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Title: Simulation of a high-average power free-electron laser oscillator

Abstract

In this paper, we compare the 10 kW-Upgrade experiment at the Thomas Jefferson National Accelerator Facility in Newport News, VA, with numerical simulations using the medusa code. medusa is a three-dimensional FEL simulation code that is capable of treating both amplifiers and oscillators in both the steady-state and time-dependent regimes. medusa employs a Gaussian modal expansion, and treats oscillators by decomposing the modal representation at the exit of the wiggler into the vacuum Gaussian modes of the resonator and then analytically determining the propagation of these vacuum resonator modes through the resonator back to the entrance of the wiggler in synchronism with the next electron bunch. The bunch length in the experiment is of the order of 380–420 fsec FWHM. The experiment operates at a wavelength of about 1.6 microns and the wiggler is 30 periods in length; hence, the slippage time is about 160 fsec. Because of this, slippage is important, and must be included in the simulation. The observed single pass gain is 65%–75% and, given the experimental uncertainties, this is in good agreement with the simulation. Multipass simulations including the cavity detuning yield an output power of 12.4 kW, which is also in good agreement with themore » experiment.« less

Authors:
; ;
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility, Newport News, VA
Sponsoring Org.:
USDOE - Office of Energy Research (ER)
OSTI Identifier:
910127
Report Number(s):
JLAB-ACT-07-669; DOE/OR/23177-0095
Journal ID: ISSN 1098-4402; TRN: US0704094
DOE Contract Number:
AC05-06OR23177
Resource Type:
Journal Article
Resource Relation:
Journal Name: Phys.Rev.ST Accel.Beams; Journal Volume: 10
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; AMPLIFIERS; CEBAF ACCELERATOR; ELECTRONS; FREE ELECTRON LASERS; OSCILLATORS; RESONATORS; SIMULATION; WAVELENGTHS

Citation Formats

H.P. Freund, M. Shinn, and S.V. Benson. Simulation of a high-average power free-electron laser oscillator. United States: N. p., 2007. Web. doi:10.1103/PhysRevSTAB.10.030702.
H.P. Freund, M. Shinn, & S.V. Benson. Simulation of a high-average power free-electron laser oscillator. United States. doi:10.1103/PhysRevSTAB.10.030702.
H.P. Freund, M. Shinn, and S.V. Benson. 2007. "Simulation of a high-average power free-electron laser oscillator". United States. doi:10.1103/PhysRevSTAB.10.030702.
@article{osti_910127,
title = {Simulation of a high-average power free-electron laser oscillator},
author = {H.P. Freund and M. Shinn and S.V. Benson},
abstractNote = {In this paper, we compare the 10 kW-Upgrade experiment at the Thomas Jefferson National Accelerator Facility in Newport News, VA, with numerical simulations using the medusa code. medusa is a three-dimensional FEL simulation code that is capable of treating both amplifiers and oscillators in both the steady-state and time-dependent regimes. medusa employs a Gaussian modal expansion, and treats oscillators by decomposing the modal representation at the exit of the wiggler into the vacuum Gaussian modes of the resonator and then analytically determining the propagation of these vacuum resonator modes through the resonator back to the entrance of the wiggler in synchronism with the next electron bunch. The bunch length in the experiment is of the order of 380–420 fsec FWHM. The experiment operates at a wavelength of about 1.6 microns and the wiggler is 30 periods in length; hence, the slippage time is about 160 fsec. Because of this, slippage is important, and must be included in the simulation. The observed single pass gain is 65%–75% and, given the experimental uncertainties, this is in good agreement with the simulation. Multipass simulations including the cavity detuning yield an output power of 12.4 kW, which is also in good agreement with the experiment.},
doi = {10.1103/PhysRevSTAB.10.030702},
journal = {Phys.Rev.ST Accel.Beams},
number = ,
volume = 10,
place = {United States},
year = 2007,
month = 3
}
  • The design and feasibility of a 1-MW continuous wave (CW) free electron laser (FEL) oscillator are reviewed. The proposed configuration will include a short-period planar wiggler, a sheet electron beam, a 0.5--1.0 MV thermionic electron gun, a hybrid waveguide/quasi-optical resonator, commercial dc power supplies, and a depressed collector. Cavity ohmic RF losses are estimated to be extremely low ({approx lt} 10--100 W/cm{sup 2}) at 1-MW output power, while thermal heat transfer studies conservatively indicate that wall cooling up to 1500 W/cm{sup 2} should be possible.
  • The three-dimensional optical pattern generated in a single pulse by a high-power free-electron-laser system when the {ital e}{sup {minus}}-beam radius is small compared to the laser-beam radius is shown to be determined by the solution of a simple one-dimensional integral equation. This strong-diffraction-limit equation is of the convolution form and, while it is mostly easily solved numerically, it is shown to have nontrivial analytic solutions of interest.
  • A microwave field can be used to accelerate electrons as they lose energy to radiation in an FEL, thereby maintaining synchronism and, used in conjunction with an optical klystron, providing high conversion efficiencies. The microwave can be programmed to increase in time with the optical power level in the FEL so that high gain is maintained over a wide range of power levels. In this paper, parameter constraints for such an FEL are discussed, leading to a structure design that integrates a wiggler with a linac. It is shown that conversion efficiencies of 50 percent at lambda = 10 ..mu..mmore » with a 2 m wiggler length can be achieved for typical FEL parameter values without sacrificing small-signal gain.« less
  • We have demonstrated high-average-power second-harmonic generation with an output power of 5.6 W at 532 nm by intracavity frequency doubling using Type II KTiOPO/sub 4/ in a Nd:YAG laser oscillator acousto-optically Q switched at 5 kHz./sup 1/ The average power achieved, limited only by the power-supply current available in these experiments, was about three times higher than what has been obtained in a state-of-the-are device using LiIO/sub 3/ as the doubler. More significantly, since no intrinsic limitations, such as saturation and material damage, have yet been observed, further improvement in the power output should be achievable. It is pointed outmore » that previous studies on intracavity second-harmonic generation have been limited to the small-signal case; the present result shows the feasibility of operating an internally doubled oscillator for efficiently converting the fundamental to itgs harmonic in a high-power device.« less
  • In this paper a comparison is described between the three-dimensional nonlinear analysis and simulation code, ARACHNE, and a recent 33.4-GHz, collective, free-electron laser amplifier experiment at MIT. The experiment has demonstrated power levels of 61 ME ({approx}27% efficiency) without recourse to tapered magnetic fields, using a 750-keV/300-A electron beam with a nominal axial energy spread of 1.5% propagating through a cylindrical drift tube in the presence of a helical wiggler (B{sub w} {le} 1.8 kG, {lambda}{sub w} = 3.18 cm) and an axial guide magnetic field (B{sub 0} {le} 12 kG). Significant differences in the character of the emission weremore » found based upon the direction of the guide magnetic field. The ARACHNE simulation is in substantial agreement with the experiment. The source of this power reduction appears to be a previously unsuspected effect on the electron orbits due to the wiggler inhomogeneity. Agreement with the much lower power levels found when the wiggler and guide fields are parallel, however, requires the assumption of a substantial increase in the energy spread of the beam.« less