85 research outputs found
Observation of minor and major disruption processes in the KSTAR plasmas with ECEI diagnostics
No full textFast-ion redistribution and loss due to edge perturbations in the ASDEX Upgrade, DIII-D and KSTAR tokamaks
No full textThe impact of edge localized modes (ELMs) and externally applied resonant and non-resonant magnetic perturbations
(MPs) on fast-ion confinement/transport have been investigated in the ASDEX Upgrade (AUG), DIII-D and KSTAR
tokamaks. Two phases with respect to the ELM cycle can be clearly distinguished in ELM-induced fast-ion losses.
Inter-ELM losses are characterized by a coherent modulation of the plasma density around the separatrix while
intra-ELM losses appear as well-defined bursts. In high collisionality plasmas with mitigated ELMs, externally
applied MPs have little effect on kinetic profiles, including fast-ions, while a strong impact on kinetic profiles is
observed in low-collisionality, low
q
95
plasmas with resonant and non-resonant MPs. In low-collisionality H-mode
plasmas, the large fast-ion filaments observed during ELMs are replaced by a loss of fast-ions with a broad-band
frequency and an amplitude of up to an order of magnitude higher than the neutral beam injection prompt loss signal
without MPs. A clear synergy in the overall fast-ion transport is observed between MPs and neoclassical tearing
modes. Measured fast-ion losses are typically on banana orbits that explore the entire pedestal/scrape-off layer. The
fast-ion response to externally applied MPs presented here may be of general interest for the community to better
understand the MP field penetration and overall plasma response.Ministerio de Economía y Empresa ((RYC-2011-09152 y ENE2012-31087)Marie Curie (Grant PCIG11-GA-2012-321455)US Department of Energy (DE-FC02-04ER54698, SC-G903402, DE-FG02-04ER54761, DE-AC02-09CH11466 and DE-FG02- 08ER54984)NRF Korea contract 2009-0082012MEST under the KSTAR projec
The coexistence of multiple mode structures during the inter-ELM-crash period in KSTAR H-mode plasma
No full textA comprehensive study on rotation reversal in KSTAR: experimental observations and modelling
No full textInternational audienceDedicated experiments have been performed in KSTAR Ohmic plasmas to investigate the detailed physics of the rotation reversal phenomena. Here we adapt the more general definition of rotation reversal, a large change of the intrinsic toroidal rotation gradient produced by minor changes in the control parameters (Camenen et al 2017 Plasma Phys. Control. Fusion 59 034001), which is commonly observed in KSTAR regardless of the operating conditions. The two main phenomenological features of the rotation reversal are the normalized toroidal rotation gradient (u') change in the gradient region and the existence of an anchor point. For the KSTAR Ohmic plasma database including the experiment results up to the 2016 experimental campaign, both features were investigated. First, the observations show that the locations of the gradient and the anchor point region are dependent on q(95). Second, a strong dependence of u' on nu(eff) is clearly observed in the gradient region, whereas the dependence on R/L-Ti, R/L-Te, and R/L-ne is unclear considering the usual variation of the normalized gradient length in KSTAR. The experimental observations were compared against several theoretical models. The rotation reversal might not occur due to the transition of the dominant turbulence from the trapped electron mode to the ion temperature gradient mode or the neoclassical equilibrium effect in KSTAR. Instead, it seems that the profile shearing effects associated with a finite ballooning tilting well reproduce the experimental observations of both the gradient region and the anchor point; the difference seems to be related to the magnetic shear and the q value. Further analysis implies that the increase of u' in the gradient region with the increase of the collisionality would occur when the reduction of the momentum diffusivity is comparatively larger than the reduction of the residual stress. It is supported by the perturbative analysis of the experiments and the nonlinear gyrokinetic simulations. The absence of the sign change of u' even when a much lower collisionality is produced by additional electron cyclotron heating brings further experimental support to this interpretation
Measurement of poloidal rotation velocity of long-wavelength density turbulence with microwave imaging reflectometry in KSTAR
No full textRapid transition of the toroidal eigenmode number of the edge localized modes in KSTAR plasmas
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