Development of a helicon-wave excited plasma facility with high magnetic field for plasma–wall interactions studies

Zhang, Guilu; Huang, Teng; Chen, Jin; Wu, Xuemei; Zhuge, Lanjian; Ji, Hantao

doi:10.1088/2058-6272/aac014

Cited by 10 publications

(6 citation statements)

References 33 publications

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“…The plasma density and ionization rate in the blue core region are considerably higher. The phenomenon had been studied by researchers under certain conditions in many helicon plasma apparatuses [17,30,[41][42][43][44][45]. The blue core was also regarded as a new transition mode after the traditional wave mode (W mode) [37,46].…”

Section: Introductionmentioning

confidence: 99%

Effect of neutral pressure on the blue core in Ar helicon plasma under an inhomogeneous magnetic field

Wang

Liu²,

Sun³

et al. 2023

Plasma Sci. Technol.

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The effect of neutral pressure on blue core in Ar helicon plasma under inhomogeneous magnetic field was investigated in this work. The neutral pressure was set to 0.08 Pa, 0.36 Pa and 0.68 Pa. Nikon camera, intensifies charge coupled device (ICCD), optical emission spectrometer (OES), and Langmuir probe were used to diagnose the blue core in helicon plasma. Helicon plasma discharges experienced density jumps from E-, H- to W-mode before power just rose to 200 W. The plasma density increased and maintained the central peak with the increase of neutral pressure. However, the brightness of the blue core gradually decreased. It demonstrated that the relative intensity of Ar II spectral lines and the ionization ratio in the central area were reduced. Radial electron temperature profiles were flattened and became hollow as neutral pressure increased. It demonstrated that increasing the neutral pressure weakened the central heating efficiency dominated by helicon wave and strengthened the edge heating efficiency governed by the TG wave and skin effect. Therefore, the present experiment successfully reveals how the neutral pressure affects the heating mechanism of helicon plasma in inhomogeneous magnetic field.

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Section: Introductionmentioning

confidence: 99%

Effect of neutral pressure on the blue core in Ar helicon plasma under an inhomogeneous magnetic field

Wang

Liu²,

Sun³

et al. 2023

Plasma Sci. Technol.

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“…Common features have been drawn from this mode such as azimuthal instabilities driven by radial pressure gradients, and high-beta (beta is the ratio of particle pressure to magnetic field pressure) effects [16]. Previous studies mainly employed optical camera and/or spectrometer to characterise these features after the blue-core formation [10,11,[17][18][19], however, little attention was given to the transitional behaviours from non-blue-core mode to bluecore mode. Especially, to our best knowledge, there is no measurement yet about the wave field and power absorption inside and outside the blue-core plasma column, respectively.…”

Section: Introductionmentioning

confidence: 99%

Wave propagation and power deposition in blue-core helicon plasma

2022

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The wave propagation and power deposition inside and outside the blue-core helicon plasma are computed, together with their transitional behaviours prior to and after the blue-core formation. Computations refer to the experiments on the CSDX (controlled shear decorrelation experiment) (Thakur et al., Plasma Sources Science and Technology 23: 044,006, 2014 and Thakur et al., IEEE Transactions on Plasma Science 43: 2754–2759, 2015). 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 blue-core column, which is consistent with the experimental observation of coherent high m modes through Bessel function. The axial profiles of wave field indicate that the decay length shortens for increased external field strength, especially when the blue-core mode has been achieved, and this length is relatively longer inside the core than that outside. The wave energy density is overall lower in two orders after blue-core formation than that prior to, and the energy distribution shows a periodic boundary layer near the edge of blue-core column. The dispersion relation inside the blue-core column suggests the presence of two radial modes, while outside the blue-core column it shows no variation, i.e. constant wave number with changed frequency. The power deposition appears to be off-axis in the radial direction, forming a hollow profile, and when the blue-core mode has been formed it shows periodic structure in the axial direction. Analyses based on the step-like function theory and introduced blue-core constant provide consistent results and more physics understanding. These details of wave propagation and power deposition during the blue-core formation are presented for the first time, and helpful for understanding the mechanism of blue-core phenomenon. The equivalence of blue-core plasma column to optical fiber for electromagnetic communication is also explored, and preliminary calculation shows that total reflection can indeed occur if the incident angle is larger than a threshold value. This may inspire a novel application of helicon plasma, and is one of the most interesting findings of present work.

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“…The profile deviates from the Gaussian shape obviously, as is shown by the blue dashed line in figure 5. The peak density is at 𝑟 = 20 mm and in the center region, 𝑛 𝑒 is lower, indicating a hollow 𝑛 𝑒 profile, which is different from 𝑛 𝑒 profiles in most other linear plasma devices worldwide [18,19]. Surprisingly, when 𝐵 𝑧 ≥ 115 mT, 𝑛 𝑒 drops sharply.…”

Section: Experiments Resultsmentioning

confidence: 73%

“…𝐵 𝑧 scanning experiment on other helicon plasma devices also showed drop of density under strong magnetic field [19,24]. To explain the results of 𝐵 𝑧 scanning experiment, detailed experimental studies on instability and transport are planned.…”

Section: Discussionmentioning

confidence: 96%

The first plasma in a newly constructed linear device for plasma turbulence research

Yu,

Xiao,

Liu

et al. 2024

J. Inst.

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Parameters of the first plasma in a newly built middle-size multi-functional linear plasma device named LEAD (Linear Experimental Advanced Device) were presented. The LEAD device is built to serve as a multi-purpose laboratory plasma experiment platform for various topics, including plasma turbulence, plasma-material interaction, and other fundamental plasma physics. This device is also useful for testing new diagnostic systems. It will be complementary to the HL-2A/HL-3 tokamaks in Southwestern Institute of Physics. The plasma was generated by a large-area helicon plasma source with a multi-ring antenna driven by a 13.56 MHz, 5 kW radio frequency (RF) power source. Argon plasma parameters were measured by a Langmuir probe in different external parameters including RF power, axial magnetic field, and neutral pressure. The threshold power for helicon mode transition is empirically confirmed to be 180 W. Steady-state argon plasma with a density of higher than 1019 m-3 was generated when RF power reached 3 kW. Plasma parameters are crucially influenced by the axial magnetic field. With a weak magnetic field, the radial density profile is Gaussian-like. However, with a stronger magnetic field, shear and reversion of azimuthal rotation velocity reversion appear, resulting in a hollow-shaped density profile. When further increasing the magnetic field, plasma density decreases. Steady-state plasma discharges were achieved under a wide range of argon neutral pressure from 0.1 Pa to over 10 Pa. With increasing neutral pressure, plasma density increases to its maximum at 2.5 Pa and then drops, while electron temperature drops monotonically.

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Development of a helicon-wave excited plasma facility with high magnetic field for plasma–wall interactions studies

Cited by 10 publications

References 33 publications

Effect of neutral pressure on the blue core in Ar helicon plasma under an inhomogeneous magnetic field

Effect of neutral pressure on the blue core in Ar helicon plasma under an inhomogeneous magnetic field

Wave propagation and power deposition in blue-core helicon plasma

The first plasma in a newly constructed linear device for plasma turbulence research

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