AAC Photos
Presentation Instructions
AAC'04 Agenda
AAC'04 Poster
Organizing Committee
Workshop Working Groups


















No Working Group Specified - Poster
  A wake field set up in a planar dielectric having tall but finite height by the passage of a train of relativistic electron bunches (Vavilov-Cherenkov radiation) is considered here. We study peculiarities of excitation at the entrance boundary, namely the appearance of a “quenching wave” and transition radiation. The former cancels Vavilov-Cherenkov wake field radiation in the region between the entrance and a front moving with the group velocity, while the latter distorts the wake field. Exact expressions for transition and Vavilov-Cherenkov radiation are obtained, and the spatial profile of the field excited by an electron bunch of finite size is computed numerically. Wake field excitation by a train of equally-spaced fsec bunches is investigated.
Chunguang Jing: Mode Analysis in Multilayer Dielectric-Loaded Accelerating Structure
  In this paper, multilayer dielectric loaded structure is adopted to increase the Quality Factor Q and shunt impedance R for dielectric based accelerator. Comparing with the conventional single layer dielectric-loaded accelerator structure, this multilayer structure is capable of reducing the RF transmission attenuation introduced by the wall loss on copper jacket and improving the shunt impedance at the same time. A general analysis of this multilayered structure which covers the mode solutions for both TM (acceleration) modes and HEM (hybrid transverse mode related to the beam instabilities) is presented along with their characteristic parameters such as Q and R. A numerical example for X-band (11.424 GHz) structure which shows that attenuation of accelerating field can be significantly reduced by using mere 2 – 4 layers is also given. Significant improvement of overall accelerating efficiency is achieved while maintaining other accelerating parameters comparable with higher gradient accelerator. An easy to implement damping method for the hybrid modes is also presented and discussed.
Matthew Thompson: Plasma Density Transition Trapping of Electrons in Plasma Wake Field Accelerators
  Plasma density transition trapping is a self-injection scheme for plasma wake-field accelerators. This technique uses a sharp, downward plasma density transition to trap and accelerate background plasma electrons in a plasma wake-field. The performance of density transition trapping is competitive with laser based plasma injector schemes when the techniques are used at similar densities. Unlike most laser plasma injector schemes, however, density transition trapping is not dependent on the ability to achieve sub-ps timing requirements. A proof-of-principle plasma density transition trapping experiment is underway at the Fermilab/NICADD Photoinjector Laboratory (FNPL). The goal of experiment is to capture a 100 pC beam with 4% rms energy spread out of a 2 x 10^13 cm^-3 peak density plasma using a ~ 6nC, 14 MeV drive beam. Progress and status of the experiment will be reported.
Stanislav Zhilkov: Light beam transformation and the energy exchange with 2-D particle cluster
  Transformation of optical wave (OB) by loaded dielectric structure and the proper directing of electron beam (EB) commonly provide the conditions for the resonant energy’s transferring OB-EB. Alternatively, OB, which transformed by SLM (spatial light modulator), can also transfer the energy effectively. SLM separates the laser pulse in a set of partial waves. If in the interaction region the partial waves appear one after another having time delay as half-period and neighboring waves have suitable phase difference, then cumulative field will act so that the particle experiences stable-directed accelerating. Such solution explains non-relativistic effects that detected in coherent control experiments. The approach promises to be productive for relativistic study as well. Inverse problem (energy transfer for light modulation by driven EB) is researched recent years. The today’s technology makes it available to achieve the modulation rate of order 5% of frequency of OB (i.e., theoretical limit). In general, we observe that the dualistic idea, according with which the regrouping of charged particles’ assembly and shaping of OB enable to exchange an energy effectively during the phase-dependant cross correlation, is now realized for different practical needs due to the technology’s readiness.
Amit Kesar: Experimental Status of The 17 GHz RF Gun at MIT
