Resonant power absorption in helicon plasma sources

Abstract

Helicon discharges produce plasmas with a density gradient across the confining magnetic field. Such plasmas can create a radial potential well for nonaxisymmetric whistlers, allowing radially localized helicon ͑RLH͒ waves. This work presents new evidence that RLH waves play a significant role in helicon plasma sources. An experimentally measured plasma density profile in an argon helicon discharge is used to calculate the rf field structure. The calculations are performed using a two-dimensional field solver under the assumption that the density profile is axisymmetric. It is found that RLH waves with an azimuthal wave number m = 1 form a standing wave structure in the axial direction and that the frequency of the RLH eigenmode is close to the driving frequency of the rf antenna. The calculated resonant power absorption, associated with the RLH eigenmode, accounts for most of the rf power deposited into the plasma in the experiment.

Measurements and modeling of radio frequency field structures in a helicon plasma

“…The maximum value of the damping rate calculated in Ref. 9 was consistent with the experimentally measured rate. 8 Nonetheless, the conclusion of Refs.…”

“…The goal of Ref. 9 was to investigate this hypothesis by simulating, for the experimental plasma density profile, the rf field structure excited by the antenna. The simulation showed that the antenna indeed excited an RLH wave that formed a standing wave in the axial direction.…”

“…As a result, the frequency of this wave is consistent with the discharge operational frequency. 7 There have been two recent experimental works 8,9 aimed at determining whether the waves excited by the helicon antenna are RLH waves and at understanding the role of RLH waves in the global power balance. Both experiments were performed on the same device.…”

Mode conversion of nonaxisymmetric modes in strongly nonuniform helicon-sustained plasma

“…Furthermore, the dispersion relations ͑16͒ and ͑18͒ reveal different scalings with the axial wavenumber k z , that is, respectively, linear and quadratic scalings. The quadratic dependence of the dispersion relation ͑18͒ on the parallel wavenumber k z was observed in experiment 11 and recently also confirmed by numerical calculations 12 for the condition in which the relation ͑17͒ is fulfilled. The dependence on the radial density profile can also be deduced from computations for m = + 1 helicon mode propagation in a nonuniform plasma cylinder.…”

Heat flux estimation of a plasma rocket helicon source by solution of the inverse heat conduction problem

“…Boswell and Chen [2,3] have written a review of helicon research. Helicon devices use an RF power source and antenna operating between the electron and ion cyclotron frequencies to excite electromagnetic waves which damp in the region of maximum density gradient [4,5]. The layout of this first section is shown in Fig.…”