Confinement characteristics of ECH plasmas in Heliotron J

Obiki, T.; Mizuuchi, T.; Okada, H.; Nagasaki, K.; Sano, F.; Kobayashi, S.; Hanatani, K.; Ijiri, Y.; Senju, T.; Yaguchi, K.; Sakamoto, K.; Tohshi, K.; Shibano, Masaya; Kondo, K.; Nakasuga, M.; Nakamura, Yuji; Wakatani, Masahiro; Besshou, S.; Manabe, Yukio; Satō, Hiroyuki; Ang, W.L.; Kawazome, H.; Maeno, S.; Takeda, Masahiko; Tomiyama, Koji; Tsuru, Hideo; Iriguchi, M.; Kaneko, Shingo; Kubo, Hiroshi; Nishioka, Yuichiro; Ohno, Yoichi; Takamiya, T.; Yukimoto, Hidetoshi; Fukagawa, Y.; Nakazawa, Shingo; Morita, Yoshiro; Nishio, S.; Takahashi, Koichi; Tsuboi, S.; Yamada, Masaki; Nishino, Norikazu; Tribaldos, V.; Tabarés, F.L.

doi:10.1088/0029-5515/44/1/005

Cited by 14 publications

(3 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The Heliotron J is a medium-sized helical-axis heliotron device with a low magnetic shear [18]. The major radius (R) is 1.2 m and the average plasma minor radius (a) is 0.1-0.2 m. The coil system consists of an L=1, M=4 continuous helical coil, two sets of toroidal coils, and three pairs of vertical coils.…”

Section: Heliotron J Devicementioning

confidence: 99%

See 1 more Smart Citation

High-density experiments with hydrogen ice pellet injection and analysis of pellet penetration depth in Heliotron J

Motojima¹,

Okada²,

Okazaki³

et al. 2019

Plasma Phys. Control. Fusion

Self Cite

View full text Add to dashboard Cite

A hydrogen cryogenic pellet injection system was fabricated and applied to high-density experiments in a Heliotron J device. The fueling through pellet injection was conducted in Heliotron J by using an injection barrel with a tapered structure for a small pellet with low speed. A single pellet with a speed of 260±30 m s −1 and a typical size of 1.1-1.2 mm was injected into NBI+ECH plasmas and NBI-only plasmas. In both cases, a significant increase in electron density was observed upon pellet injection. The increase in line-averaged electron density due to pellet injection was 4.0±0.7×10 19 m −3 in both cases. Pellet fueling leads to high stored energy in the high-electron-density regime. A peaked electron density profile with high core density is obtained in NBI-only plasmas after pellet injection, while the edge density is kept at a lower level. An innovative H α array measurement shows that the pellet has penetrated into the magnetic axis in NBI+ECH plasmas, while the penetration depth in NBI-only plasmas is beyond the magnetic axis, which is deeper than that in NBI+ECH plasmas. The difference in penetration depth cannot be explained by the simulation results of the ablation code, in which the effect of fast electrons/ions on pellet ablation is not considered. These results suggest that the effect of fast electrons/ions should be taken into account in the ablation code in order to explain the present experimental results.

show abstract

Section: Heliotron J Devicementioning

confidence: 99%

“…In the Heliotron J [18], which is a medium-sized heliotron device similar to the TJ-II, the optimization of gas fueling scenarios has been studied in order to improve the plasma performance. The Heliotron J is equipped with several fueling systems.…”

Section: Introductionmentioning

confidence: 99%

High-density experiments with hydrogen ice pellet injection and analysis of pellet penetration depth in Heliotron J

Motojima¹,

Okada²,

Okazaki³

et al. 2019

Plasma Phys. Control. Fusion

Self Cite

View full text Add to dashboard Cite

show abstract

“…According to the ECH experiments in Heliotron J with a well-focused microwave beam [27], both the on-and off-axis heating conditions can produce plasmas of a wide density region n e < 2×10 19 m -3 , where the upper density range is probably limited by the cut-off of the second harmonic X-mode in the central region. However, optimal heating (i.e.…”

Section: Effects Of Heating Profi Lementioning

confidence: 99%

Experimental Conditions for Improved Confinement Modes in Heliotron J

Mizuuchi

Sano

Kondo

et al. 2005

J. Plasma Fusion Res.

View full text Add to dashboard Cite

ECH/NBI experiments in Heliotron J have revealed the existence of a spontaneous transition to improved confi nement modes. Based on the experimental database obtained up to now, the characteristics of the transition and the density and power thresholds are discussed paying attention to the confi guration effects. For ECH+NBI discharges with injection powers of P ECH ~ 0.29 MW and P NBI ~ 0.57 MW, transition phenomena were observed in almost all ι(a)/2π confi gurations. The global plasma confi nements before and after the transition are affected by the value of the edge rotational transform ι(a)/2π. During the improved mode, the ι(a)/2π-dependence of the plasma stored energy is mitigated compared to the pre-transition phase. The database indicates the existence of a critical value in the lineaveraged electron density under which the transition cannot be observed. This threshold line-averaged density is in the range of 1.1-2.0×10 19 m -3 in most confi gurations, indicating that it is not a strong function of the injection power and/or the heating method. The existence of an ι(a)/2π value where the transition was not observed for ECH-only discharges but observed for NBI-only or ECH+NBI discharges suggests the existence of a confi guration effect and/or heating-method effect on the threshold power.

show abstract