Effect of Resonant Magnetic Perturbation on erosion of divertor region in KSTAR

Abstract

Typical H-mode plasmas in tokamaks are accompanied by Edge localized modes (ELMs). ELM crash leads to a transient, but much higher heat load on the divertor, for instance, heat flux deposited during typical type I ELM in JET is several ten MW/m2. ELMs have to be suppressed or mitigated to protect divertor structure, even that made of tungsten. In order to control ELMs in H-mode, Resonant Magnetic Perturbation (RMP) is often applied. For instance, KSTAR has successfully suppressed ELMs by applying n = 1 and 2 RMP. RMP bifurcates separatrix into several smaller segments resulting in reduction of local heat load on divertor due to the use of much wider areas. Nevertheless, erosion, deposition and recycling behavior in divertor region have been changed significantly by applying RMP. This paper reports the effect of RMP on erosion of divertor region in KSTAR compared with standard H-mode plasmas. In H-mode plasmas without RMP, toroidal slit samples are eroded with an erosion rate of 0.96 nm/s. In H-mode plasmas with n = 1 and n = 2 mixed RMP, toroidal slit samples are eroded with erosion rate of 1.40 nm/s and with n = 2 RMP, poloidal slit samples show significant erosion with erosion rate of 1.42 nm/s. Those results indicate that RMP could enhance local erosion significantly by a factor of 50%. Results from more detailed analysis will be reported in this paper.