  High frequency photocathode injectors (RF Guns) are important as sourcesfor ultra-relativistic colliders due to their high brightness electronbunch output. A 3 cell 17 GHz RF Gun designed and built at HaimsonResearch Corporation (HRC) is being tested at MIT Plasma Science andFusion Center. A 1 ps, 10 micro-joule laser pulse is injected into theback of the first cell in order to emit the electron bunch. The drivingpower into the RF Gun is supplied by an HRC 17 GHz relativistic klystronand is coupled into the middle cell by dual RF ports. This cell has aracetrack geometry design in order to achieve a highly symmetrized TM01pi-mode operation which is necessary for reducing the emittance. Thediagnostic setup consists of a slit array, YAG screen and a CCD camerafor beam imaging and emittance measurement, and deflecting coils and aFaraday Cup for energy and bunch charge measurement, respectively. TheRF Gun currently produces 10 pC bunches having energy of 0.5 MeV. Ourgoal is to increase the input power in order to obtain a 1 MeV energygain and to measure the resulting beam emittance. An update on theexperimental results will be presented.
Philippe Piot: Laser-acceleration of electrons at Fermilab/NICADD photoinjector laboratory
  The possibility of using a laser to accelerate electrons in a waveguide structure with dimension much larger than the laser wavelength was first proposed by Pantell [NIM A 393 pg 1-5 (1997)] and investigated analytically by M. Xie [reports LBNL-40558 (1997) and LBNL-42055 (1998) available from LBNL Berkeley]. In the present paper we present the status of our experimental plan to demonstrate the laser interaction on an electron beam with initial momentum of 40-50 MeV/c. A laser (lambda=1.06 micron) operating on the TM*01 mode has been developed. The large wavenumber (k~6x10^6) together with the initial low electron momentum pose a serious problem for efficient acceleration. In the present report we especially discuss the various options regarding phase matching of the laser with the electron beam along with our choice for the coupling structure.
Levi Schachter: Roughness Effect on a Microbunch
  In this study we investigate the properties of the electromagnetic wake-field generated by an electron bunch moving in the vicinity of an optical structure of finite roughness. The model employed consists of a metallic cylindrical waveguide to which grooves of random width, height and location are attached. Based on this model analytic expressions have been developed for the average energy emitted per groove and for its standard-deviation. As expected, both quantities are virtually independent of the momentum in a highly relativistic regime and the average energy emitted per groove is proportional to the roughness parameter. Moreover, it has been found that the standard-deviation of the energy emitted per groove is proportional to the standard-deviation of the roughness parameter to the power of 1/4. The cumulative effect of surface roughness was studied resorting to both periodic and quasi-periodic structures – significant differences in the spectrum have been observed only for low frequencies.
Changbiao Wang: Rectangular Dielectric-lined Accelerator Structure
  Results are reported from analysis of a rectangular X-band dielectric-lined accelerator structure operating in the symmetric LSM-11 mode that has a number of favorable attributes, by comparison with dielectric-lined cylindrical structures. These attributes include use of two planar one-piece precision-ground TiN coated dielectric slabs free of joints, open slots along two opposing metallic faces to suppress all anti-symmetric higher-order modes and to facilitate high-speed pumping, and significant reduction of wall losses by use of evanescent vacuum gaps beyond the dielectric slabs. It is shown that a structure operating at 11.424 GHz can be built with a shunt impedance >60 Mohm/m using low-loss alumina as the dielectric.
Sergey Shchelkunov: A New Nondestructive Method for Measuring the RMS Length of Charge Bunches Using Their Wake Field Radiation Spectrum*
  We report progress in the development of a nondestructive technique to measure bunch rms-length in the psec range and below, and eventually in the fsec range, by measuring the high- frequency spectrum of wake field radiation which is caused by the passage of a relativistic electron bunch through a channel surrounded by a dielectric. We demonstrate both experimentally and numerically that the generated spectrum is determined by the bunch rms-length, while the choice of the axial and longitudinal charge distribution is not important. Measurement of the millimeter-wave spectrum will determine the bunch rms-length in the psec range. This has been done using a series of calibrated mesh filters and the charge bunches produced by the 50MeV rf linac system at ATF, Brookhaven. We have developed the analysis of the factors crucial for achieving good accuracy in this measurement, and find the experimental data are fully understood by the theory. We also discuss the application of this technique for measuring fsec bunch lengths, using a prepared microstructure.

