"Measurement and Modelling of Heat Fluxes Received by a Surface in A Magnetized RF Plasma"

"Excessive heating of the RF electrode/antenna due to high heat flux has detrimental impacts on fusion or plasma material processing perspectives. Acceleration of ions in the rectified potential in front of the RF antenna can sputter the material and create impurities inside the plasma. Heating due to electrons can raise the surface temperature and melt the material, eventually reducing the power coupling efficacy of the antenna. Since ion cyclotron resonance heating (ICRH) is one of the auxiliary heating mechanisms in modern fusion reactors and a new system is being developed based on capacitive coupling discharge for first mirror cleaning in tokamaks, investigations of particle flux/heat flux to the antenna/electrode surface in a magnetized RF environment has supreme importance. The presented thesis attempts to understand factors affecting heat flux by performing an experimental exercise and benchmarking the same with simple analytical/theoretical models. Experiments are performed in the ALINE (A LINEar) Experimental device with three electrodes using two RF power coupling mechanisms (Direct and capacitive coupling).  Sputtering experiments are performed using RF electrodes with a grounded copper wall. RF compensated Langmuir probe measurements revealed that the in-homogeneous sputtering pattern is due to the non-uniform distribution of the plasma density around the RF electrode caused by the drift and hot electron beams due to stochastic heating at the surface of the RF sheaths. This can also lead to non-uniform heating of the RF electrode. The heating of the RF electrode is measured using an IR camera, and heat flux is calculated using the code TEDDY for the one-faced tungsten and pure tungsten electrodes. In CCP mode, probe measurements near the one-faced RF electrode show positive bias and reversal of the electric field in front of the RF electrode at high magnetic fields and low pressures (0.6 Pa, 0.1 T). Higher heating of the RF electrode is observed when the bias is positive, meaning the positive bias can reduce the sputtering of the RF electrode by pushing the positive ions back into the plasma, but not the heating. Experiments with the tungsten electrode showed higher heating of the RF electrode in direct coupling than in capacitive coupling. Higher heat flux and normalized heat flux (normalization with density) are measured for direct coupling at 0° tilt angle than the grazing angle (5°)."