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Title: An inverse free electron laser accelerator: Experiment and theoretical interpretation

Abstract

Experimental and numerical studies of the Inverse Free Electron Laser using a GW-level 10.6 μm CO 2 laser have been carried out at Brookhaven`s Accelerator Test Facility. An energy gain of 2.5 % (ΔE/E) on a 40 MeV electron beam has been observed E which compares well with theory. The effects on IFEL acceleration with respect to the variation of the laser electric field, the input electron beam energy, and the wiggler magnetic field strength were studied, and show the importance of matching the resonance condition in the IFEL. The numerical simulations were performed under various conditions and the importance of the electron bunching in the IFEL is shown. The numerical interpretation of our IFEL experimental results was examined. Although good numerical agreement with the experimental results was obtained, there is a discrepancy between the level of the laser power measured in the experiment and used in the simulation, possibly due to the non-Gaussian profile of the input high power laser beam. The electron energy distribution was studied numerically and a smoothing of the energy spectrum by the space charge effect at the location of the spectrometer was found, compared with the spectrum at the exit of the wiggler. Themore » electron bunching by the IFEL and the possibility of using the IFEL as an electron prebuncher for another laser-driven accelerator were studied numerically. We found that bunching of the electrons at 1 meter downstream from the wiggler can be achieved using the existing facility. The simulation shows that there is a fundamental difference between the operating conditions for using the IFEL as a high gradient accelerator, and as a prebuncher for another accelerator.« less

Authors:
 [1]
+ Show Author Affiliations
  1. Columbia Univ., New York, NY (United States)
Publication Date:
Research Org.:
Columbia Univ., New York, NY (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
484578
Report Number(s):
DOE/ER/40669-T1; CU-133
ON: DE97007692; TRN: 97:011291
DOE Contract Number:
FG02-91ER40669
Resource Type:
Thesis/Dissertation
Resource Relation:
Other Information: TH: Thesis (Ph.D.); PBD: 1997
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; FREE ELECTRON LASERS; DESIGN; COMPUTERIZED SIMULATION; ACCELERATORS; CARBON DIOXIDE LASERS; BEAM BUNCHING; BEAM MONITORING

Citation Formats

Fang, Jyan-Min. An inverse free electron laser accelerator: Experiment and theoretical interpretation. United States: N. p., 1997. Web. doi:10.2172/484578.
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Fang, Jyan-Min. An inverse free electron laser accelerator: Experiment and theoretical interpretation. United States. doi:10.2172/484578.
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Fang, Jyan-Min. Wed . "An inverse free electron laser accelerator: Experiment and theoretical interpretation". United States. doi:10.2172/484578. https://www.osti.gov/servlets/purl/484578.
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@article{osti_484578,
title = {An inverse free electron laser accelerator: Experiment and theoretical interpretation},
author = {Fang, Jyan-Min},
abstractNote = {Experimental and numerical studies of the Inverse Free Electron Laser using a GW-level 10.6 μm CO2 laser have been carried out at Brookhaven`s Accelerator Test Facility. An energy gain of 2.5 % (ΔE/E) on a 40 MeV electron beam has been observed E which compares well with theory. The effects on IFEL acceleration with respect to the variation of the laser electric field, the input electron beam energy, and the wiggler magnetic field strength were studied, and show the importance of matching the resonance condition in the IFEL. The numerical simulations were performed under various conditions and the importance of the electron bunching in the IFEL is shown. The numerical interpretation of our IFEL experimental results was examined. Although good numerical agreement with the experimental results was obtained, there is a discrepancy between the level of the laser power measured in the experiment and used in the simulation, possibly due to the non-Gaussian profile of the input high power laser beam. The electron energy distribution was studied numerically and a smoothing of the energy spectrum by the space charge effect at the location of the spectrometer was found, compared with the spectrum at the exit of the wiggler. The electron bunching by the IFEL and the possibility of using the IFEL as an electron prebuncher for another laser-driven accelerator were studied numerically. We found that bunching of the electrons at 1 meter downstream from the wiggler can be achieved using the existing facility. The simulation shows that there is a fundamental difference between the operating conditions for using the IFEL as a high gradient accelerator, and as a prebuncher for another accelerator.},
doi = {10.2172/484578},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Jan 01 00:00:00 EST 1997},
month = {Wed Jan 01 00:00:00 EST 1997}
}
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Thesis/Dissertation:
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DOI:  10.2172/484578
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  • ;
    We present data from our study of a device known as the inverse free electron laser. First, numerical simulations were performed to optimize the design parameters for an experiment that accelerates electrons in the presence of an undulator by stimulated absorption of radiation. The Columbia free electron laser (FEL) was configured as an auto-accelerator (IFELA) system; high power (MW`s) FEL radiation at ~1.65 mm is developed along the first section of an undulator inside a quasi-optical resonator. The electron beam then traverses a second section of undulator where a fraction of the electrons is accelerated by stimulated absorption of themore » 1.65 mm wavelength power developed in the first undulator section. The second undulator section has very low gain and does not generate power on its own. We have found that as much as 60% of the power generated in the first section can be absorbed in the second section, providing that the initial electron energy is chosen correctly with respect to the parameters chosen for the first and second undulators. An electron momentum spectrometer is used to monitor the distribution of electron energies as the electrons exit the IFELA. We have found; using our experimental parameters, that roughly 10% of the electrons are accelerated to energies as high as 1100 keV, in accordance with predictions from the numerical model. The appearance of high energy electrons is correlated with the abrupt absorption of millimeter power. The autoaccelerator configuration is used because there is no intense source of coherent power at the 1.65 mm design wavelength other than the FEL.« less

