Overview of new MAST physics in anticipation of first results from MAST Upgrade
Overview of new MAST physics in anticipation of first results from MAST Upgrade
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DOI：
10.1088/1741-4326/ab121c
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发表时间：
2019-11-01
期刊：
影响因子：
3.3
通讯作者：
Wilson, H. R.
中科院分区：
文献类型：
--
作者：
Harrison, J. R.;Akers, R. J.;Wilson, H. R.
兆安培球形托卡马克（MAST）是一种低长径比装置（R/a = 0.85/0.65，近似于1.3），其极向截面与其它中型托卡马克相似。物理方案集中于解决关键的物理问题的操作ITER，设计演示和未来的球形托卡马克通过利用高分辨率诊断测量密切结合理论和建模，以显着推进我们的理解。有利于更高的功率，更低的碰撞设备的能量约束时间的经验缩放是一致的电子尺度湍流的回旋动力学模型。在上下对称的等离子体中，用束发射光谱和回旋动力学模型测量离子尺度湍流，发现湍流的对称性被流动剪切破坏。在非线性稳定性阈值附近，剪切使密度脉动相关函数发生倾斜，使脉动幅度分布发生偏斜。快粒子物理研究的结果包括观察到锯齿以同等程度重新分配从中性束注入器注入的通过和捕获的快粒子，这表明m = 1微扰和快离子轨道之间的共振可能在快速离子中发挥主导作用离子传输。从中子相机和带电聚变产物探测器测量的D-D聚变产物比TRANSP/NUBEAM的预测低40%，突出了指导中心近似可能存在的缺陷。在共振磁扰动（RMP）的存在下，快速离子损失的建模可以重现在实验中观察到的趋势时，等离子体响应和电荷交换损失占。在合并压缩启动期间用中性粒子分析仪进行的测量表明离子和电子的加速。在等离子体边缘的运输已得到改善，通过往复式探头测量，其特点是在欧姆L-模式等离子体和粒子在细胞建模的边缘测地线声学模式，提高了解释等离子体电位估计从圆珠笔探头。RMPs的应用导致了L模和H模中粒子约束的减少和芯电离源的增加。I型ELMs后次级细丝的喷射与X点附近表面的相互作用有关。对刮除层中成对细丝之间相互作用的模拟表明，这会导致它们的速度发生适度变化，并且在大多数情况下可以被视为独立移动。基于非相互作用细丝叠加的刮削层轮廓形成的随机模型与测量的时间平均轮廓吻合得很好。偏滤器中的输运已经通过快速照相机成像得到改善，表明在X点附近存在一个没有灯丝的静止区域，从分界线延伸到psi（n），类似于1.02。偏滤器中湍流输运的模拟表明，偏滤器腿之间的曲率矢量的角度强烈影响运输到私人通量区域通过交换机制。相干成像测量显示，由于气体膨胀增加了气体电离的场线上的压力，杂质逆流流动。MAST升级是在原有MAST装置的基础上进行的，它大大提高了与Super-X偏滤器一起运行的能力，以测试偏滤器延伸腿的概念。SOLPS-ITER模型预测，与传统配置相比，在Super-X中，就上游密度而言，脱离阈值将降低2倍以上，并且辐射前沿运动在到达X点之前被动稳定。一维流体模型揭示了动量和动力损失机制在控制拆离开始和演化中的关键作用。分析模型表明，长腿放置在大的主半径，或相当于低B在目标相比，X点弧更容易受到外部控制。随着MAST升级实验预计在2019年进行，已经对固有误差场的来源进行了彻底的表征，并制定了缓解策略。
The mega amp spherical tokamak (MAST) was a low aspect ratio device (R/a = 0.85/0.65 similar to 1.3) with similar poloidal cross-section to other medium-size tokamaks. The physics programme concentrates on addressing key physics issues for the operation of ITER, design of DEMO and future spherical tokamaks by utilising high resolution diagnostic measurements closely coupled with theory and modelling to significantly advance our understanding. An empirical scaling of the energy confinement time that favours higher power, lower collisionality devices is consistent with gyrokinetic modelling of electron scale turbulence. Measurements of ion scale turbulence with beam emission spectroscopy and gyrokinetic modelling in up-down symmetric plasmas find that the symmetry of the turbulence is broken by flow shear. Near the non-linear stability threshold, flow shear tilts the density fluctuation correlation function and skews the fluctuation amplitude distribution. Results from fast particle physics studies include the observation that sawteeth are found to redistribute passing and trapped fast particles injected from neutral beam injectors in equal measure, suggesting that resonances between the m = 1 perturbation and the fast ion orbits may be playing a dominant role in the fast ion transport. Measured D-D fusion products from a neutron camera and a charged fusion product detector are 40% lower than predictions from TRANSP/NUBEAM, highlighting possible deficiencies in the guiding centre approximation. Modelling of fast ion losses in the presence of resonant magnetic perturbations (RMPs) can reproduce trends observed in experiments when the plasma response and charge-exchange losses are accounted for. Measurements with a neutral particle analyser during merging-compression start-up indicate the acceleration of ions and electrons. Transport at the plasma edge has been improved through reciprocating probe measurements that have characterised a geodesic acoustic mode at the edge of an ohmic L-mode plasma and particle-in-cell modelling has improved the interpretation of plasma potential estimates from ball-pen probes. The application of RMPs leads to a reduction in particle confinement in L-mode and H-mode and an increase in the core ionization source.The ejection of secondary filaments following type-I ELMs correlates with interactions with surfaces near the X-point. Simulations of the interaction between pairs of filaments in the scrape-off layer suggest this results in modest changes to their velocity, and in most cases can be treated as moving independently. A stochastic model of scrape-off layer profile formation based on the superposition of non-interacting filaments is in good agreement with measured time-average profiles. Transport in the divertor has been improved through fast camera imaging, indicating the presence of a quiescent region devoid of filament near the X-point, extending from the separatrix to psi(n) similar to 1.02. Simulations of turbulent transport in the divertor show that the angle between the divertor leg on the curvature vector strongly influences transport into the private flux region via the interchange mechanism. Coherence imaging measurements show counter-streaming flows of impurities due to gas puffing increasing the pressure on field lines where the gas is ionised. MAST Upgrade is based on the original MAST device, with substantially improved capabilities to operate with a Super-X divertor to test extended divertor leg concepts. SOLPS-ITER modelling predicts the detachment threshold will be reduced by more than a factor of 2, in terms of upstream density, in the Super-X compared with a conventional configuration and that the radiation front movement is passively stabilised before it reaches the X-point. 1D fluid modelling reveals the key role of momentum and power loss mechanisms in governing detachment onset and evolution. Analytic modelling indicates that long legs placed at large major radius, or equivalently low B at the target compared with the X-point arc more amenable to external control. With MAST Upgrade experiments expected in 2019, a thorough characterisation of the sources of the intrinsic error field has been carried out and a mitigation strategy developed.