A local theory of effect of beam pre-modulation on gain and efficiency in a surface wave pumped free electron laser

2014 ◽  
Vol 32 ◽  
pp. 1460351
Author(s):  
Jyotsna Sharma ◽  
Suresh C. Sharma ◽  
Anuradha Bhasin ◽  
V. K. Jain
Keyword(s):  
Growth Rate ◽  
Surface Wave ◽  
Free Electron ◽  
High Frequency ◽  
Free Electron Laser ◽  
Millimeter Waves ◽  
Local Theory ◽  
Vacuum Region ◽  
Laser Instability ◽  
Frequency Radiation

A pre-modulated relativistic electron beam (REB) counter propagating to the surface wave in the vacuum region Compton backscatters the surface wave into a high frequency radiation. The surface wave extends into the vacuum region and can be employed as a wiggler for the generation of sub-millimeter waves. The growth rate and gain were evaluated for a typical FEL (Free Electron Laser) parameters and It is found that the growth rate and gain of the surface wave pumped free electron laser increases with the modulation index. Moreover, the growth rate of the FEL (Free electron Laser) instability scales as one-third power of the beam density in the Compton regime.

Effect of beam pre-bunching on gain and efficiency in a surface wave-pumped free electron laser

2012 ◽  
Vol 78 (6) ◽  
pp. 635-640 ◽  
Author(s):  
SURESH C. SHARMA ◽  
JYOTSNA SHARMA ◽  
ANURADHA BHASIN ◽  
RITU WALIA
Keyword(s):  
Growth Rate ◽  
Surface Wave ◽  
Free Electron ◽  
Free Electron Laser ◽  
Wave Number ◽  
Large Wave ◽  
Vacuum Region ◽  
Radiation Wave ◽  
Large Wave Number ◽  
Radiation Plasma

AbstractA pre-bunched relativistic electron beam (REB) counter-propagating to the surface wave in the vacuum region Compton backscatters the surface wave into a high-frequency coherent radiation. Plasma supports the surface wave that acquires a large wave number k0z around pump wave frequency $\omega _0 = {{\omega _p } {/ {\vphantom {{\omega _p } {\sqrt 2 }}} \kern-\nulldelimiterspace} {\sqrt 2 }}$, where ωp is the plasma frequency. The surface wave extends into the vacuum region and can be employed as a wiggler for the generation of sub-millimeter waves. The growth rate, efficiency, and gain were evaluated based on experimentally known parameters relevant to free electron laser (FEL). It was found that the growth rate, efficiency, and gain of the surface wave-pumped FEL increase with the modulation index Δ, which has the maximum value when approaching unity in addition to when the frequency and wave number of the pre-bunched beam are comparable to that of the radiation wave, i.e., ω01 ~ ω1 and k01 ~ k1. The growth rate of FEL instability scales as one-third power of beam density in the Compton regime.

Non-local theory of a transverse magnetic mode pumped free electron laser

2008 ◽  
Vol 74 (5) ◽  
pp. 585-594
Author(s):  
B. S. SHARMA ◽  
N. K. JAIMAN
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Free Electron ◽  
Free Electron Laser ◽  
Cyclotron Frequency ◽  
Axial Magnetic Field ◽  
Local Theory ◽  
Instability Growth ◽  
Non Local ◽  
Gamma Factor

AbstractA non-local theory is used to study the effects of the corrugation parameter ε of a plasma-filled slow wave structure, the cyclotron frequency of a pumped magnetic field Ω and the relativistic gamma factor γ0 on the instability growth Γ of a free electron laser in the presence of an external finite axial magnetic field. The dispersion relation is derived and the growth rate is formulated in the Raman regime. The growth rate is approximately proportional to ε. There is a considerable decrease in the instability growth when the cyclotron frequency is close to ω0. The growth rate approximately scales inversely as the 19/2 power of the relativistic gamma factor.

scholarly journals Pulse shapes for absolute and convective free-electron-laser instabilities

1988 ◽  
Vol 40 (1) ◽  
pp. 1-37 ◽  
Author(s):  
John A. Davies ◽  
Ronald C. Davidson ◽  
George L. Johnston
Keyword(s):  
Free Electron ◽  
High Frequency ◽  
Free Electron Laser ◽  
Relativistic Electron Beam ◽  
Practical Interest ◽  
Delta Function ◽  
Momentum Spread ◽  
Field Pulse ◽  
Pinch Point ◽  
Frequency Radiation

This paper contains an analysis of pulse shapes produced by a delta-function disturbance of the equilibrium state of a relativistic electron beam propagating through a constant-amplitude, helical magnetic wiggler field. Pulse shapes are determined by using the relativistic pinch-point techniques developed by Bers, Ram and Francis. Two pulses are produced corresponding to a convective upshifted pulse (representing the production of the high-frequency radiation desired in a free electron laser) and a downshifted pulse. The downshifted instability may be convective or absolute, depending upon the beam density and momentum spread. Parameter regimes in which the downshifted instability is convective are investigated. It is found that momentum spreads sufficiently large to suppress the absolute instability reduce the growth rate of the upshifted pulse to negligible values. Pulse shapes computed by using the Raman and Compton approximations are compared with exact pulse shapes. It is found that the Raman approximation should be applied to the downshifted regime for most systems of practical interest.

Numerical investigations on the effects of geometrical parameters on free electron laser instability

2008 ◽  
Vol 74 (6) ◽  
pp. 741-747
Author(s):  
B. S. SHARMA ◽  
N. K. JAIMAN
Keyword(s):  
Growth Rate ◽  
Electron Beam ◽  
Free Electron ◽  
Free Electron Laser ◽  
Instability Growth Rate ◽  
Magnetized Plasma ◽  
Geometrical Parameters ◽  
Uniform Density ◽  
Backward Wave Oscillator ◽  
Instability Growth

AbstractIn this paper we numerically investigate the effects of various geometrical parameters of a backward wave oscillator (BWO), filled with a magnetized plasma of uniform density and driven by a mild relativistic solid electron beam, on the instability growth rate (Γ) of a free electron laser (FEL). The FEL instability is numerically calculated and the result is compared with the instability growth rate of an annular electron beam for the same set of parameters. The instability growth for a solid electron beam scales inversely to the seventh power of relativistic gamma factor γ0 and directly proportional to the corrugation amplitude.

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