Contaminant and surface effects on the impedance and plasma emission of a high voltage beam diode

Summary form only given. Experiments have proven that both the surface contaminants and the surface topography on the cathode of an e-beam diode influence impedance collapse and emission current. The primary surface contaminant on systems that open to air is H/sub 2/O. Time-resolved optical emission spectroscopy is being used to view contaminant and bulk cathode plasma emission versus transported axial beam current. Experiments utilize the Michigan Electron Long Beam Accelerator (MELBA) at parameters: V=-0.7 to -1.0 MV, I/sub diode/=1-10 kA, and /spl tau//sub e-beam/=0.4 to 1.0 /spl mu/s MELBA is used to study thermal and stimulated desorption of contaminants from anode surfaces due to electron deposition, and breakdown of contaminants from cathode surfaces during the high voltage pulse. Experiments are also underway to characterize effective cleaning protocols for high voltage A-K gaps. RF cleaning techniques using Ar and Ar/O/sub 2/ mixtures are being investigated.