03 Linear Colliders, Lepton Accelerators and New Acceleration Techniques

A13 New Acceleration Techniques

Paper Title Page
WEOBG02 Experimental Results of a Plasma Wakefield Accelerator Using Multiple Electron Bunches 1912
 
  • E. Kallos, T. C. Katsouleas, P. Muggli
    USC, Los Angeles, California
  • W. D. Kimura
    STI, Washington
  • K. Kusche, J. H. Park, I. Pogorelsky, D. Stolyarov, V. Yakimenko
    BNL, Upton, Long Island, New York
  
  We present some preliminary experimental results of a plasma wakefield accelerator technique which utilizes multiple electron bunches in order to drive a plasma wave. The experiments were performed at the Accelerator Test Facility of Brookhaven National Laboratory where 5-8 equidistant bunches with a spacing which was varied between 100-250 m were fed into a 6mm-long capillary discharge plasma. By varying the time delay of the bunches with respect to the discharge different plasma densities could be tuned, and the effects of the plasma on the bunches were recorded. Such multiple bunch schemes are of great interest because they can provide increased efficiencies and high transformer ratios for advanced accelerators.  
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WEPP124 The Status of Turkish Accelerator Complex Project 2788
 
  • A. Aksoy, Ö. Karsli, B. Ketenoglu, O. Yavas
    Ankara University, Faculty of Engineering, Tandogan, Ankara
  • A. K. Ciftci
    Ankara University, Faculty of Sciences, Tandogan/Ankara
  • S. Sultansoy
    TOBB ETU, Ankara
  
  The Turkish Accelerator Complex (TAC) is proposed as a regional facility for accelerator based fundamental and applied research in 1997 with support of Turkish State Planning Organization (DPT). The feasibility and conceptual design phases of TAC proposal were completed in 2001 and 2005, respectively. Again with support of DPT, the technical design phase of TAC was started at the beginning of 2006. The complex will include 1 GeV electron linac and 3.56 GeV positron ring for linac on ring type electron-positron collider as a charm factory and a few GeV proton linac. Besides the particle factory, it is also planned to produce SASE FEL from electron linac and synchrotron radiation from positron ring. It is planed that the TDR of TAC Project will be completed in 2011 and the construction will be performed during following ten years .  
WEPP125 Analysis of the Vertical Beam Instability in CTF3 Combiner Ring and New RF Deflector Design 2791
 
  • D. Alesini, C. Biscari, A. Ghigo, F. Marcellini
    INFN/LNF, Frascati (Roma)
  
  In the last CTF3 run (November 2007) a vertical beam instability has been found in the Combiner Ring during operation. Possible sources of the instability are the vertical deflecting modes excited by the beam in the RF deflectors. In the first part of the paper we illustrate the results of the beam dynamics analysis obtained by a dedicated tracking code that allows including the induced transverse wake field and the multi-bunch multi-passage effects. To reduce the effects of such vertical trapped modes, the RF deflectors have been modified and two new deflectors have been designed. They have been made in aluminium and have two more ports in the input and output coupler cells to absorb the beam induced field on the vertical modes. The design of the new deflectors and the RF measurements are then presented in the paper.  
WEPP127 ALaDyn: a High Accuracy Code for the Laser-plasma Interaction 2794
 
  • C. Benedetti, A. Sgattoni
    Bologna University, Bologna
  • P. Tomassini
    INFN-Milano, Milano
  
  ALaDyn (Acceleration by LAser and DYNamics of charged particles) is a relativistic fully parallelized PIC code to investigate the interaction of a laser pulse with a plasma and/or an externally injected beam. The code is based on compact high order finite differences schemes ensuring higher spectral accuracy compared to standard Yee schemes. We present the main features and the performances of the code together with a set of validation tests obtained comparing the results with well-established analytical/numerical results. A preliminary benchmarking with the PIC code VORPAL is also presented. An application to a physically relevant case concerning the externally-injected configuration proposed for the CNR-INFN experiment PLASMONX will be analyzed.  
WEPP129 Digital Acceleration Scheme of the KEK All-ion Accelerator 2797
 
