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Title: Neutral depletion and the helicon density limit

It is straightforward to create fully ionized plasmas with modest rf power in a helicon. It is difficult, however, to create plasmas with density >10{sup 20} m{sup −3}, because neutral depletion leads to a lack of fuel. In order to address this density limit, we present fast (1 MHz), time-resolved measurements of the neutral density at and downstream from the rf antenna in krypton helicon plasmas. At the start of the discharge, the neutral density underneath the antenna is reduced to 1% of its initial value in 15 μs. The ionization rate inferred from these data implies that the electron temperature near the antenna is much higher than the electron temperature measured downstream. Neutral density measurements made downstream from the antenna show much slower depletion, requiring 14 ms to decrease by a factor of 1/e. Furthermore, the downstream depletion appears to be due to neutral pumping rather than ionization.
Authors:
; ; ; ; ;  [1]
  1. West Virginia University, Morgantown, West Virginia 26506 (United States)
Publication Date:
OSTI Identifier:
22218388
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 20; Journal Issue: 12; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ANTENNAS; ELECTRON TEMPERATURE; HIGH-FREQUENCY DISCHARGES; ION TEMPERATURE; IONIZATION; KRYPTON; MHZ RANGE; PLASMA; PLASMA DENSITY; PLASMA DIAGNOSTICS; PLASMA PRODUCTION; TIME RESOLUTION