Stable sustainment of plasmas with electron internal transport barrier by ECH in the LHD

Yoshimura, Y.; Kasahara, Hiroshi; Tokitani, M.; Sakamoto, R.; Ueda, Y.; Marushchenko, N. B.; Seki, R.; Kubo, S.; Shimozuma, Τ.; Igami, H.; Takahashi, H.; Tsujimura, Toru Ii; Makino, R.; Kobayashi, S.; Ito, Satoshi; Mizuno, Yoshinori; Okada, K.; Akiyama, Tsuyoshi; Tanaka, K.; Tokuzawa, T.; Yamada, I.; Yamada, H.; Mutoh, T.; Takeiri, Y.

doi:10.1088/1361-6587/aa9950

Cited by 5 publications

(3 citation statements)

References 20 publications

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“…The density along the minor radius is higher without divertor pumping, whereas the temperature along the minor radius is higher with divertor pumping. In LHD, electron internal transport barrier (e-ITB) plasma with a large temperature gradient in the plasma core (r eff /a 99 <0.3) was observed in ECH heating [23][24][25]. Such a large temperature gradient in the plasma core was not observed in the discharges reported in this study.…”

Section: Long-pulse Discharge Using Divertor Pumpmentioning

confidence: 47%

“…Figure 9 shows the time evolution of ECH deposition power normalized by line-averaged electron density, P dep / n e , which is the parameter discussed in Ref. [23][24][25] related to the threshold condition for the ITB formation. As shown in figure 5(f), the core electron temperature appears to be higher in the case without divertor pumping at t=5 s, with an e-ITB-like gradient similar to that with divertor pumping.…”

Section: Discussionmentioning

confidence: 99%

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Particle control in long-pulse discharge using divertor pumping in LHD

et al. 2022

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Density control is crucial for maintaining stable confined plasma. Divertor pumping, where neutral particles are compressed and exhausted in the divertor region, was developed for this task for the Large Helical Device. In this study, neutral particle pressure, which is related to recycling, was systematically scanned in the magnetic configuration by changing the magnetic axis position. High neutral particle pressure and compression were obtained in the divertor for a high plasma electron density and the inner magnetic axis configuration. Density control using divertor pumping with gas puffing was applied to electron cyclotron heated plasma in the inner magnetic axis configuration, which provides high neutral particle compression and exhaust in the divertor. Stable plasma density and electron temperature were maintained with divertor pumping. A heat analysis shows that divertor pumping did not affect edge electron heat conductivity, but it led to low electron heat conductivity in the core caused by electron-internal-transport-barrier-like formation.

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Section: Long-pulse Discharge Using Divertor Pumpmentioning

confidence: 47%

Section: Discussionmentioning

confidence: 99%

Particle control in long-pulse discharge using divertor pumping in LHD

et al. 2022

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“…The results reported in this section are from ECRH plasma tangentially injected in a horizontal port [34]. Perpendicular injection was not performed in order to avoid damage to divertor cyro-pumps, which are located on the inner torus side.…”

Section: Isotope Effects Of Ecrh Plasma On Adjusting Operational Para...mentioning

confidence: 99%

Isotope effects on transport in LHD

Tanaka

Nagaoka

Ida

et al. 2021

Plasma Phys. Control. Fusion

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Isotope effects are one of the most important issues for predicting future reactor operations. Large helical device (LHD) is the presently working largest stellarator/helical device using super conducting helical coils. In LHD, deuterium experiments started in 2017. Extensive studies regarding isotope effects on transport have been carried out. In this paper, the results of isotope effect studies in LHD are reported. The systematic studies were performed adjusting operational parameters and nondimensional parameters. In L mode like normal confinement plasma, where internal and edge transport barriers are not formed, the scaling of global energy confinement time (τ E) with operational parameters shows positive mass dependence (M 0.27; where M is effective ion mass) in electron cyclotron heating plasma and no mass dependence (M 0.0) in neutral beam injection heating plasma. The non-negative ion mass dependence is anti-gyro-Bohm scaling. The role of the turbulence in isotope effects was also found by turbulence measurements and gyrokinetic simulation. Better accessibility to electron and ion internal transport barrier (ITB) plasma is found in deuterium (D) plasma than in hydrogen (H). Gyro kinetic non-linear simulation shows reduced ion heat flux due to the larger generation of zonal flow in deuterium plasma. Peaked carbon density profile plays a prominent role in reducing ion energy transport in ITB plasma. This is evident only in plasma with deuterium ions. New findings on the mixing and non-mixing states of D and H particle transports are reported. In the mixing state, ion particle diffusivities are higher than electron particle diffusivities and D and H ion density profiles are almost identical. In the non-mixing state, ion particle diffusivity is much lower than electron diffusivity. Deuterium and hydrogen ion profiles are clearly different. Different turbulence structures were found in the mixing and non-mixing states suggesting different turbulence modes play a role.

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