In recent experiments, a local gas puff was found to be an effective way to tailor the scrape-off layer (SOL) density and improve the ion cyclotron range of frequency (ICRF) power coupling in tokamaks. In order to quantitatively reproduce these experiments, to understand the corresponding physics and to optimize the gas valve positions and rates, simulations were carried out with the 3D edge plasma transport code EMC3-EIRENE in ASDEX Upgrade. An inter-ELM phase of an H-mode discharge with a moderate gas puff rate (1.2 × 1022 electrons s−1) is used in our simulations. We simulated cases with gas puff in the lower divertor, the outer mid-plane and the top of the machine while keeping other conditions the same. Compared with the lower divertor gas puff, the outer mid-plane gas puff can increase the local density in front of the antennas most effectively, while a toroidally uniform but significantly smaller enhancement is found for the top gas puff. Good agreement between our simulations and experiments is obtained. With further simulations, the mechanisms of SOL density tailoring via local gas puffing and the strategies of gas puff optimization are discussed in the paper.
Effect of a deuterium gas puff on the edge plasma in NSTX