Development of synthetic diagnostics for diagnosing the interaction between fast ions and MHD instabilities in MAST Upgrade

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In fusion plasmas, fast ions have energies much higher than the thermal plasma background. Fast ions are generated by external auxiliary heating such as Neutral Beam Injection (NBI) and Ion Cyclotron Resonance Heating(ICRH) or by the fusion reactions themselves. In the former cases, fast ions are hydrogen isotopes with energies in the range from tens of keVs up to a few MeVs. Fusion reactions produce, in addition to hydrogen isotopes, alpha particles with energies in the MeV range. Fast ions play an important role in heating the plasma, maintaining the high temperatures necessary to sustain the fusion reactions and crucial in achieving a burning plasma. NBI heating is also important for current drive, that is for long pulse operation of tokamaks beyond the inductive regime and therefore for the realization of a fusion reactor. Confining fast ions in the plasma for time long enough so that they can transfer their energy to the background plasma is therefore crucial for achieving the goal of a power plant based on thermonuclear fusion reactions. However, fast ion confinement is degraded by plasma instabilities some of which are triggered by the fast ion themselves. In this case, energy exchange between the fast ions and the instabilities result in the redistribution and loss of fast ions, ultimately reducing the performances of fusion reactors. Furthermore, the loss of fast ions in the plasma can result in the damage of the reactor first wall, an issue particularly for the very energetic alpha particles that will be produced in ITER and DEMO.MAST Upgrade unique capabilities provide the opportunity to study the interplay between fast ions and plasma instabilities in a wide range of plasma scenarios that are not achievable in other present day conventional tokamaks. The combination of broader NBI power deposition profiles and low magnetic field allows the study of the behavior and confinement properties of super-Alfvénic fast ions in a wide range of fast ion physics scenarios that are ITER and fusion reactor relevant. Modelling of the interaction between fast ions and MHD instabilities relies on the accurate description of the plasma equilibrium perturbations both in terms of their spatial structure and time evolution. Numerical codes are used to compute the perturbation eigenfunctions but their experimental verification is limited to magnetic field flux measurements outside of the plasma region using pick-up coils. No direct measurement of the perturbation spatial profile and amplitude is available. MAST Upgrade is equipped with a wide range of diagnostics dedicated to the study of lost fast ions (a fast ion loss detector, a fast ion D-alpha monitor) and of confined fast ions (a collimated neutron flux monitor array, a fast ion D-alpha monitor and a compact neutral particle analyzer) thus providing a large amount of experimental measurements against which simulation predictions can be tested.The aim of this project is the development of two synthetic diagnostics, the first one aimed at simulation the the SXR emission from MAST Upgrade plasmas and the second one aimed at modeling the expected measurements of an Imaging Neutral Particle Analyzer diagnostic for MAST Upgrade. Soft-X rays emission can be potentially used to infer the structure of the magnetic perturbations affecting the fast ions on a very fast time scale (sub millisecond) which is comparable with their time evolution while the INPA will provide additional information on their redistribution and losses. MAST Upgrade is equipped with an array of SXR detectors which provide a good coverage of the whole plasma region. Thie SXR synthetic diagnostic will ne based on the forward modelling of the SXR emission and on its validation against experimental measurements with the aim to constrain the spatial profile and amplitude of the plasma perturbation affecting the confinement of fast ions in a wide range of operating scenarios. Inversion methods (such as tomo