Modeling of profile effects for inductive helicon plasma sources

Abstract

Abstract-A computer code for modeling existing and new helicon sources for materials processing has been developed. The Nagoya type-111, helical, and Stix coil antennas have been modeled to study and examine plasma density and temperature profile effects on power absorption of a small fraction ( n f e / n e N 5%) of fast electrons (T,+,* N 40 eV) which provide ionization of the neutral gas in the experiment, and bulk (T,,1,, N 3 eV) electron distributions in an argon gas. The "ANTENA" computer code, originally written by B. McVey to study ion cyclotron waves, was modified and used to study and model helicon sources. A collisional model that includes radial density and temperature profiles was added to the code to study the effect of collisions on the heating mechanisms. The competing effects of collisional and Landau damping heating mechanisms have been investigated in detail, and results indicate that collisions play an important role in the plasma absorption profile at high densities (ne 2 1013 emp3).The radio frequency wave absorption profiles are sensitive to the plasma density and temperature profiles. The partial-turn helix antenna, that solely excites the m = +1 azimuthal mode, is found to be more efficient in coupling the power to an assumed plasma profile than the Nagoya type-111. The Stix coil is also found to be promising due to its on-axis peaking of the wave heating fields.

Generalized theory of helicon waves. II. Excitation and absorption

“…In Sec. IV, we give numerical results illustrating the difference between our result and that obtained by using, for the example the approach used in the ANTENA code 6,7 . We also explore the moderate magnetic field in detail.…”

“…If the plasma is divided into constant-density shells, the terms proportional to u(r) become delta-functions at the interfaces, representing charges and currents accumulating there from charged-particle motions along the magnetic field. The resulting jumps in boundary values are neglected in codes such as the ANTENA code 6,7 . These effects can be evaluated simply by comparing the solution of Eq.…”

“…Many previous authors treated antenna coupling without considering the TG waves 2,4 , thereby missing their critical contributions. Other authors approximated the density variation with a series of constant-density shells 6,7 . In doing this, they used the exact constant-density solution in each shell and required that the fields be continuous at the interfaces, thus neglecting the charges and currents there.…”

Wave propagation and absorption simulations for helicon sources

“…Cho and Kwak 12 have investigated power absorption profiles using numerical integration methods for radially nonuniform helicon plasmas with finite axial lengths. Mouzouris and Scharer 13 developed the ANTENA2 simulation code, an improved version of the original ANTENA code 14 and suitable for describing helicon sources, to examine onedimensional radial density and temperature profile effects on power absorption that include both collisional and collisionless damping mechanisms. In this work we extend previous studies by simultaneously including the effects of the axial, as well as radial, variation of the plasma density observed in experiments and an iterative solution incorporating Landau damping to the wave propagation and power absorption calculation, taking into account the full antenna spectra.…”

“…Several one-dimensional models that assume radially nonuniform plasma density and temperature profiles and axially uniform applied magnetic field and plasma density, have been presented in the literature. [9][10][11][12][13] Fischer et al 9 examined helicon wave coupling and power absorption in a finite plasma column, assuming an axially uniform plasma and applied magnetic field. Their model includes temperature effects in the plasma dielectric tensor, which are necessary to model Landau damping.…”