The plasma current profile during current reversal in AC operation of the CT-6B tokamak

Alternating current operation with one full cycle at a plasma current level of 2.5 kA has been achieved in the CT-6B tokamak. The poloidal magnetic field in the plasma is measured with two internal magnetic probes in repeated discharges. The plasma current distribution is reconstructed with an inversion algorithm. The reversed plasma current first appears on the low field side due to decreasing poloidal beta. Two plasma current components flow in opposite directions when the net current vanishes. The existence of the magnetic surfaces and rotational transform provides particle confinement in the current reversal phase.