Low n electromagnetic modes in spherical tokamaks

Chowdhury, Jugal; McMillan, B. F.

doi:10.1088/1361-6587/ac031b

Cited by 3 publications

(2 citation statements)

References 67 publications

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“…Two species were simulated, a thermal deuterium and electron species. It should be highlighted that no fast ions were included in this work, but must be examined in future work as they may have a significant impact on the micro-stability [20,21]. Furthermore, the impact of including tritium and impurities is also left as future work.…”

Section: Numerical Setupmentioning

confidence: 99%

Linear gyrokinetic stability of a high β non-inductive spherical tokamak

et al. 2021

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Spherical tokamaks (STs) have been shown to possess properties desirable for a fusion power plant such as achieving high plasma β and having increased vertical stability. To understand the confinement properties that might be expected in the conceptual design for a high β ST fusion reactor, a 1 GW ST plasma equilibrium was analysed using local linear gyrokinetics to determine the type of micro-instabilities that arise. Kinetic ballooning modes and micro-tearing modes are found to be the dominant instabilities. The parametric dependence of these linear modes was determined and, from the insights gained, the equilibrium was tuned to find a regime marginally stable to all micro-instabilities at θ 0 = 0.0. This work identifies the most important micro-instabilities expected to generate turbulent transport in high β STs. The impact of such modes must be faithfully captured in first-principles-based reduced models of anomalous transport that are needed for predictive simulations.

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Section: Numerical Setupmentioning

confidence: 99%

Linear gyrokinetic stability of a high β non-inductive spherical tokamak

et al. 2021

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“…The gradient in the plasma profile can drive several temperature and density gradient instabilities, such as ITG [6,[27][28][29][30], trapped electron mode (TEM) [31,32], universal drift modes [33,34] etc which are electrostatic in nature. Similar profile gradients may also produce electromagnetic instabilities such as kinetic ballooning mode (KBM) [35][36][37][38][39][40] and micro tearing mode [41][42][43][44][45] if the plasma β is high [46,47]. In the present study, the core plasma beta β = 2µ 0 n 0e T 0e /B 2 0 , where T 0e , n 0e and B 0 are the on-axis electron temperature, density and the magnetic field strength with the values of n 0e = 2.3 × 10 19 m −3 , T 0e = 250 eV and B 0 = 1.0 T is approximately 0.1%.…”

Section: Linear Gyrokinetic Simulations With Orb5 and Glogystomentioning

confidence: 99%

Gyrokinetic simulation of short wavelength ion temperature gradient instabilities in the ADITYA-U tokamak

et al. 2023

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In this work, linear and nonlinear collisionless electrostatic simulation studies of the standard and short wavelength ion temperature gradient mode (SWITG) for experimental profiles and parameters of ADITYA-U tokamak are performed using the linear global eigenvalue gyrokinetic code GLOGYSTO and the nonlinear global gyrokinetic PIC code ORB5. All simulations are carried out with non-adiabatic ions and adiabatic electrons. The ADITYA-U tokamak which has recently been upgraded to divertor configuration, is small in size and well suited for investigation of micro-instabilities in the presence of density and temperature gradients. Due to steep density and temperature gradients, simulation shows that SWITG mode naturally exists along with the standard ITG mode in ADITYA-U. In this work, the experimental shot# 33536 of ADITYA-U tokamak is considered as a reference. Good agreement in growth rate and real frequency values between GLOGYSTO and ORB5 with variations of less than 25%. Two maxima of growth rate versus mode number are obtained, the first around kθ ρs ≃ 0.4 is the standard ITG, the second around kθ ρs ≃ 1.2 is the SWITG. Additionally, using linear stability analysis, it is observed that the SWITGs are suppressed for low values of R0 /LT i.e., only the standard ITG mode remains unstable. For the ADITYA-U tokamak, nonlinear global simulations with ORB5 are also carried out. Nonlinearly, SWITG dominating case results are compared with the conventional ITG case, where SWITG is relatively suppressed. The nonlinear contribution of the SWITG mode to the total thermal ion heat transport is found to be minimal due to an increased zonal flow shearing effect on the SWITG mode suppression, even though it may be linearly more unstable than the conventional long wavelength (kθ ρs < 1) ITG mode.

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Global gyrokinetic study of shaping effects on electromagnetic modes at NSTX aspect ratio with ad hoc parallel magnetic perturbation effects

et al. 2022

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Plasma shaping may have a stronger effect on global turbulence in tight-aspect-ratio tokamaks than in conventional-aspect-ratio tokamaks due to the higher toroidicity and more acute poloidal asymmetry in the magnetic field. In addition, previous local gyrokinetic studies have shown that it is necessary to include parallel magnetic field perturbations in order to accurately compute growth rates of electromagnetic modes in tight-aspect-ratio tokamaks. In this work, the effects of elongation and triangularity on global, ion-scale, linear electromagnetic modes are studied at National Spherical Torus Experiment (NSTX) aspect ratio and high plasma β using the global gyrokinetic particle-in-cell code XGC. The effects of compressional magnetic perturbations are approximated via a well-known modification to the particle drifts that was developed for flux-tube simulations [Joiner et al., Phys. Plasmas 17, 072104 (2010)], without proof of its validity in a global simulation, with the gyrokinetic codes GENE and GEM being used for local verification and global cross-verification. Magnetic equilibria are re-constructed for each distinct plasma profile that is used. Coulomb collision effects are not considered. Within the limitations imposed by the present study, it is found that linear growth rates of electromagnetic modes (collisionless microtearing modes and kinetic ballooning modes) are significantly reduced in a high-elongation and high-triangularity NSTX-like geometry compared to a circular NSTX-like geometry. For example, growth rates of kinetic ballooning modes at high- β are reduced to the level of that of collisionless trapped electron modes.

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Low n electromagnetic modes in spherical tokamaks

Cited by 3 publications

References 67 publications

Linear gyrokinetic stability of a high β non-inductive spherical tokamak

Linear gyrokinetic stability of a high β non-inductive spherical tokamak

Gyrokinetic simulation of short wavelength ion temperature gradient instabilities in the ADITYA-U tokamak

Global gyrokinetic study of shaping effects on electromagnetic modes at NSTX aspect ratio with ad hoc parallel magnetic perturbation effects

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