Toroidal modeling of 3D perturbations generated by current filaments in scrape-off layer in tokamak with biased divertor targets

Abstract

The divertor biasing technique offers a promising alternative to control the edge localized mode (ELM) as well as the divertor heat load in tokamaks, as compared to the resonant magnetic perturbation (RMP) generated by magnetic coils. The linear resistive MHD code MARS-F [Liu et al. Phys. Plasmas 7, 3681 (2000)] is employed to study the plasma response to the $n=2$ ($n$ is the toroidal mode number) field perturbation in HL-2A, produced by the divertor biasing current filaments flowing in the scrape-off layer (SOL) region. The response field due to biasing currents is compared with the RMP field utilized for ELM control in HL-2A. The strength of the radial resonant field perturbation, produced by the biasing currents of 100 A level, is found to be comparable with RMP generated by several kA of ELM control coil currents for the reference plasma. The plasma normal displacement near the X-point and {the associated neoclassical toroidal viscosity torque are} also computed to be similar between these two techniques. The modeling results thus strongly suggest that the biasing technique can be applied to control ELMs. Moreover, the biasing currents produce field perturbations, including the plasma response, that are localized more near the plasma edge (compared to the RMP counterpart), thus reducing the chance of mode locking associated with core perturbations. Particle orbit tracing also reveals that the biasing current produced magnetic perturbation tends to widen the heat deposition region and induce the strike point splitting of the ion saturation flow on the outer divertor surface, consistent with experimental observations in HL-2A. These toroidal modeling results confirm the possibility of ELM control and plasma exhaust solution by the divertor biasing technique.

Effect of resonant magnetic perturbations including toroidal sidebands on magnetic footprints and fast ion losses in HL-2M

“…In addition, the REORBIT module was recently implemented in the MARS-F code [53] to study the influence of field perturbations on magnetic footprints [22] on the divertor target surface and on the fast particle confinement/loss [21,37,61]. REORBIT is employed to trace the field lines and the guidingcenter drift orbit trajectories of fast ions in this work.…”

“…The efficiency of the RMP technique for suppressing and/or mitigating ELM has been demonstrated in many devices, such as DIII-D [5], JET [6], MAST [7], KSTAR [8], EAST [9], ASDEX Upgrade [10] and HL-2A [11]. The RMP coil efficiency depends on both the amplitude and spectrum of field perturbations, which are mainly determined by the plasma equilibrium parameters and by the RMP coil configuration [12][13][14][15][16][17][18][19][20][21][22]. The RMP technique will be applied to control ELMs in the International Thermonuclear Experimental Reactor (ITER) [23].…”

Effects of toroidally-distributed-divertor biasing on scrape-off-layer (SOL) current drive, divertor particle flux and fast electron confinement in the QUEST spherical tokamak

“…Magnetic field perturbations by SOL currents automatically resonate with the safety factor in the pedestal region. Recently, it is confirmed by numerical simulations that RMPs produced by SOL current localize only near the pedestal edge without enhancing error field perturbations in the plasma core [37]. The TDDB is advantageous for fundamental studies of both particle transport responses to and parallel current drive in the SOL from the applied electrical biasing.…”

Chasing the multi-modal plasma response in MAST-U

“…In addition, the effect of magnetic field perturbations on the footprints on the outer divertor target surface is studied using the REORBIT module recently implemented in the MARS-F code [32][33][34]. The module traces the field linesor the guiding-center drift orbit trajectories of test thermal particles-for a given field, including both 3D perturbation and 2D equilibrium field.…”