Investigations of high speed neutral particle injection into KSTAR plasmas

This thesis is devoted to the investigation of one of the fuelling methods, namely the supersonic molecular beam injection (SMBI). A maintenance of a high density level and a compensation of the particle losses, caused by the radial transport, are required to fulfil the ignition condition. Therefore, refuelling of plasma while a tokamak operates is essential for the realisation of a sustainable fusion reaction. The overview of the experiments reveals the benefits of SMBI compared to the traditional gas puff injection (GP). In case of SMBI the plasma response on the injection is faster, penetration depth of neutrals is deeper and consequently the fuelling efficiency is higher. In addition, the suppression of edge localized modes (ELMs) and large amplitude fluctuations was observed in experiments with SMBI, but no consistent theory exists to explain this effect.
Calculations of the injection parameters of supersonic molecular beam corresponding to SMBI system on Korea Superconducting Tokamak Advanced Research (KSTAR) are performed for two operation regimes: with the working gas at the room temperature and the gas cooled under 105 K. The influence of SMBI on plasma depends on the operation regime is analysed based on the KSTAR experimental data.
The main focus of this thesis is the numerical investigation of the interactions of fusion plasma with the high speed molecular beam. Dynamical interactions of the molecules and atoms are implemented in a drift-fluid model, which describes the dynamics of the plasma at the outer mid-plane of a tokamak. The increase of the plasma density, decrease of the temperature and reduction of the fluctuation level of the plasma density fluctuations which were observed in experiments with SMBI, are reproduced in the numerical simulations. The dependency of those effects, as well as the fuelling efficiency, on the beam parameters is investigated and discussed in this work. The qualitative comparison of the numerical results with results of other models, with KSTAR experimental data and earlier experimental observations on other tokamaks is presented in this thesis.