A reduced model for the ITER divertor based on SOLPS solutions for ITER Q=10 baseline conditions: A. identifying options for the control parameters

Edge codes such as SOLPS coupled to neutral codes such as EIRENE have become so comprehensive and sophisticated that they now constitute, in effect, "code-experiments' that, as for actual experiments, can benefit from interpretation using simple models and conceptual frameworks, i.e. reduced models. The first task is the identification of options for the reduced model control parameters that are best suited for control of the action of the divertor, i.e. for control of target power loading and sputter-erosion, primarily. A strong correlation between the electron temperature at the divertor target, T-e,T-t, and the neutral deuterium D-2 density at the target, n(D2,t), flux-tube resolved, has recently been reported for a number of code studies including SOLPS-4.3 modeling of a set of similar to 50 ITER baseline cases: Q(DT) = 10, q(95) = 3, P-SOL = 100 MW, metallic walls, and Ne seeding (Pitts et al 2019 Nucl. Mater. Energy 20 100696). This part A of the present study reports new results for largely the same ITER cases, confirming the strong correlations reported earlier between local values of T-e,T-t, and (i) n(D2,t), and (ii) normalized volumetric losses of power and pressure in the divertor. Strong correlations have now also been found, and are reported here for the first time, between T(e,t )and all of the divertor target quantities of practical interest. A physical explanation for this surprising result has not been fully identified; nevertheless it has encouraging implications for reduced modeling of the ITER divertor. For such ITER conditions, (i) the global Ne injection rate, InjNe (Ne s(-1)), and (ii) the electron temperature at the location on the target where the peak power deposition occurs, T-e,T-t@q(+/-,pk) (eV), are found to be promising reduced model control parameters. In the companion report, part B, a reduced model for the ITER divertor is The input to the reduced model is a value of the variable pair (T-e,T-t@q(+/-,pk), Inj(Ne) )developed and described in detail, based on reversed-direction 2 point modelling, Rev2PM. and the output are values of the various target as well as divertor-entrance quantities of practical interest,e.g. q(1,pk), n(e,Xpt) (the electron density at the poloidal location of the X-point), etc. In part B the reduced model is quantitatively characterized using one half of the code cases; it is then used to successfully predict (replicate) the code values of e.g. n(e),X(pt )for the other half of the cases.