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Title: Scaling of gain with energy spread and energy in the PEP FEL

Abstract

The Sag Harbor paper on the PEP FEL discusses the scaling of various FEL parameters with energy spread {sigma}{sub {var_epsilon}}. I will repeat some of this material here and then examine the benefit of increasing the energy spread. How much energy spread can be achieved with damping wigglers is the next topic. Finally, I consider the dependence of gain and saturation length on beam energy and undulator field.

Authors:
Publication Date:
Research Org.:
Brookhaven National Lab., Upton, NY (United States)
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
10169661
Report Number(s):
BNL-47803; CAP-85-92R
ON: DE92019248
DOE Contract Number:
AC02-76CH00016
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 13 Jul 1992
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; 42 ENGINEERING; FREE ELECTRON LASERS; SCALING LAWS; GAIN; PEP STORAGE RINGS; WIGGLER MAGNETS; BEAM EMITTANCE; DAMPING; BEAM LUMINOSITY; 430400; 430200; 426002; STORAGE RINGS; BEAM DYNAMICS, FIELD CALCULATIONS, AND ION OPTICS; LASERS AND MASERS

Citation Formats

Fisher, A.S. Scaling of gain with energy spread and energy in the PEP FEL. United States: N. p., 1992. Web. doi:10.2172/10169661.
Fisher, A.S. Scaling of gain with energy spread and energy in the PEP FEL. United States. doi:10.2172/10169661.
Fisher, A.S. 1992. "Scaling of gain with energy spread and energy in the PEP FEL". United States. doi:10.2172/10169661. https://www.osti.gov/servlets/purl/10169661.
@article{osti_10169661,
title = {Scaling of gain with energy spread and energy in the PEP FEL},
author = {Fisher, A.S.},
abstractNote = {The Sag Harbor paper on the PEP FEL discusses the scaling of various FEL parameters with energy spread {sigma}{sub {var_epsilon}}. I will repeat some of this material here and then examine the benefit of increasing the energy spread. How much energy spread can be achieved with damping wigglers is the next topic. Finally, I consider the dependence of gain and saturation length on beam energy and undulator field.},
doi = {10.2172/10169661},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1992,
month = 7
}

Technical Report:

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  • The Sag Harbor paper on the PEP FEL discusses the scaling of various FEL parameters with energy spread {sigma}{sub {var epsilon}}. I will repeat some of this material here and then examine the benefit of increasing the energy spread. How much energy spread can be achieved with damping wigglers is the next topic. Finally, I consider the dependence of gain and saturation length on beam energy and undulator field.
  • This paper proposed an extension of the Madey gain-spread theorem to two-dimensional wigglers and shown it to be quite generally valid. It has the important consequence that an Free Electron Laser(FEL) wiggler which yields gain must at the same time generate either energy spread or transverse excitation. Furthermore it was found that in an FEL operating quasi linearly in a storage ring, that laser gain guarantees the production of entropy with every pass through the wiggler. Consequently the laser radiation generated is restricted to be some small fraction of the synchrotron radiation and our analysis suggests that this fraction ismore » of the order of the fractional energy aperture. This leads us to the conclusion that the achievement of high efficiency steady stage storage ring operation in a quasi linear regime is not possible. Nonetheless, it appears that gain expanded wigglers may have superior linear gain as compared with conventional wigglers and thus prove to be useful for application in storage rings with large fractional energy aperture.« less
  • It is shown that in the small signal-low gain regime, an analytic expression for the gain can be derived, which is correct for general electron distribution function and general longitudinal variation of the transverse magnetic field pump. This expression is used to evaluate the effects on the gain curve due to transverse momentum spread in the beam as well as the inaccuracies (incoherence) in the magnetic pump phase and amplitude. The restricting criteria for the neglect of these effects are derived.
  • When plasma ions and electrons are accelerated in the same direction to different velocities, r-f signals are amplified along the plasma. Since the thermal velocity spread of the particles makes the imparted velocity difference less pronounced, the observed gain should be less than that predicted by the simple theory for "cold" streams. Calculations are presented that verify this reduction. Typically, the optimum gain is reduced to two-thirds of the "cold" value for a random electron velocity of about 10% of the relative drift velocity. The plasma equations are linearized, and it is assumed that the plasma is nearly electrically neutral,more » that hydrogen ions are used, that the thermal ion velocity fs small compared with the ion drift velocity, that the frequencies considered are relatively small, and that the electron drift velocity is only slightly larger than the ion drift velocity. Below certain values of thermal spread, the gain passes through a maximum as the frequency is varied. As the thermal spread increases, the frequency at which this optimum occurs decreases. The gain disappears completely when the thermal velocities become very large compared with the relative drift velocity. (auth)« less
  • The concept of using mutual charge exchange to create high energy and high power neutral beams is described. Analytical models to simulate beam neutralization are derived and solved numerically. 4 refs., 6 figs.