ion temperature gradient
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Author(s):  
Yihao Duan ◽  
Yong Xiao ◽  
Zhihong Lin

Abstract Gyro-average is a crucial operation to capture the essential finite Larmor radius effect (FLR) in gyrokinetic simulation. In order to simulate strongly shaped plasmas, an innovative multi-point average method based on non-orthogonal coordinates has been developed to improve the accuracy of the original multi-point average method in gyrokinetic particle simulation. This new gyro-average method has been implemented in the gyrokinetic toroidal code (GTC). Benchmarks have been carried out to prove the accuracy of this new method. In the limit of concircular tokamak, ion temperature gradient (ITG) instability is accurately recovered for this new method and consistency is achieved. The new gyro-average method is also used to solve the gyrokinetic Poisson equation, and its correctness has been confirmed in the long wavelength limit for realistic shaped plasmas. The improved GTC code with the new gyro-average method has been used to investigate the ITG instability with EAST magnetic geometry. The simulation results show that the correction induced by this new method in the linear growth rate is more significant for short wavelength modes where the finite Larmor radius (FLR) effect becomes important. Due to its simplicity and accuracy, this new gyro-average method can find broader applications in simulating the shaped plasmas in realistic tokamaks.


2022 ◽  
Author(s):  
Guillaume Brochard ◽  
Jian Bao ◽  
Chang Liu ◽  
Nikolai N Gorelenkov ◽  
Gyungjin Choi ◽  
...  

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.


2022 ◽  
Vol 17 (01) ◽  
pp. C01018
Author(s):  
C.W. Domier ◽  
J. Dannenberg ◽  
Y. Zhu ◽  
X. Liu ◽  
J.R. Sirigiri ◽  
...  

Abstract A previous 5-channel tangential high-k scattering system is being replaced by an 8-channel, poloidal high-k scattering system on the National Spherical Torus eXperiment Upgrade (NSTX-U) device located in Princeton, NJ, USA. The 693 GHz poloidal scattering system replaces a 280 GHz tangential scattering system to study high-k electron density fluctuations on NSTX-U, thereby considerably enhancing planned turbulence physics studies by providing a measurement of the k θ -spectrum of both electron temperature gradient (ETG) and ion temperature gradient (ITG) modes. Two approaches to generating the 693 GHz probe beam are under development: an optically-pumped far-infrared (FIR) laser that generates ∼50 mW, and a compact gyrotron that can potentially generate in excess of 5 W. Large aperture optics collect radiation scattered from density fluctuations in the plasma core at 8 simultaneous scattering angles ranging from 2 to 15° corresponding to poloidal wavenumbers that extend to >40 cm−1. Steerable launch optics coupled with receiver optics mounted on a 5-axis receiver carriage allow the scattering volume to be placed radially from r/a = 0.3 out to the pedestal region (r/a ∼ 0.99) and translated horizontally as needed to satisfy wavenumber matching.


2022 ◽  
Vol 29 (1) ◽  
pp. 012303
Author(s):  
J. M. Duff ◽  
B. J. Faber ◽  
C. C. Hegna ◽  
M. J. Pueschel ◽  
P. W. Terry

2021 ◽  
Author(s):  
Shaokang Xu ◽  
Shinya Maeyama ◽  
Tomohiko Watanabe

Abstract The present study reveals that the anomalous tungsten particle transport based on the nonlinear gyrokinetic simulations shares some similarities with that of the linear gyrokinetic study, meanwhile there exist some significant differences. In particular, nonlinear excitation of the linearly stable modes plays a non-negligible role in anomalous tungsten particle transport. The highlighted results are the downshift of the critical density gradient for zero tungsten particle transport and the mod- ification of the poloidal profile of the outward tungsten particle transport, which are both related to the small scale turbulent fluctuations. The former one is due to the outward particle convection produced by the linearly stable modes. The later one is brought by both the linearly stable modes and the large-scale eddies with finite ballooning angle, which flatten the poloidal profile of the particle diffusion and further shift the peak positions of the strongest outward particle transport to the high poloidal angle regions.


Author(s):  
Guodong Zhang ◽  
Weixin Guo ◽  
Lu Wang

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.