  • T. S. Dixit
    GUAS/AS, Ibaraki
  • Y. Arakida, T. Iwashita, K. Takayama
    KEK, Ibaraki
  
  R&D works to realize an all-ion accelerator (AIA)*-capable of accelerating all ions of any possible charge state, based on the induction synchrotron concept, which was demonstrated using the KEK 12 GeV-PS in 2006 **, is going on. In the induction synchrotron, unlike an RF synchrotron, operational performance is not limited due to the frequency band-width, since the switching power supply to energize the induction acceleration system is triggered by signals obtained from the bunch monitor. For a POP experiment of AIA, argon ions will be accelerated in the KEK-500 MeV booster ring, a Rapid Cycle Synchrotron (f=20 Hz) and the RCS requires a dynamic change in the acceleration voltage. Since the induction acceleration voltage per pulse is fixed, a novel technique combining the pulse density control and intermittent operation of multi-acceleration cells has been proposed. The acceleration scheme of the AIA fully employing this technique was verified by computer simulation and demonstrated at our test facility, where a new induction acceleration cell generating an acceleration voltage pulse of 2 μsec long was triggered by a beam simulator to mimic a circulating Ar beam in the KEK-AIA

* K. Takayama, Y. Arakida, T. Iwashita, Y. Shimosaki, T. Dixit, K. Torikai, J. of Appl. Phys. 101, 063304 (2007).
**K. Takayama et al., Phys. Rev. Lett. 98, 054801 (2007).

 
WEPP131 RF-breakdown Experiments at the CTF3 Two-beam Test-stand 2800
 
  • M. Johnson, T. J.C. Ekelöf, R. J.M. Y. Ruber, V. G. Ziemann
    UU/ISV, Uppsala
  • H.-H. Braun
    CERN, Geneva
  
  The Two-beam Test-stand (TBTS) in the CLIC Test Facility CTF3 offers unique possibilities to conduct RF-breakdown related experiments on the accelerating structures and the power extraction and transfer structures with beam. We report on the set-up of two such experiments, one for the measurement of the transverse kick and the other for the measurement of positive ion currents. The purpose of the transverse kick measurements is to determine the effects of a RF-breakdown event on the beam. Five BPMs in the TBTS will be used to study the trajectory of a pulse train after a RF-breakdown event, with important implications for the operation of CLIC. Ion currents ejected from accelerating structures during RF-breakdown events have already been observed at the 30 GHz test stand at the present test facility. Results and their implications for RF-breakdown physics are presented, as well as plans for similar measurements at the TBTS.  
WEPP132 Efficiency Enhancement of Active High-Power Pulse Compressors 2803
 
  • S. V. Kuzikov, Yu. Danilov, A. A. Vikharev
    IAP/RAS, Nizhny Novgorod
  
  High power microwaves needed to accelerate particles in multi-TeV colliders can be produced using active pulse compressors. An active compressor has a storage cavity whose Q-factor is modulated by means of RF switch. An efficiency of such compressor is limited due to diffraction losses at power accumulation regime and in conventional case does not exceed 81.4%. A new microwave pulse compressor operated with a superposition of quasi-degenerated modes is suggested. A proper choice of eigen frequencies and Q-factors of these modes allows essential enhancement of efficiency (asymptotically up to 100%). A 30 GHz project of multi-megawatt compressor based on dual-mode circular cross-section cavity is considered.  
WEPP134 Ultra-short x-ray Radiation coming from a Laser Wakefield Accelerator 2809
 
  • V. Leurent, L. Divol, T. Doeppner, D. H. Froula, S. H. Glenzer, P. Michel, J. Palastro
    LLNL, Livermore, California
  • C. E. Clayton, C. Joshi, K. A. Marsh, A. E. Pak, J. E. Ralph, T.-L. Wang
    UCLA, Los Angeles, California
  • B. B. Pollock, G. R. Tynan
    UCSD, La Jolla, California
  
