Observations of neutral depletion and plasma acceleration in a flowing high-power argon helicon plasma

Authors

C. Mark Denning
Matt Wiebold, College of Saint Benedict/Saint John's UniversityFollow
John E. Scharer

Document Type

Article

Publication Date

7-2008

Disciplines

Physics | Plasma and Beam Physics

Abstract

Neutral depletion effects are observed in a steady-state flowing argon helicon plasma with a magnetic nozzle for high rf input powers (up to 3 kW). Noninvasive diagnostics including 105 GHz microwave interferometry and optical spectroscopy with collisional-radiative modeling are used to measure the electron density (n_e), electron temperature (T_e), and neutral density (n_n). A region of weak neutral depletion is observed upstream of the antenna where increasing rf power leads to increased electron density (up to n_e = 1.6×10¹³ cm^-3) while T_e remains essentially constant and low (1.7–2.0 eV). The downstream region exhibits profound neutral depletion (maximum 92% line-averaged ionization), where T_e rises linearly with increasing rf power (up to 4.9 eV) and n_e remains constrained (below 6.5×10¹² cm^-3). Flux considerations indicate accelerated plasma flow (Mach 0.24) through the antenna region due to an axial pressure gradient with reduced collisional drag from neutral depletion.

Comments

© 2008 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.

The following article appeared in Physics of Plasmas 15(7): 072115 and may be found at (http://dx.doi.org/10.1063/1.2950301).

Recommended Citation

Denning CM, Wiebold M, Scharer JE. 2008. Observations of neutral depletion and plasma acceleration in a flowing high-power argon helicon plasma. Physics of Plasmas 15(7): 072115.