Effect of the tokamak size in edge transport modelling and implications for DEMO

Abstract

The edge plasma of four devices, AUG, JET, ITER and a prototypical DEMO near ignition, is modelled with B2-EIRENE with a linear neutral model, carbon impurity, and variable throughput and scrape-off layer power. The scaling from ITER to DEMO is quantified as a power law scaling in device size, and JET and AUG simulations are compared to this scaling. Compared to ITER at the same scrape-off layer power per unit device volume and the same operating point relative to the edge-based density limit, edge helium density and peak power per unit area is found to be similar, and helium influx lower, for DEMO with impurity seeding. With a full neutral model, helium parameters are improved by a factor 3. Results of core modelling show that ignited operation of DEMO is possible with the impurity seeding required to render peak power loads compatible with a helium-cooled divertor. ________________________________________________________________ JNM keywords: T0100, P0500, P0600 2

Impurity seeding and scaling of edge parameters in ITER

“…The plasma contains ions and atoms of D (representing both D and T), He, and C, as well as D 2 molecules. The present paper extends the previous simulations by a) updating the scaling of the edge parameters (from that of [2]) for variations of DT flux and helium density and flux with pumping speed and neutral pressure, b) removing carbon and introducing seed neon impurity to commence simulation of the later phase of ITER operation, and c) determining the effect of the impurity seeding on the operating window of ITER following [5,6].…”

“…Initial results reported in [2] with the nonlinear neutral model indicated that the DT neutral flux was higher (factor 2) and the helium density and flux at the separatrix were lower (factor 0.33) than for the less complete linear neutral model but the scaling had then not yet been determined. We have now varied both pumping speed and throughput (i.e.…”

“…As shown in [2] the DT separatrix density varies as € µ 0.43 , i.e. the density analogue of € µ is the ratio of the edge density to that at detachment,…”

“…In previous work ( [2] and references therein) the key parameter for determining the edge plasma parameters was found to be…”

“…We now use routinely the B2-Eirene code package version solps4.2 [1][2][3][4], which relies on a nonlinear model of neutral particle transport, including neutral-neutral and molecule-ion collisions. The model assumptions are those of [1].…”