Collaborative Research: Understanding Ion Losses to Plasma Boundaries Sheaths and Presheaths
- Univ. of Wisconsin, Madison, WI (United States)
Sheaths are common to all bounded steady-state plasmas. This includes laboratory, industrial, fusion, and in some cases even space plasmas. They form in general to balance particle loss and maintain quasi-neutrality in plasmas. Electrons are lighter than the ions by 2000 times or more (depending on the gas), and in most plasmas ion temperatures are rarely higher than the electron temperature and generally much lower. Thus in most cases, negative potential sheaths occur to confine electrons and allow ions to be freely lost. We have investigated how a plasma locally response to a positive bias on a small electrode, and have established area criteria which plasma reacts differently to the positive bias – first a pure electron sheath, and a global non-ambipolar regime where all electrons are lost to the electrode, and a double layer structure identified as a virtual cathode forms to limiting electron loss and maintain quasi-neutrality, and finally a anode spot regime where a secondary discharge occurs in front of the electrode, turning it into the major loss area of the entire plasma. Electrode area and plasma parameters criteria for these regimes were established, and the effect of the virtual cathode on the electrode’s I-V characteristics was investigated. We have also developed a global non-ambipolar electron source to replace hollow cathodes in a number of plasma applications. This eliminates the lifetime limitation and maintenance cost of hollow cathodes as they easily wear out easily and cannot be replaced in space applications.
- Research Organization:
- Univ. of Wisconsin, Madison, WI (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Fusion Energy Sciences (FES)
- DOE Contract Number:
- FG02-97ER54437
- OSTI ID:
- 1226918
- Report Number(s):
- DOE-UW-ER54437
- Country of Publication:
- United States
- Language:
- English
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