Spontaneous L–H transitions under marginal hot cathode biasing in the Tohoku University Heliac

Kitajima, S.; Takahashi, H.; Takeda, Yutaka; Utoh, Hiroyasu; Yokoyama, M.; Inagaki, S.; Suzuki, Y.; Nishimura, K.; Shinde, J.; Ogawa, Masayuki; Iwazaki, K.; Aoyama, Hiroshi; Okamoto, Atsushi; Shinto, K.; Sasao, M.

doi:10.1088/0741-3335/48/5a/s24

Cited by 5 publications

(4 citation statements)

References 27 publications

(34 reference statements)

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“…Electrode biasing can drive E × B rotation in a small device resulting in an improved confinement mode. In Tohoku University Heliac (TU-Heliac), negative biasing experiments have been carried out to study the transition to the improved mode [3][4][5][6][7][8][9][10][11]. A hot cathode made of LaB 6 was used for electron injection into the plasma and a negative potential profile was formed.…”

Section: Introductionmentioning

confidence: 99%

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

Takeda

Kitajima

Sasao

et al. 2008

Plasma and Fusion Research

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The ohmic heated plasma in TU-Heliac was biased by a hot-cathode to drive E × B poloidal rotation. Coincident measurements of the line density and ion saturation currents revealed the existence of density collapse accompanied by fluctuation in the poloidally rotating plasma. The radial density profiles just before and after the collapse were estimated. The steep density gradient vanished with the density collapse. The power spectra of the fluctuation were calculated from the ion saturation current obtained with a high-speed triple probe. The frequency of fluctuation was compared to the E × B poloidal rotation frequency, where the fluctuation appeared with density collapse. The fluctuation frequency was 2 to 3 times the rotation frequency. This suggested that the poloidal mode number of fluctuation was m =2 or 3.

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Section: Introductionmentioning

confidence: 99%

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

Takeda

Kitajima

Sasao

et al. 2008

Plasma and Fusion Research

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“…Viewline of Hα at 2O port with the scaling law of the global energy confinement time called ISS95 scaling [15]. Electrode-biasing experiments are also tried in several helical devices TJ-II [16] and TU-Heliac [17] in order to study the causality of E r and E r to the transition and improved confinement. In the H-1 heliac, H-mode-like transition was observed in low temperature plasmas [18] and E r /E r roles were studied in detail [19].…”

Section: U-location (6u Port) O-location (5o Port) I-location (3i Por...mentioning

confidence: 99%

Toroidally non-uniform formation of the edge-transport-barrier by low-to-high confinement transition on the Compact Helical System

et al. 2008

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In the Compact Helical System, the radial structure of the edge-transport-barrier (ETB) and the characteristics of electrostatic fluctuations were measured for the first time at three toroidally separated locations (the upper side of the vertically elongated section and the outboard and inboard sides in the horizontally elongated section) by using triple Langmuir probes. Electron density (n e ) near the plasma edge increased noticeably across the low-to-high confinement (L-H) transition without a clear electron temperature rise. A rapid vertical expansion and outward shift of the formed particle ETB were observed just after the transition. Radial profiles of n e and radial electric field at the inboard of the torus evolved to a peculiar shape across the transition, suggesting the presence of a sizable magnetic island at the rational surface of ι/2π = 1 (ι/2π: rotational transform). Turbulent particle flux derived experimentally was clearly reduced at the upper and outboard locations just after transition, but enhanced at the inboard location. Total turbulent flux passing through a whole LCFS is inferred to be reduced.

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“…In small tabletop machines it is almost impossible to excite the spontaneous H-mode. However in TU-Heliac spontaneous L-H transitions appeared with delay times under the marginal biasing condition, which was a lower condition than that required for the transition and was precisely tuned by the biasing voltage and heating power for a hot cathode [27].…”

Section: Introductionmentioning

confidence: 95%

Study of ion viscosity by spontaneous L–H transitions under marginal hot cathode biasing in the Tohoku University Heliac

Kitajima¹,

Takahashi²,

Takeda³

et al. 2008

Nucl. Fusion

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Using the spontaneous transition condition under marginal hot cathode biasing, the ion viscosity at the L–H transition was estimated in various magnetic configurations in the Tohoku University Heliac. The critical viscosity, which is the viscosity at the transition point, was experimentally estimated from the J × B driving force. The critical viscosities in different magnetic configurations were in agreement with the neoclassical predictions within a factor of 2 and were compared with the viscosities obtained in the externally forced biasing experiments. Although the transition points were spread over a wide range, poloidal Mach numbers at the transition point were concentrated near the viscosity maxima predicted by the theory.

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Spontaneous L–H transitions under marginal hot cathode biasing in the Tohoku University Heliac

Cited by 5 publications

References 27 publications

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

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

Toroidally non-uniform formation of the edge-transport-barrier by low-to-high confinement transition on the Compact Helical System

Study of ion viscosity by spontaneous L–H transitions under marginal hot cathode biasing in the Tohoku University Heliac

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