EM Structure-Based Accelerators Working Group Summary

The theoretical study of Inverse Free Electron Lasers (IFEL) as a potential mode of electron acceleration has been pursued at Brookhaven National Laboratory(BNL) for a number of years. As part of this program a proof-of-principle experiment with a single module accelerator unit has been recently successfully carried out. The IFEL accelerator made use of the 40 MeV linac beam and high power CO/sub 2/ laser beam of the Accelerator Test Facility (ATF), at BNL, in conjunction with a fast excitation, tapered period, wiggler. Basic aspects of the design of this single module IFEL accelerator will be presented, together with the experimental results of /spl Delta/E/E as a function of the IFEL parameters. Comparison with analytical and 1,3-D numerical simulations clearly establish the IFEL character of the electron-EM wave energy exchange, permitting thereby scaling to higher laser power magnitude and acceleration gradients. In addition, planned near term IFEL accelerator development will be indicated, incorporating the use of the IFEL as a beam prebuncher preceding a Inverse Cherenkov Accelerator, and the use of two IFEL modules in cascade in order to more realistically test the feasibility of a multi-module IFEL accelerator.

The staged electron laser acceleration (STELLA) experiment demonstrated staging between two laser-driven devices, high trapping efficiency of microbunches within the accelerating field and narrow energy spread during laser acceleration. These are important for practical laser-driven accelerators. STELLA used inverse free electron lasers, which were chosen primarily for convenience. Nevertheless, the STELLA approach can be applied to other laser acceleration methods, in particular, laser-driven plasma accelerators. STELLA is now conducting experiments on laser wakefield acceleration (LWFA). Two novel LWFA approaches are being investigated. In the first one, called pseudo-resonant LWFA, a laser pulse enters a low-density plasma where nonlinear laser/plasma interactions cause the laser pulse shape to steepen, thereby creating strong wakefields. A witness e-beam pulse probes the wakefields. The second one, called seeded self-modulated LWFA, involves sending a seed e-beam pulse into the plasma to initiate wakefield formation. These wakefields are amplified by a laser pulse following shortly after the seed pulse. A second e-beam pulse (witness) follows the seed pulse to probe the wakefields. These LWFA experiments will also be the first ones driven by a CO(2) laser beam.

Compact, table-top sized accelerators are key to improving access to high-quality beams for use in industry, medicine and academic research. Among laser-based accelerating schemes, the inverse free-electron laser (IFEL) enjoys unique advantages. By using an undulator magnetic field in combination with a laser, GeV m(-1) gradients may be sustained over metre-scale distances using laser intensities several orders of magnitude less than those used in laser wake-field accelerators. Here we show for the first time the capture and high-gradient acceleration of monoenergetic electron beams from a helical IFEL. Using a modest intensity (~10(13) W cm(-2)) laser pulse and strongly tapered 0.5 m long undulator, we demonstrate >100 MV m(-1) accelerating gradient, >50 MeV energy gain and excellent output beam quality. Our results pave the way towards compact, tunable GeV IFEL accelerators for applications such as driving soft X-ray free-electron lasers and producing γ-rays by inverse Compton scattering.

We employed periodic trains of femtosecond electron bunches for testing several novel concepts of acceleration. A microwave‐driven linac sends a 45‐MeV electron beam (e‐beam) through a magnetic wiggler wherein the e‐beam energy is modulated via the inverse free electron laser (IFEL) technique by interacting with a 30‐GW CO2 laser beam, so creating 3 fs long microbunches separated by a 30 fs laser period. We show several examples of utilizing such a femtosecond bunch train in advanced accelerator and radiation source research. We demonstrated that microbunching improves the performance of the laser acceleration process compared to the previously investigated single‐bunch technique. Specifically, microbunches were phased to the electromagnetic wave of the CO2 laser beam inside a matched tapered wiggler where ∼80% of electrons gained energy as an ensemble while maintaining a narrow energy spread (i.e., monoenergetic). Another plasma wakefield acceleration (PWFA) experiment explored resonant wakefield excitation in an electric discharge plasma with the plasma frequency matched to that of the CO2 laser. Simulations predict orders‐of‐magnitude enhancement in the wakefield’s amplitude compared with that attained with single bunches. In the Particle Acceleration by Stimulated Emission of Radiation (PASER) experiment, we tested a prediction that an active laser medium can produce particle acceleration by stimulating the emission of radiation. The process benefits from the action of a periodic train of microbunches resonating with the laser transition. Finally, we analyze prospects for using partially coherent x‐ray sources based on Thomson backscattering from the electron microbunch train.

