Optical spectroscopy of plasma and plasma processing in high power microwave pulse shortening experiments

Summary form only given, as follows. Spectroscopic measurements have been performed to characterize the undesired plasma in a multi-megawatt coaxial gyrotron. This gyrotron is driven by the Michigan Electron Long Beam Accelerator (MELBA) at parameters: V=-800 kV, I/sub tube/=0.3 kA, and pulselengths of 0.5-1 /spl mu/s. Pulse shortening typically limits the highest (/spl sim/40 MW) microwave power pulselength to 50-100 ns. Potential explanations of pulse shortening are being investigated, particularly plasma production inside the cavity and at the e-beam collector. The source of this plasma is believed to be due to water vapor. Plasma H-/spl alpha/ line radiation has been characterized and correlated with microwave power and microwave cutoff. Experiments are underway to determine the effects of RF plasma processing of the coaxial cavity and collector. A collaborative effort is underway with the Stanford Linear Accelerator Center/U.C. Davis to study RF cavity breakdown. A SEM is being used to examine the surface effects of RF processing cavity parts.