H-mode phenomena during ICRF heating on JFT-2M

Matsumoto, Hiroshi; Ogawa, T.; Tamai, Hiroshi; Odajima, K.; Hasegawa, Mitsuru; Hoshino, K.; Kasai, S.; Kawakami, T.; Kawashima, H.; Matoba, T.; Matsuda, Toshiaki; Miura, Y.; Mori, Masahiro; Ogawa, Hideyuki; Ohtsuka, Hokuto; Sengoku, S.; Shoji, T.; Suzuki, Norio; Takada, Suguru; Uesugi, Yoshihiko; Yamamoto, T.; Yamauchi, Toshihiko

doi:10.1088/0029-5515/27/7/012

Cited by 30 publications

(12 citation statements)

References 6 publications

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“…The range of the plasma density at which the H-mode exists extends up to 1 x 10 14 cm" 3 and may be higher. Lower densities have been found generally for H-modes in other devices [7][8][9][10][11][12][13][14][15][16][17]. It is likely that the density scales as qB T /R, not only in the L-mode but also in the H-mode.…”

Section: Characteristics Of the Jipp T-iiu Limiter H-modementioning

confidence: 99%

“…Thus, ICRF heating is considered to be disadvantageous for obtaining the H-mode because there is strong interaction at the plasma periphery. Actually, there are very few cases where the H-mode was achieved with ICRF heating (JFT-2M [17] and ASDEX [18]; recently, the H-mode was attained also in JET with ICRF heating only).…”

Section: Introductionmentioning

confidence: 99%

“…5. Time behaviour of the loading resistances of eight antennas, (a) Loading resistances (numbers in brackets indicatethe port number of the antennas); their behaviour is similar, except for r p(17), for which the calibration may not be correct, (b) Total loading resistance and RF voltage on the antenna, showing an inverse correlation to each other. The curve for the H a signal is also shown as a reference for interpretation of the time behaviour of the other signals.…”

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confidence: 99%

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Limiter H-mode and other improved confinement regimes with ICRF and NBI heating in JIPP T-IIU

et al. 1990

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The H-mode, an improved confinement regime, was attained recently in JIPP T-IIU high power heating experiments, in a limiter configuration without any shaping of the plasma cross-section. This H-mode is unusual because it was obtained with heating in the ion cyclotron range of frequencies (ICRF). It was also attained with combined ICRF and neutral beam injection (NBI) heating. The threshold power level obtained with ICRF alone is similar to or less than that obtained in the combined heating case. The dependence of the power threshold of the H-mode on various plasma parameters has been studied. It increases with the plasma current and is insensitive to the plasma density, and there is an optimum value of the toroidal field intensity. The power deposition profile for ICRF heating has been analysed with a ray tracing code and used to explain the observed dependence on the toroidal magnetic field. The paper also discusses a class of discharges with improved confinement observed in the same series of experiments. These discharges had a power level close to the H-mode threshold power and exhibited a marked improvement of confinement. They were, however, different from H-mode discharges in the time evolution of the profiles.

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Section: Characteristics Of the Jipp T-iiu Limiter H-modementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Limiter H-mode and other improved confinement regimes with ICRF and NBI heating in JIPP T-IIU

et al. 1990

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“…8 The H mode has also been realized in limiter discharges. 3,9,10 This Letter reports the first observation of the H mode in limiter discharges with lower-hybrid current drive (LHCD). We observed sharp L-to-H and H-to-L transitions in distinction from the particle-confinement improvement during LHCD in Versator II.…”

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confidence: 99%

Observation of the limiter H mode in the JT-60 tokamak with lower-hybrid current drive

Tsuji¹,

Ushigusa²,

Ikeda³

et al. 1990

Phys. Rev. Lett.

