Optical spectroscopy of plasma in high power microwave pulse shortening experiments driven by a μs e-beam

Author

Gilgenbach, Ronald M. ; Hochman, Jonathan M. ; Jaynes, Reginald L. ; Cohen, William E. ; Rintamaki, Joshua I. ; Peters, Chris W. ; Vollers, Doyle E. ; Lau, Y.Y. ; Spencer, Thomas A.

Author_Institution

Intense Energy Beam Interaction Lab., Michigan Univ., Ann Arbor, MI, USA

Volume

26

Issue

3

fYear

1998

fDate

6/1/1998 12:00:00 AM

Firstpage

282

Lastpage

289

Abstract

Microwave pulse shortening experiments have been performed on a rectangular-cross-section (RCS) gyrotron driven by the Michigan Electron Long Beam Accelerator (MELBA) at parameters V=-800 kV, I_tube=0.3 kA and pulselengths of 0.5-1 μs. Pulse shortening typically limits the highest (10 MW level) microwave power pulselength to 100-200 ns. Potential explanations of pulse shortening are being investigated, particularly plasma production inside the cavity and at the e-beam-collector. We report the first optical spectroscopy diagnostic measurements inside an operating gyrotron as a means of exploring plasma effects on pulse shortening. Plasma hydrogen H-α line radiation has been characterized in both time-integrated and temporally-resolved measurements and correlated with microwave power/cutoff. Hydrogen is believed to originate from water absorbed on internal tube surfaces in the gyrotron

Keywords

electron beams; gyrotrons; microwave generation; microwave tubes; plasma devices; plasma diagnostics; plasma production; -800 kV; 0.3 kA; 0.5 to 1 mus; 10 MW; 100 to 200 ns; H-α line radiation; Michigan electron long beam accelerator; electron beam-collector; gyrotron; high power microwave pulse shortening experiments; internal tube surfaces; microwave cutoff; microwave power; microwave power pulselength; microwave pulse shortening; operating gyrotron; optical spectroscopy; optical spectroscopy diagnostic measurements; plasma effects; plasma production; pulse shortening; pulselengths; rectangular-cross-section gyrotron; temporally-resolved measurements; time-integrated measurements; water; Electron beams; Electron optics; Gyrotrons; Hydrogen; Optical pulses; Plasma accelerators; Plasma diagnostics; Plasma measurements; Pulse measurements; Spectroscopy;

fLanguage

English

Journal_Title

Plasma Science, IEEE Transactions on

Publisher

ieee

ISSN

0093-3813

Type

jour

DOI

10.1109/27.700755

Filename

700755