ELM Energy Losses in Peeling Limited Pedestals in JET

Sammanfattning

Nuclear fusion is a research topic that attracts a lot of interest. If properly harnessed, it promises to be an energy source that circumvents problems that current energy sources have. As such, fusion warrants research aimed at understanding and dealing with its varied issues. Fusion is regularly recreated on earth by heating a hydrogen plasma to around a hundred million degrees Celsius. Confining this plasma requires special machines due to the extreme heat. There are multiple types of machines recreating plasma for research purposes, the most common is called tokamak. Tokamaks confine the plasma in a toroidal shape using powerful magnetic fields that prevent particles from escaping. Relevant for this work is the tokamak JET, where the treated experiment has been conducted, and ITER, which is currently under construction and meant to be the next step in fusion research. An important phenomenon are so called Edge Localized Modes (ELMs). ELMs are short bursts of energy expulsions from the plasma that results in a loss of energy and can cause damage to components facing the plasma. While not necessarily present in all operational modes ELMs are present in JET and will be present in ITER. Therefore it is very important to understand ELMs and how they are affected by certain parameters. Especially important is the dependency of ELM size on collisionality, a measurement on how much particles in the plasma interact with each other. Due to how ITER is supposed to operate it will have a very low collisionality, something that previous studies have linked with large ELM energy losses. This work investigates how parameters, plasma density, gas fueling rate, effective mass, strength of the magnetic field and collisionality affect ELMs. This work calculates the energy losses for ELMs and investigates whether they are related to certain parameters. To calculate the energy loss two methods are deployed. One method relies on measurements of the diamagnetic flux. The other utilizes measurements of temperature and density with thomson scattering, electron cyclotron emission and reflectometry. Both techniques compare the energy in the plasma before and after an ELM to deduce the energy loss. For both methods, ELMs in a time interval are grouped and their data is used to calculate a typical energy loss. The results show that the energy losses from both methods are comparable with previous measurements at similar collisionality. The methods produce comparable results although the results for singular cases are not always in agreement. Ion cyclotron resonance heating is identified as worsening the agreement. A combination of the results being too noisy and there not being enough data means that no clear trends were observed in the investigated parameters.