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

Linear theory of the two-stream free-electronlaser consisting of a relativistic electron beam transportedalong the axis of thermal plasma-loaded helical wiggler isproposed and investigated. The dispersion relation isderived employing linear fluid theory. The characteristicsof the dispersion relation are analyzed by numerical solutions.The results show in that in the special values of theplasma temperature the growth rate is considerablyenhanced. It is also shown that the growth rate after criticalplasma density gradually decreases. Moreover, in the presenceof the two-electron beam the growth rate of electrostaticmode is two times greater than that forelectromagnetic mode.