scholarly journals Verification and validation of linear gyrokinetic and kinetic-MHD simulations for internal kink instability in DIII-D tokamak

2022 ◽  
Author(s):  
Guillaume Brochard ◽  
Jian Bao ◽  
Chang Liu ◽  
Nikolai N Gorelenkov ◽  
Gyungjin Choi ◽  
...  
Keyword(s):  
Growth Rate ◽  
Emission Measurement ◽  
Ion Temperature ◽  
Ion Temperature Gradient ◽  
Kink Mode ◽  
Mhd Simulations ◽  
Equilibrium Reconstruction ◽  
Magnetic Perturbations ◽  
Kinetic Effects ◽  
Kink Instability

Abstract Verification and linear validation of the internal kink instability in tokamak have been performed for both gyrokinetic (GTC) and kinetic-MHD codes (GAM-solver, M3D-C1-K, NOVA, XTOR-K). Using realistic magnetic geometry and plasma profiles from the same equilibrium reconstruction of the DIII-D shot #141216, these codes exhibit excellent agreement for the growth rate and mode structure of the internal kink mode when all kinetic effects are suppressed. The simulated radial mode structures, obtained from linear simulations, are in reasonable agreement with the normalised electron cyclotron emission measurement after adjusting, within the experimental uncertainty, the safety factor q=1 flux-surface location in the equilibrium reconstruction. Compressible magnetic perturbations strongly destabilize the kink, while poloidal variations of the equilibrium current density reduce the growth rate of the kink. Furthermore, kinetic effects of thermal ions are found to decrease the kink growth rate in kinetic-MHD simulations, but increase the kink growth rate in gyrokinetic simulations, due to the additional drive of the ion temperature gradient and parallel electric field. Kinetic thermal electrons are found to have negligible effects on the internal kink instability.

The effects of magnetic island on toroidal ion temperature gradient mode instability

2021 ◽  
Author(s):  
Guodong Zhang ◽  
Weixin Guo ◽  
Lu Wang
Keyword(s):  
Growth Rate ◽  
Temperature Gradient ◽  
Kinetic Equations ◽  
Plasma Pressure ◽  
Linear Growth Rate ◽  
Ion Temperature ◽  
Magnetic Island ◽  
Mode Structure ◽  
Ion Temperature Gradient ◽  
Eigen Value

Abstract In this work, we have investigated the influences of magnetic island (MI) on electrostatic toroidal ion temperature gradient (ITG) mode, where the ions are described by gyro-kinetic equations including MI, and adiabatic approximation is used for electrons. The eigen-equation for short-wavelength toroidal ITG mode in Fourier-ballooning representation is derived, and the corresponding eigen-value as well as mode structure are solved. Both the flattening effects of MI on plasma pressure and MI-scale shear flow are considered. It is found that when only considering the flattening effects of MI, ITG mode can be stabilized as compared to the case without MI. While, the effective drive of toroidal ITG mode could be enhanced by including MI-scale flow, which indicates the dominant destabilizing by MI-scale flow over the stabilizing by flattening profile and results in higher growth rate than the case without MI. It is also found that the total flow shearing may prevent the ITG turbulence spreading from X-point of MI but not strong enough to prevent spreading from the seperatrix across O-point of larger MI via comparison between the flow shearing rate and the linear growth rate. Furthermore, the corresponding width of lowest-order mode structure in ballooning angle is slightly widened (narrowed) for the case without (with) MI-scale flow, as compared to the case without MI. Besides, the shifted even symmetry in ballooning angle is not qualitatively influenced by the presence of MI. The mode structure is radially asymmetric, but is symmetric with respect to the phase of MI at the O-point.

