An instability of a cold

relativistic beam of electrons gyrating in a combined solenoidal and longitoudinally polarized periodic wiggler magnetic field interacting with a peniotron electromagnetic field is studied. It is shown that the instability works at the hybrild frequency of ω≈ωc+kwv

and its working mechanism is based on the peniotron’ s. Therefore

this device has merits of both high frequency and efficiency. An efficiency of 36% is found in computational calculations. Furthermore

its output power is adjustable with the wiggler field.