It is straightforward to create fully ionized plasmas with modest rf power in a helicon. It is difficult, however, to create plasmas with density , 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.
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December 2013
Research Article|
December 19 2013
Neutral depletion and the helicon density limit
R. M. Magee;
R. M. Magee
a)
West Virginia University
, Morgantown, West Virginia 26506, USA
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M. E. Galante;
M. E. Galante
West Virginia University
, Morgantown, West Virginia 26506, USA
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J. Carr, Jr.;
J. Carr, Jr.
West Virginia University
, Morgantown, West Virginia 26506, USA
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G. Lusk;
G. Lusk
West Virginia University
, Morgantown, West Virginia 26506, USA
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D. W. McCarren;
D. W. McCarren
West Virginia University
, Morgantown, West Virginia 26506, USA
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E. E. Scime
E. E. Scime
West Virginia University
, Morgantown, West Virginia 26506, USA
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a)
Electronic mail: rmagee@trialphaenergy.com
Phys. Plasmas 20, 123511 (2013)
Article history
Received:
May 31 2013
Accepted:
December 02 2013
Citation
R. M. Magee, M. E. Galante, J. Carr, G. Lusk, D. W. McCarren, E. E. Scime; Neutral depletion and the helicon density limit. Phys. Plasmas 1 December 2013; 20 (12): 123511. https://doi.org/10.1063/1.4849376
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