Simulations of scrape-off layer power width for EAST H-mode plasma and ITER 15 MA baseline scenario by 2D electrostatic turbulence code

Abstract

The scrape-off layer power width (\lambda_q) is an important parameter for characterizing the divertor heat loads. Many experimental, theoretical, and numerical studies have been performed in recent years. In this paper, a 2D electrostatic turbulence code, BOUT-HESEL, has been upgraded to simulate H-mode plasmas for the first time. The code is validated against the previous implementation and the experiments. The simulated \lambda_q is found to agree quite well with the Eich scaling for the EAST H-mode discharge. The code is utilized to simulate the ITER 15MA baseline scenario. The ITER simulation reveals that the radial particle/heat transports are dominated by blobby transports, and predicts \lambda_{q,ITER} = 9.6 mm, which is much larger than the prediction by the Eich scaling. Based on the EAST modified cases, an estimated HESEL H-mode scaling, \lambda_q=0.51R_c^1.1B_t^(-0.3)q_95^1.1 is proposed. This scaling predicts \lambda_{q,ITER} = 9.3 mm, which agrees surprisingly well with that for the ITER case. A further investigation combined with the basic parameters in the database of the Eich scaling shows that the missing positive scaling dependence on the machine size (Rc) in the Eich scaling appears to be shaded by the negative scaling dependence on the toroidal magnetic field (Bt) for current devices. This is however not the case for ITER, explaining why simulations in recent studies and in this paper can reproduce the Eich scaling for current devices, but predict a much larger \lambda_q for ITER. According to the simulation results, the strong positive scaling dependence of \lambda_q on Rc is due to a combination of slowing down the parallel heat transports by increasing the parallel connection length and the enhancement of the radial ExB turbulent heat transports when the machine size is increased.