Measurement of the parallel velocity distribution function of the electron beam in a quasi-optical gyrotron by electron cyclotron emission

摘要

The parallel velocity distribution function of the weakly relativistic electron beam of a quasi-optical gyrotron (QOG) has been determined by measuring the Doppler-shifted Electron Cyclotron Emission (ECE) at an angle (theta)=15(sup o) with respect to the external magnetic DC-field. Due to the Doppler shift, the frequency of the spontaneous cyclotron emission at the fundamental ((nu)(sub 0)=100 GHz) is upshifted to 140 GHz. A broadening of the spectrum up to 10 GHz (Full Width at Half Maximum FWHM) was measured. The measured mean frequency agrees well with the theoretical predictions, but the observed line-width, and hence the parallel velocity distribution function, is 2-3 times larger than expected. Considerations on ECE-measurements of the electron beam energy spread, performed at larger angles (theta), are also discussed. (author) 12 figs., 18 refs. (Atomindex citation 27:033629)