Density Collapse and Fluctuation Observed in Poloidally Rotating Plasma on TU-Heliac

Takeda, Yutaka; Kitajima, S.; Sasao, M.; Utoh, Hiroyasu; Aoyama, Hiroshi; Iwazaki, K.; Umetsu, H.; Ishii, K.; Okamoto, Atsushi; Kobuchi, T.; Inagaki, S.; Suzuki, Yasuhiro; Takahashi, H.

doi:10.1585/pfr.3.s1055

Cited by 3 publications

(4 citation statements)

References 11 publications

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“…In the biased plasma, the steep density profile around the core plasma region suddenly collapsed, accompanied with high-frequency bursting turbulent fluctuation (100 kHz < f < 500 kHz). The frequency was 2-3 times the E × B plasma rotation frequency and agreed well with the frequency obtained from the dispersion relation of flute instability [13,16], in which however the time and space structure of fluctuation level were not precisely analysed. In this paper, we report the dynamic behaviour of micro-turbulence induced by electrode biasing in TU-Heliac.…”

Section: Introductionsupporting

confidence: 82%

“…In the biased plasma, we have observed the bursting turbulent fluctuation and density collapse in the ion saturation current with Langmuir probes [13][14][15][16][17]. Figure 3 shows typical time evolutions of electrode current I E , electron density n e , electron temperature T e and ion saturation current I s at ρ = 0.2, measured with the Langmuir probe at φ = 0 • .…”

Section: Density Collapse and Bursting Fluctuation In Tu-heliacmentioning

confidence: 99%

“…Observed Lissajous diagrams of turbulence and gradients demonstrated clockwise and counterclockwise hysteresis loops [5][6][7][8][9][10][11][12]. In Tohoku University Heliac (TU-Heliac), we have carried out electrode biasing experiments and observed the density collapse and high-frequency bursting fluctuation [13][14][15][16][17]. Because of the low temperature plasma in TU-Heliac, we have the advantages of measuring high-frequency fluctuations in ion saturation currents and floating potential with high spaceand time-resolution using a Langmuir probe.…”

Section: Introductionmentioning

confidence: 99%

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Bursting high-frequency fluctuation observed in biased plasma in TU-Heliac

Koike¹,

Kitajima²,

Okamoto³

et al. 2014

Nucl. Fusion

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In the biased plasma in TU-Heliac, a steep density profile around the core plasma region suddenly collapsed, accompanied with a high-frequency bursting turbulent fluctuation (100 kHz < f < 500 kHz). Envelope analysis was applied and the moment of the bursting event occurrence was detected in the biased plasma. The profile of the density gradient and bursting fluctuation were obtained using two Langmuir probes, one as a monitor probe for the bursting fluctuation and the other as a profile scan probe with a conditional average method. The fluctuation increased and showed a peak at the low field side of the steep gradient, from which the fluctuation propagated to the inner and outer directions at a velocity of 1 km s−1. The density gradient and the fluctuation had a non-linear relation and indicated a hysteresis loop.

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Section: Introductionsupporting

confidence: 82%

Section: Density Collapse and Bursting Fluctuation In Tu-heliacmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Bursting high-frequency fluctuation observed in biased plasma in TU-Heliac

Koike¹,

Kitajima²,

Okamoto³

et al. 2014

Nucl. Fusion

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“…In TU-Heliac, we observed that density collapse accompanied high-frequency bursting fluctuations [3]. To survey the characteristics of the MHD fluctuations, we developed a magnetic probe sensitive to magnetic fluctuations and insensitive to capacitive pickup noises.…”

mentioning

confidence: 99%

Development of a High CMRR Magnetic Probe for the Biased Plasma in TU-Heliac

Koike

Kitajima

Okamoto

et al. 2014

Plasma and Fusion Research

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The plasma in Tohoku University Heliac (TU-Heliac) is biased by a hot cathode that drives the J × B poloidal rotation. In the biased plasma, a density collapse accompanied by high-frequency bursting density and potential fluctuations was observed. To eliminate the effect of potential fluctuations and to measure the magnetic fluctuation, a high common mode rejection ratio (CMRR) magnetic probe with a preamplifier at the probe head in a vacuum vessel was designed and installed. Owing to the absolute calibration, the magnetic probe has a high magnetic sensitivity of 10 4 V/T (@100 kHz), high CMRR of −75 dB (@500 kHz), and frequency bandwidth DC −1 MHz. In the biased plasma, the power spectrum of the normal mode signal was 10 4 times larger than that of the common mode signal in all frequency ranges, which indicates that the probe can successfully minimize the capacitive pickup noise relative to the actual magnetic fluctuation signal. In addition, we successfully observed the broad spectrum (100 kHz < f < 300 kHz) of the magnetic fluctuation and MHD instability in the biased plasma in TU-Heliac.

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Sudden collapse of a pressure profile generated by off-axis heating in a linear magnetized plasma

2022

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The features of an unexpected, large event that arises spontaneously during a basic heat transport experiment are presented. It consists of the sudden collapse of the radial plasma pressure profile, akin to disruption events observed in toroidal magnetic confinement devices. The experiment is performed on the Large Plasma Device at the University of California, Los Angeles (UCLA). It uses a LaB6 thermionic emitter of annular shape to induce off-axis heating of a cold, afterglow plasma, in a linear magnetic geometry. The temporal evolution consists of three regimes. During an early, quiescent period, classical heat transport along and across the magnetic field arises from Coulomb collisions. After significant pressure gradients develop, drift-Alfvén waves become unstable. Upon reaching large amplitude, they trigger avalanche events that flatten the outer part of the heated region, which, in turn, quenches the instability. Due to the sustained heating, the pressure profile rebuilds and the process repeats, leading to a relatively long, second regime that displays multiple avalanches, but suddenly, the annular pressure profile is observed to collapse. After this collapse, the system enters a third regime with large fluctuations. Before the collapse, a rapid, runaway heating environment arises whose time evolution exhibits a self-similar dependence on the applied voltage. The time evolution, morphology, and scaling of the collapse event are presented, and an examination is made of the underlying mechanisms.

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Density Collapse and Fluctuation Observed in Poloidally Rotating Plasma on TU-Heliac

Cited by 3 publications

References 11 publications

Bursting high-frequency fluctuation observed in biased plasma in TU-Heliac

Bursting high-frequency fluctuation observed in biased plasma in TU-Heliac

Development of a High CMRR Magnetic Probe for the Biased Plasma in TU-Heliac

Sudden collapse of a pressure profile generated by off-axis heating in a linear magnetized plasma

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