Field reversal effects on divertor plasmas under radiative and detached conditions in JT-60U

Abstract

Reversal effects of the toroidal field Bt on the principal divertor plasma parameters were investigated under radiative and detached divertor conditions in L mode discharges. The ion flux to the inboard separatrix strike point decreased before a MARFE occurred, irrespective of the ion Del B drift direction. The local electron temperature, Te, div, decreased to around 10 eV. The maximum fraction of power radiated in the divertor was comparable between the two directions of Bt. With the power flowing into the two divertor fans being slightly larger on the outboard than on the inboard, a nearly symmetric in-out heat load was observed for the ion Del B drift away from the target. This was due to the outboard enhanced asymmetries in the particle flux and radiation loss distributions. From the viewpoint of in-out symmetry in the target heat load and Te, div, operation with the ion Del B drift away from the target plate is desirable as long as the attached divertor condition is maintained. On the contrary, during the MARFE, although deterioration of the energy confinement as well as the increase in the fuelling efficiency were comparable, for the ion Del B drift towards the target the plasma did not detach completely, and the strong in-out asymmetry in the particle recycling was relaxed to a relatively symmetric distribution. From the viewpoint of particle exhaust to the divertor, operation with the ion Del B drift towards the target is favourable

Physics of ultimate detachment of a tokamak divertor plasma

“…Matsubara et al 2006;Hayashi et al 2016) and the tokamaks (see e.g. Petrie et al 1992;Asakura et al 1996;Wenzel et al 1997;Loarte et al 1999;Potzel et al 2013;Reimold et al 2015b). In the tokamaks, the frequency of these fluctuations varies from device to device and spans over a range from ∼10 Hz (Loarte et al 1999) to ∼10 kHz (Potzel et al 2013), which suggests that the physical mechanisms of these fluctuations are different.…”

Density limits in toroidal plasmas

“…[75] but was not studied extensively until the early 1990's [75,72,[76][77][78][79][80][81]. Detachment does not occur on all flux surfaces simultaneously, but begins near the separatrix and extends radially outward into the SOL as the density is raised [82,46].…”

Effects of heating power on divertor in-out asymmetry and scrape-off layer flow in reversed field on Experimental Advanced Superconducting Tokamak

“…1 Divertor in-out asymmetry in target power deposition was observed in some tokamaks, with an outboard-enhanced heat load in lower single null (LSN) for normal field (ion rB drift direction toward the lower X-point), and with a balanced or even inboard-enhanced heat load for reversed field (ion rB drift direction away from the lower X-point). [2][3][4][5][6][7] Some effects have been considered to influence divertor asymmetry, such as B Â rB drift, diamagnetic drift, E Â B drift, parallel scrape-off layer (SOL) flow, divertor radiation, plasma rotation, Shafranov shift, divertor geometry, as well as the effect of ballooning-like transport and resulting asymmetry of inboard/outboard connection length. In normal field LSN configuration, it is considered that the poloidal E Â B drift in SOL region enhances the outboard-favored divertor asymmetry in heat flux, while the radial E Â B drift enhances the inboard-favored divertor asymmetry.…”