*This work was supported by Department of Energy High Energy Physics Division

Evgenya Smirnova: Progress on the MIT Photonic Band Gap accelerator experiment
  We report the progress on the design and cold test of metal PBG resonatorsand accelerator structures. First, an 11 GHz photonic band gap (PBG) cell,which can be utilized as an accelerator cavity with reduced long-rangewakefields, was constructed and tested. The higher-order-modes suppressionwas proved in the cold test. A Q-factor of 5000 was achieved for a brazedresonator. Next, the 11 GHz design was scaled to 17.137 GHz to construct a6-cell 17.137 GHz PBG accelerator structure with reduced long-rangewakefields. The accelerator design was performed with HFSS and a bolted withscrews structure was built and cold-tested. Engineering efforts are underwayin order to build a high Q 6-cell 17.137 GHz PBG accelerator. A PBGaccelerator will be tested with high power at Massachusetts Institute ofTechnology.
Noboru Yugami: Radiation from Interaction between Short Pulse and Ultra High Power Laser and Magnetized Plasma
  The radiation from the interaction between the ultra-short andultra-high power laser(0.5 TW, 100 fs)and the weakly magnetized plasmais studied. We observed the short pulse radiation (200 ps) in themicrowave region(~100 GHz). Two kind of radiations whose frequenciesare much lower than the plasma frequency, are observed. One isin the higer frequency region and polarized in parallel to theexternal B field(up to 6 kG). The frequency doesnt depend on the thestrength of the B field. On the other hand, other componets of theemitted radiation is vertically polarized and its frequency depends onthe strength of the B field. The experimental results suggest that theformer radiation is generated by the electron oscillation along the Bfield and the latter is by the electron Bernstein mode.
Kazuhisa Nakajima: Head-on injection and acceleration of a high quality femtosecond electron bunch in a plasma
  High quality intense relativistic beams are generated by the interaction of two head-on colliding laser pulses to inject plasma electrons into a wakefield excited by one of laser pulses. The mechanism of injection is analyzed theoretically and generation of a high quality electron beam is verified by the numerical simulations. An electron beam has a small energy spread of 1%, ultrashort pulse duration less than 10fs and normalized transverse emittance less than 1 pi mm mrad.
Scott Anderson: Sub-picosecond Compton scattering x-ray generation using a velocity bunched electron beam at PLEIADES
  The velocity bunching technique has been employed to compress a high brightness photo-electron beam to 300 femtosecond duration. The longitudinal and transverse beam dynamics were studied experimentally and compared to theory and simulation. The compressed electron beam has been utilized in the PLEIADES Compton scattering x-ray source at LLNL to produce sub-picosecond, 78 keV x-ray pulses. We present measurements of the compression achieved in this implementation of velocity bunching as well as aspects of the use of a velocity-bunched beam directly in Compton scattering experiments.
Suzhi Deng: wake generation and beam stabilization in self-ionized plasma wakefield accelerators
  A two-stage wake generation mechanism is found in self-ionized plasma accelerators. This two-stage mechanism offers the possibility to eliminate traditional electron hosing, while introduces a new hosing instability—ionization-induced hosing. The growth rate of the ionization hosing is studied and found to be less than that of the traditional electron hosing. Analytical and 3-D PIC simulation results are given.
Adnan Doyuran: Nonlinear Harmonic Measurements of the Transverse Thomson Scattering Experiment at UCLA
  We propose a Thomson scattering experiment, which will investigate nonlinear properties of the scattering utilizing the MARS terawatt CO2 laser in Neptune Laboratory at UCLA. When the normalized amplitude of the vector potential a0 is larger than unity the scattering occurs in the nonlinear region therefore higher harmonics are also produced. We discuss the experimental setup and procedure to measure the angular and spectral distribution of the higher harmonics. We also present a calculation tool for the Double Differential Spectrum (DDS) distribution and total number of photon produced for both head-on and 90o scattering. We decided to do the experiment at 90o to avoid complications due to strong diffraction of the incoming laser. We discuss the electron and laser beam parameters for the experiment.
Bonggu Shim: Time-resolved harmonic generation from exploding noble-gas clusters
  Title of proposed report: "Time-resolved harmonic generation from exploding noble-gas clusters"Summary: Clustered gases are an attractive medium for plasma channels and accelerators, because they absorb intense laser light efficiently and can develop large 3rd-order optical nonlinearities. I propose to report recent, unpublished experiments performed in M. Downers laboratory (U. Texas) in which we measure the third-order susceptibility of clustered plasma as a function of time after absorption of a femtosecond pump pulse. Argon clusters were initially heated by an intense 400nm pump laser and then allowed to freely expand. An 800nm probe beam was then used to probe the micro-plasma and generate harmonics. By varying the time delay between the pump and probe beams using collinear and non-collinear pump-probe schemes, we have found evidence of a resonance condition in the third harmonic production that is different from linear absorption cases. The third harmonic resonance comes at an earlier time delay than the linear absorption resonance case and it has much shorter time duration and we model it using PIC simulations. Results will be discussed in the light of a model of the nonlinear response that involves collective modes of a cold electron core confined within a positively charged ion background. Implications for plasma channeling and acceleration will be discussed. Preliminary versions of the work were presented at Frontiers in Optics (Oct.5-9, Tucson), the APS Division of Plasma Physics meeting (Oct. 27-31, Albuquerque) and SILAP (Nov. 16-19) in 2003. We will present latest results at the upcoming IQEC `04 May 16-21 in San Francisco.
Rafal Zgadzaj: Channeling Experiments and Wakefield Diagnostics
  Channel Experiments: We report on recent ultrafast pump-probe experiments in He plasma waveguides using 800 nm, 80fs pump pulses of 0.2x10^18 W/cm^2 peak guided intensity, and single orthogonally-polarized 800nm probe pulses with ~0.1% of pump intensity. The main results, which are being published in J. Opt. Soc. Am. B (2004), are: (1) We observe frequency-domain interference between the probe and a weak, depolarized component of the pump that differs substantially in mode shape from the injected pump pulse; (2) we observe spectral blue-shifts in the transmitted probe that are not evident in the transmitted pump. The evidence indicates that pump depolarization and probe blue-shifts both originate near the channel entrance. I will also report on current experiments in which we inject pulses of fully relativistic intensity into plasma channels generated in a differentially-pumped cell.

