Fast ion physics studies on MAST Upgrade with a neutron diagnostic

在聚变等离子体中，快离子的能量远远高于热等离子体背景。快离子是由外部辅助加热产生的，如中性束注入(NBI)和离子回旋共振加热(ICRH)，或者由聚变反应本身产生。在前一种情况下，快离子是氢同位素，能量范围从几十个凯夫到几个梅夫。除了氢同位素外，聚变反应还会产生能量在MeV范围内的阿尔法粒子。快离子在加热等离子体、维持维持聚变反应所需的高温方面发挥着重要作用，对实现燃烧的等离子体至关重要。NBI加热对电流驱动也很重要，也就是托卡马克在感应区域以外的长脉冲运行，从而实现聚变反应堆。因此，在等离子体中进行足够长的时间限制快离子，使它们能够将能量传递到背景等离子体，对于实现基于热核聚变反应的发电厂的目标至关重要。然而，快离子约束被等离子体不稳定性降低，其中一些不稳定性是由快离子本身触发的。在这种情况下，快离子与不稳定性之间的能量交换导致快离子的重新分布和损失，最终降低聚变堆的性能。此外，等离子体中快离子的损失可能导致反应堆第一壁的损坏，这对将在ITER和DEMO中产生的非常高能量的阿尔法粒子来说尤其是一个问题。MAST升级独特的能力提供了在广泛的等离子体情景中研究快离子和等离子体不稳定性之间的相互作用的机会，这在当今的其他常规托卡马克中是不可能实现的。较宽的NBI功率沉积分布和较低的磁场相结合，可以研究超AlfvéNic快离子的行为和限制特性。Mast Upgrade配备了一系列专门研究快离子的诊断设备：升级的中子相机、快速离子损失探测器、快速离子D-α监测器、紧凑的中性粒子分析仪和带电聚变产物探测器。综合起来，这些诊断将提供迄今为止对球形托卡马克中快离子限制的最详尽描述，并将使用于设计聚变反应堆运行场景的模拟代码的基准测试和开发成为可能。该项目将专注于分析和模拟最近安装的存在各种不稳定情况下的6通道中子测量，如锯齿、鱼骨、环状Alfvén本征模、长寿命模和边缘局域模，以及评估轴上和离轴NBI加热在抑制高能粒子模式的驱动和非感应驱动等离子体电流方面的作用。这主要是一个实验项目，其中包括参加CCFE的桅杆升级实验以及达勒姆大学的数据分析和建模。将使用TRANSP和NUBEAM程序进行建模，这两个程序与综合诊断模拟程序相结合，用于比较实验和模拟观测结果。

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. MAST Upgrade is equipped with a wide range of diagnostics dedicated to the study of fast ions: an upgraded neutron camera, a fast ion loss detector, a fast ion D-alpha monitor, a compact neutral particle analyzer and a charged fusion product detector. Combined, these diagnostic will provide the most exhaustive description of fast ion confinement in spherical tokamak to date and will enable the benchmarking and development of the simulations codes that are used to design fusion reactor operating scenarios extrapolating from present day devices.The project will focus on the analysis and modelling of the recently installed 6-channels neutron measurements in the presence of a wide range of instabilities such as sawteeth, fishbones, toroidal Alfvén eigenmodes, long-lived modes and edge localized modes, as well as assessing the role of on-axis and off-axis NBI heating in suppressing the drive of energetic particle modes and in driving plasma current non-inductively. This is mainly an experimental project which includes participation to experiments at MAST Upgrade at CCFE and data analysis and modelling at Durham University. Modelling will be carried out using the codes TRANSP and NUBEAM which, in combination with synthetic diagnostics simulation codes, are used to compare experimental and simulations observations.