A. S. Kukushkin

Scaling laws for edge plasma parameters in ITER from two-dimensional edge modelling

Results of a detailed study of the parameter space of the ITER divertor with the B2-Eirene code are presented. Relations between plasma parameters at the separatrix, the interface between the core and edge plasma, are parametrized to provide a set of boundary conditions for the core models. The reference ITER divertor geometry is compared with the straight target option, and the possibility of controlling the edge density by shifting the plasma equilibrium in ITER is explored.

Effect of neutral transport on ITER divertor performance

This paper describes the present state of the development of the computational model of the ITER edge plasma. Neutral–neutral collisions and molecular dynamics are introduced into the self-consistent scheme. First results of ITER modelling including these effects indicate that the operational window for the ITER divertor shifts towards higher neutral pressure in the private-flux region, retaining the operational flexibility determined in the previous analyses.

Operating window of ITER from consistent core–pedestal–SOL modelling with modified MMM transport and carbon

Integrated core–pedestal–SOL modelling is performed for ITER using the MMM95 model for energy transport, modified with additional magnetic shear stabilization to produce a pedestal. The additional stabilization term is calibrated against experiment. The operating space of ITER predicted by the model with neoclassical accumulation of intrinsic carbon impurity is determined. The relationship to an SOL-based density limit is investigated. A reasonable window for operation, with Q larger than 10 is found.

Core plasma operation consistent with SOL parameters in ITER

The constraints of divertor operation have been applied to ITER core plasma simulations by imposing boundary conditions on the calculation, implemented as a set of scaling relations derived from B2-Eirene modelling which describe the effect of the divertor. The core plasma simulations use the integrated core pedestal sol (ICPS) model, based on ITG transport for ions and RLW-like transport for electrons, which includes an increase of transport when the ballooning limit is attained in order to simulate the effect of ELMs in a time-averaged fashion. At the nominal average core density for ITER with the ICPS transport model stationary operation with a fusion power multiplier Q of 12–16 is obtained and a reasonable operating range exists for realistic pumping speeds and particle throughput at a peak divertor power load controlled to remain below 10 MW m−2. Fuelling of the plasma must be predominantly direct core fuelling, and the resulting required core-fuelling rates are realistic. Increased pumping speed and particle throughput are beneficial for maximizing Q. The relaxation to these stationary conditions is very slow, and transient values of fusion multiplier are appreciably higher.

Modelling of ITER improved H-mode operation with the integrated core pedestal SOL model

The hypothesis that improved H-modes result from reduction of transport where low-order rational surfaces are sparse is investigated with the integrated core pedestal SOL model. A function which expresses this sparseness is defined and a strength of reduction is determined which reproduces the improvement in confinement observed in Asdex-UG. The same dependence then agrees approximately with JET results. In application to ITER, the improved confinement gives improved fusion performance only if additional neoclassical impurity accumulation can be reduced or eliminated.