Gyrokinetic studies of the effect of β on drift-wave stability in the National Compact Stellarator Experiment

Abstract

The gyrokinetic turbulence code GS2 was used to investigate the effects of plasma b on linear, collisionless ion temperature gradient (ITG) modes and trapped electron modes (TEM) in National Compact Stellarator Experiment (NCSX) geometry. Plasma b affects stability in two ways: through the equilibrium and through magnetic fluctuations. The first was studied here by comparing ITG and TEM stability in two NCSX equilibria of differing b values, revealing that the high b equilibrium was marginally more stable than the low b equilibrium in the adiabatic-electron ITG mode case. However, the high b case had a lower kinetic-electron ITG mode critical gradient. Electrostatic and electromagnetic ITG and TEM mode growth rate dependencies on temperature gradient and density gradient were qualitatively similar. The second b effect is demonstrated via electromagnetic ITG growth rates' dependency on GS2's b input parameter. A linear benchmark with gyrokinetic codes GENE and GKV-X is also presented. V C 2012 American Institute of Physics.

Comparing linear ion-temperature-gradient-driven mode stability of the National Compact Stellarator Experiment and a shaped tokamak

“…Therefore, turbulence could be increasingly relevant in stellarator experiments. Several gyrokinetic studies of drift-wave-driven turbulence in stellarator geometry have been done [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] with a variety of gyrokinetic codes, such as GS2, 27 GENE, 15,28 GKV-X, 16,17 and FULL. 10 These codes have all been linearly benchmarked against each other for nonaxisymmetric geometries.…”

“…10 These codes have all been linearly benchmarked against each other for nonaxisymmetric geometries. 18,19 Progress has even been made in optimizing stellarator designs to have reduced turbulent transport. 29 Besides comparing good stellarator configurations (as was done in Refs.…”

Collisionless microinstabilities in stellarators. II. Numerical simulations

“…The simplest expression, neglecting the non-adiabatic response of the electrons and the finite magnetic drift frequency ω d for both species is [Eq. (9) …”

“…Instabilities including kinetic electrons have not been studied extensively in stellarators. Although there are some results focusing on W7-X 6,7 and NCSX [8][9][10] as well as comparisons of different stellarators 11 , these are not sufficient to explain why certain stellarators are more resilient against microinstabilities than others. In the present paper, two stellarators approaching quasi-isodynamicity, W7-X and QIPC, are compared with the DIII-D tokamak and the NCSX stellarator, which are both distinctly non-quasi-isodynamic.…”

A reduced model for ion temperature gradient turbulent transport in helical plasmas

“…3 Since the turbulence simulations require expensive computational costs, it is not practical to perform nonlinear gyrokinetic simulations a large number of times for the purpose of surveying the transport levels in a wide space of multiple parameters corresponding to various experimental conditions. Especially, gyrokinetic simulations for helical systems such as stellarators and heliotrons [4][5][6][7] tend to consume much larger computational resources than for tokamaks because of the higher spatial resolutions required by the complicated helical field structure. Therefore, it is desired to establish a reduced transport model which can quickly reproduce the nonlinear simulation results within allowable errors.…”