On the mechanism of density peak at low magnetic field in argon helicon plasmas

Zhu, Wanying; Cui, Ruilin; He, Feng; Zhang, Tianliang; Ouyang, Jiting

doi:10.1063/5.0091471

Cited by 3 publications

(6 citation statements)

References 54 publications

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“…The experimental setup is shown in figure 1(a). Details of the setup were provided elsewhere [7,28,29].…”

Section: Methodsmentioning

confidence: 99%

“…Plasma density and electron temperature were diagnosed using an RF-compensated Langmuir probe (LP, ALP system, Impedans), and the wave field structure was measured using a B-dot probe [7,27].…”

Section: Methodsmentioning

confidence: 99%

“…This is the so-called 'low-field peak' (e.g. [7,40]). We will not discuss this phenomenon in the current work.…”

Section: Ne-b 0 Map At Different Rf Powersmentioning

confidence: 99%

“…In a system without a reflection endplate, the axial wavenumber k z can be determined by the power spectrum of the half-helical antenna [7,17,41]. For the component of the azimuthal number m = + 1, the axial wavenumber k z is…”

Section: Eigenvalue Of Axial Modesmentioning

confidence: 99%

“…Helicon plasma sources have attracted considerable interest due to various potential applications in material processing and electric propulsion [1][2][3][4]. Configuration of a helicon discharge setup basically consists of a cylindrical tube, an axial magnetic field (typically B 0 < 1 kG [5][6][7]) and a radio frequency (RF) antenna (single-loop, double saddle field (DSF), Nagoya type or helical [8][9][10]) powered by an RF source (typically f = ω/2π = 13.56 MHz) between ion and electron cyclotron frequencies (i.e. ω ci < ω < ω ce ).…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

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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“…The experimental setup is shown in figure 1(a). Details of the setup were provided elsewhere [7,28,29].…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…This is the so-called 'low-field peak' (e.g. [7,40]). We will not discuss this phenomenon in the current work.…”

Section: Ne-b 0 Map At Different Rf Powersmentioning

confidence: 99%

Section: Eigenvalue Of Axial Modesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The wave mode transition of argon helicon plasma

Cui,

Zhang,

et al. 2024

Plasma Sources Sci. Technol.

Self Cite

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Characteristics and mechanism of low-field peak in argon helicon plasma of single loop antenna

Xia,

Zhang,

Cui

et al. 2024

Physics of Plasmas

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Low magnetic field density peak (LFP) is a typical nonlinear phenomenon in helicon wave discharge, which is characterized by the nonlinear increase in electron density with the magnetic field in lower magnetic fields. In this paper, the characteristics and generation mechanism of LFPs of argon helicon wave plasma excited by m = 0 single-loop antenna are studied by experiment and numerical simulation. Experimental results show that plasma density shows two peaks at increasing magnetic field in the range of 0–100 G. The first peak appears around 10 G, and the second one appears between 30 and 50 G. The peak density is related to gas pressure, radio frequency power, and tube dimension. From B-dot measurement, there exists obvious helicon wave structure in plasma at field strength around the LFP, with component of standing wave. Theoretical analysis demonstrated that the first density peak occurs on the demarcation line in density-magnetic field map where the H-wave limited by radial boundary condition begins to propagate, while the second peak is due to the fact that the axial wavenumber of H-wave decreases gradually with the increased magnetic field and the heating effect by standing wave resonance coupling is weakened above a critical magnetic field, leading to a sudden decrease in plasma density. Simulation by HELIC code shows that the change of radial distribution of power deposition reflects the conversion of heating mechanism from single TG-wave mode to H-TG wave coupled mode heating in low magnetic fields. The axial wavenumber with the maximum absorbed power decreases with the increased magnetic field, corresponding to the change of wave structure.

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Effects of cavity resonance and antenna resonance on mode transitions in helicon plasma

Zhang,

Cui,

Xia

et al. 2024

Plasma Sources Sci. Technol.

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Mechanisms of cavity resonance and antenna resonance and their coupling effect on mode transition in argon helicon plasma excited by a half-helical antenna (14 cm in length) were investigated in this paper. Cavity length was changed to distinguish the effects of cavity and antenna resonances. Plasma parameters in various conditions such as input power (0-2500 W), magnetic field (0-1000 G) and cavity length (10-42 cm) were measured. Characteristics of helicon discharges and mode transitions in cases of fixed and continuously changed cavity lengths were compared. The results show that multiple axial eigenmodes (at least five in the present work) were observed in both cases. In fixed-length cavity, helicon discharge changes abruptly during mode transitions, while in changeable-length cavity, discharge features can change continuously (e.g. in large range of density from 1.7×1012 to 1.3×1013 cm-3) without mode transition. Mode transitions also occur as the cavity length increasing at fixed input power and magnetic field with periodical variations of plasma parameters. Cavity resonance plays a dominant role in formation of standing helicon wave of eigenmodes and mode transition, while antenna resonance affects significantly the transition from inductively coupled mode to helicon wave mode. Enhanced inter-coupling of cavity resonance and antenna resonance appears at specific axial wavelengths of eigenmodes. Threshold conditions for mode transitions were deduced and the overall transition path and the corresponding density were predicted quantitatively, which shows that cavity resonance determines the transition path, while antenna resonance gives the lower limit of the path. Axial wavenumber is closely related to the helicon discharge characteristics. Cavity and antenna resonances influence the helicon discharge and mode transition by determining the axial wavenumber of eigenmodes.

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On the mechanism of density peak at low magnetic field in argon helicon plasmas

Cited by 3 publications

References 54 publications

The wave mode transition of argon helicon plasma

The wave mode transition of argon helicon plasma

Characteristics and mechanism of low-field peak in argon helicon plasma of single loop antenna

Effects of cavity resonance and antenna resonance on mode transitions in helicon plasma

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