Termination of the runaway electroncurrent generated during plasma disruptions is found in JT-60U duringsimulated vertical plasma displacement events where the safetyfactor at the plasma surface qs decreases. For all discharges withrunaway electron generation, the runaway current disappears for qs⩾2 withthe appearance of spikes in the magnetic fluctuations. The growth rate of thespikes in the magnetic fluctuations decreases by an order of magnitudeduring the termination of runaway current. Corresponding to the lossof runaway electrons by magnetic fluctuations, heat flux pulses aremeasured at the inner divertor plates, which indicates interaction of the wall with the runaway electrons. The halo current during runaway termination is small and increases after runawaytermination with a dominant toroidal mode of n = 1.
Analysis of runaway electron discharge formation during Joint European Torus plasma start-up