Overview of Studies on Energetic‐Ion‐Driven MHD Instabiities in Stellarator/Helical Plasmas and Comparison with Tokamaks

Toi, K.; Isobe, M.; Osakabe, M.; Ogawa, K.; Spong, D. A.; Todo, Y.; Group, LHD Experiment

doi:10.1002/ctpp.200900044

Cited by 5 publications

(7 citation statements)

References 48 publications

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“…In addition to the formation of the RS configuration in high beta LHD plasmas, the RS configuration with q (ρ o ) < 0 was also produced by counter-NBCD provided the energetic ion contribution is significant [51][52][53][54]. Figure 10 shows the time evolution of electron temperature measured at various radial locations with an electron cyclotron emission (ECE) diagnostic and spectrograms of magnetic probe signal in the RS plasma with NBCD.…”

Section: Aes In Reversed Magnetic Shear Configurations Of Tokamak And...mentioning

confidence: 99%

Energetic-ion-driven global instabilities in stellarator/helical plasmas and comparison with tokamak plasmas

Toi¹,

Ogawa

Isobe³

et al. 2011

Plasma Phys. Control. Fusion

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Comprehensive understanding of energetic-ion-driven global instabilities such as Alfvén eigenmodes (AEs) and their impact on energetic ions and bulk plasma is crucially important for tokamak and stellarator/helical plasmas and in the future for deuterium-tritium (DT) burning plasma experiments. Various types of global modes and their associated enhanced energetic ion transport are commonly observed in toroidal plasmas. Toroidicity-induced AEs and ellipticity-induced AEs, whose gaps are generated through poloidal mode coupling, are observed in both tokamak and stellarator/helical plasmas. Global AEs and reversed shear AEs, where toroidal couplings are not as dominant were also observed in those plasmas. Helicity induced AEs that exist only in 3D plasmas are observed in the large helical device (LHD) and Wendelstein 7 Advanced Stellarator plasmas. In addition, the geodesic acoustic mode that comes from plasma compressibility is destabilized by energetic ions in both tokamak and LHD plasmas. Nonlinear interaction of these modes and their influence on the confinement of the bulk plasma as well as energetic ions are observed in both plasmas.In this paper, the similarities and differences in these instabilities and their consequences for tokamak and stellarator/helical plasmas are summarized through comparison with the data sets obtained in LHD. In particular, this paper focuses on the differences caused by the rotational transform profile and the 2D or 3D geometrical structure of the plasma equilibrium. Important issues left for future study are listed.

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Section: Aes In Reversed Magnetic Shear Configurations Of Tokamak And...mentioning

confidence: 99%

Energetic-ion-driven global instabilities in stellarator/helical plasmas and comparison with tokamak plasmas

Toi¹,

Ogawa

Isobe³

et al. 2011

Plasma Phys. Control. Fusion

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“…Both the measurement and theory show that the EGAM is a global mode with mode frequency inside the GAM continuum spectrum. Since then EGAM has been observed in other tokamaks [7][8][9] as well as in the Large Helical Device (LHD) [10][11]. Extensive theoretical and numerical work has been done on the linear physics of EGAM in the past decade [12][13][14][15][16][17][18][19][20][21][22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

Linear properties of global energetic particle induced geodesic acoustic mode with bump-on-tail distribution in tokamak plasmas

Xiang

2019

Physics of Plasmas

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A systematic study of Energetic particle-induced geodesic acoustic mode (EGAM) has been carried for bump-on-tail energetic distribution in tokamak plasmas using linear global hybrid simulation. The stability threshold of EGAM in energetic particle pressure is found to be very low. The eignemode structure becomes more and more radially extended as beam ion distribution evolves from bump tail distribution to fully slowing down distribution. The mode radial width increase with energetic particle gyroradius while the growth rate is maximized at / 0.3 A v v = .

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“…Significant drop of neutron emission rate due to fishbone instability indicating that the instability degrades the confinement of the fast ions because neutrons are mainly created due to beam-thermal reactions in these discharges [11][12][13][14][15][16]. In stellarators and helical devices, energetic ion physics research has been studied in the LHD using intensive neutral beam injections (NBs) [17]. The energetic particle driven MHD mode called the helically-trapped energetic-ion-driven resistive interchange mode (EIC) are often excited by intensive perpendicular NB injections.…”

Section: Introductionmentioning

confidence: 99%

Effect of the helically-trapped energetic-ion-driven resistive interchange modes on energetic ion confinement in the Large Helical Device

Ogawa

Isobe

Kawase

et al. 2018

Plasma Phys. Control. Fusion

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The effect of the helically-trapped energetic-ion-driven resistive interchange modes (EICs) on energetic ion confinement is studied in the Large Helical Device (LHD) deuterium plasmas. Neutron diagnostics such as the neutron flux monitor (NFM) and the vertical neutron camera (VNC) are used in order to measure neutrons mainly created by beam-plasma reactions. The line-integrated neutron profiles are obtained by VNC in magnetohydrodynamic-quiet plasma with various neutral beam (NB) injection patterns.The profiles are consistent with that expected by the beam ion density calculated using orbit-following simulations. Significant decreases of the total neutron emission rate (Sn) and the neutron counting rate of the VNC (Cn) in central cords are observed to be synchronized with EIC bursts with perpendicular-NB injection. The drop rates of both Sn and Cn increase with EIC amplitude and reach around 50 %. The line-integrated neutron profiles before and after EIC burst show that in the central cords, Cn decrease due to EIC burst whereas there is almost no change in the other cords. The experimental results suggests that the effect of EIC on helically-trapped beam ion is substantial, however the effect of passing beam ion is not significant.

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Overview of Studies on Energetic‐Ion‐Driven MHD Instabiities in Stellarator/Helical Plasmas and Comparison with Tokamaks

Cited by 5 publications

References 48 publications

Energetic-ion-driven global instabilities in stellarator/helical plasmas and comparison with tokamak plasmas

Energetic-ion-driven global instabilities in stellarator/helical plasmas and comparison with tokamak plasmas

Linear properties of global energetic particle induced geodesic acoustic mode with bump-on-tail distribution in tokamak plasmas

Effect of the helically-trapped energetic-ion-driven resistive interchange modes on energetic ion confinement in the Large Helical Device

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