Sensitivity of kinetic ballooning mode instability to tokamak equilibrium implementations

Global gyrokinetic particle simulations show that equilibrium radial electric field (Er) shear reduces the linear growth rate, ion heat conductivity, and nonlinear turbulence amplitude for both the ion temperature gradient (ITG) and kinetic ballooning mode (KBM) microturbulence with tilting the poloidal mode structure. Increase in the magnetic shear enhances the stabilizing performance of the Er shear on linear growth rate for ITG case but has no effect on that for KBM case. The radial correlation length of the ITG turbulence is decreased by increasing the magnetic shear in a weak ion diamagnetic flow shear condition with low β, leading to a reduction in effective ExB shearing rate, which weakens the suppression performance of the Er shear on ITG turbulence amplitude. In contrast, under a larger ion diamagnetic flow shear for higher β, increase in magnetic shear strengthens the suppression performance of the Er shear on KBM turbulence amplitude due to increase in the effective shearing rate by increasing the radial correlation length of the turbulence.

Section: Stabilizing Effects Of the Radial Electric Field Shearsupporting

confidence: 82%

“…The ion gyro-radius is ρ i /R 0 = 2.86 × 10 −3 with the device size a/ρ i = 125. The radial profile of the safety factor in the cyclone base case (Dimits et al 2000, Xie et al 2016…”

Section: Simulation Parametersmentioning

confidence: 99%

The performance of equilibrium radial electric field shear on microturbulence with different magnetic shears in tokamak plasmas

Chen

Qin

Sun

et al. 2023

“…The detailed function utilized in GTC are shown in [21,22]. Benchmarks among GTC and other gyrokinetic simulation codes on electrostatic (ITG and TEM) and electromagnetic (KBM) instabilities have been carried out to evaluate the accuracy of this code, and the results agree well with that of other codes [14,[23][24][25]. Part of the simulation setups are set as follows after performing a series of convergence tests.…”

Section: Simulation Model and Setupsmentioning

confidence: 78%

“…Previous research on KBM mainly focus on those situations with T i ⩾ T e . For Cyclone base case (T i = T e ) [13], KBM dominate over TEM at ρ = 0.5 when β e > 1.5% and the frequency exhibits a jump from positive value to negative value [14], which indicates that KBM propagates in the ion diamagnetic direction. KBM is partly stabilized by strong magnetic shear and sensitive to temperature gradient rather than density gradient [15].…”

Section: Introductionmentioning

confidence: 97%

Gyrokinetic simulation of electromagnetic instabilities in the high β _p scenario on EAST

Zheng

Zhang

et al. 2023

High poloidal beta scenarios with favorable plasma performance (β_p~2.0,H_98~1.3) have be demonstrated on Experimental Advanced Superconducting Tokamak (EAST) since the 2018 IAEA. Linear electromagnetic gyrokinetic simulations using GTC code are performed based on the experimental data of a typical high β_p discharge on EAST. In the core region of plasma, an electromagnetic instability with similar β_e dependence and mode structure with kinetic ballooning mode (KBM) but exhibits positive or nearly zero frequency is observed. This instability is referred as unconventional KBM (UKBM). Simulation results demonstrate that UKBM occurs in low ion-electron temperature ratio conditions and UKBM will transit to KBM when ion-electron temperature is high. Further investigation shows the driven mechanism of UKBM differs at different electron beta region. When the electron beta exceeds the threshold of electrostatic instability to UKBM, UKBM is driven by electron pressure gradient. When electron beta is close to the beta threshold of UKBM, the main driven mechanism is ηe. Reversed magnetic shear is found to have a significant stabilize effect on UKBM.

“…But for negative shear, the Shafranov shift destabilizes the ballooning mode [45]. Subtle effects of equilibrium representation can be important for correctly resolving KBM growth rates [46].…”

Section: Details Of the Equilibriamentioning

confidence: 99%

Low n electromagnetic modes in spherical tokamaks

Chowdhury

McMillan

2021

The performance of spherical tokamak reactors depends on plasma β, and an upper limit is set by long-wavelength kinetic ballooning modes (KBMs). We examine how these modes become unstable in spherical-tokamak reactor relevant plasmas, which may contain significant fast-ion pressure. In a series of numerically generated equilibria of increasing β, the KBM becomes unstable at sufficiently high plasma β, and for such cases, it is also significantly unstable even in the long-wavelength limit. The β threshold for the KBMs is similar to the ideal Magnetohydrodynamics (MHD) threshold, and in cases without fast ions, their frequencies are as predicted by diamagnetic-drift stabilised MHD. To isolate and explore the KBMs, simulations are performed where the pressure gradient is entirely due to the density profile, or entirely due to the temperature profile; the resulting KBMs have similar properties in the long-wavelength regime. The introduction of energetic ions restricts the KBMs to longer wavelengths, and reduces the β threshold somewhat; for parameter regimes of current-day devices, this is such long wavelength that a global analysis would become necessary. Mode frequencies in plasmas with a significant fast particle population are seen to be controlled by fast particle precession frequencies.