SOLPS-ITER simulations to study the impact of aspect ratio on edge fueling neutrals in tokamaks

Abstract

In this paper, we examine the role of the aspect ratio on the neutral penetration and poloidal distribution for fixed magnetic geometry and plasma profiles using SOLPS-ITER. We start from an H-mode discharge from MAST (Kirk et al., 2012), with its aspect ratio of 1.4. We shift the magnetic equilibrium and vessel in major radius to generate a new SOLPS-ITER simulation, doubling the aspect ratio to 2.8. The neutral density profile perpendicular to the magnetic flux surfaces is fitted by an exponential. We find that the opaqueness, defined as the ratio between the electron pedestal density width and the neutral penetration depth, is unaffected by changes in the aspect ratio. We observe an increase in the neutral density close to the X-point on the high field side (HFS) as the aspect ratio increases. This poloidal angle averaged 44 % increase for the aspect ratio 2.8 case compared to the MAST geometry on the lower HFS is linked to an increase in the poloidal surface-integrated particle fluxes (1/s) towards the inner divertor.

Keywords

• Spherical tokamak
• Plasma edge modeling
• Neutral opaqueness