph, C. Joshi, J.B. Rosenzweig, C. Sung, S. Tochitsky
  UCLA, Los Angeles, California

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.

• 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

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.

• L.H. Shao, D. Cline, F. Zhou
  UCLA, Los Angeles, California

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.

• 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
  ,

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.

• N. Hafz, H. Suk
  KERI, Changwon
• D.-K. Ko, J. Lee
  APRI-GIST, Gwangju

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.

• M.S. Hur, G.-H. Kim, H. Suk
  KERI, Changwon
• A.E. Charman, R.R. Lindberg, J.S. Wurtele
  LBNL, Berkeley, California

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).

• 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

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).

• 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

• 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

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.

• 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

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).

• S.-Y. Chen, C.-L. Chang, W.-T. Chen, T.-Y. Chien, C.-H. Lee, J.-Y. Lin, J. Wang
  IAMS, Taipei

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.

• 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

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.

• 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

• 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

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.

• 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

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.

• F. Zhou, D. Cline
  UCLA, Los Angeles, California
• M. Babzien, V. Yakimenko
  BNL, Upton, Long Island, New York
• W.D. Kimura
  STI, Washington

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.

• E.A. Seddon, M.W. Poole
  CCLRC/DL, Daresbury, Warrington, Cheshire

• S. Khan
  BESSY GmbH, 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.

• H. Schlarb
  DESY, Hamburg

• A. Zholents
  LBNL, Berkeley, California

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.

• F.X. Kaertner, H. Byun, J. Chen, F J. Grawert, F.O. Ilday, J. Kim, A. Winter
  MIT, Cambridge, Massachusetts

• 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

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.

• K. Sakakibara, T. Hattori, N. Hayashizaki, T. Ito
  RLNR, Tokyo
• H. Kashiwagi
  JAERI/ARTC, Gunma-ken
• M. Okamura
  RIKEN, Saitama

• 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

• 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

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.

• A. Burrill, I. Ben-Zvi, D. Pate, T. Rao, Z. Segalov
  BNL, Upton, Long Island, New York
• D. Dowell
  SLAC, Menlo Park, California

• 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

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).

• N.A. Moody, D.W. Feldman, P.G. O'Shea
  IREAP, College Park, Maryland
• K. Jensen
  NRL, Washington, DC

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).

• 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

• R. Xiang, Y.T. Ding, J. Hao, S.L. Huang, X.Y. Lu, S.W. Quan, B.C. Zhang, K. Zhao
  PKU/IHIP, Beijing

• A. Mizuno, H. Dewa, H. Hanaki, T. Taniuchi, H. Tomizawa
  JASRI/SPring-8, Hyogo
• M. Uesaka
  UTNL, Ibaraki

• L. Xiao, R.F. Boyce, D. Dowell, Z. Li, C. Limborg-Deprey, J.F. Schmerge
  SLAC, Menlo Park, California

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.

• 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

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.

• V. Gorgadze
  UCB, Berkeley, California
• J.S. Wurtele
  LBNL, Berkeley, California

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.

• H. Wang, R.A. Rimmer, G. Wu
  Jefferson Lab, Newport News, Virginia

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.

• 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

• 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

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).

• 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

• 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

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.

• B.M. Cowan
  SLAC, Menlo Park, California

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.

• A.A. Mikhailichenko
  Cornell University, Department of Physics, Ithaca, New York

• J.U. Urakawa
  KEK, Ibaraki

• Y. Muttoni, J.-P. Corso, R. V. Valbuena
  CERN, Geneva

• R.C. McCrady
  LANL, Los Alamos, New Mexico

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.

• S.A. Helus, D.R. Bruce, J.J. Error, J.J. Fazekas, J.R. Maines
  ORNL, Oak Ridge, Tennessee

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.

• R.T. Roseberry, S. Assadi, G.R. Murdoch
  ORNL, Oak Ridge, Tennessee

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.

• M. Emamian, M.D. Busch, S. Mikhailov
  DU/FEL, Durham, North Carolina
• N. Gavrilov
  BINP SB RAS, Novosibirsk

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.

• E. Trakhtenberg, J.T. Collins, P.K. Den Hartog, M. White
  ANL, Argonne, Illinois

• 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

• 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

• 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

• 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

• 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

• M. Boscolo, M. Ferrario, M.  Migliorati
  INFN/LNF, Frascati (Roma)
• F. Castelli, S. Cialdi, A.F. Flacco
  INFN-Milano, Milano

• 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

• J. Yang, K. Kan, T. Kondoh, T. Kozawa, Y. Kuroda, S. Tagawa, Y. Yoshida
  ISIR, Osaka

• 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

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.

• 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

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.

• I.V. Bazarov, C.K. Sinclair
  Cornell University, Department of Physics, Ithaca, New York
• I. Senderovich
  Cornell University, Ithaca, New York

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.

• Z.M. Yusof, M.E. Conde, W. Gai
  ANL, Argonne, Illinois

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.

• 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

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.

• 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

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.

