Off-axis neutron camera for MAST Upgrade

用于 MAST 升级的离轴中子相机

• 批准号: 2910468
• 金额: --
• 依托单位: Durham University
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2910468
• 关键词: Off; axis; neutron; camera; MAST

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 is equipped with an on-axis and an off-axis neutral beam injector. The on-axis NBI, injects fast ions on MAST Upgrade equatorial plane in tangential direction resulting in fast ion deposition profile that is peak in the plasma core. The large fast ion pressure gradient resulting from the on-axis NBI system is known to drive plasma instabilities that reduce the fast ion confinement and thus the plasma performances. The off-axis NBI is also injected tangentially but approximately 60 cm above the equatorial plane, thus broadening the fast ion deposition profile and reducing the fast ion pressure gradient suppressing the drive of these plasma instabilities. Proof-of-concept of this was demonstrated on MAST and confirmed by preliminary results on MAST Upgrade.Among the wide range of diagnostics dedicated to the study of fast ions, neutron diagnostics provide information on the confined fast ions thanks to the fact that on MAST Upgrade, neutron emission is dominated by beam-thermal nuclear reactions. Neutron emission on MAST Upgrade is measured by a recently installed 6-channels collimated neutron flux monitor looking in tangential direction on the equatorial axis.The project will focus on the design, development, construction, installation and commissioning of a multi-channel, collimated neutron flux monitor dedicated to the measurement of the neutron emissivity off-axis, where the fast ions are being deposited by the off-axis NBI. Analysis of initial observations are expected to be part of this project.

在聚变等离子体中，快离子的能量远高于热等离子体背景。快离子是通过中性束注入（NBI）和离子回旋共振加热（IC​​RH）等外部辅助加热或聚变反应本身产生的。在前一种情况下，快离子是氢同位素，能量范围为数十 keV 至几 MeV。聚变反应除了产生氢同位素外，还产生能量在 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方面发挥着重要作用，对于实现燃烧等离子体至关重要。 NBI 加热对于电流驱动也很重要，即托卡马克超出感应范围的长脉冲操作，从而实现聚变反应堆。因此，将快离子限制在等离子体中足够长的时间，以便它们能够将能量转移到背景等离子体，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，快离子限制会因等离子体不稳定性而降低，其中一些不稳定性是由快离子本身触发的。在这种情况下，快离子之间的能量交换和不稳定性导致快离子的重新分布和损失，最终降低聚变反应堆的性能。此外，等离子体中快离子的损失可能会导致反应堆第一壁损坏，这对于 ITER 和 DEMO 中产生的高能阿尔法粒子来说尤其如此。MAST Upgrade 配备了同轴和离轴中性束注入器。轴上 NBI 在 MAST Upgrade 赤道面上沿切线方向注入快离子，从而产生在等离子体核心达到峰值的快离子沉积剖面。众所周知，轴上 NBI 系统产生的大快离子压力梯度会导致等离子体不稳定性，从而降低快离子限制，从而降低等离子体性能。离轴 NBI 也切向注入，但距赤道面约 60 cm，从而拓宽了快离子沉积剖面并降低了快离子压力梯度，从而抑制了这些等离子体不稳定性的驱动。 MAST 上对此进行了概念验证，并通过 MAST Upgrade 的初步结果得到证实。在致力于快离子研究的各种诊断中，中子诊断提供了有关受限快离子的信息，这要归功于在 MAST Upgrade 上，中子发射主要由束流热核反应主导。 MAST Upgrade 上的中子发射是通过最近安装的 6 通道准直中子通量监测仪从赤道轴切线方向观察来测量的。该项目将重点关注多通道准直中子通量监测仪的设计、开发、建造、安装和调试，该监测仪专用于测量离轴中子发射率，其中快离子由离轴 NBI 沉积。初步观察结果的分析预计将成为该项目的一部分。