Directional power absorption in helicon plasma sources excited by a half-helix antenna

Abstract

This paper deals with the investigation of the power absorption in helicon plasma excited through a half-helix antenna driven at 13.56 MHz. The simulations were carried out by means of a code, HELIC. They were carried out by taking into account different inhomogeneous radial density profiles and for a wide range of plasma densities, from 10 cm 11 3 to 10 cm. 13 3-The magnetic field was 200, 400, 600 and 1000 G. A three-parameter function was used for generating various density profiles with different volume gradients, edge gradients and density widths. The density profile had a large effect on the efficient Trivelpiece-Gould (TG) and helicon mode excitation and antenna coupling to the plasma. The fraction of power deposition via the TG mode was extremely dependent on the plasma density near the plasma boundary. Interestingly, the obtained efficient parallel helicon wavelength was close to the anticipated value for Gaussian radial density profile. Power deposition was considerably asymmetric when the n B 0 ratio was more than a specific value for a determined density width. The longitudinal power absorption was symmetric at approximately n 10 cm , 0 11 3 = irrespective of the magnetic field supposed. The asymmetry became more pronounced when the plasma density was 10 cm. 12 3-The ratio of density width to the magnetic field was an important parameter in the power coupling. At high magnetic fields, the maximum of the power absorption was reached at higher plasma density widths. There was at least one combination of the plasma density, magnetic field and density width for which the RF power deposition at both side of the tube reached its maximum value.

Axial profiles of argon helicon plasma by optical emission spectroscope and Langmuir probe

“…There are two helical waves in the helicon discharge, Hand TG-waves. In helical plasma, the electron density was considered to be proportional to the magnetic at a given wave number [27,32,33]. However, this is not true in some cases.…”

“…There are two kinds of helical waves in the W-mode. One is the Trivelpiece-Gould wave (or TG-wave), which is a surface mode conversion and mainly concentrated in the boundary of plasma [25][26][27]. The other is the helicon wave (or H-wave), which is mainly concentrated in the center of the discharge tube and away from the plasma boundary, generally shown as 'big blue' [28][29][30][31].…”

Wave field structure and power coupling features of blue-core helicon plasma driven by various antenna geometries and frequencies

“…The radial profiles of plasma density are fitted from experimental data, except when the external magnetic field of 0.04 T, which refers to the configuration in previous study. [27] Regarding Eq. ( 7), the constructed plasma density parameters for HELIC are listed in Table 1.…”

Influence of magnetic field on power deposition in high magnetic field helicon experiment

“…[5] Since Aigrain [6] first proposed the concept of the H wave and Boswell [7] first realized the discharge of HWP, Chen, [8] Blackwell, [9] Shamrai, [10] and others had been dedicated to studying the power deposition mechanism of HWP. Although the current hypothesis of the Trivelpiece-Gould wave (TG wave) energy deposition mechanism has gradually become the mainstream consensus, [11,12] the research on the influence of magnetic field on the power deposition needs further discussion. In this regard, this article has launched a study on the effect of magnetic field on the power deposition based on HMHX.…”