Self-field effects on instability of wave modes in a free-electron laser with background plasma

Abstract

A dispersion relation for the plasma loaded free-electron laser (FEL), with a helical wiggler and an axial magnetic field is derived. The cold fluid formulation is used with self-fields of the electron beam taken into account. By solving the dispersion relation numerically the influence of self-fields on the FEL resonance and the two-stream instability is investigated. It was found that although self-fields have strong effect on the FEL resonance, their effects on the two-stream instability is much weaker.

Comparative study of Gaussian- and uniform-profile models of the equilibrium electron beam in a free-electron laser

“…approximately regarded as a dc current flowing parallel to the longitudinal direction [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Based on Gauss's law and Ampere's law, the corresponding self-fields generated by the equilibrium electron beam can be deduced as…”

“…In the published literature, however, the situation on the equilibrium electron motion is to the contrary: the Gaussianprofile density model was seldom employed in numerical simulations [8][9][10][11][12]. Although an analytical expression of the Gaussian-profile density of equilibrium electrons was derived by Davidson and Uhm as early as the 1980s [13], it was not convenient for application due to its abstract definitions, and consequently, it was hardly employed in the analytical calculation on the equilibrium electron beam; instead, a simple model, the uniform-profile density, was often employed [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28].…”

Dispersion relation and growth rate of a relativistic electron beam propagating through a Langmuir wave wiggler

“…Shi et al (2003) investigated a cylindrical waveguide with a cold plasma-loaded FEL; he found that the growth rate is enhanced at low frequency, and it is decreased at high frequency. In plasma loaded FELs (Tripathi and Liu 1990;Qian et al 1994;Tsui and Serbeto 1998;Wen-Bing and Ya-Shen 1988;Petrillo and Maroli 2000;Yang et al 2002;Shi et al 2003;Wang et al 2003;Liu et al 2004;Babaei and Maraghechi 2008), plasma can increase the spacecharge limiting current that can be propagated in a drift tube, and therefore allows the operation of microwave devices at currents significantly higher than the vacuum space-charge limit (Matsko and Rostovtsev 1998;Mehdian et al 2008;Ghazavi et al 2010). Besides, it can significantly slow-down the radiation mode thereby relaxing the beam energy requirement considerably.…”

Wave mode instabilities in a two-stream free-electron laser with a background plasma

“…The instability is enhanced when the space-charge of the beam electrons is coupled to that of the background plasma. Several studies have been reported about plasma-loaded FELs [10][11][12][13][14][15][16][17][18][19][20][21]. Enhancement of the efficiency of the plasma loaded FEL is shown by Wen-Bing and Ya-Shen [10] when the plasma is introduced into the interaction region.…”

“…The kinetic theory of cold [19] and warm [20] electron beams in a plasma-loaded FEL has also been investigated. Self-field effects on a FEL with a background plasma were studied in [21]. In [22][23][24], the operation of a helix plasma-assisted slow-wave oscillator was studied.…”