Neutral depletion and the helicon density limit

Journal Article · Sun Dec 15 04:00:00 EST 2013 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4849376· OSTI ID:22218388

Magee, R. M.; Galante, M. E.; Carr, J. Jr.; Lusk, G.; McCarren, D. W.; Scime, E. E. ^[1]

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1. West Virginia University, Morgantown, West Virginia 26506 (United States)

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.

• OSTI ID: 22218388
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 12 Vol. 20; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

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