Description
In order to characterise the response to gas-puff fuelling of ITER plasma and inform the initial development of the density control system, a series of fully integrated core-SOL simulations has been performed with the COCONUT suit of codes (JETTO+EDGE2D).
The scenarios analysed are 5 MA / 2.56 T and 7.5 MA / 2.65 T hydrogen L mode plasmas with 10 MW of ECRH. Steps in gas puff rate were applied to model the plasma density response and provide the ITER team with a dataset starting from which synthetic diagnostic could be developed and an initial tuning of the density control system could be performed. In this paper we present the results and compare them with those form older fully integrated core-SOL simulations.
The main findings are that, to sustain a density corresponding to a Greenwald density fraction $f_G$ ~ 30%-40% gas puff rates in the order of 1.0-1.5×10$^{22}$ el/s are necessary and at this density the plasma is sensitive to small variations of the fuelling rate. Moreover, it was found that fuelling rates <1.0×10$^{22}$ are not sufficient to sustain the required Greenwald fraction, whereas fuelling rates >1.5×10$^{22}$ can cause the SOL to become opaque and the plasma insensitive to gas-puff fuelling.
These findings suggest that the gains of the plasma density control systems will have to be finely tuned to remain in the window where gas puff fuelling can be effective and not to incur in either underfuelling of the plasma core or overfuelling of the SOL. They also confirm that pellets will be necessary to fuel the plasma in conditions where gas puff cannot be used.