Low-frequency fluctuations in scrape-off layer of tokamak plasma with limiter biasing

2011 ◽  
Vol 77 (6) ◽  
pp. 733-748
Author(s):  
N. BISAI ◽  
RAMESWAR SINGH ◽  
R. SINGH
Keyword(s):  
Growth Rate ◽  
Temperature Gradient ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Tokamak Plasma ◽  
Equilibrium Density ◽  
Ion Temperature ◽  
Ion Temperature Gradient ◽  
Electron Temperature Gradient ◽  
Field Mobility

AbstractThe effects of limiter biasing on the equilibrium density and potential profiles of the scrape-off layer (SOL) in tokamak plasma are investigated by including ionization and cross-field mobility. It is shown that a broadening of SOL can take place by the inclusion of ionization for low negative biasing. Various microinstabilities relevant for SOL plasmas have been studied. Generalized low-frequency dispersion relation is derived. It is shown that limiter biasing significantly modifies the SOL fluctuations. It is also shown that growth rate of conductive wall instability is smaller for negative biasing than positive biasing case. New mode, the modified Simon–Hoh, and ion temperature gradient instabilities are found to contribute significantly to the growth of curvature- and electron temperature-gradient-driven conductive wall instabilities.

scholarly journals Stabilization of the kinetic internal kink mode by a sheared poloidal flow

1999 ◽  
Vol 61 (4) ◽  
pp. 543-552 ◽  
Author(s):  
HIROSHI NAITOU ◽  
TOSHIMITSU KOBAYASHI ◽  
SHINJI TOKUDA
Keyword(s):  
Growth Rate ◽  
Skin Depth ◽  
Mode Number ◽  
Larmor Radius ◽  
Parameter Study ◽  
Pressure Gradients ◽  
Minor Radius ◽  
Kink Mode ◽  
Kinetic Effects ◽  
The Magnetic Field

The effects of a sheared poloidal flow on the m = 1 (poloidal mode number) and n = 1 (toroidal mode number) kinetic internal kink mode are simulated by the linearized version of the gyro-reduced MHD code, GRM3D-2F, based on a two-field and two-fluid gyro-reduced MHD model, including the kinetic effects of electron inertia and the perturbed electron pressure gradients along the magnetic field. A parameter study for different values of de (collisionless electron skin depth) with a fixed value of ρs = 0 (ion Larmor radius estimated by the electron temperature) shows that the smaller-de case, which has the smaller growth rate, is stabilized by the smaller sheared poloidal flow. When ρs is raised to ρs > de for a fixed value of de, the instability is stabilized by the smaller shear flow compared with the case of ρs < de, although the growth rate without the flow is larger for ρs > de. Since de is very much less than the minor radius, and ρs > de for the existing and future experiments, it is possible that even a quite small sheared poloidal flow may have a crucial influence on the kinetic internal kink mode.

scholarly journals Effects of magnetic perturbations and radiation on the runaway avalanche

2021 ◽  
Vol 87 (2) ◽  
Author(s):  
P. Svensson ◽  
O. Embreus ◽  
S. L. Newton ◽  
K. Särkimäki ◽  
O. Vallhagen ◽  
...  
Keyword(s):  
Growth Rate ◽  
Runaway Electrons ◽  
Plasma Parameters ◽  
Perturbative Approach ◽  
Efficient Simulation ◽  
Strong Current ◽  
Magnetic Perturbations ◽  
Space Dynamics ◽  
Stochastic Magnetic Fields ◽  
Mitigation Methods

The electron runaway phenomenon in plasmas depends sensitively on the momentum- space dynamics. However, efficient simulation of the global evolution of systems involving runaway electrons typically requires a reduced fluid description. This is needed, for example, in the design of essential runaway mitigation methods for tokamaks. In this paper, we present a method to include the effect of momentum-dependent spatial transport in the runaway avalanche growth rate. We quantify the reduction of the growth rate in the presence of electron diffusion in stochastic magnetic fields and show that the spatial transport can raise the effective critical electric field. Using a perturbative approach, we derive a set of equations that allows treatment of the effect of spatial transport on runaway dynamics in the presence of radial variation in plasma parameters. This is then used to demonstrate the effect of spatial transport in current quench simulations for ITER-like plasmas with massive material injection. We find that in scenarios with sufficiently slow current quench, owing to moderate impurity and deuterium injection, the presence of magnetic perturbations reduces the final runaway current considerably. Perturbations localised at the edge are not effective in suppressing the runaways, unless the runaway generation is off-axis, in which case they may lead to formation of strong current sheets at the interface of the confined and perturbed regions.

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