Investigations of turbulent transport and intrinsic torque of toroidal momentum at the edge of J-TEXT tokamak with electrode biasing

Abstract

The influences of electrode biasing (EB) on toroidal rotation and turbulent (toroidal) momentum transport at the plasma edge have been experimentally studied in the J-TEXT tokamak. In the absence of bias (i.e. the bias current I b = 0 A), plasma toroidal rotation at the edge of the confined region is intrinsically towards the co-I p direction (parallel to plasma current); in the presence of bias, edge rotation can be greatly modified, and shows positive correlation with the bias current. As the dominant term in the turbulent momentum flux, the toroidal-radial Reynolds stress term is found to give rise to an intrinsic torque in the experiments. The local momentum balance is provided by a viscous damping-like term on the velocity. Moreover, the existence of intrinsic torque at the edge is directly verified by cancelling out the local rotation under negative bias (I b ≈ −60 A). The corresponding intrinsic torque density at the plasma edge is about 0.65 N m−2, in the co-I p direction. Further comparison shows that this intrinsic torque can be reasonably explained by the measured residual stress, providing direct evidence for the hypothesis that the residual stress is the origin of the intrinsic rotation.

Edge biasing and its impact on the edge and SOL turbulence

“…The magnitude of the fluctuations has been represented by error bars. Similar behavior has been found in reference [3,22,50]. The perpendicular current density can be obtained from equation ( 2)…”

Effect of electrode biasing on m/n = 2/1 tearing modes in J-TEXT experiments

“…Motivated by existing experimental and numerical results, an electrode biasing (EB) system for driving plasma rotation has been designed and installed on JTEXT tokamak, being able to insert into the plasma by a reciprocating drive during the discharge [29][30][31]. Experiments have been carried out to change the edge plasma rotation by using EB and to study the corresponding effect on the m/n = 2/1 TM, as presented in this paper.…”

Generation of parasitic axial flow by drift wave turbulence with broken symmetry: Theory and experiment

“…11 A electrode biasing experiment on J-TEXT achieves a nearly zero toroidal rotation profile, and its results show that the intrinsic torque can be reasonably explained by the measured residual stress. 12 The residual stress profile has also been measured at edge of TEXTOR tokamak by canceling the toroidal rotation using counter-current NBI torque. 13 The observations demonstrate that there is a minimum value for the E r × B flow to trigger the residual stress, and that this stress scales with edge pressure gradient when the E r shear threshold is exceeded.…”