High density hydrogen helicon plasma in a non-uniform magnetic field

Mori, Yoshitaka; Nakashima, H.; Baity, F. W.; Goulding, R. H.; Carter, Mark D.; Sparks, D. O.

doi:10.1088/0963-0252/13/3/009

Cited by 38 publications

(44 citation statements)

References 38 publications

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“…VII. Some experiments [15][16][17] indicate that a helicon discharge is fired at a minimal rf power provided that magnetic field is within some range around the value given by Eq. (24) although the range of allowed magnetic fields widens as rf power increases.…”

Section: Discussionmentioning

confidence: 99%

On the density limit in the helicon plasma sources

Kotelnikov

2014

Physics of Plasmas

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Existence of the density limit in the helicon plasma sources is critically revisited. The lowand high-frequency regimes of a helicon plasma source operation are distinguished. In the lowfrequency regime with ω < √ ωciωce the density limit is deduced from the Golant-Stix criterion of the accessibility of the lower hybrid resonance. In the high-frequency case, ω > √ ωciωce, an appropriate limit is given by the Shamrai-Taranov criterion. Both these criteria are closely related to the phenomenon of the coalescence of the helicon wave with the Trivelpiece-Gould mode. We argue that theoretical density limits are not achieved in existing devices but might be met in the future with the increase of applied rf power.

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Section: Discussionmentioning

confidence: 99%

On the density limit in the helicon plasma sources

Kotelnikov

2014

Physics of Plasmas

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“…To eliminate the reflection from axial endplates, the domain is assumed to be infinitely long, although the actual length of −0.63 ≤ z ≤ 0.63 (m) is considered, and computations are limited to the spectral range of 5 ≤ k ≤ 50 (1/m) for the conditions used. Specific parameters are listed in Table , which are typical measurements in various helicon discharge experiments . We assume that the plasma has no axial structure to focus on the effect of radial density gradient on helicon power absorption and only consider the original Spitzer collision frequency for simplicity.…”

Section: Numerical Computationmentioning

confidence: 99%

The role of second‐order radial density gradient for helicon power absorption

Wang

Chang

et al. 2019

Contributions to Plasma Physics

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To demonstrate the mysterious and still controversial mechanism of high ionization efficiency during helicon discharges, this work focuses particularly on the role of second‐order radial density gradient (SRDG) in helicon power absorption, both analytical and numerical. It was found that the positive or negative sign of SRDG and radial location of vanishing SRDG determine the radial profile of power absorption remarkably. First, by measuring SRDG at two radial locations (near plasma core and edge) where power absorption usually peaks, and varying it as a function of free parameter, we see that: (a) the power absorption from the antenna to plasma increases for positive SRDG and decreases for negative SRDG when viewed in the same x‐coordinate direction of SRDG and (b) the power absorption is maximized near the position where this local SRDG vanishes, consistent with the theory of radially localized helicon mode (B. N. Breizman and A. V. Arefiev, Phys. Rev. Lett., 84:3863, 2000). Second, by choosing the whole radial profiles of typical plasma distribution that have zero‐crossing SRDG, we find that the power absorption redistributes significantly when the location of vanishing SRDG moves radially outwards, and specifically when the radial locations of maximum power absorption and vanishing SRDG move in the same direction near the plasma core but noticeably in the opposite direction near the plasma edge. These findings are very interesting for helicon plasma applications that require certain power distribution or heat flux configuration, for example, material processing, which can be controlled by adjusting the radial profile of SRDG, especially the zero‐crossing SRDG.

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“…The cavity is metal, leading to conducting boundary conditions. Referring to most helicon discharges [17,9,18,19], we choose argon and spectral range of 5 < k < 50 m −1 , and set the background pressure and temperature to be 3 eV and 10 mTorr, respectively. Moreover, we consider four types of RF antennas: half helix, Boswell and Nagoya III to excite m = 1 mode and loop to excite m = 0 mode.…”

Section: Theoretical Model and Computational Schemementioning

confidence: 99%

Coupling of RF antennas to large volume helicon plasma

Chang

Gao

et al. 2018

AIP Advances

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Large volume helicon plasma sources are of particular interest for large scale semiconductor processing, high power plasma propulsion and recently plasmamaterial interaction under fusion conditions. This work is devoted to studying the coupling of four typical RF antennas to helicon plasma with infinite length and diameter of 0.5 m, and exploring its frequency dependence in the range of 13.56 − 70 MHz for coupling optimization. It is found that loop antenna is more efficient than half helix, Boswell and Nagoya III antennas for power absorption; radially parabolic density profile overwhelms Gaussian density profile in terms of antenna coupling for low-density plasma, but the superiority reverses for high-density plasma. Increasing the driving frequency results in power absorption more near plasma edge, but the overall power absorption increases with frequency. Perpendicular stream plots of wave magnetic field, wave electric field and perturbed current are also presented. This work can serve as an important reference for the experimental design of large volume helicon plasma source with high RF power.

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High density hydrogen helicon plasma in a non-uniform magnetic field

Cited by 38 publications

References 38 publications

On the density limit in the helicon plasma sources

On the density limit in the helicon plasma sources

The role of second‐order radial density gradient for helicon power absorption

Coupling of RF antennas to large volume helicon plasma

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