• R.P. Fliller, H. Edwards
  Fermilab, Batavia, Illinois
• W. Hartung
  NSCL, East Lansing, Michigan

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.

• J.L. Li, J.L. Li
  Rochester University, Rochester, New York
• P. Piot, R. Tikhoplav
  Fermilab, Batavia, Illinois

• 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

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.

• 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

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.

• 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

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.

• A. Gallo, D. Alesini, M. Bellaveglia, R. Boni, G. Di Pirro, F. Tazzioli
  INFN/LNF, Frascati (Roma)

• A.J. Moss
  CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire

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.

• Y. Zhao, I. Ben-Zvi, R.H. Beuttenmuller, X.Y. Chang, C. Chen, R. Di Nardo, T. Rao
  BNL, Upton, Long Island, New York

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.

• D.J. Gibson, C.P.J. Barty, S.M. Betts, K. Crane, I. Jovanovic
  LLNL, Livermore, California

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.

• 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

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.

• 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

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.

• 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

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.

• J. Li, C. Sun, Y.K. Wu
  DU/FEL, Durham, North Carolina

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.

• K. Holldack, S. Khan, T. Quast
  BESSY GmbH, Berlin
• R. Mitzner
  Universität Muenster, Physikalisches Institut, Muenster

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.

• S. Khan, K. Holldack, T. Kachel, T. Quast
  BESSY GmbH, Berlin
• R. Mitzner
  Universität Muenster, Physikalisches Institut, Muenster

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.

• S. Khan
  BESSY GmbH, 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.

• J.M. Byrd, Z. Hao, M.C. Martin, D. Robin, F. Sannibale, R.W. Schoenlein, A. Zholents, M.S. Zolotorev
  LBNL, Berkeley, California

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.

• 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

• C. Steier, D. Robin, F. Sannibale, R.W. Schoenlein, W. Wan, W. Wittmer, A. Zholents
  LBNL, Berkeley, California

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.

• 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

• Y. Yoshida, T. Kondo, J. Yang
  ISIR, Osaka

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.

• 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. Doyuran, R.J. England, C. Joshi, J. Lim, J.B. Rosenzweig, S. Tochitsky, G. Travish, O. Williams
  UCLA, Los Angeles, California

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.

• T. Kondoh, T. Kozawa, S. Tagawa, T. Tomosada, J. Yang, Y. Yoshida
  ISIR, Osaka

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.

• M. Chung, R.C. Davidson, P. Efthimion, E.P. Gilson, R. M. Majeski, E. Startsev
  PPPL, Princeton, New Jersey

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.

• C. Gabor, H. Klein, O. Meusel, U. Ratzinger
  IAP, Frankfurt-am-Main
• J. Pozimski
  Imperial College of Science and Technology, Department of Physics, London

• E.D. Gazazyan, K.A. Ispirian, A.T. Margaryan
  YerPhI, Yerevan
• D.K. Kalantaryan
  YSU, Yerevan
• E.M. Laziev
  CANDLE, Yerevan

• S. Casalbuoni, H. Schlarb, B. Schmidt, B. Steffen
  DESY, Hamburg
• P. Schmüser, A. Winter
  Uni HH, Hamburg

• B. Steffen, S. Casalbuoni, E.-A. Knabbe, H. Schlarb, B. Schmidt
  DESY, Hamburg
• P. Schmüser, A. Winter
  Uni HH, Hamburg

• R.B. Wilcox, J.W.  Staples
  LBNL, Berkeley, California
• R. Holzwarth
  Menlo Systems GmbH, Martinsried

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.

• 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

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.

• 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

• D. Mihalcea, C.L. Bohn
  Northern Illinois University, DeKalb, Illinois
• U. Happek
  UGA, Athens, Georgia
• P. Piot
  Fermilab, Batavia, Illinois

• 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

• 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

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.

• 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

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.

• X. Liu, Y. He, Y. Li
  Cornell University, Department of Physics, Ithaca, New York
• M.R. Adams
  Cornell University, Ithaca, New York

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.

• 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

• D. Wang, W. Graves, D. Wang, T. Zwart
  MIT, Middleton, Massachusetts
• P. Emma, J. Wu
  SLAC, Menlo Park, California
• G. Huang
  LBNL, Berkeley, California

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.

• C. Limborg-Deprey, P. Emma
  SLAC, Menlo Park, California

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.

• G. Penn, A. Zholents
  LBNL, Berkeley, California

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.

• A. Winter, P. Schmüser
  Uni HH, Hamburg
• J. Chen, F.O. Ilday, F.X. Kaertner, J. Kim
  MIT, Cambridge, Massachusetts
• H. Schlarb
  DESY, Hamburg

• 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

• P. Emma, Z. Huang, J. Wu
  SLAC, Menlo Park, California

• Y. Liu, J.R. Beene, C.C. Havener, J. F. Liang
  ORNL, Oak Ridge, Tennessee
• A.C. Havener
  University of Tennessee, Knoxville, Tennessee

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.

• 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

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.

• 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

• H. Okamoto
  HU/AdSM, Higashi-Hiroshima

• 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

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.