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Park, Hyeon Keo
Fusion Plasma Stability and Confinement Research Lab
Research Interests
  • Fusion, plasma, MHD, turbulence, imaging

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Investigation of MHD instabilities and control in KSTAR preparing for high beta operation

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Title
Investigation of MHD instabilities and control in KSTAR preparing for high beta operation
Author
Park, Y. S.Sabbagh, S. A.Bialek, J. M.Berkery, J. W.Lee, S. G.Ko, W. H.Bak, J. G.Jeon, Y. M.Park, J. K.Kim, J.Hahn, S. H.Ahn, J. -W.Yoon, S. W.Lee, K. D.Choi, M. J.Yun, G. S.Park, Hyeon KeoYou, K. -I.Bae, Y. S.Oh, Y. K.Kim, W. -C.Kwak, J. G.
Keywords
Control performance; Crystal spectrometer; H-mode operations; Internal inductance; Korea superconducting tokamak advanced researches; MHD instabilities; Plasma stored energy; Steady state profiles
Issue Date
2013-08
Publisher
INT ATOMIC ENERGY AGENCY
Citation
NUCLEAR FUSION, v.53, no.8, pp.083029 -
Abstract
Initial H-mode operation of the Korea Superconducting Tokamak Advanced Research (KSTAR) is expanded to higher normalized beta and lower plasma internal inductance moving towards design target operation. As a key supporting device for ITER, an important goal for KSTAR is to produce physics understanding of MHD instabilities at long pulse with steady-state profiles, at high normalized beta, and over a wide range of plasma rotation profiles. An advance from initial plasma operation is a significant increase in plasma stored energy and normalized beta, with W-tot = 340 kJ, beta(N) = 1.9, which is 75% of the level required to reach the computed ideal n = 1 no-wall stability limit. The internal inductance was lowered to 0.9 at sustained H-mode duration up to 5 s. In ohmically heated plasmas, the plasma current reached 1 MA with prolonged pulse length up to 12 s. Rotating MHD modes are observed in the device with perturbations having tearing rather than ideal parity. Modes with m/n = 3/2 are triggered during the H-mode phase but are relatively weak and do not substantially reduce W-tot. In contrast, 2/1 modes to date only appear when the plasma rotation profiles are lowered after H-L back-transition. Subsequent 2/1 mode locking creates a repetitive collapse of beta(N) by more than 50%. Onset behaviour suggests the 3/2 mode is close to being neoclassically unstable. A correlation between the 2/1 mode amplitude and local rotation shear from an x-ray imaging crystal spectrometer suggests that the rotation shear at the mode rational surface is stabilizing. As a method to access the ITER-relevant low plasma rotation regime, plasma rotation alteration by n = 1, 2 applied fields and associated neoclassical toroidal viscosity (NTV) induced torque is presently investigated. The net rotation profile change measured by a charge exchange recombination diagnostic with proper compensation of plasma boundary movement shows initial evidence of non-resonant rotation damping by the n = 1, 2 applied field configurations. The result addresses perspective on access to low rotation regimes for MHD instability studies applicable to ITER. Computation of active RWM control using the VALEN-3D code examines control performance using midplane locked mode detection sensors. The LM sensors are found to be strongly affected by mode and control coil-induced vessel current, and consequently lead to limited control performance theoretically
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DOI
10.1088/0029-5515/53/8/083029
ISSN
0029-5515
Appears in Collections:
PHY_Journal Papers
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0029-5515_53_8_083029.pdf Download

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