Electrostatic quasi-neutral formulation of global cross-separatrix particle simulation in field-reversed configuration geometry

Abstract

A quasi-neutral blended drift-Lorentz particle model of the field-reversed configuration (FRC) has been developed and implemented in the particle-in-cell code named ANC. A field-aligned mesh and corresponding mesh operations are constructed for solving self-consistent electric fields in FRC geometry. Particle dynamics are described in cylindrical coordinates to allow for cross-separatrix simulation coupling the core and scrape-off layer regions of the FRC. This new model is successfully verified against analytically derived dispersion relations, and FRC turbulence is studied using the blended model for the first time.

Effects of equilibrium radial electric field on ion temperature gradient instability in the scrape-off layer of a field-reversed configuration

“…The SOL region, on the other hand, does not have those advantages, and thus both electron and ion scale drift-waves can be unstable in the SOL with critical pressure gradient comparable to the experimentally measured threshold [11]. Subsequent nonlinear simulations using the global particle code ANC [12] find that linear drift-wave instabilities first grow in the SOL, then turbulence nonlinearly spreads from SOL to core, resulting in a toroidal wavenumber spectrum consistent with the experimental measurements [13,14]. The induced transport in the FRC core is also shown to be quite different from tokamaks in these simulations.…”

Effects of zonal flows on ion temperature gradient instability in the scrape-off layer of a field-reversed configuration

“…Consistent with these experimental observations, local linear gyrokinetic simulations using the gyrokinetic toroidal code (GTC) [8] find that ion temperature gradient (ITG) mode can be unstable in the SOL with a critical pressure gradient comparable to the experimentally measured threshold, but the ion-scale ITG mode is mostly stable in the core [9][10][11]. Subsequent global nonlinear simulations using the ANC code [12] find that linear ITG instability first grows in the SOL, and then the turbulence spreads from the SOL to the core, resulting in a steady state spectrum characterized by lower amplitude core fluctuations and larger SOL fluctuations consistent with experimental measurements [13]. Finally, nonlinear simulations using the GTC-X code [14] find that equilibrium E × B flow shear can reduce the ITG instability growth rate, saturation amplitude, and ion heat transport in the SOL by reducing both the turbulence intensity and eddy size [15].…”

“…Previous studies show that the ion-scale turbulence is mainly driven by the ITG instability in the FRC SOL, which nonlinearly spreads to the core region [12,13]. For simplicity, the current simulations of the effects of zonal flows on the long wavelength ITG instability are carried out only in the SOL.…”

Simulation of equilibrium and transport in advanced FRCS

“…Perpendicular turbulent transport is modeled using the 3D PIC codes ANC [17,18], GTC [19] and GTC-X [20]. In previous simulations [20][21][22], a gyrokinetic particle push was used, necessitating the removal of magnetic null regions from the simulation domain.…”

“…Nevertheless, nonlinear simulations find qualitative agreement in fluctuation spectrum with experimental Doppler back scattering (DBS) measurements [23]. To correctly include the magnetic null regions in global simulations, which entail a significant fraction of figure-8 and betatron orbits, a 'blended' drift-Lorentz particle pusher [24] without requirement of gyrokinetic validity has recently been implemented in ANC, and a corresponding δ f model has been developed and applied [18]. Using this new particle model, linear and nonlinear results are found to be consistent with the previous gyrokinetic simulations.…”