Author(s):  
Debing Zhang ◽  
Limin Yu ◽  
Erbing Xue ◽  
Xianmei Zhang ◽  
Haijun Ren

Abstract In the nowadays and future fusion devices such as ITER and CFETR, as the use of various heating schemes, the parallel and perpendicular temperature of plasmas can be different; this temperature anisotropy may have significant effects on the turbulence. In this work, the anomalous transport driven by the ion temperature gradient instability is investigated in an anisotropic deuterium-tritium (D-T) plasma. The anisotropic factor $\alpha$, defined as the ratio of perpendicular temperature to parallel temperature, is introduced to describe the temperature anisotropy in the equilibrium distribution function of D. The linear dispersion relation in local kinetic limit is derived, and then numerically evaluated to study the dependence of mode frequency on the anisotropic factor $\alpha$ and the proportion for T particle $\vareT$ by choosing three sets of typical parameters, denoted as the cyclone base case (CBC), ITER and CFETR cases. Based on the linear results, the mixing length model approximation is adopted to analyze the quasi-linear particle and energy fluxes for D and T. It is found that choosing small $\alpha$ and large $\vareT$ is beneficial for the confinement of particle and energy for D and T. This work may be helpful for the estimation of turbulent transport level in the ITER and CFETR devices.


Author(s):  
Ge Dong ◽  
Zhihong Lin

Abstract The clear understanding of the wave-particle interaction and associated transport mechanism of different particle species in the drift wave instabilities is important for accurate modeling and predictions of the plasma confinement properties. Our global gyrokinetic simulations find that electron particle and heat transport decreases to a very low level, while ion heat transport level has no dramatic change when wave-particle resonance is suppressed in the collisionless trapped electron mode (CTEM) turbulence in the tokamak core. Similarly, ion heat transport in the self-consistent ion temperature gradient (ITG) turbulence simulation is qualitatively similar to that in the test-particle simulation using the static ITG turbulence fields. These simulation results show that electron transport is primarily driven by the wave-particle resonance in the CTEM turbulence, but the ion transport is mostly driven by the nonlinear wave-particle scattering in both the CTEM and ITG turbulence.


2021 ◽  
Author(s):  
Shawn Angelo Zamperini ◽  
J.H. Nichols ◽  
Peter C. Stangeby ◽  
David Donovan ◽  
Jonah David Duran ◽  
...  

Abstract Near-separatrix impurity accumulation between the crown and the outer midplane of tokamaks is a common feature in results from codes such as SOLPS-ITER and DIVIMP; however, experimental evidence of accumulation has only recently been obtained and is reported here. The codes find that the poloidal distribution of impurity ions in the scrape-off layer (SOL) depends primarily on toroidal field (BT)-dependent parallel flow patterns of the background plasma and the parallel ion temperature gradient (∇||Tion) force. Experimentally, Mach probes used in L-mode plasmas with favorable (for H-mode access) BT measure fast (M~0.3-0.5) inner-target-directed (ITD) background plasma flows at the crown of single-null discharges. This study reports a set of DIVIMP simulations for two similar H-mode discharges from the DIII-D W Metal Rings Campaign differing primarily in BT-direction to assess the effect that fast ITD flows have on the distribution of W ions in the SOL. It is found that for imposed ITD flows of M = 0.3, W ions that otherwise accumulate due to the ∇||Tion-force are largely flushed out. It is also found that doubling the radial diffusion coefficient from 0.3 to 0.6 m2/s prevents accumulation due to rapid cross-field transport into the far-SOL, where background plasma flows drain W ions to the divertors. Far-SOL W distributions from DIVIMP are then used to specify input to the impurity transport code 3DLIM, which is used to interpretively model collector probe deposition patterns measured in the “wall-SOL.” It is demonstrated that the deposition patterns are consistent with the DIVIMP predictions of near-SOL accumulation for the unfavorable-BT direction, and little/no accumulation for the favorable-BT direction. The wall-SOL collector probes have thus provided the first experimental evidence, albeit indirect, of near-SOL W accumulation – finding it occurs for the unfavorable-BT direction only. For the favorable-BT direction, fast flows can largely prevent accumulation from occurring.


2021 ◽  
Vol 49 (1) ◽  
Author(s):  
U. Zakir ◽  
◽  
K. Aziz ◽  
Q. Haque ◽  
A. Murad ◽  
...  

The specific role of ion heat flux on the characteristics of the linear and nonlinear ion temperature gradient (ηi) driven mode in inhomogeneous electron-positron-ion plasma is presented. Inhomogeneity in density, temperature, and the magnetic field is considered. A modified linear dispersion relation is obtained, and its different limiting cases are when ηi 2/3, ωD(gradient in magnetic field) = 0 and β(density ratio of plasma species) = 1 are discussed. Furthermore, an expression for the anomalous transport coefficient of the present model is obtained. Nonlinear structure solutions in the form of solitons and shocks show that mode dynamics enhance in the presence of ion heat flux in electron-positron-ion plasma. The present study is essential in energy confinement devices such as tokamak because the heat flux observed experimentally in tokamak plasma is much higher than those described by collisions. Further, it could be helpful to understand the nonlinear electrostatic excitations in the interstellar medium.


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