Role of Trapped Electrons on Global Gyrokinetic Linear Stability of Collisionless Microtearing Modes

Swamy, Aditya Krishna; Ganesh, R.; Chowdhury, Jugal; Brunner, S.; Václavík, J.; Villard, L.

doi:10.1088/1742-6596/561/1/012017

Cited by 7 publications

(3 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The growth rates of the KBM modes increase with β; these growth rates peak at long wavelength, k y ρ s ∼ 0.15 but the growth rate in the long wavelength limit is not much lower than the peak growth rate, as in the density-gradient driven case. For all but the lowest β case, the vector potential of the modes in the electron diamagnetic direction exhibit even parity (consistent with tearing modes [52][53][54]) and are therefore microtearing modes [52,[55][56][57][58]. A comparison for A ∥ in the ballooning space is shown in figure 6 for β = 8.1% and for k y ρ s = 0.414 and k y ρ s = 0.77 which exhibit real frequency respectively in the ion and electron direction.…”

Section: Linear Simulations Two-species Casesmentioning

confidence: 76%

Low n electromagnetic modes in spherical tokamaks

Chowdhury

McMillan

2021

Plasma Phys. Control. Fusion

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: Linear Simulations Two-species Casesmentioning

confidence: 76%

Low n electromagnetic modes in spherical tokamaks

Chowdhury

McMillan

2021

Plasma Phys. Control. Fusion

Self Cite

View full text Add to dashboard Cite

show abstract

“…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

View full text Add to dashboard Cite

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.

show abstract

“…In gyrokinetic simulations, MT were found unstable in the conventional tokamaks JET 7,8,11 , ASDEX Upgrade 32,33 , and DIII-D [34][35][36][37] , in spherical tokamaks [38][39][40][41][42][43][44][45][46][47][48] , and in the reversed-field pinch 49,50 . Recently, different techniques have been developed to track magnetic fluctuations in JET 7 or the dynamical frequency evolution of MT in DIII-D 36 , in order to validate nonlinear simulations against tokamak pedestal data and leading to a quantitative description of the experimentally observed magnetic fluctuations, highlighting the need to determine the role played by this micro-instability in transport and confinement.…”

Section: Introductionmentioning

confidence: 99%

On the impact of electric field fluctuations on microtearing turbulence

et al. 2023

View full text Add to dashboard Cite

The magnetic drift and the electric potential play an important role in microtearing destabilization by increasing the growth rate of this instability in the presence of collisions, while in electrostatic plasma micro-turbulence, zonal electric potentials can have a strong impact on turbulent saturation. A reduced model has been developed, showing that the Rechester–Rosenbluth model is a good model for the prediction of electron heat diffusivity by microtearing turbulence. Here, nonlinear gyrokinetic flux-tube simulations are performed in order to compute the characteristics of microtearing turbulence and the associated heat fluxes in tokamak plasmas and to assess how zonal flows and zonal fields affect saturation. This is consistent with a change in saturation mechanism from temperature corrugations to zonal field- and zonal flow-based energy transfer. It is found that removing the electrostatic potential causes a flux increase, while linearly stabilization is observed.

show abstract

Role of Trapped Electrons on Global Gyrokinetic Linear Stability of Collisionless Microtearing Modes

Cited by 7 publications

References 24 publications

Low n electromagnetic modes in spherical tokamaks

Low n electromagnetic modes in spherical tokamaks

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

On the impact of electric field fluctuations on microtearing turbulence

Contact Info

Product

Resources

About