Modeling of Globus-M connected double-null discharge

Abstract

Two Ohmic H-mode discharges of the tokamak Globus-M with similar parameters and different magnetic configurations were simulated with SOLPS-ITER code. One of the discharges has two separatrices and an active low X-point—the disconnected double null (DDN) configuration. The second discharge has a connected double null configuration (CDN). The modelled plasma parameters were matched to the experimentally measured values. The scrape-off layer (SOL) width and energy loads on the divertor targets were analysed for both cases. It is demonstrated that for the Globus-M CDN configuration discharge the energy peak load at the lower outer divertor plate is approximately half of that in the case of the DDN configuration. It is also shown that the electric currents flowing from the plasma to the target plates significantly change the energy flux to the plates in both cases with respect to the flux that would be expected for the floating potential at the plates. Two types of electric currents flowing to the plates were observed. The first is a well-known thermoelectric current flowing between magnetically connected plates with different electron temperatures. This current is more pronounced in the DDN case and is strongly reduced in the CDN case, where the difference between the temperatures at the lower and upper plates is smaller. Additionally, a new second type of electric current to the plates is observed which could be called the plate closing current (PCC). These currents close radial currents in the SOL and private region. For the DDN case the PCC is comparable with the thermoelectric currents, while for CDN case the PCC is dominant.