Potential loss of energetic ions including alphas and radio-frequency tail ions due to classical orbit effects and magnetohydrodynamic instabilities (MHD) are central physics issues in the design and experimental physics programme of the SPARC tokamak. The expected loss of fusion alpha power due to ripple-induced transport is computed for the SPARC tokamak design by the ASCOT and SPIRAL orbit-simulation codes, to assess the expected surface heating of plasma-facing components. We find good agreement between the ASCOT and SPIRAL simulation results not only in integrated quantities (fraction of alpha power loss) but also in the spatial, temporal and pitch-angle dependence of the losses. If the toroidal field (TF) coils are well-aligned, the SPARC edge ripple is small (0.15–0.30 %), the computed ripple-induced alpha power loss is small ( ${\sim } 0.25\,\%$ ) and the corresponding peak surface power density is acceptable ( $244\ \textrm{kW}\ \textrm {m}^{-2}$ ). However, the ripple and ripple-induced losses increase strongly if the TF coils are assumed to suffer increasing magnitudes of misalignment. Surface heat loads may become problematic if the TF coil misalignment approaches the centimetre level. Ripple-induced losses of the energetic ion tail driven by ion cyclotron range of frequency (ICRF) heating are not expected to generate significant wall or limiter heating in the nominal SPARC plasma scenario. Because the expected classical fast-ion losses are small, SPARC will be able to observe and study fast-ion redistribution due to MHD including sawteeth and Alfvén eigenmodes (AEs). SPARC's parameter space for AE physics even at moderate $Q$ is shown to reasonably overlap that of the demonstration power plant ARC (Sorbom et al., Fusion Engng Des., vol. 100, 2015, p. 378), and thus measurements of AE mode amplitude, spectrum and associated fast-ion transport in SPARC would provide relevant guidance about AE behaviour expected in ARC.

中文翻译：

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SPARC 中的快离子物理

由于经典轨道效应和磁流体动力学不稳定性 (MHD) 导致的高能离子（包括 α 离​​子和射频尾离子）的潜在损失是 SPARC 托卡马克设计和实验物理计划中的核心物理问题。由 ASCOT 和 SPIRAL 轨道模拟代码为 SPARC 托卡马克设计计算由于波纹引起的传输而导致的聚变 α 功率的预期损失，以评估面向等离子组件的预期表面加热。我们发现 ASCOT 和 SPIRAL 模拟结果之间的一致性很好，不仅在积分量（α 功率损失的分数）方面，而且在损失的空间、时间和俯仰角依赖性方面。如果环形场 (TF) 线圈对齐良好，SPARC 边缘纹波很小 (0.15–0.30 %)，计算出的纹波引起的 alpha 功率损耗很小 ( ${\sim } 0.25\,\%$ ）和相应的峰值表面功率密度是可以接受的（ $244\ \textrm{kW}\ \textrm {m}^{-2}$ ）。然而，如果假设 TF 线圈的失准幅度越来越大，则纹波和纹波引起的损耗会大大增加。如果 TF 线圈未对准接近厘米级，表面热负荷可能会成为问题。由离子回旋频率范围 (ICRF) 加热驱动的高能离子尾的纹波引起的损失预计不会在标称 SPARC 等离子体场景中产生显着的壁或限制器加热。由于预期的经典快离子损失很小，SPARC 将能够观察和研究由 MHD 引起的快离子再分布，包括锯齿和 Alfvén 本征模 (AE)。SPARC 的 AE 物理参数空间即使在中等 $Q$ 显示合理地重叠示范电厂 ARC（Sorbom等。,融合工程设计, 卷。100, 2015, p. 378），因此在 SPARC 中测量 AE 模式幅度、光谱和相关的快离子传输将为 ARC 中预期的 AE 行为提供相关指导。