Wakefield Diagnostics: We report on recent progress on the development of an optimized real-time single-shot diagnostic (Optimized Frequency Domain Holography, OFDH) for measuring spatio-temporal structure of wakefields and other ultrafast phenomena. Using a short (70fs) and a long (1 ps) second harmonic probe pulse in a colinear geometry we have demonstrated the feasibility of the technique by measuring temporally and spatially resolved cross-phase modulation of the long probe due to a short pump in a glass coverslip. Real-time measurement and analysis capability enables us to fine-tune the laser and probe parameters during the experiment to optimize generation and measurement of the wakefield. Our current work is focused on developing methods for tailoring the OFDH technique for optimal sensitivity to wakefield structures, and I will present numerical results demonstrating the effectiveness of our optimization procedure. I will also report on our current experiments to measure the wakefields.

  A new S-band Plane-Wave-Transformer (PWT) photoinjector with capabilities to achieve high vacuum is under development at DULY Research Inc. The PWT is equipped with NEG pumps and a cathode load lock which is designed to handle semiconductor photocathodes such as GaAs. Polarized electrons with high charge, low emittance and high rep rate can be produced from the PWT, suitable for future linear colliders and other high brightness beam applications. Ultra short bunches can also be produced from the PWT for advanced accelerators and light sources.

