DESIGN STUDY OF A G-BAND FEL AMPLIFIER FOR APPLICATION TO CYCLOTRON RESONANT HEATING IN MAGNETIC FUSION-REACTORS

A G-band (140-150 GHz) free-electron laser is described using a coaxia l hybrid iron (CHI) wiggler. The CHI wiggler is produced by insertion into a solenoid of a central rod and an outer ring composed of alterna ting ferrite and nonferrite spacers. The position of the spacers is su ch that the ferrite (nonferrite) spacers on the central rod are opposi te the nonferrite (ferrite) spacers on the outer ring. The field is cy lindrically symmetric and exhibits minima in the center of the gap pro viding for enhanced beam focusing. We describe a tapered wiggler ampli fier for plasma heating applications. Preliminary design studies using a nonlinear simulation indicates that output powers of 3.5 MW are pos sible using a 690 kV/40 A electron beam for a total efficiency of 13%. It is important to note that no beam loss was observed even for reali stic values of beam energy spread.