reports an assessment, using the SOLPS5.0 (B2-EIRENE) code, of the relative importance of two key aspects of divertor-baffle geometry: (i) divertor closure, and (ii) field-target angle. A wide range of the degree of divertor closure and field-target angle were modeled. An unexpectedly strong and simple correlation has been discovered in these data (and is reported here) between the electron temperature, T et , and the D 2 density, n D t 2 at the target, for T et < 10 eV and extending over two orders of magnitude for each correlate:f vol pwr loss is so strongly correlated with n D t 2 . To address these questions, in future work 2PMF analysis will be extended to compute the individual contributions to − − f vol pwr loss .

Dedicated experiments for the scaling of divertor power footprint width have been performed in the ITER-relevant radio-frequency (RF)-heated H-mode scheme under the lower single null, double null and upper single null divertor configurations in the Experimental Advanced Superconducting Tokamak (EAST) under lithium wall coating conditioning. A strong inverse scaling of the edge localized mode (ELM)-averaged power fall-off width with the plasma current (equivalently the poloidal field) has been demonstrated for the attached type-III ELMy H-mode as by various heat flux diagnostics including the divertor Langmuir probes (LPs), infra-red (IR) thermograph and reciprocating LPs on the low-field side. The IR camera and divertor LP measurements show that , in good agreement with the multi-machine scaling trend during the inter-ELM phase between type-I ELMs or ELM-free enhanced Dα (EDA). H-mode. However, the magnitude is nearly doubled, which may be attributed to the different operation scenarios or heating schemes in EAST, i.e., dominated by electron heating. It is also shown that the type-III ELMs only broaden the power fall-off width slightly, and the ELM-averaged width is representative for the inter-ELM period. Furthermore, the inverse Ip (Bp) scaling appears to be independent of the divertor configurations in EAST. The divertor power footprint integral width, fall-off width and dissipation width derived from EAST IR camera measurements follow the relation, λint ≅ λq + 1.64S, yielding . Detailed analysis of these three characteristic widths was carried out to shed more light on their extrapolation to ITER.

SOLPS-EIRENE edge code analysis shows that a gas-tight slot divertor geometry with a small-angle (glancing-incidence) target, named the small angle slot (SAS) divertor, can achieve cold, dissipative/detached divertor conditions at relatively low values of plasma density at the outside midplane separatrix. SAS exhibits the following key features: (1) strong enhancement of the buildup of neutral density in a localized region near the plasma strike point on the divertor target; (2) spreading of the cooling front across the divertor target with the slot gradually flaring out from the strike point, thus effectively reducing both heat flux and erosion on the entire divertor target surface. Such a divertor may potentially provide a power and particle handling solution for long pulse advanced tokamaks.

Using the SOLPS5.0 code, an assessment has been undertaken of the relative importance of two key aspects of divertor baffle geometry: (i) divertor closure, and (ii) field-target angle. The figures of merit (FOMs) have been taken to be achieving specified (low) values of electron temperature at the target, T et , and parallel power flux density at the target, q ‖t , at the lowest possible 'upstream' density, n e,sep,OMP , for a given power input. As expected, it was found that increased closure for both orthogonal targets and small glancing-angle targets make for a better divertor, based on these FOMs. It was also found that the combination of these aspects is significantly more effective than either aspect separately. The latter appears to be related to a strong correlation between T et and deuterium gas density at the target, which is the subject of a companion paper (Stangeby P.C. and Sang C.F. 2017 Nucl. Fusion 57 056007).