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The parallel velocity distribution function of the weakly relativistic electron beam of a quasi-optical gyrotron has been determined by measuring the Doppler-shifted Electron Cyclotron Emission (ECE) at an angle theta=15 degrees with respect to the external magnetic dc-field. Due to the Doppler shift, the frequency of the spontaneous cyclotron emission at the fundamental (v(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.

Additional information

Authors: SOUMAGNE G ET AL, Centre de Recherches en Physique des Plasmas, Association Euratom - Confédération Suisse, Ecole Polytechnique Fédérale de Lausanne (CH);HOGGE J P, Plasma Fusion Center, Massachusetts Institute of Technology, Cambridge (US)
Bibliographic Reference: Article: Physics of Plasmas, Vol. 3 (1996) No. 9, pp. 3501-3506
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