Study on divertor plasma behavior through sweeping strike point in new lower divertor on EAST

A series of L-mode discharges have been conducted in the new‘corner slot’divertor on the Experimental Advanced Superconducting Tokamak(EAST)to study the divertor plasma behavior through sweeping strike point.The plasma control system controls the strike point sweeping from the horizontal target to the vertical target through poloidal field coils,with keeping the main plasma stability.The surface temperature of the divertor target cools down as the strike point moves away,indicating that sweeping strike point mitigates the heat load.To avoid the negative effect of probe tip damage,a method based on sweeping strike point is used to get the normalized profile and study the decay length of particle and heat flux on the divertor target λ_(js),_λ(q).In the discharges with high radio-frequency(RF)heating power,electron temperature T_(e) is lower and λ_(js)is larger when the strike point locates on the horizontal target compared to the vertical target,probably due to the corner effect.In the Ohmic discharges,λ_(js),λ_(q) are much larger compared to the discharges with high RF heating power,which may be attributed to lower edge T_(e).

Strike Point Control on EAST Using an Isoflux Control Method

For the advanced tokamak,the particle deposition and thermal load on the divertor is a big challenge.By moving the strike points on divertor target plates,the position of particle deposition and thermal load can be shifted.We could adjust the Poloidal Field（PF） coil current to achieve the strike point position feedback control.Using isoflux control method,the strike point position can be controlled by controlling the X point position.On the basis of experimental data,we establish relational expressions between X point position and strike point position.Benchmark experiments are carried out to validate the correctness and robustness of the control methods.The strike point position is successfully controlled following our command in the EAST operation.

Divertor Plasma Properties for a Lower Single-Null Discharge in EAST

Divertor plasma properties for lower single-null （LSN） configuration in EAST, under a water-cooling graphite wall condition, are presented. A typical shot is selected for analyzing electron temperature, density and power flux at targets. Both higher electron density and lower electron temperature are found at the inboard target, compared to those at the outboard target. A higher power flux is also found to be at the outboard target because of in-out asymmetries for LSN-shaped discharge.

Study on divertor heat flux under n=3 and n=4 resonant magnetic perturbations using infrared thermography diagnostic in EAST

Resonant magnetic perturbations(RMPs)with high toroidal mode number n are considered for controlling edge-localized modes(ELMs)and divertor heat flux in future ITER H-mode operations.In this paper,characteristics of divertor heat flux under high-nRMPs(n=3 and 4)in H-mode plasma are investigated using newly upgraded infrared thermography diagnostic in EAST.Additional splitting strike point(SSP)accompanying with ELM suppression is observed under both RMPs with n=3 and n=4,the SSP in heat flux profile agrees qualitatively with the modeled magnetic footprint.Although RMPs suppress ELMs,they increase the stationary heat flux during ELM suppression.The dependence of heat flux on q_(95)during ELM suppression is preliminarily investigated,and further splitting in the original strike point is observed at q 495=during ELM suppression.In terms of ELM pulses,the presence of RMPs shows little influence on transient heat flux distribution.