Collisionless trapped-electron-mode turbulence and transport in fluid descriptions

2007 ◽  
Vol 73 (5) ◽  
pp. 731-740 ◽  
Author(s):  
H. NORDMAN ◽  
P. STRAND ◽  
X. GARBET
Keyword(s):  
Fluid Transport ◽  
Fluid Model ◽  
Transport Coefficients ◽  
Ion Temperature ◽  
Plasma Parameters ◽  
Ion Temperature Gradient ◽  
Electron Mode ◽  
Mode Tem ◽  
Gyrokinetic Simulations ◽  
Trapped Electron

AbstractA study of particle and electron heat transport in tokamaks due to trapped-electron-mode (TEM) turbulence is presented. The study is based on the Weiland fluid model for ion-temperature-gradient (ITG) modes and TEMs, complemented and compared with a trapped electron fluid treatment which retains contributions from the weakly trapped electrons. The dependence of the fluid transport coefficients on magnetic shear and other plasma parameters is discussed and compared with results obtained from nonlinear gyrokinetic simulations. Inward (pinch) flows of particles and heat, previously reported for the coupled ITG–TEM system, are also found in the TEM dominated regime.

scholarly journals Stellarator microinstabilities and turbulence at low magnetic shear

2018 ◽  
Vol 84 (5) ◽  
Author(s):  
B. J. Faber ◽  
M. J. Pueschel ◽  
P. W. Terry ◽  
C. C. Hegna ◽  
J. E. Roman
Keyword(s):  
Cost Savings ◽  
Ion Temperature ◽  
Magnetic Shear ◽  
Ion Temperature Gradient ◽  
Electron Mode ◽  
Local Shear ◽  
Inner Scale ◽  
Mode Tem ◽  
Gyrokinetic Simulations ◽  
Trapped Electron

Gyrokinetic simulations of drift waves in low-magnetic-shear stellarators reveal that simulation domains comprised of multiple turns can be required to properly resolve critical mode structures important in saturation dynamics. Marginally stable eigenmodes important in saturation of ion temperature gradient modes and trapped electron modes in the Helically Symmetric Experiment (HSX) stellarator are observed to have two scales, with the envelope scale determined by the properties of the local magnetic shear and an inner scale determined by the interplay between the local shear and magnetic field-line curvature. Properly resolving these modes removes spurious growth rates that arise for extended modes in zero-magnetic-shear approximations, enabling use of a zero-magnetic-shear technique with smaller simulation domains and attendant cost savings. Analysis of subdominant modes in trapped electron mode (TEM)-driven turbulence reveals that the extended marginally stable modes play an important role in the nonlinear dynamics, and suggests that the properties induced by low magnetic shear may be exploited to provide another route for turbulence saturation.

Study of turbulence in the high betap discharge using only RF heating on EAST

2022 ◽  
Author(s):  
shuyu Zheng ◽  
Debing Zhang ◽  
Erbing Xue ◽  
Limin Yu ◽  
Xianmei Zhang ◽  
...  
Keyword(s):  
Electron Collision ◽  
Rf Heating ◽  
Plasma Parameters ◽  
Equilibrium Data ◽  
Electron Mode ◽  
Radio Frequency Waves ◽  
Thermal Diffusivities ◽  
Gyrokinetic Simulations ◽  
Trapped Electron ◽  
Scale Length

Abstract High poloidal beta scenarios with favorable energy confinement (β_p~1.9, H_98y2~1.4) have been achieved on Experimental Advanced Superconducting Tokamak (EAST) using only radio frequency waves heating. Gyrokinetic simulations are carried out with experimental plasma parameters and tokamak equilibrium data of a typical high β_p discharge by the GTC code. Linear simulations show that electron temperature scale length and electron density scale length destabilize the turbulence, collision effects stabilize the turbulence, and the instability propagates in the electron diamagnetic direction. These indicate that the dominant instability in the core of high β_p plasma is collisionless trapped electron mode. Ion thermal diffusivities calculated by nonlinear gyrokinetic simulations are consistent with the experimental value, in which the electron collision effects play an important role. Further analyses show that instabilities with k_θ ρ_s>0.38 are suppressed by collision effects and collision effects reduce the radial correlation length of turbulence, resulting in the suppression of the turbulence.

