Dispersion relation and growth rate in a free-electron laser with a background plasma

2015 ◽  
Vol 81 (3) ◽  
Author(s):  
T. Mohsenpour ◽  
B. Maraghechi
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Dispersion Relation ◽  
Plasma Density ◽  
Free Electron ◽  
Free Electron Laser ◽  
Axial Magnetic Field ◽  
Background Plasma ◽  
Positive Energy ◽  
Induced Velocity

The method of perturbation has been applied to derive a general dispersion relation for a free-electron laser (FEL) with background plasma and helical wiggler in the presence of an axial magnetic field. This dispersion relation is solved numerically to find unstable interactions among all of the wave modes. Numerical calculations show that new coupling between the left wave and positive-energy space-charge of electron beam are found when wiggler induced velocity is large. This coupling does not change with increasing the plasma density. The growth rate of FEL is changed with increasing the plasma density and the normalized axial magnetic field.

Effect of axial magnetic field tapering on whistler-pumped FEL amplifier in collective Raman regime operation

2018 ◽  
Vol 7 (4) ◽  
pp. 2044
Author(s):  
Ram Gopal ◽  
Pradip Kumar Jain ◽  
Pradip Kumar Jain
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Magnetic Fields ◽  
Plasma Density ◽  
Cyclotron Frequency ◽  
Axial Magnetic Field ◽  
Electron Cyclotron ◽  
Interaction Region ◽  
Background Plasma ◽  
Transfer Energy

The dispersion relation of the FEL Amplifiers is sensitive to the linear tapered strong axial magnetic fields, electron cyclotron frequency and plasma frequency of electrons. For the synchronism of the pumped frequency, it should be closed to electron cyclotron frequency which is resonantly enhanced the wiggler wave number that produces the amplifier radiation for higher frequency from sub millimeter wave to optical ranges. The guiding of radiation signal into the waveguide and charge neutralization phenomenon, the beam density should be greater than the background plasma density with tapered strong axial magnetic field. It is quite considerable that radiation signal slowed down at much higher background plasma density comparable to the density of beams and enhanced the instability growth rate also. In Raman Regime operation, the growth rate decreases as increases with operation frequency of the amplifier, however, the growth rate is larger in this regime. It is noted that as increases with background plasma density, the beat wave frequency of the Ponderomotive waves is increases thus the mechanism of background plasma density can serve for tenability of the higher frequencies. The tapering of the strong guided magnetic field is a crucial role for enhancing the efficiency of the net transfer energy as well as reduction of interaction region along the axis. It is observed that, an efficiency of the transfer energy enhanced by while the reduction along the interaction region of about with the variation of tapering in a strong axial guided magnetic fields.  

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 Compton and Raman free electron laser stability properties for a cold electron beam propagating through a helical magnetic wiggler

1985 ◽  
Vol 33 (3) ◽  
pp. 387-423 ◽  
Author(s):  
John A. Davies ◽  
Ronald C. Davidson ◽  
George L. Johnston
Keyword(s):  
Magnetic Field ◽  
Electron Beam ◽  
Dispersion Relation ◽  
Free Electron ◽  
Free Electron Laser ◽  
Relativistic Electron Beam ◽  
Cold Electron ◽  
Wiggler Magnetic Field ◽  
Laser Stability

This paper gives an extensive characterization of the range of validity of the Compton and Raman approximations to the exact free electron laser dispersion relation for a cold, relativistic electron beam propagating through a constantamplitude helical wiggler magnetic field. The electron beam is treated as infinite in transverse extent. Specific properties of the exact and approximate dispersion relations are investigated analytically and numerically. In particular, a detailed numerical analysis is carried out to determine the range of validity of the Compton approximation.

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