Helicon antenna radiation patterns in a high-density hydrogen linear plasma device

Caneses, J. F.; Blackwell, B. D.; Piotrowicz, Pawel

doi:10.1063/1.5000848

Cited by 31 publications

(41 citation statements)

References 31 publications

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“…Interestingly, quasi-periodic structures are formed axially on both sides of the boundary layer, and the periodic length inside is close to twice that outside. This structure looks similar to the beat pattern of helicon radiation observed earlier [23,34], and is consistent with the whistler bouncing at sharp plasma edge [35,36]. Moreover, the wave energy distribution becomes off-axis when it expands from the source region to the diffusion region.…”

Section: Wave Propagationsupporting

confidence: 87%

Wave propagation and power deposition in blue-core helicon plasma

Chang¹,

Caneses²,

Thakur³

et al. 2022

Preprint

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The wave propagation and power deposition in blue-core helicon plasma are computed referring to recent experiments. It is found that the radial profile of wave electric field peaks off-axis during the blue-core formation, and the location of this peak is very close to that of particle transport barrier observed in experiment; the radial profile of wave magnetic field shows multiple radial modes inside the bluecore column, which is consistent with the experimental observation of coherent high m modes through Bessel function. The axial profiles of wave field indicate that, once the blue-core mode has been achieved, waves can only propagate inside the formed column with distinct phase compared to that outside. The wave energy distribution shows a clear and sharp boundary at the edge of blue-core column, besides which periodic structures are observed and the axial periodicity inside is nearly twice that outside. The dispersion relation inside the blue-core column exhibits multiple modes, a feature of resonant cavity that selects different modes during frequency variation, while the dispersion relation outside gives constant wave number with changed frequency. The power deposition appears to be off-axis in the radial direction and periodic in the axial direction, and mostly inside the blue-core column. Analyses based on steplike function theory and introduced blue-core constant provide consistent results. The equivalence of blue-core column to optical fiber for electromagnetic communication is also explored and inspires a novel application of helicon plasma, which may be one of the most interesting findings of present work.

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Section: Wave Propagationsupporting

confidence: 87%

Wave propagation and power deposition in blue-core helicon plasma

Chang¹,

Caneses²,

Thakur³

et al. 2022

Preprint

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“…Several authors were able to explain the damping of the fast-wave in high density light-ion plasmas with a calculated collisional damping given by electron neutral and Coulomb collisions. 5,27,29 However, the authors admit that since diagnostic access limits accessing the region directly under the helicon antenna, measurements of the gradients of electron density and temperature in this region are absent. This leaves the possibility of electron temperature increasing to values where collisional damping is no longer an effective damping mechanism of the fast-wave.…”

Section: Discussionmentioning

confidence: 99%

Direct measurement of the transition from edge to core power coupling in a light-ion helicon source

et al. 2018

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We present time-resolved measurements of an edge-to-core power transition in a light-ion (deuterium) helicon discharge in the form of infra-red camera imaging of a thin stainless steel target plate on the Proto-Material Exposure eXperiment device. The time-resolved images measure the twodimensional distribution of power deposition in the helicon discharge. The discharge displays a mode transition characterized by a significant increase in the on-axis electron density and core power coupling, suppression of edge power coupling, and the formation of a fast-wave radial eigenmode. Although the self-consistent mechanism that drives this transition is not yet understood, the edge-to-core power transition displays characteristics that are consistent with the discharge entering a slow-wave anti-resonant regime. RF magnetic field measurements made across the plasma column, together with the power deposition results, provide direct evidence to support the suppression of the slow-wave in favor of core plasma production by the fast-wave in a light-ion helicon source.

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“…The cold plasma dispersion relation can be written for the perpendicular wavenumber as a function of the parallel wavenumber, electron density, magnetic field strength, and the driving frequency [32]. The expected parallel wavenumber propagating in the plasma can be estimated by the vacuum spectrum of the antenna [34] which is shown in figure 4. The driving frequency, electron density, and magnetic field strength are all inputs into the electromagnetic simulation.…”

Section: Dispersion Analysismentioning

confidence: 99%

Helicon normal modes in Proto-MPEX

Piotrowicz

Caneses

Green

et al. 2018

Plasma Sources Sci. Technol.

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The Proto-MPEX helicon source has been operating in a high electron density 'helicon-mode'. Establishing plasma densities and magnetic field strengths under the antenna that allow for the formation of normal modes of the fast-wave are believed to be responsible for the 'heliconmode'. A 2D finite-element full-wave model of the helicon antenna on Proto-MPEX is used to identify the fast-wave normal modes responsible for the steady-state electron density profile produced by the source. We also show through the simulation that in the regions of operation in which core power deposition is maximum the slow-wave does not deposit significant power besides directly under the antenna. In the case of a simulation where a normal mode is not excited significant edge power is deposited in the mirror region.

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Helicon antenna radiation patterns in a high-density hydrogen linear plasma device

Cited by 31 publications

References 31 publications

Wave propagation and power deposition in blue-core helicon plasma

Wave propagation and power deposition in blue-core helicon plasma

Direct measurement of the transition from edge to core power coupling in a light-ion helicon source

Helicon normal modes in Proto-MPEX

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