Wave propagation and absorption simulations for helicon sources

Abstract

A two-dimensional ͑2-D͒, finite-difference computer code is developed to examine helicon antenna coupling, wave propagation, collisionless Landau, and collisional heating mechanisms. The code calculates the electromagnetic wave fields and power absorption in an inhomogeneous, cold, collisional plasma. The current distribution of the launching antenna, which provides the full antenna spectra, is included in the model. An iterative solution that incorporates warm plasma thermal effects has been added to the code to examine the contribution of collisionless ͑Landau͒ wave absorption by electrons. Detailed studies of the wave fields and electron heating profiles at low magnetic fields (B 0 Ͻ100 G), where both Trivelpiece-Gould ͑TG͒ and helicon ͑H͒ modes are present, are discussed. The effects of the applied uniform magnetic field (B 0 ϭ10-1000 G), 2-D (r,z) density profiles (n e0 ϭ10 11 -10 13 cm Ϫ3 ), neutral gas pressures of 1-10 mTorr and the antenna spectrum on collisional and collisionless wave field solutions and power absorption are investigated. Cases in which the primarily electrostatic ͑TG͒ surface wave dominates the heating and the power is absorbed near the edge region and cases in which the propagating helicon wave transports and deposits its energy in the core plasma region are examined.

Is the bulk mode conversion important in high density helicon plasma?

“…The surface power absorption by the TG wave excited by the surface mode conversion has been studied intensively. [11][12][13][14] Comparisons of numerical models including finite electron mass effect (i.e., TG wave) with experimental data show good agreement with experiments. [15][16][17] The major contribution of the TG wave for the surface power deposition is widely accepted.…”

Helicon experiments and simulations in nonuniform magnetic field configurations

“…We have developed MAXEB, 18,19 a new 2-D (r,z) cylindrical plasma wave code, which can treat both axial and radial variations in the plasma density and magnetic field. The code calculates the three-dimensional ͑3-D͒ electromagnetic wave fields and collisionless Landau as well as collisional linearized power absorption in an inhomogeneous, warm plasma.…”

“…We have carried out experiments and measurements on the effects of nonuniform magnetic fields on the source operation including axial and radial density profiles, the position and role of the electron cyclotron resonance (ϭ ce ), the gradient in the magnetic field, the antenna input impedance, the wave magnetic field variation and wave number spectrum, and the transverse and longitudinal electron temperatures. In addition to this, we have utilized a new two-dimensional ͑2-D͒ (r,z) finitedifference, full-wave, helicon simulation code we developed, MAXEB,18,19 to compare with the experimental results. This research has been carried out to explore the physics involved and enhanced ionization efficiency occurring in nonuniform magnetic fields for efficient plasma production.…”

Wave mode conversion and mode transition in very high radio frequency helicon plasma

“…[1][2][3][4] Many previous results asserted that the power absorption in the helicon plasma is due to the Trivelpiece-Gould mode ͑TG mode͒. [5][6][7][8] Although many researchers have been trying to explain the mechanisms of efficient power absorption, it has not been clearly examined yet due to difficulties in its detection. 5,9 As the TG mode tends to be localized in a thin surface layer, the direct measurement is too difficult.…”