Gyrokinetic simulations of electrostatic microturbulence in ADITYA-U tokamak

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The effect of impurity on the electrostatic microturbulence in ADITYA-U tokamak is assessed using global gyrokinetic simulations. The realistic geometry and experimental profiles of the ADITYA-U are used, before and after argon gas seeding, to perform the simulations. Before the impurity seeding, the simulations show the existence of the trapped electron mode (TEM) instability in three distinct regions on the radial-poloidal plane. The mode is identified by its linear eigenmode structure and its characteristic propagation in the electron diamagnetic direction. The simulations with Ar1+ impurity ions in the outer-core region show a significant reduction in the turbulence and transport due to a reduction in the linear instability drive, with respect to the case without impurity. A decrease in particle and heat transport in the outer-core region modifies the plasma density profile measured after the impurity seeding. It, thus, results in the stabilization of the TEM instability in the core region. Due to the reduced turbulence activity, the electron and ion temperatures in the central region increase by about 10%.

Section: Microturbulence Simulationssupporting

confidence: 90%

Section: Gas Seeding Experiments In Aditya-umentioning

confidence: 99%

Gyrokinetic simulations of electrostatic microturbulence in ADITYA-U tokamak with argon impurity

Singh,

Shah,

Sharma

et al. 2024

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“…The discharges used in present study are in LOC regime, from the linear relation between plasma density and energy confinement time [45]. Also, the Gyro-kinetic simulation studies in similar LOC discharges [46] shows that TEM are most dominant modes in our machine [47]. In LOC regime, there is a possibility of existence of TEM turbulence and can contribute to electron heat diffusivity, given the electron temperature gradient in discharges is above the critical threshold [46].…”

Section: Discussionmentioning

confidence: 75%

Role of magnetohydrodynamic activity in sawtooth induced heat pulse propagation in ADITYA tokamak

Patel

Ghosh²,

Chowdhuri³

et al. 2023

Fast propagation of sawtooth induced heat pulse propagation is observed in the magneto-hydrodynamic (MHD) active plasmas of ADITYA tokamak. The sawtooth crash deposits heat beyond the inversion radius, which gets transported to the edge region of the plasma and is, reflected as inverted sawtooth modulation in the edge channels of electron cyclotron emission (ECE) and Hα spectral line emission. The time-lag analysis on ECE signals reveals the propagation time from plasma core to edge of ~ 150 µs. From this analysis, the estimated transient electron heat diffusivity χe hp is found to be ~ 50 – 60 m2/s, which is ten times higher than that of power balance heat diffusivity, χe pb, in the MHD active discharges of ADITYA. It has been observed that the presence of MHD (m/n = 2/1, 3/1) activity in the intermediate region between the q = 1 and the edge radii, significantly influences the heat transport from the plasma core to the edge region. Stochastic magnetic field region formation with overlapping m/n = 2/1 and 3/1 MHD islands facilitates the fast heat-pulse propagation during a sawtooth crash in ADITYA tokamak. The disparity between the measured and the power-balance estimated diffusivity is significantly reduced by considering the heat-diffusivity due to stochastization of magnetic field in the intermediate region.

“…A fluidkinetic hybrid model [57] has been implemented in GTC to overcome these limitations. This model has been used earlier to simulate the micro-instabilities in LHD [36], W7-X [58] stellarators, and tokamak [24]. In this model, the electron distribution function is written as a sum of adiabatic and nonadiabatic parts, fe = f 0 e eϕ/Te + δge.…”

Section: Model Equationsmentioning

confidence: 99%

“…Advancements in high-performance computing have made it possible to validate the gyrokinetic model. Several attempts in this direction have shown that gyrokinetics accurately describes turbulence and transport in fusion plasmas [22][23][24][25][26]. However, the gyrokinetic simulations of microturbulence using realistic device geometries and experimental profiles face severe numerical challenges.…”

Section: Introductionmentioning

confidence: 99%

Global gyrokinetic simulations of electrostatic microturbulent transport in LHD stellarator with boron impurity

Singh,

Nicolau,

Nespoli

et al. 2023

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Global gyrokinetic simulations of electrostatic microturbulent transport for discharge # 166256 of the Large Helical Device stellarator in the presence of boron impurity show the co-existence of the ion temperature gradient (ITG) turbulence and trapped electron mode (TEM) turbulence before and during boron powder injection. ITG turbulence dominates in the core, whereas TEM dominates near the edge, consistent with the experimental observations. Linear TEM frequency increases from ∼ 80 kHz to ∼ 100 kHz during boron injection, and ITG frequency decreases from ∼ 20 kHz to ∼ 13 kHz, consistent with the experiments. The poloidal wave number spectrum is broad for both ITG (0–0.5 mm−1) and TEM (0–0.25 mm−1). The nonlinear simulations with boron impurity show a reduction in the heat conductivity compared to the case without boron. The comparison of the nonlinear transport before and during boron injection shows that the ion heat transport is substantially reduced in the region where the TEM is dominant. However, the average electron heat transport throughout the radial domain and the average ion heat transport in the region where the ITG is dominant are similar. The simulations with boron show the effective heat conductivity values qualitatively agree with the estimate obtained from the experiment.