Edge localised mode-like instability driven plasma edge burst study in the TJ-II Stellarator

In this paper we study the edge plasma and recycling dynamics during edge localised mode (ELM)-like instabilities in the TJ-II Stellarator. The instabilities generate what we call edge bursts (EB): the partial loss of particles and heat from a confined plasma region inside the Separatrix towards the plasma periphery and walls. It is shown that the phenomenology in the plasma edge is similar to the crash of ELMs. The plasma density profile becomes flatter and the temperature is increased by a factor of two at the edge during the crash that lasts some hundred microseconds. This is measured with the spectroscopic He I ratio technique using a highspeed spectroscopic camera system that allows the 2D imaging of n(e) and T-e. The knowledge of these parameters is used to interpret the H-alpha-emission during the recycling process. The goal is to understand how the particle and heat expulsion changes the edge plasma and the subsequent wall recycling response during and after the crash as well as the recovery phase of the plasma profiles. We derive from the analysis that the EB-crash produces significant hydrogen desorption attributed to surface heating, this process lasting longer than the instability itself. The contribution to the fuelling of this dynamic process is significant and must influence the recovery of the plasma profiles. Finally, we also look on the turbulent filamentary plasma structure during the ELM-like events. The characteristic turbulent pattern of the plasma edge (blobs) is significantly stronger during the instabilities than in the quiet periods in-between.