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The H mode was achieved in limiter discharges of a tokamak with lower-hybrid current drive for the first time. Simultaneous application of rf powers at two different frequencies such as 1.74 and 2.23 GHz or 1.74 and 2.0 GHz appeared to be effective in the attainment of the H mode. The threshold lowerhybrid power was as low as the Ohmic-heating power with hydrogen plasmas. A nearly steady-state edge-localized-mode-free H mode with a duration up to 3.3 sec was established without significant impurity accumulation.PACS numbers: 52.55.Fa, 52.35.Hr, 52.55.Pi Since the discovery of a phase of improved confinement during neutral-beam-injection (NBI) heating, known as the H mode, in the poloidal divertor configuration of ASDEX, x the H mode has been obtained with several heating schemes such as ioncyclotron-resonance heating (ICRH), 2 " 4 a combination of NBI and electron-cyclotron heating (ECH), 5 ECH, 6 7 and Ohmic heating alone. 8 The H mode has also been realized in limiter discharges. 3,9,10 This Letter reports the first observation of the H mode in limiter discharges with lower-hybrid current drive (LHCD). We observed sharp L-to-H and H-to-L transitions in distinction from the particle-confinement improvement during LHCD in Versator II. 11 The threshold LH power of the //-mode transition was about 1.2 MW with hydrogen plasmas.In JT-60, the H mode was obtained in the outer or lower divertor configuration with NBI heating and combined heating with NBI and ICRH or NBI and LH. 12 The threshold heating power was about 16 MW. In contrast to the beam-heated H mode with frequent edge localized modes (ELM) in the divertor configuration, the limiter H mode with LHCD produced ELM-free H phases longer than 3 sec.Typical plasmas of the present experiments had R =3.04 m, a =0.89 m, and nearly circular cross section which contacted inner bumper-type limiters. The gap between the outermost flux surface and the outside limiters was about 5 cm. Graphite first walls were conditioned by Taylor-type discharge cleaning. The plasma was developed from hydrogen gas at B t =4.5 T, and the plasma current was 1.5 MA resulting in ^Sur~4.7. The LH power was applied from two launchers; a conventional grill of 8 (torroidal) x 4 (poloidal) and a multijunction type of 24x4 phased-array wave guides. ,3,14 The launchers were located at the outer (low field) side of the torus at an upward angle of 40° from the midplane. Most of the experiments were conducted with LH waves at two different frequencies of 1.74 and 2.23 GHz from the multijunction and conventional launchers, respectively. The phase differences between adjacent wave guides were 180° and 90°, the phasing of which provides high directivity for current drive. The peaks of the refractive index parallel to the magnetic field were about 2.1 and 1.5, respectively.Typical traces of an //-mode discharge with LHCD are shown in Fig. 1. The LH power of about 1.4 MW was launched for 3 sec. The gas feed was turned off just E11295 4 5 6 7 8 9 t (sec)FIG. 1. Time evolution of plasma stored energy eva...

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“…PACS numbers: 52.70.Nc, 52.25.Fi, 52.55.Fa Since the //-mode transition was first found in ASDEX [1,2], //-mode discharges have been obtained in almost all tokamaks regardless of the heating method and of the configuration [3][4][5][6][7][8][9][10][11][12]. The //-mode transition is now regarded as a general physics phenomenon in high-temperature toroidal plasmas.…”

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Rapid change of the neutral hydrogen energy distribution at theL/Htransition in the JFT-2M tokamak

et al. 1992

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Rapid changes of the main ion energy distribution at transitions from L to //, H to L, and during edge localized modes (ELMs) are studied with the time-of-flight neutral measurement on the JFT-2M tokamak. At the L to H transition, 200-400 /us prior to the start of the H a drop, an increase of the high-energy outflux above an energy of 200 eV is observed. An energy of more than 200 eV for hydrogen corresponds to the collisionless condition v*, < 1 just inside the separatrix. A change of the energy distribution preceding that of the H c signal is also found for ELMs.

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H-mode phenomena during ICRF heating on JFT-2M

Cited by 30 publications

References 6 publications

Limiter H-mode and other improved confinement regimes with ICRF and NBI heating in JIPP T-IIU

Limiter H-mode and other improved confinement regimes with ICRF and NBI heating in JIPP T-IIU

Observation of the limiter H mode in the JT-60 tokamak with lower-hybrid current drive

Rapid change of the neutral hydrogen energy distribution at theL/Htransition in the JFT-2M tokamak

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