Configuration Control for the Confinement Improvement in Heliotron J

Mizuuchi, T.; Sano, F.; Nagasaki, K.; Okada, H.; Kobayashi, S.; Hanatani, K.; Torii, Y.; Ijiri, Y.; Senju, T.; Yaguchi, K.; Sakamoto, K.; Toko, Kiyoshi; Shibano, Masaya; Kondo, K.; Nakamura, Yuji; Kaneko, Masashi; Arimoto, Hajime; Motojima, G.; Fujikawa, Shigeo; Kitagawa, Hirohisa; Nakamura, Hidenori; Tsuji, Takayuki; Uno, Masatoshi; Watanabe, Shinya; Yabutani, H.; Matsuoka, Satoshi; Nosaku, M.; Watanabe, Nobuyuki; Yamamoto, Satoshi; Watanabe, K. Y.; Suzuki, Y.; Yokoyama, M.

doi:10.13182/fst06-a1256

Cited by 11 publications

(11 citation statements)

References 17 publications

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“…Figure 7 shows another example of the time traces of the same parameters shown in figure 6 but for the discharges sustained only by NBI (co-injection) in a high-bumpiness (HB) configuration with almost the same edge rotational transform [15], where the magnetic axis is inwardly shifted by about ∼0.8 cm (on average along the torus) compared with that in the standard configuration. In this discharge condition, the direction of the confinement field was reversed (B < 0).…”

Section: Methodsmentioning

confidence: 97%

Spontaneous shift of divertor plasma footprints during a discharge in a helical-axis heliotron device

et al. 2007

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A spontaneous shift of diverted plasma position during a discharge was investigated in Heliotron J. The shift of a few cm was observed for discharges with a non-inductive plasma current < 3 kA and the plasma stored energy < 3 kJ. The observed shift was related to the change in the plasma current more closely than the stored energy. The most plausible mechanism for the observed shift is the change of the edge field topology caused by the plasma current. The three-dimensional finite-β equilibrium calculations assuming profiles of plasma pressure and plasma current density indicate that the effect of the plasma current depends not only on the current flow direction but also on the current density profile. This experiment points out not only the importance of current control to fix the divertor plasma position in a low shear helical device but also the possibility of "divertor swing" for reduction of the divertor particle/heat load by controlling a small amount of plasma current within a tolerable influence on the plasma performance.

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Section: Methodsmentioning

confidence: 97%

Spontaneous shift of divertor plasma footprints during a discharge in a helical-axis heliotron device

et al. 2007

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“…The quantitative calculation and the comparison with the experimental data should be the future task. The dependence of single-particle confinement on the magnetic field configuration is in contrast to the global energy confinement experimentally observed in a high-density regime; that is, the stored energy is higher in ripple bottom heating and standard configuration heating [19]. This difference may be because the global confinement is determined by the whole magnetic field structure.…”

Section: Effect Of Magnetic Field Ripplementioning

confidence: 57%

Effect of magnetic field ripple on electron cyclotron current drive in Heliotron J

et al. 2010

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Electron cyclotron current drive (ECCD) experiments have been conducted in the helical heliotron device, Heliotron J. A wide configuration scan shows that the electron cyclotron (EC) driven current is strongly dependent on the magnetic ripple structure where the EC power is deposited. As the EC power is deposited on the deeper ripple bottom, the EC current flowing in the Fisch–Boozer direction decreases, and the reversal of directly measured EC driven current is observed. Measurement results using electron cyclotron emission and soft-x ray spectrum diagnostics imply that high-energy electrons are generated for ripple top heating while they are suppressed for ripple bottom heating, indicating that the generation and confinement of trapped electrons have an important role on ECCD. For ripple top heating, the typical ECCD efficiency is estimated as γ = n e I EC R/P EC = 0.8 × 1017 A W−1 m−2 and , where n e is in 1020 m−3, I EC in A, R in m, P EC in W and T e in keV. The normalized ECCD efficiency is found to be independent of the absorbed EC power for both ripple top and bottom heating cases.

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“…To investigate the effect of the bumpy component for the particle confinement, three configurations are selected; the bumpy ratios (B 04 /B 00 , where B 00 is the averaged magnetic field strength) are 0.01, 0.06 and 0.15 at the normalized minor radius ρ = 0.67. The other parameters such as the toroidal component, the helical component, the plasma volume and iota are kept constant [1]. This experiment has been performed in the low-density deuteron plasmas (0.4 × 10 19 m −3 ) with minority protons since the plasma should be in the low collision regime to generate fast ions.…”

Section: Dependence Of the High-energy Ion Formation And Confinement ...mentioning

confidence: 99%

“…The role of one of the Fourier components, bumpiness, is a key issue for the design principle of the magnetic field of Heliotron J, where the particle confinement is controlled by bumpiness [4]. The bumpy component of the magnetic field is controlled by changing the current ratio of the toroidal A coils to the toroidal B coils [1]. The proper bumpiness causes deeply trapped particles to be confined in the small grad-B region.…”

Section: Introductionmentioning

confidence: 99%

Dependence of the confinement of fast ions generated by ICRF heating on the field configuration in Heliotron J

Okada¹,

Torii²,

Kobayashi³

et al. 2007

Nucl. Fusion

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A formation and confinement experiment for fast ions is performed using the ion cyclotron range of frequencies (ICRF) minority heating scheme with a proton minority and a deuteron majority in Heliotron J, a low-shear helical-axis heliotron. The effect of the magnetic configuration on the fast-ion confinement is one of the most important issues in helical devices. In this paper, the effect of bumpiness, one of the Fourier components of the field strength, on the trapped fast-ion confinement is clarified by using ICRF minority heating. The role of the bumpiness is a key issue for the design principle of the magnetic field of Heliotron J, where the particle confinement is controlled by the bumpiness. Here, the bumpiness or the bumpy ripple is defined by the Fourier harmonic ratio εb ≡ B 04/B 00 in (Mizuuchi T et al 2006 Fusion Sci. Technol. 50 352), where B 04 is the bumpy component and B 00 is the averaged magnetic field strength. The proper bumpiness causes deeply trapped particles to be confined in the small grad-B region. High-energy ions are produced up to 10 keV by injecting an ICRF pulse into an electron cyclotron heating target plasma where ion temperature at the centre T i(0) = 0.2 keV, electron temperature at the centre T e(0) = 0.8 keV and line-averaged electron density . For the study of the configuration dependence of the fast particle confinement, three configurations are selected; the bumpy ripples are 0.01, 0.06 and 0.15 at the normalized minor radius ρ = 0.67. The measured tail temperatures by using a charge-exchange neutral energy analyser are 1.10 keV, 0.88 keV and 0.50 keV for the ripples of 0.15, 0.06 and 0.01, respectively. The heating efficiency of the bulk ion is also better in the high bumpy case. A Monte-Carlo analysis also indicates good confinement of the high energy ions in the high bumpy case although the difference is not very large compared with the experiment.

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Configuration Control for the Confinement Improvement in Heliotron J

Cited by 11 publications

References 17 publications

Spontaneous shift of divertor plasma footprints during a discharge in a helical-axis heliotron device

Spontaneous shift of divertor plasma footprints during a discharge in a helical-axis heliotron device

Effect of magnetic field ripple on electron cyclotron current drive in Heliotron J

Dependence of the confinement of fast ions generated by ICRF heating on the field configuration in Heliotron J

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