Continuum kinetic modelling of cross‐separatrix plasma transport in a tokamak edge including self‐consistent electric fields

Abstract

Eulerian kinetic calculations are presented for the axisymmetric cross‐separatrix plasma transport at the edge of a tokamak. The simulations are performed with a high‐order finite volume code COGENT, which solves the long‐wavelength limit of the full‐f ion gyrokinetic equation including the non‐linear Fokker–Plank collision model. Self‐consistent 2D electrostatic potential variations are obtained from the quasi‐neutrality (∇·j = 0) equation coupled to an isothermal fluid electron response. Illustrative solutions presented for parameters characteristic of the DIII‐D tokamak show qualitative agreement with experimental data.

Systematic errors in tokamak magnetic equilibrium reconstruction: a study of EFIT++ at tokamak COMPASS

“…As argued in [14], the interplay between the radial force balance (closed field lines) and the sheath potential drop (open field lines) causes the plasma potential Φ to peak near the separatrix, which results in a profile in the radial electric field E r = −dΦ/dr and in the poloidal velocity v p = E r × B t -that is, a VSL. This argumentation is rather crude, but despite that a Φ peak, or the corresponding E r = 0, has been observed in experiment [13,15], gyrofluid turbulence simulations [16], fluid simulations [17] and continuum kinetic simulations [18] alike.2 In this paper, we exploit the fact that COMPASS probes routinely record a Φ peak to carry out a statistical comparison of the VSL position to the magnetically reconstructed separatrix position.…”

“…1Refer to[10] for discussion on additional constraining input and reconstruction settings in COMPASS EFIT. 2The exact relation of the separatrix and the VSL position is currently unknown -some studies suggest that the VSL forms 0.5-1 cm outside the separatrix[4,15,16,18,19] while others place it up to 1 cm inside the separatrix[17,20]. It is likely that their relative position depends on a number of factors, including the connection length, plasma collisionality, attachement/detachment and more.…”

Reduced models for ETG transport in the pedestal

“…Reduced models will also faciliate rapid analysis of pedestal transport, thus expanding the number of discharges and scenarios for which pedestal transport can be analyzed and paving the way for real-time analysis. Moreover, reduced models for ETG may also become a useful complement to the new generation of edge gyrokinetic codes [5,6,7,8], which are developing comprehensive capabilities for modeling edge turbulence but will likely find the task of brute-force multiscale simulations-spanning the whole range from ion scales to electron scales-beyond even exascale ambitions.…”

Modelling of electrostatic ion‐scale turbulence in divertor tokamaks with the gyrokinetic code COGENT

“…However, complexities in the magnetic geometry of a tokamak edge, such as the presence of a magnetic separatrix, provide a challenge for efficient continuum simulations that utilize field‐aligned grid structure in order to handle strong anisotropy of plasma transport. Various approaches to deal with a divertor geometry in both fluid and gyrokinetic simulations of edge plasmas have been developed over the last decade, [ 1–5 ] and recently, the first proof‐of‐principle 5D full‐F continuum gyrokinetic simulation of ion‐scale microturbulence in a single‐null geometry was demonstrated with the finite‐volume code COGENT. [ 6 ] The COGENT code solves the long‐wavelength limit of the full‐F gyrokinetic equation for ion species coupled to a vorticity equation for electrostatic potential variations, where a fluid model is used for an electron response.…”