Anomalous ion heating and superthermal electrons in the MST reversed-field pinch
Anomalous ion heating and superthermal electron populations have been studied in the MST reversed-field pinch. The ion heating is much stronger than that given by classical electron-ion friction, and is particularly strong during dynamo bursts. The heating displays a marked density dependence: in a 350-kA discharge with a maximum {bar n} = 0.9 {times} 10{sup 13} cm{sup {minus} 3}, T{sub i} rises sharply as {bar n} drops below 0.4 {times} 10{sub 13} cm{sup {minus}3} late in the discharge. Superthermal electrons are produced in the core, with temperatures of T{sub eh}, = 350--700 eV while the bulk core temperature is T{sub e}o = 130--230 eV. The fraction of superthermal electrons decreases with increasing density, from 40% at {bar n} = 0.5 {times} 10{sup 13} cm{sup {minus}3} to 8% at {bar n} = 1.9 {times} 10{sup 13} cm{sup {minus}3} at I = 350 kA. However, data with similar plasma parameters but higher oxygen impurity content had a lower T{sub eh} and higher hot fraction. The edge superthermal electron distribution is well fit by a drifted bi-Maxwellian distribution with T{sub {parallel}} {approximately} T{sub e0} and relative drift speed v{sub d}/v{sub th} = 0.4. With the assumption that the parallel heat flux measured with a pyroelectric probe is carried by superthermal electrons, the measured electron current is consistent with T{sub {perpendicular}} {approximately} T{sub ea} {approximately} T{sub e0}/3 and accounts for over half of the total edge parallel current measured with magnetic probes.
- Research Organization:
- Wisconsin Univ., Madison, WI (United States). Dept. of Physics
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG02-85ER53198
- OSTI ID:
- 10175054
- Report Number(s):
- DOE/ER/53198-203; IAEA-CN-56/C-3-2; CONF-920913-9; ON: DE92041011
- Resource Relation:
- Other Information: PBD: Sep 1992
- Country of Publication:
- United States
- Language:
- English
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