*Work supported by DOE SBIR grant number DE-FG02-03ER83846

Serguei Kalmykov: Laser wakefield acceleration by petawatt ultra-short laser pulses
  Focusing an ultra-short (about 30 fs) petawattlaser pulse in a wide focal spot (with a radius up to 100 microns) in rarefiedplasma (electron density of order 10^{17} cm^{-3}) gives an opportunity toaccelerate electrons up to 1 GeV by means of laser wake-fieldacceleration scheme without pulse channelling. In theseconditions, the laser pulse with an over-critical power forrelativistic self-focusing propagates in plasmas quite similar tovacuum. The nonlinear quasi-plane wake plasma wave, whoseamplitude and phase velocity vary along the path of laser pulse,effectively traps and accelerates injected electrons with a widerange of initial energies. Electrons accelerated within twice theRayleigh length (about 8 cm) can gain the energy up to 1 GeV. Inparticular, acceleration of a rather long(about 0.3 ps) non-resonant electron bunchwith initial energy of particles about 1 MeV forms a bunch of lowemittance electrons with the energies in the range 900 MeV and energy spread about 50 MeV.All these conclusions follow from two-dimensional simulationsperformed in cylindrical geometry by means of fully relativisticparticle code WAKE.
  Performance and design features of metal PBG and rod-loaded cavities for single-beam and multi-beam rf accelerating/generating devices are considered. Fundamental differences of the performance between single-defect and multi-defect structures are identified. A six-beam cavity design with external coupler is optimized for a multi-beam PBG klystron. Preliminary design of a compact, 6-beam, X-band MBK demonstrates feasibility of generating high power with high efficiency.

*Work supported by DOE SBIR grant number DE-FG02-03ER83845

Mitsuru Uesaka: X-band RF gun and linac for medical Compton scattering X-ray source
  Compton scattering hard X-ray source for 10~80keV are under construction using the X-band (11.424GHz) electron linear accelerator and YAG laser at Nuclear Engineering Research laboratory, University of Tokyo. This work is a part of the national project on the development of advanced compact medical accelerators in Japan. National Institute for Radiological Science is the host institute and U.Tokyo and KEK are working for the X-ray source. Main advantage is to produce tunable monochromatic hard (10-80 keV) X-rays with the intensities of 10^8-10 photons/s (at several stages) and the table-top size. Second important aspect is to reduce noise radiation at the beam dump by adopting the deceleration of electrons after the Compton scattering. This realizes one beam line of a 3rd generation SR source at small facilities without heavy shielding. The final goal is that the linac and laser are installed on the moving gantry. We have designed the X-band (11.424 GHz) traveling-wave-type linac for the purpose. Numerical consideration by CAIN code and luminosity calculation are performed to estimate the X-ray yield. X-band thermionic-cathode RF-gun and RDS(Round Detuned Structure) type X-band accelerating structure are applied to generate 50 MeV electron beam with 20 pC microbunches (10^4) for 1 microsecond RF macro-pulse. The X-ray yield by the electron beam and Q-switch Nd:YAG laser of 2 J/10 ns is 10^7 photons/RF-pulse (10^8 photons/sec in 10 pps). We design to adopt a technique of laser circulation to increase the X-ray yield up to 10^9 photons/pulse (10^10 photons/s). 50 MW X-band Klystron and compact modulator have been constructed and now under tuning. The construction of the whole system starts. X-ray generation and medical application will be performed in the early next year.
Winthrop Brown: Development of a Higher Brightness, Ultra-Fast Thomson Scattering X-ray Source for Dynamic Diffraction on Atomic Time Scales
  Thomson scattering of a short, intense laser pulse by a relativistic electron bunch is a promising method for producing high brightness, hard x-ray pulses capable of probing the structural dynamics of high-Z materials at ultra-fast (femtosecond) time scales. The success of such sources depends heavily on the ability to produce high quality electron beams capable of meeting the femtosecond pulse duration, kilo-amp peak current, and micro-meter spot size requirements needed to push the performance of Thomson x-ray sources to the next level. In this talk, the dynamics of electron beam production and final focus are discussed, along with the practical limitations on the electron beam parameters. In addition, the dynamics of Thomson scattering is reviewed and scaling laws relating x-ray source flux and brightness to the electron beam emittance, pulse duration, and spot size are introduced. The PLEIADES facility has produced 5 x 10^6 photons per pulse in the 40-80 keV range, with an estimated peak x-ray brightness of 10^16 photons/s/mm^2mrad^2/0.1%b.w., by colliding a 50-60 MeV, 10 picosecond, 0.25 nC electron beam with an 800 nm, 50 fs laser pulse. Details of the current experiment will be discussed, and upgrade paths for enhancing the x-ray source performance will be examined, including the use of ultra-high gradient permanent magnet quadrupole magnets for minimizing the electron beam spot size, and longitudinal electron bunch compression for minimizing the x-ray pulse duration. In addition, the production of chirped x-ray pulses for subsequent slicing and/or compression will be discussed in detail. It is shown that sufficient temporal correlation in the scattered x-ray spectrum to achieve sub-100 fs resolution can be produced from state of the art, high brightness electron beams.
  Beam dynamics calculations of a 15.6 GHz ceramic rf power generator have been performed for an experiment at the upgraded AWA facility at ANL. The expected peak power to be generated is 100-150 MW. Analytical and numerical calculations address the following issues: 50A+ heavy beam loading in both linac and slow-wave structures, beam breakup and dipole mode suppression, end-to-end beam dynamics and transport, generated rf waveform and spectrum. Comparison is made with an earlier DULY/CERN/ANL 21GHz experiment.

