Plasma Resonance in a Radio-Frequency Probe

Takayama, K.; Ikegami, H.; Miyazaki, S.

doi:10.1103/physrevlett.5.238

Cited by 156 publications

(87 citation statements)

References 12 publications

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“…Particularly, sheath-plasma waves [29,30] and sheath-plasma resonances [28,31,32] were identified as early as the 1960's, and it is still an open question whether these physical phenomena yield significant effects on tokamak operations.…”

Section: Radio-frequency Sheathsmentioning

confidence: 99%

Numerical analysis of radio-frequency sheath-plasma interactions in the ion cyclotron range of frequencies

2012

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Electromagnetic plasma waves in the ion cyclotron range of frequencies (ICRF) are routinely used in magnetic fusion experiments to heat plasmas and drive currents. However, many experiments have revealed that wave energy losses in the plasma edge and at the wall are significant, and detected that the acceleration of ions into the walls due to the formation of radio-frequency (RF) sheaths is one of the root causes of this problem. Since the RF-enhanced sheaths have many undesirable effects, such as impurity production and hot spot generation, a predictive numerical tool is required to quantitatively evaluate these effects with complicated boundary shapes of tokamaks taken into account.In this thesis the numerical code that solves self-consistent RF sheath-plasma interactions in the scrape-off layer for ICRF heating is developed based on a nonlinear finite element technique and is applied to various problems in the one-dimensional (1D) and two-dimensional (2D) domains corresponding to simplified models for the poloidal plane of a tokamak. The present code solves for plasma waves based on the cold plasma model subject to the sheath boundary condition, in which the most important physics that happens in the sheath is captured without using the field quantities in the sheath.Using the developed finite element code, several new properties of the RF sheathplasma interactions are discovered. First, it is found in the 1D domain that multiple roots can be present due to the resonance of the propagating slow wave and its nonlinear interaction with the sheath. Second, sheath-plasma waves are identified in a 2D slab geometry, and it is proved in conjunction with an electrostatic 2D sheath mode analysis that the sheath-plasma wave only appears in the vicinity of the sheath surface if the plasma density is greater than the lower hybrid density, and its wavelength depends on various parameters. Third, as a consequence of the selfconsistent interaction between the propagating slow wave and the sheath, it is shown that the electric field distribution pattern in the plasma smoothly varies along the magnetic field lines between the conducting-wall and quasi-insulating limits.In the numerical analysis employing the 2D domain whose scale is equivalent to the Alcator C-Mod device, it is demonstrated that the calculated sheath potential can reach the order of kV, which is sufficient to yield enhanced sputtering at the wall. In addition, it is shown that the sheath potential in the close vicinity of the antenna current strap can be insensitive to the direction of the background magnetic field in the RF sheath dominated regime. Further, it is found from a series of nonlinear calculations that the sheath potential sensitively varies depending on the plasma density and electron temperature, which is consistent with the scaling derived from the Child-Langmuir law and the definition of the RF sheath potential.Lastly, a new finite element approach, which is named the finite element wavepacket method, is developed for the purpose of so...

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Section: Radio-frequency Sheathsmentioning

confidence: 99%

Numerical analysis of radio-frequency sheath-plasma interactions in the ion cyclotron range of frequencies

2012

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“…[23][24][25] High-frequency sheath-plasma processes, which occur in the vicinity of the local plasma frequency, have been widely studied in laboratory experiments. 6,7,13 Thus, the highfrequency sheath instability has been observed at the sheathplasma antiresonance frequency, Ϸ p ͑ p is the plasma frequency͒, of a positively biased electrode; 6 the nature of the instability is connected with the finite electron transit time through the sheath. On the other hand, the sheathplasma series resonance 13 has been observed as a narrow resonant enhancement in the shot noise below the plasma frequency.…”

Section: Introductionmentioning

confidence: 97%

“…6,7,13 Thus, the highfrequency sheath instability has been observed at the sheathplasma antiresonance frequency, Ϸ p ͑ p is the plasma frequency͒, of a positively biased electrode; 6 the nature of the instability is connected with the finite electron transit time through the sheath. On the other hand, the sheathplasma series resonance 13 has been observed as a narrow resonant enhancement in the shot noise below the plasma frequency. 7 Low-frequency sheath processes have drawn considerable attention in the past decades.…”

Section: Introductionmentioning

confidence: 97%

“…[6][7][8][9][10] This deep interest to sheath processes is stimulated mainly by their great importance for every device used in fundamental and applied plasma studies, such as plasma diagnostic techniques, [11][12][13][14] plasma diodes 15 and discharges, 2,9,[16][17][18] antennas in plasmas, 6,7,13,19 current systems in space, [20][21][22][23] and satellite charging processes. [23][24][25] High-frequency sheath-plasma processes, which occur in the vicinity of the local plasma frequency, have been widely studied in laboratory experiments.…”

Section: Introductionmentioning

confidence: 99%

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Low-frequency sheath instability stimulated by an energetic ion component

et al. 2006

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“…Antenna impedance in a plasma has been an active area of research for many years, with the largest amount of work, both theoretical and experimental, conducted before 1980 [1]- [8]. Most of this research was for spacecraft and rocket mounted plasma diagnostics for electron density measurements in the ionosphere.…”

Section: Introductionmentioning

confidence: 99%

Antenna Impedance Measures in a Magnetized Plasma. Part 1. Spherical Antenna

Blackwell¹,

Walker²,

Messer³

et al. 2006

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The input impedance of a metal sphere immersed in a magnetized plasma is measured with a network analyzer at frequencies up to 1 GHz. The experiments were done in the Space Physics Simulation Chamber at the Naval Research Laboratory. The hot-filament argon plasma was varied between weakly (w ce < w pe ) and strongly (w ce > w pe ) magnetized plasma with electron densities in the range 10 7 -10 10 cm -3 . It is observed that the lower-frequency resonance of the impedance characteristic previously associated with series sheath resonance w sh in the unmagnetized plasma occurs at a hybrid sheath frequency of w r = w sh + kw ce , with k a constant 0.5 < k < 1. As seen in previous experiments, the higher frequency resonance associated with the electron plasma frequency w pe in the unmagnetized plasma is relocated to the upper hybrid frequency w uh = w pe + w ce . As with the unmagnetized plasma, the maximum power deposition occurs at the lower frequency resonance w r . i REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188 DATES COVERED (From -To) Standard Form 298 (Rev. 8-98)Prescribed by ANSI Std. Z39.18Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

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Plasma Resonance in a Radio-Frequency Probe

Cited by 156 publications

References 12 publications

Numerical analysis of radio-frequency sheath-plasma interactions in the ion cyclotron range of frequencies

Numerical analysis of radio-frequency sheath-plasma interactions in the ion cyclotron range of frequencies

Low-frequency sheath instability stimulated by an energetic ion component

Antenna Impedance Measures in a Magnetized Plasma. Part 1. Spherical Antenna

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