Sensitivity of kinetic ballooning mode instability to tokamak equilibrium implementations

2016 ◽  
Vol 82 (5) ◽  
Author(s):  
H. S. Xie ◽  
Y. Xiao ◽  
I. Holod ◽  
Z. Lin ◽  
E. A. Belli
Keyword(s):  
Ion Temperature ◽  
Ion Temperature Gradient ◽  
Order Difference ◽  
Ballooning Mode ◽  
Electron Mode ◽  
Tokamak Edge ◽  
Global Equilibrium ◽  
Global Profile ◽  
Shafranov Shift ◽  
Trapped Electron

Global, first-principles study of the kinetic ballooning mode (KBM) is crucial to understand tokamak edge physics in high-confinement mode (H-mode). In contrast to the ion temperature gradient mode and trapped electron mode, the KBM is found to be very sensitive to the equilibrium implementations in gyrokinetic codes. In this paper, we show that a second-order difference in Shafranov shift or geometric coordinates, or a difference between local and global profile implementations can bring a factor of two or more discrepancy in real frequency and growth rate. This suggests that an accurate global equilibrium is required for validation of gyrokinetic KBM simulations.

scholarly journals Transport through dissipative trapped electron mode and toroidal ion temperature gradient mode in TEXTOR

1988 ◽  
Vol 28 (6) ◽  
pp. 1053-1073 ◽  
Author(s):  
A. Rogister ◽  
G. Hasselberg ◽  
F.G. Waelbroeck ◽  
J. Weiland
Keyword(s):  
Temperature Gradient ◽  
Ion Temperature ◽  
Ion Temperature Gradient ◽  
Electron Mode ◽  
Trapped Electron ◽  
Gradient Mode

scholarly journals Turbulent impurity transport simulations in Wendelstein 7-X plasmas

2021 ◽  
Vol 87 (1) ◽  
Author(s):  
J. M. García-Regaña ◽  
M. Barnes ◽  
I. Calvo ◽  
F. I. Parra ◽  
J. A. Alcusón ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Ion Temperature ◽  
Trace Impurities ◽  
Ion Temperature Gradient ◽  
Electron Temperature Gradient ◽  
Impurity Transport ◽  
Impurity Species ◽  
Nonlinear Simulations ◽  
Electron Mode ◽  
Mode Tem

A study of turbulent impurity transport by means of quasilinear and nonlinear gyrokinetic simulations is presented for Wendelstein 7-X (W7-X). The calculations have been carried out with the recently developed gyrokinetic code stella. Different impurity species are considered in the presence of various types of background instabilities: ion temperature gradient (ITG), trapped electron mode (TEM) and electron temperature gradient (ETG) modes for the quasilinear part of the work; ITG and TEM for the nonlinear results. While the quasilinear approach allows one to draw qualitative conclusions about the sign or relative importance of the various contributions to the flux, the nonlinear simulations quantitatively determine the size of the turbulent flux and check the extent to which the quasilinear conclusions hold. Although the bulk of the nonlinear simulations are performed at trace impurity concentration, nonlinear simulations are also carried out at realistic effective charge values, in order to know to what degree the conclusions based on the simulations performed for trace impurities can be extrapolated to realistic impurity concentrations. The presented results conclude that the turbulent radial impurity transport in W7-X is mainly dominated by ordinary diffusion, which is close to that measured during the recent W7-X experimental campaigns. It is also confirmed that thermodiffusion adds a weak inward flux contribution and that, in the absence of impurity temperature and density gradients, ITG- and TEM-driven turbulence push the impurities inwards and outwards, respectively.

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