*Work supported by DOE SBIR grant number DE-FG03-01ER83232

Michael LaPointe: A Status Report on Ka-band Transmission Line Component Development*
  The development of the 34 GHz magnicon in the Omega-P, / Yale Universtiy Beam Physics Lab requires various transmission line components to transport the mm-wave power from the magnicon to other devices to be tested (accelerator section, surface fatigue experiment, etc.). Components include dual directional couplers in WR28, phase shifters, calorimetric loads, mode converters from rectagular to circular waveguide, 13mm -63mm tapers, low loss miter bends with mode converters, windows, pumping ports for 13mm annd 63.5mm circular waveguide, a resonant ring for high power testing. Current staus and future plans will be presented.

*Research sponsored by U.S. Department of Energy, Division of High Energy Physics.

Richard Hubbard: Prospects for Integrated Injection and Acceleration Experiments with Capillary Discharge Guiding
Several laboratories are planning integrated injection and acceleration experiments to demonstrate the basic principles of a channel guided laser wakefield accelerator (LWFA). This paper discusses several recent advances in experimental techniques and theoretical/simulation modeling that have improved the prospects for successful demonstration experiments in the near future. (1) Simulation and Hamiltonian models have demonstrated that a channel-guided LWFA may produce high quality, ultrashort accelerated electron bunches without precisely-phased, monoenergetic injection of an ultrashort bunch. (2) Recently demonstrated all-optical injectors that produce injected bunches with large energy spreads are potentially capable of producing high quality accelerated electron beams in a LWFA. (3) New laser-triggered ablative wall capillaries have demonstrated deeper plasma channels and guiding at substantially higher intensities, thus reducing laser power requirements. (4) The required minimum energy for injection may be substantially lower in a channel than in a uniform plasma because of a favorable shift in the size and phase of the portion of the wake that is both accelerating and focusing. (5) Finally, this phase shift can also result in a significant increase in the dephasing length and thus the overall final energy of the accelerated bunch. This combination of factors should significantly relax the requirements for successful near-term demonstration experiments. *Supported by the Department of Energy and Office of Naval Research
Kei Nakamura: Laser triggered injection of electrons in a laser wakefield accelerator with colliding pulse method.
  Laser driven acceleration in plasmas has succeeded in producing electron beams containing multi-nCs of charge, with some fraction of the electrons having energies in excess of 10s of MeVs but 100 % energy spread. One of the current challenges is to produce electron beams with much reduced energy spread. We report on experimental progress in the laser triggered injection of electrons in a laser wakefield accelerator using the colliding pulse method [1], [2]. The experiments use the lOASIS multi-beam 10 Hz high power Ti:Al2O3 laser system [3]. In the present experiments, two counter propagating beams 30˚ angle are focused onto a high density (~1019/cm3) gas jet. Preliminary results indicate that electron beam properties are affected by the second beam. Details of the experiments will be shown as well as comparisons with simulations. This work supported by DoE under contract No DE-AC-03-76SF0098. C. G. R. Geddes acknowledges support from the Hertz Foundation.

