Contamination and surface effects on the impedance and plasma emission of a high voltage beam diode
- Univ. of Michigan, Ann Arbor, MI (United States). Nuclear Engineering and Radiation Sciences
- Sandia National Labs., Albuquerque, NM (United States)
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 {tau}{sub e-beam} = 0.4 to 1.0 {micro}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. Microscopic and macroscopic E-fields on the cathode are also being varied to characterize the scaling of plasma emission and current for contaminants versus the bulk material of the cathode. Pre-shot analysis using a residual gas analyzer (RGA) exhibits up to 80% water and 3% hydrogen. Post-shot RGA analysis can yield 50% water and 32% hydrogen, indicating that surface H{sub 2}O is the source of the hydrogen.
- Research Organization:
- Sandia National Laboratories (SNL), Albuquerque, NM, and Livermore, CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 346871
- Report Number(s):
- CONF-980601-; TRN: 99:006135
- Resource Relation:
- Conference: 25. international conference on plasma science, Raleigh, NC (United States), 1-4 Jun 1998; Other Information: PBD: 1998; Related Information: Is Part Of IEEE conference record -- Abstracts. 1998 IEEE international conference on plasma science; PB: 343 p.
- Country of Publication:
- United States
- Language:
- English
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