  A Laser Wakefield Accelerator (LWFA) is under development at LLNL Jupiter Laser Facility to produce multi-GeV electron bunches promising to provide a bright and compact source of x-ray radiation for high energy density studies. The interaction of a high power (200 TW), short laser (50 fs) pulse with neutral He gas can accelerate monoenergetic electrons up to 1 GeV in a stable self-guiding regime*, over a dephasing length of 1 cm (for a plasma density of 1.5x1018 cm-3), overcoming the limitation of vacuum diffraction and allowing long interaction lengths for LWFA. The waveguide can be extended over several centimeters by using a novel scheme, which employs an external magnetic field (up to 5 T uniform along 12 cm) to control the radial heat flux** resulting from the interaction of a high energy (100 J), long pulse (1 ns) laser with a gas tube. The acceleration of electrons over several centimeters can produce multi-GeV bunches and thus a powerful x-ray source. Analysis will be presented on femtosecond x-ray radiation produced by wiggling an electron bunch with energy above 1 GeV in this new LWFA scheme.

* W. Lu et al., Phys. Rev. Spec. Top-ac 10, 061301 (2007)
** D. H. Froula et al., Phys. Rev. Lett. 98, 135001 (2007)

 
WEPP136 Femtosecond and Attosecond Bunches of Electrons upon Field Emission in a Combined Quasi-static and Laser Electric Field 2812
 
  • V. A. Papadichev
    LPI, Moscow
  
  Obtaining short pulses of particles and of electromagnetic radiation is of interest for investigating fast processes in physics, chemistry, biology and medicine*,**. A new method of modulating an electron beam is proposed to obtain electron bunches of 100-as to 20-fs duration. For this purpose, two electric fields – quasi-static and the variable field of a laser with wavelength in the 0.25 – to 10 microns range – simultaneously act on a single-spiked or multi-spiked cathode. Current from 0.01 to 100 A from one spike having a curvature radius of 1 micron corresponds to a maximal intensity of total electric field of 70 to 280 MV/cm for a 10-micron laser wavelength. For a 1-micron laser, total fields of 300 – 400 MV/cm should be used for 1 – 20 A currents. A regime of device operation was determined for which the emitting surface of a copper cathode is not damaged. Obtaining a single bunch or a sequence of bunches with a repetition rate up to1330 THz was considered. Using multi-spiked cathodes permits to obtain bunches with current up to 10 kA.

*P. Emma. Issues and challenges for short pulse radiation production, Proc. EPAC04, p. 225, Lucerne, Suisse.
**S. Rimjuem et al. Generation of femtosecond electron pulses, Proc. EPAC04, p. 431.

 
WEPP137 Accelerating and Transporting Attosecond and Femtosecond Bunches of Electrons 2815
 
  • V. A. Papadichev
    LPI, Moscow
  
  Dynamics of short bunches of electrons obtained upon field emission in a quasi-static electric field and a variable electric field of a laser has been studied*. The equation of longitudinal motion of electrons was numerically integrated. Emitted electrons are accelerated by quasi-static potential applied to the spike and this drastically reduces initial energy spread in the bunch preventing its fast elongation. When the forces of space charge have little effect, grouping part of the beam due to velocity spread acquired in the laser field permits to obtain bunches of about 200-as duration when using a carbon dioxide laser and about 6-as with a neodymium laser. Analytical models were used to evaluate the influence of the space charge of the bunch on the longitudinal motion of electrons in it. It has been shown that the proper choice of the intensities of both fields can cancel such an influence. There have been considered methods of lateral focusing of the beam taking into account possible initial angular divergence and space charge effects. Such electron bunches could be used directly in experiments or for generation of short pulses of coherent UV- and X-ray radiation.

*V. A. Papadichev, Femtosecond and Attosecond Bunches of Electrons Upon Field Emission in a Combined Quasi-static and Laser Electric Field, submitted to this Conference.

