Dispersion relation and growth rate in two-stream thermal plasma-loaded free-electron laser with helical wiggler

Linear theory of the two-stream free-electron laser consisting of a relativistic electron beam transported along the axis of thermal plasma-loaded helical wiggler is proposed and investigated. the dispersion relation is derived employing linear fluid theory. the characteristics of the dispersion relation are analyzed by numerical solu- tions. the results show in that in the special values of the plasma temperature the growth rate is considerably enhanced. it is also shown that the growth rate after critical plasma density gradually decreases. moreover, in the pre- sence of the two-electron beam the growth rate of elec- trostatic mode is two times greater than that for electromagnetic mode.