[1] E. Esarey et al., Phys. Rev. Lett. 79, 2682 (1997).[2] C. B. Schroeder et al., Phys. Rev. E 59, 6037 (1999).[3] W.P. Leemans et al., Phys. Rev. Lett. 89, 174802 (2002).

Michail Tzoufras: Electron acceleration from 650fsec and 50fsec ultraintense laser pulses
  In order to obtain a better understanding of the mechanisms related to theelectron acceleration observed in recent laser-plasma interaction experimentswe have performed PIC simulations with the code OSIRIS. Two regimes have beeninvestigated. For the first regime, which corresponds to a 650fsec, 1PW laser pulse travelling through underdense deuterium plasma, we haveperformed 2D3V simulations. Even though the pulse shows no sigificant selfmodulation, electrons up to 350 MeV are observed. The main acceleration mechanismis believed to be stochastic direct acceleration by the laser field.

   The second acceleration regime is generated by the interaction of 50fsec (5-25)TW laser pulseswith underdense plasma. Clear wakefield structure is observed that accelerates particles up to 100 MeV. Full 3D (and 2D3V) simulations have been performed for this regime for a variety of plasma densities.

Ionization effects will be addressed.

Chieh Sung: Study of a THz IFEL prebuncher for laser-plasma accelerators
  For monoenergetic acceleration of electrons, the injected particles need to be bunched with the same periodicity as the accelerating structure. In the Plasma Beat Wave Acceleration experiment in the Neptune laboratory, the accelerating structure has a periodicity of 340 μm. The plasma wave is phase-locked to the CO2 beat-wave used to drive it. We are proposing to use the same beat-wave to generate a high power 340 μm EM radiation via difference frequency mixing in GaAs. This radiation would have the same phase relationship as the plasma wave and therefore can be used to prebunch an existing nominally 10 MeV electron beam based on an IFEL concept. We will present the design of such a prebuncher which uses a 50 cm long undulator. The injected 5ps long electron beam is expected to form a series of 45 μm long microbunches containing over 40% of the injected current after 1.6 m drift space following the undulator.
Vladimir Gorgadze: Beam Physics Studies in Nonneutral Plasmas: Injection, Virtual Cathodes, and Autoresonant Control
  Nonneutral plasmas have been put forward over the last five years as a novel system with which to conduct intense beam transport studies. Other aspects of beams physics can be investigated with nonneutral plasma systems. The surprisingly rich injection physics in nonneutral plasmas has been studied both theoretically and experimentally [1]. Simulations using a PIC code have confirmed experiment results and offer insights into the phase space structure beyond what is observed experimentally. This includes two-stream instabilities, virtual cathodes, and self-field induced changes to the transverse emission profile. Theoretical estimates are consistent with the simulations. Autoresonance has been intensively studied by Friedland and co-workers in a wide range of physical systems. Basically, the idea is to control a driven nonlinear oscillator through a frequency chirped drive. Recently, we considered using an unpowered external circuit with a frequency chirp to extract power from a diocotron oscillation. The connection of these ideas to beam physics will be presented. [1] G. Gorgadze, T. Pasquini, J. Fajans, and J. Wurtele, in preparation. Co-Authors Joel Fajans, Jonathan Wurtele, UC Berkeley/LBNL Lazar Friedland, Hebrew University