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Title: 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 (RLH) 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.

Authors:
; ; ; ; ;  [1];  [2];  [2];  [2];  [2];  [2]
  1. Department of Aerospace Engineering and Engineering Mechanics, University of Texas, Austin, Texas 78712 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20860469
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 13; Journal Issue: 12; Other Information: DOI: 10.1063/1.2402913; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ABSORPTION; ANTENNAS; ARGON; AXIAL SYMMETRY; HIGH-FREQUENCY DISCHARGES; MAGNETIC FIELDS; PLASMA; PLASMA DENSITY; PLASMA POTENTIAL; STANDING WAVES; TRAPS; TWO-DIMENSIONAL CALCULATIONS; WHISTLERS

Citation Formats

Chen Guangye, Arefiev, Alexey V., Bengtson, Roger D., Breizman, Boris N., Lee, Charles A., Raja, Laxminarayan L., Institute for Fusion Studies, University of Texas, Austin, Texas 78712, Physics Department, University of Texas, Austin, Texas 78712, Institute for Fusion Studies, University of Texas, Austin, Texas 78712, Department of Electrical and Computer Engineering, University of Texas, Austin, Texas 78712, and Department of Aerospace Engineering and Engineering Mechanics, University of Texas, Austin, Texas 78712. Resonant power absorption in helicon plasma sources. United States: N. p., 2006. Web. doi:10.1063/1.2402913.
Chen Guangye, Arefiev, Alexey V., Bengtson, Roger D., Breizman, Boris N., Lee, Charles A., Raja, Laxminarayan L., Institute for Fusion Studies, University of Texas, Austin, Texas 78712, Physics Department, University of Texas, Austin, Texas 78712, Institute for Fusion Studies, University of Texas, Austin, Texas 78712, Department of Electrical and Computer Engineering, University of Texas, Austin, Texas 78712, & Department of Aerospace Engineering and Engineering Mechanics, University of Texas, Austin, Texas 78712. Resonant power absorption in helicon plasma sources. United States. doi:10.1063/1.2402913.
Chen Guangye, Arefiev, Alexey V., Bengtson, Roger D., Breizman, Boris N., Lee, Charles A., Raja, Laxminarayan L., Institute for Fusion Studies, University of Texas, Austin, Texas 78712, Physics Department, University of Texas, Austin, Texas 78712, Institute for Fusion Studies, University of Texas, Austin, Texas 78712, Department of Electrical and Computer Engineering, University of Texas, Austin, Texas 78712, and Department of Aerospace Engineering and Engineering Mechanics, University of Texas, Austin, Texas 78712. Fri . "Resonant power absorption in helicon plasma sources". United States. doi:10.1063/1.2402913.
@article{osti_20860469,
title = {Resonant power absorption in helicon plasma sources},
author = {Chen Guangye and Arefiev, Alexey V. and Bengtson, Roger D. and Breizman, Boris N. and Lee, Charles A. and Raja, Laxminarayan L. and Institute for Fusion Studies, University of Texas, Austin, Texas 78712 and Physics Department, University of Texas, Austin, Texas 78712 and Institute for Fusion Studies, University of Texas, Austin, Texas 78712 and Department of Electrical and Computer Engineering, University of Texas, Austin, Texas 78712 and Department of Aerospace Engineering and Engineering Mechanics, University of Texas, Austin, Texas 78712},
abstractNote = {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 (RLH) 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.},
doi = {10.1063/1.2402913},
journal = {Physics of Plasmas},
number = 12,
volume = 13,
place = {United States},
year = {Fri Dec 15 00:00:00 EST 2006},
month = {Fri Dec 15 00:00:00 EST 2006}
}
  • Analytic expressions are presented for electromagnetic waves excited by Boswell and Nagoya III type antennae [F. F. Chen, J. Vac. Sci. Technol. A {bold 10}, 1389 (1992)] in a uniform plasma column, and profiles of the wave field and power absorption are calculated. The Trivelpiece-Gould mode is found to be dominant causing the surface electron heating, while the linear dependence of the plasma density on the magnetic field is obeyed. In addition, the fast helicon wave approximation, with which the electron inertia is neglected, is examined in detail and its validity is discussed. {copyright} {ital 1996 American Institute of Physics.}
  • The simulations of the spatial distribution of rf power absorbed in a helicon ion source reveal a correlation between the depth of penetration of rf power into the plasma and the tilt angle of lines of force of the outer magnetic field. The deeper field penetration and greater power absorption were observed at large tilt angles of the field line to the plasma surface. The evaluations as to the possibility of excitation of helicon waves in compact rf ion sources were performed.
  • Time- and space-resolved magnetic (B-dot) probe measurements in combination with measurements of the plasma parameters were carried out to investigate the relationship between the formation and propagation of helicon modes and the radio frequency (rf) power deposition in the core of a helicon plasma. The Poynting flux and the absorbed power density are deduced from the measured rf magnetic field distribution in amplitude and phase. Special attention is devoted to the helicon absorption under linear and nonlinear conditions. The present investigations are attached to recent observations in which the nonlinear nature of the helicon wave absorption has been demonstrated bymore » showing that the strong absorption of helicon waves is correlated with parametric excitation of electrostatic fluctuations.« less
  • A two-dimensional (2-D), 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 (Landau) wave absorption by electrons. Detailed studies of the wave fields and electron heating profiles at low magnetic fields (B{sub 0}{lt}100thinspG), where both Trivelpiece{endash}Gouldmore » (TG) and helicon (H) modes are present, are discussed. The effects of the applied uniform magnetic field (B{sub 0}=10{endash}1000thinspG), 2-D (r,z) density profiles (n{sub e0}=10{sup 11}{endash}10{sup 13}thinspcm{sup {minus}3}), neutral gas pressures of 1{endash}10 mTorr and the antenna spectrum on collisional and collisionless wave field solutions and power absorption are investigated. Cases in which the primarily electrostatic (TG) 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. {copyright} {ital 1998 American Institute of Physics.}« less
  • A Surface Plasma Source (SPS) with plasma generation by a saddle type antenna is discussed. The following features of the helicon discharge with a saddle type antenna in magnetic field are identified: efficient plasma generation in resonant condition, low gas density, strong separation of plasma from the wall, possibility to control plasma flux distribution by magnetic field configuration. Applications of saddle type antenna in SPS for accelerators for Homeland Security and for Neutral Beam Injectors (NBI) are considered.