 
WEPP138 Experimental Demonstration of Ultrashort μJ-Class Pulses in the Terahertz Regime from a Laser Wakefield Accelerator 2818
 
  • G. R.D. Plateau, C. G.R. Geddes, N. H. Matlis, C. B. Schroeder, C. Toth, J. van Tilborg
    LBNL, Berkeley, California
  • O. Albert
    LOA, Palaiseau
  • E. Esarey, W. Leemans
    University of Nevada, Reno, Reno, Nevada
  
  Ultrashort terahertz pulses with energies in the μJ range can be generated with laser wakefield accelerators (LWFA), which are novel, compact accelerators that produce ultrashort electron bunches with energies up to 1 GeV* and energy spreads of a few-percent. Laser pulses interacting with a plasma create accelerated electrons which upon exiting the plasma emit terahertz pulses via transition radiation. Because they are only tens of femtoseconds long, electron bunches can radiate coherently (CTR) in a wide bandwidth (~ 1 - 10 THz) yielding terahertz pulses of high intensity**,***. In addition to providing a non-invasive bunch-length diagnostic**** and thus feedback for the LWFA, these high peak power THz pulses are suitable for high field (MV/cm) pump-probe experiments. Here we present energy-based measurements using a Golay cell and a single-shot electro-optic technique which were used to characterize the full waveform of these μJ-class THz pulses, including phase and amplitude information.

*W. P. Leemans et al. N. P. 2/696 (2006).
**W. P. Leemans et al. P. R.L. 91/074802 (2003).
***C. B. Schroeder et al. P. R.E 69/016501 (2004).
****J. van Tilborg et al. P. R.L. 96/014801 (2006).

 
WEPP139 The CTF3 Two-beam Test-stand Installation and Experimental Program 2821
 
  • V. G. Ziemann, T. J.C. Ekelöf, M. Johnson, R. J.M. Y. Ruber
    UU/ISV, Uppsala
  • H.-H. Braun, S. Doebert, G. Geschonke, G. Riddone, J. P.H. Sladen, I. Syratchev, W. Wuensch
    CERN, Geneva
  
  The Two-beam Test-stand in CTF3 will be used to investigate the power-generation and accelerating structures for the Compact Linear Collider CLIC. We report on its design and construction which was recently completed and discuss the imminent commissioning phase as well as the following experimental program that initially will be devoted to the test of power generation structures in the drive-beam.  
WEPP140 X-band PASER Experiment 2824
 
  • A. Kanareykin, P. Schoessow
    Euclid TechLabs, LLC, Solon, Ohio
  • S. P. Antipov
    ANL, Argonne, Illinois
  • L. Schächter
    Technion, Haifa
  
  The PASER concept for particle acceleration entails the direct transfer of energy from an active medium to a charged particle beam. The PASER was originally formulated for optical (laser) media; we are pursuing a PASER demonstration experiment based on an optically pumped paramagnetic medium active in the X-band. We report on the development of a relatively high energy density microwave active medium consisting of a fullerene (C60) derivative in a toluene solution. We discuss both the bench test of an amplifier and a beam acceleration experiment under construction that employ this medium as a power source. Applications of the technology to accelerators and microwave components will be presented.  
WEPP142 Simulation of and Progress towards a Micron-scale Laser-powered Dielectric Electron Source 2827
 
  • G. Travish, J. B. Rosenzweig, J. Xu
    UCLA, Los Angeles, California
  • S. Boucher
    RadiaBeam, Marina del Rey
  • R. B. Yoder
    Manhattan College, Riverdale, New York
  
  A dielectric, slab-symmetric structure for generating and accelerating low-energy electrons has been under study for the past two years. The resonant device is driven by a side-coupled laser and is configured to maintain field provide necessary for synchronous acceleration and focusing of nonrelativistic particles. Intended applications of the structure include the production of radiation for medical treatments, imaging, and industrial uses. The details of the structure geometry and its resonant properties have been studied with 2D and 3D electromagnetic codes, the results of which are present here.