  • The problem with generating shorter wavelengths in a standard Compton FEL is that the requirements on the electron-beam energy and electron-beam quality, or brightness, increase as the wavelength gets shorter. This dissertation addresses two improvements in FELs to address separately the gain and wavelength problems: the dispersive FEL (DFEL) and the gas-loaded FEL (GFEL). The dispersive free-electron laser uses a modified magnetic wiggler structure that can increase the gain 15-fold. However, this is done at the cost of the energy spread allowable on the electron beam. The gas-loaded FEL uses a gas within the wiggler to slow the optical phasemore » velocity. This changes the synchronism requirements and provides an alternate tuning method. One benefit of this alternate tuning allows for generating shorter wavelengths with lower-energy electron beams. Although there is a substantial gain benefit implied by using lower-energy electrons, there are losses associated with scattering. There are a host of possible plasma effects to quench lasing as well. This dissertation addresses the GFEL issues theoretically and presents some experimental results, as well as the results of the DFEL simulation.« less

  • A free electron laser (FEL) oscillator based on stimulated Raman backscattering, using a 1 MeV 20 kA electron beam pumped with a weak (250 G), periodic (lambda = 8mm) transverse magnetic field is operated as a source of high power (approx. 1 MW) millimeter and submillimeter radiation, with lasing developing during the 150 nSec beam lifetime. Superluminescent and lasing operation as described at lambda approx. 1.0 mm and lambda approx. 0.6 mm. A cavity mode theory based upon orthogonal mode expansions and scalar diffraction theory is developed. Functional dependences such as radiation survival fraction and mode selectivity are found analyticallymore » as they may vary with cavity and mirror geometry and wave length. Normal cavity modes for both the open and closed laser resonator with either dielectric or conducting drift tube walls are identified and shown to depend qualitatively upon cavity Fresnel number. Integrals from the theory are evaluated numerically to present a quantitative electrodynamical description of the Columbia FEL mirror system, as well as other FEL geometries. Optimization of the FEL through mode selectivity is discussed.« less

  • With the advent of X-ray Free Electron Lasers (FELs), new methods have been developed to extend capabilities at short wavelengths beyond Self-Amplified Spontaneous Emission (SASE). In particular, seeding of a FEL allows for temporal control of the radiation pulse and increases the peak brightness by orders of magnitude. Most recently, Gennady Stupakov and colleagues at SLAC proposed a new technique: Echo-Enabled Harmonic Generation (EEHG). Here a laser microbunches the beam in an undulator and the beam is sheared in a chicane. This process is repeated with a second laser, undulator and chicane. The interplay between these allows a seeding ofmore » the X-ray laser up to the 100th harmonic of the first laser. After introducing the physics of FELs and the EEHG seeding technique, we describe contributions to the experimental effort. We will present detailed studies of the experiment including the choice of parameters and their optimization, the emittance effect, spontaneous emission in the undulators, the second laser phase effect, and measurements of the jitter between RF stations. Finally, the status and preliminary results of the Echo-7 experiment will be outlined.« less

  • Theoretical and experimental investigations of the spontaneous and laser radiation are presented. Historical overview and comparison to the early Stanford experiments are given. The theory of spontaneous undulator radiation in a waveguide FEL device, shows that the emission spectrum may differ considerably compared to the free-space result for the case of moderate waveguide aperture and electron energy. The spontaneous radiation into the different cavity modes is also calculated and used to obtain a three-dimensional form for Madey theorem. Interferometric measurements of the spectrum, confirmed the predictions of the theory. At 3 MeV electron beam energy, the laser output showed unexpectedmore » oscillation on a characteristic time scale of 5 ..mu..s and, at the same time, the laser mode swept over a discrete set of frequency modes separated by 1.3 GHz. The origin of this phenomenon is related to the accelerator terminal voltage drop during the lifetime of the pulse. The three-dimensional, small-signal FED theory is developed. A general gain expression for a diffracting optical mode interacting with an electron beam of arbitrary profile is derived and several examples including gain of a Gaussian optical mode interacting with a filamentary and cylindrical electron-beam and gain of a combination of transverse modes are discussed.« less