Study of High‐Beta Plasmas in a Helical System

Yamada, H.; Watanabe, K. Y.; Sakakibara, S.; Suzuki, Y.; Ohdachi, S.; Kobayashi, M.; Funaba, H.

doi:10.1002/ctpp.200900014

Cited by 8 publications

(3 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Application of RMP is known to stabilize the RIC mode, which is considered as a seed instability of the EIC. The original aim of RIC stabilization by RMP application is to reduce the pressure gradient of bulk plasmas at iota = 1 surface by forming a magnetic island; although it was found that the RIC could be suppressed even if an island was not formed due to the plasma response at a low RMP coil current setting [48]. Figure 12(b) shows pairs of electron line average density and RMP-coil current.…”

Section: Suppression Of the Eicmentioning

confidence: 99%

Recent results from deuterium experiments on the large helical device and their contribution to fusion reactor development

et al. 2022

View full text Add to dashboard Cite

In recent deuterium experiments on the Large Helical Device (LHD), we succeeded in expanding the temperature domain to higher regions for both electron and ion temperatures. Suppression of the Energetic particle driven resistive InterChange mode (EIC) by a moderate electron temperature increase is a key technique to extend the high temperature domain of LHD plasmas. We found a clear isotope effect in the formation of the Internal Transport Barrier (ITB) in high temperature plasmas. A new technique to measure the hydrogen isotope fraction was developed in the LHD in order to investigate the behavior of the isotope mixing state. The technique revealed that the non-mixing and the mixing states of hydrogen isotopes can be realized in plasmas. In deuterium plasmas, we also succeeded simultaneously realizing the formation of the Edge Transport Barrier (ETB) and the divertor detachment. It is found that Resonant Magnetic Perturbation (RMP) plays an important role in the simultaneous formation of the ETB and the detachment. Contributions to fusion reactor development from the engineering point of view, i.e. Negative-ion based Neutral Beam Injector (N-NBI) research and the mass balance study of tritium, are also discussed

show abstract

Section: Suppression Of the Eicmentioning

confidence: 99%

Recent results from deuterium experiments on the large helical device and their contribution to fusion reactor development

et al. 2022

View full text Add to dashboard Cite

show abstract

“…According to an LHD experimental study [6], resistive interchange instabilities degrade the beta value by almost 5%, and do not induce rapid discharge termination like tokamaks. In helical systems, there is a little research on the active control of MHD instabilities, where it is shown that the amplitude of the resonant magnetic fluctuation decreases with the increment of the external RMP, because the impact of the instabilities on the plasma confinement is not serious, as above-mentioned [7]. However, when we design a helical fusion reactor with more than 5% volume-averaged beta plasmas, we expect a possibility that the interchange instability in the peripheral region prevents greater improvement of the plasma confinement performance of an LHD type reactor.…”

Section: Introductionmentioning

confidence: 99%

Suppression of resistive interchange instability by external RMP

et al. 2023

Self Cite

View full text Add to dashboard Cite

We experimentally investigate the effect of external resonant magnetic perturbation (RMP) on resistive interchange MHD instability which is typically observed in the Large Helical Device (LHD). We apply the m/n=1/1 external RMP to discharges with the m/n=1/1 interchange instability. We find that the electron density fluctuation as well as the magnetic field one is clearly reduced without a reduction of the pressure gradient by imposing the external RMP. Moreover, the achieved beta value as well as the beta gradient at the resonant surface is a little improved under certain conditions. Next, we investigate the responses of interchange instability to the external RMP under some different operational conditions. We find that the amplitude of the external RMP to completely suppress the instability with the shielding of the external RMP has a higher correlation with the volume-averaged beta value than other plasma parameters.

show abstract

“…In the LHD, a RMP is applied as a control knob to improve the confinement performance. For example, a RMP is applied to maintain a 'stable' detached discharge [13], to control the ELM [14] and to control the resistive interchange MHD instability [15]. Figure 1 shows the magnetic fluctuation amplitude (a) and the phase (defined by the poloidal location of the island's O-point at a toroidal cross-section) of m/n = 1/1 RMP component induced by the plasma as the function of the imposed RMP coil current.…”

Section: Introductionmentioning

confidence: 99%

Dependence of the resonant magnetic perturbation penetration threshold on plasma parameters and ions in helical plasmas

et al. 2019

Self Cite

View full text Add to dashboard Cite

We investigate the penetration threshold of the RMP (Resonant Magnetic Perturbation) by the external coils in the LHD (Large Helical Device) for the various plasma aspect ratio configurations. The qualitative dependence on the collisionality is opposite to that in a high plasma aspect configuration, which is a quite unique property, and it is first found in the LHD. We also investigate the threshold dependence on the ion species, and find that the threshold in the deuterium discharges is quite smaller than that in the hydrogen discharges. In all of the cases, the thresholds are higher as the poloidal rotation is faster, which shows that the poloidal rotation is the dominant driver to the RMP threshold. It is qualitatively consistent with the torque balance model between the electro-magnetic and the poloidal viscous torque. In a configuration of the LHD, the threshold dependence on the density is qualitatively similar with that in Ohmic tokamak plasmas, but the beta dependence is opposite to that of the tokamaks. The difference would come from the cause of the viscous torque.

show abstract

Study of High‐Beta Plasmas in a Helical System

Cited by 8 publications

References 18 publications

Recent results from deuterium experiments on the large helical device and their contribution to fusion reactor development

Recent results from deuterium experiments on the large helical device and their contribution to fusion reactor development

Suppression of resistive interchange instability by external RMP

Dependence of the resonant magnetic perturbation penetration threshold on plasma parameters and ions in helical plasmas

Contact Info

Product

Resources

About