Symmetric and asymmetric mode interaction in high-power traveling wave amplifier

Abstract

High power microwave TWT amplifier operation has been studied for use in electron accelerators. The performance of the amplifiers has been marred, in some cases, by pulse shortening of the microwave signal, possibly due to hybrid HEM11 mode interaction with the beam. In this paper we describe experiments which investigate high power operation and the effects of HEM modes on the amplifier performance. We report the high output powers (>50 MW) with efficient (>54%) amplification of microwaves in an X-band traveling wave amplifier, and present preliminary data showing operation at a few megawatt output levels in Ka band. In some experiments peak power levels in X-band exceeding 120 MW were measured at an efficiency of 47%. The excitation of the asymmetric hybrid electro-magnetic mode was monitored carefully, but does not seem to have a critical impact on the main interaction process in spite of the fact that its dispersion curve almost overlaps that of the symmetric interacting mode. Theoretical analysis of ...