Spatio-temporal behavior of density jumps and the effect of neutral depletion in high-density helicon plasma

Isayama, Shogo; Shinohara, Shunjiro; Hada, Tohru; Chen, S. H.

doi:10.1063/1.5093920

Cited by 7 publications

(9 citation statements)

References 40 publications

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“…This is consistent with the experimental observation that the discharge transits from blue-colour mode to blue-core mode [9]. The decreased power for shrunk density profiles implies that certain magnitude of plasma density near edge is beneficial for power coupling, which also agrees with previous studies [40,41,42,43,44]. More interestingly, we find that the power deposition is hollow in radius for all field strengths and its peak moves closer to axis when the field strength increases.…”

Section: Power Depositionsupporting

confidence: 92%

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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: Power Depositionsupporting

confidence: 92%

“…This could be attributed to the plasma density near edge which is too low to efficiently couple the power from antenna into core. This critical role of edge density has been also claimed by other studies [40,41,42,43,44].…”

Section: Step-like Function Theorysupporting

confidence: 81%

Wave propagation and power deposition in blue-core helicon plasma

Chang¹,

Caneses²,

Thakur³

et al. 2022

Preprint

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“…It includes neutral dynamics and could certify several important temporal behaviors of power absorption, flux balance, and density jumps in high-density helicon plasma. The computed results agree well with experimental data [36,37]. Figure 5 shows the spatial profiles of electron density, electron temperature, and power absorption at three subsequent times: 12 μs, 30 μs, and 122 μs.…”

Section: Introductionsupporting

confidence: 81%

First Helicon Plasma Physics and Applications Workshop

2022

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The First Helicon Plasma Physics and Applications Workshop was held on September 23−24, 2021, through Zoom Cloud Meeting, instead of in an on-site gathering, due to the COVID-19 pandemic. It was convened by Rod Boswell (IOC) and Guangnan Luo (LOC), and organised by Lei Chang’s group. The workshop attracted 110 registrations and ∼100 online audiences from ∼30 affiliations. There were 33 presentations covering the various fundamental physics of helicon plasma and its applications to space electric propulsion, material processing, and magnetic confinement fusion. This paper highlights the presentations, discussions, and perspectives given in the workshop, serving as reference for the helicon community.

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“…Generally, a simplified dispersion relation is satisfied when weakly damping helicon (H) waves are excited and penetrate into the central region at higher magnetic fields (typically B 0 > 200 G), while the strongly damping Trivelpiece-Gould (TG) waves can be strongly absorbed near the plasma edge (∼mm) or suppressed near the surface in the antiresonance region [11][12][13][14][15][16]. However, the relation between the density and the RF power or magnetic field in experiments is divided into several stages [16][17][18][19][20][21][22][23][24][25][26][27][28][29], indicating multiple helicon modes at increasing power or magnetic fields, which was characterized by an absolute jump in plasma density, the wavelength of the helicon wave and plasma potential, etc.…”

Section: Introductionmentioning

confidence: 99%

The wave mode transition of argon helicon plasma

Cui,

Zhang,

et al. 2024

Plasma Sources Sci. Technol.

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In this paper, multiple wave modes and transitions of argon helicon plasma excited by a half right-helical in a system without any reflection endplate are investigated experimentally and theoretically at increasing radio frequency (RF) powers and external magnetic fields. Experiments show that above a critical magnetic field strength and pressure (about 250 G and 0.3 Pa in this work), two to four distinct wave coupled modes and transitions were observed at increasing RF powers and/or magnetic fields. Theoretical analysis based on dispersion relationship show that in high magnetic field helicon wave of the lowest order of axial eigenmode is always excited firstly, then the higher order axial or radial mode, hence the plasma density increases after mode jumping. There are two mechanisms responsible for the wave mode transitions in the present system, i.e., axial and radial mode transitions owning to the change of axial and radial wavenumbers from a lower eigenmode to a higher one. Higher plasma density and magnetic field are helpful for achieving more higher-order modes of helicon waves.

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Spatio-temporal behavior of density jumps and the effect of neutral depletion in high-density helicon plasma

Cited by 7 publications

References 40 publications

Wave propagation and power deposition in blue-core helicon plasma

Wave propagation and power deposition in blue-core helicon plasma

First Helicon Plasma Physics and Applications Workshop

The wave mode transition of argon helicon plasma

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