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

在聚变等离子体中，快离子的能量远高于热等离子体背景。快速离子是通过外部辅助加热，如中性束注入（NBI）和离子回旋共振加热（ICRH）或聚变反应本身产生的。在前一种情况下，快离子是氢的同位素，其能量范围从几十千伏到几兆电子伏。除了氢的同位素外，聚变反应还会产生能量在MeV范围内的α粒子。快离子在加热等离子体、维持聚变反应所需的高温以及实现等离子体燃烧方面发挥着重要作用。NBI加热对于电流驱动也很重要，即对于托卡马克在感应区以外的长脉冲运行，从而实现聚变反应堆。因此，将快速离子在等离子体中限制足够长的时间，使它们能够将能量转移到背景等离子体中，对于实现基于热核融合反应的发电厂的目标至关重要。然而，等离子体的不稳定性降低了快离子约束，其中一些是由快离子本身引发的。在这种情况下，快离子之间的能量交换和不稳定性导致了快离子的重新分布和损失，最终降低了聚变反应堆的性能。此外，等离子体中快离子的损失可能会导致反应堆第一壁的损坏，这对ITER和DEMO中将产生的高能α粒子来说尤其严重。MAST Upgrade的独特功能提供了在广泛的等离子体场景中研究快速离子和等离子体不稳定性之间相互作用的机会，这是目前其他传统托卡马克无法实现的。更宽的NBI功率沉积剖面和低磁场的结合，允许在ITER和聚变反应堆相关的大范围快离子物理场景中研究超alfv<s:1>快离子的行为和约束特性。快速离子与MHD不稳定性之间相互作用的建模依赖于等离子体平衡扰动在空间结构和时间演化方面的准确描述。数值编码用于计算微扰特征函数，但其实验验证仅限于使用拾取线圈在等离子体区域外测量磁场通量。没有摄动空间轮廓和幅度的直接测量。MAST Upgrade配备了广泛的诊断，专门用于研究丢失的快速离子（快速离子损失探测器，快速离子d - α监测器）和受限的快速离子（准直中子通量监测器阵列，快速离子d - α监测器和紧凑型中性粒子分析仪），从而提供大量的实验测量，可以对模拟预测进行测试。该项目的目的是开发两种合成诊断，第一个旨在模拟MAST升级等离子体的SXR发射，第二个旨在模拟MAST升级成像中性粒子分析仪诊断的预期测量。软x射线发射可以潜在地用于推断在非常快的时间尺度（亚毫秒）上影响快速离子的磁扰动的结构，这与它们的时间演变相当，而INPA将提供关于它们的再分布和损失的额外信息。MAST升级配备了一系列SXR探测器，可以很好地覆盖整个等离子体区域。SXR合成诊断将基于SXR发射的正演模拟及其对实验测量的验证，目的是在广泛的操作场景中约束影响快离子约束的等离子体扰动的空间分布和幅度。反演方法(如：tomo

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