Effects of misaligned electron beam on inverse free electron laser acceleration

This report describes the work on the Group of Far Field Accclerators. The work was focused on two accelerator schemes, the Inverse Free Electron Laser and the Two Wave Device. The possibilities and limitations of these two accelerators are discussed, as well as some of the requirements on the laser necessary to reach very high energies. A conceptual design of a single pass Inverse Free Electron Laser is presented.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation W. D. Kimura, M. Babzien, I. Ben-Zvi, L. P. Campbell, D. B. Cline, R. B. Fiorito, J. C. Gallardo, S. C. Gottschalk, P. He, K. P. Kusche, Y. Liu, R. H. Pantell, I. V. Pogorelsky, D. C. Quimby, K. E. Robinson, D. W. Rule, J. Sandweiss, J. Skaritka, A. van Steenbergen, L. C. Steinhauer, V. Yakimenko; STELLA experiment: Design and model predictions. AIP Conf. Proc. 12 July 1999; 472 (1): 563–572. https://doi.org/10.1063/1.58869 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

We report on a proof-of-principle demonstration of a two-stage cascaded optical inverse free-electron laser (IFEL) accelerator in which an electron beam is accelerated by a strong laser pulse after being packed into optical microbunches by a weaker initial laser pulse. We show experimentally that injection of precisely prepared optical microbunches into an IFEL allows net acceleration or deceleration of the beam, depending on the relative phase of the two laser pulses. The experimental results are in excellent agreement with simulation. The demonstrated technique holds great promise to significantly improve the beam quality of IFELs and may have a strong impact on emerging laser accelerators driven by high-power optical lasers.

We propose a "zero-slippage," inverse free electron laser that uses a waveguide to sustain the interaction by matching the group velocity of a THz pulse to an electron bunch. The THz pulse, produced by optical rectification of the same initial laser pulse which generates the electron bunch, will create a ponderomotive potential that reduces the time-of-arrival jitter of the electron bunch as it is rotated in longitudinal phase space. We have demonstrated the direct coupling of the THz pulse into a parallel plate waveguide and measured the resulting group velocity reduction. Initial simulations predict compression of 1 pC, 100 fs (rms) electron bunches generated at UCLA's Pegasus laboratory by up to a factor of 10, along with an order-of-magnitude reduction in time of arrival jitter.

For monoenergetic acceleration of electrons, the injected particles need to be bunched with the same periodicity as the accelerating structure. In a laser‐driven plasma beatwave accelerator, the accelerating structure (plasma wave) is phase‐locked to the CO2 beat‐wave used to drive it. Using the same beat‐wave to generate high power FIR radiation via difference frequency mixing in GaAs ensures that the radiation has the same phase relationship as the plasma wave before it saturates and detunes from the pump. Therefore, this radiation can be used to prebunch an existing electron beam based on an Inverse Free Electron Laser (IFEL) concept. Here we report the progress on the proposed THz microbunching experiment in the Neptune laboratory. A 50 cm long prebuncher is optimized using simulation codes for minimum FIR power required. 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. Preliminary experimental results on THz generation are also presented.

We describe a conceptual proposal to combine the Dielectric Wakefield Accelerator (DWA) with the Emittance Exchanger (EEX) to demonstrate a high-brightness DWA with a gradient of above 100 MV/m and less than 0.1% induced energy spread in the accelerated beam. We currently evaluate the DWA concept as a performance upgrade for the future LANL signature facility MaRIE with the goal of significantly reducing the electron beam energy spread. The preconceptual design for MaRIE is underway at LANL, with the design of the electron linear accelerator being one of the main research goals. Although generally the baseline design needs to be conservative and rely on existing technology, any future upgrade would immediately call for looking into the advanced accelerator concepts capable of boosting the electron beam energy up by a few GeV in a very short distance without degrading the beam's quality. Scoping studies have identified large induced energy spreads as the major cause of beam quality degradation in high-gradient advanced accelerators for free-electron lasers. We describe simulations demonstrating that trapezoidal bunch shapes can be used in a DWA to greatly reduce the induced beam energy spread, and, in doing so, also preserve the beam brightness at levels never previously achieved. This concept has the potential to advance DWA technology to a level that would make it suitable for the upgrades of the proposed Los Alamos MaRIE signature facility.

Comparative study of inverse free-electron laser interaction based on helical and planar wiggler

Recent work at BNL on electron acceleration using the Inverse Free-Electron Laser (IFEL) has considered a low-energy, high-gradient, multi-stage linear accelerator. Experiments are planned at BNL's Accelerator Test Facility using its 50-MeV linac and 100-GW CO/sub 2/ laser. We have built and tested a fast-excitation wiggler magnet with constant field, tapered period, and overall length of 47 cm. Vanadium-Permendur ferromagnetic laminations are stacked in alternation with copper, eddy-current-induced, field reflectors to achieve a 1.4-T peak field with a 4-mm gap and a typical period of 3 cm. The laser beam will pass through the wiggler in a low-loss, dielectriccoated stainless-steel, rectangular waveguide. The attenuation and transverse mode has been measured in waveguide sections of various lengths, with and without the dielectric. Results of 1-D and 3-D IFEL simulations, including wiggler errors, are presented foe several cases: the initial, single-module experiment with /spl Delta/E=39 MeV, a four-module design giving /spl Delta/E=100 MeV in a total length of 2 m, and an eight-module IFEL with /spl Delta/E=210 MeV. >

A new type of electron beam source is proposed that combines a DC field and AC field from a laser beam in between the anode-cathode gap. Prior researchers have demonstrated the ability for this configuration to produce ultrashort electron microbunches from field emission when the AC field adds constructively with the DC field. Our new source improves upon this basic scheme by creating mono-energetic electrons with low emittance that are suitable for feeding into dielectric and vacuum laser accelerators, photonic bandgap accelerators, and dielectric wakefield accelerators. The microbunches will have a length that is a fraction of the laser wavelength, corresponding to fs pulse durations. They are also produced as a train of microbunches separated by the period of the laser length and lasting for the duration of the laser pulse.

The FEL and IFEL design study for the proposed NTHU photon–electron dynamics laboratory