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首页> 外文会议>International Conference on Advanced Diagnostics for Magnetic and Inertial Fusion, Sep 3-7, 2001, Varenna Italy >FAST ION LOSS DIAGNOSTIC FOR THE WENDELSTEIN 7-X STELLARATOR
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FAST ION LOSS DIAGNOSTIC FOR THE WENDELSTEIN 7-X STELLARATOR

机译：WENDELSTEIN 7-X STELLARATOR的快速离子损失诊断

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摘要

An important issue of future reactor-like fusion devices is the confinement of fusion born alpha particles required for a burning plasma. A fast ion loss diagnostic, like proposed here, could be an adequate diagnostic tool to study the fast ion confinement properties of W7-X and, thus, could confirm at least one of the 7 optimization criteria given in Ref. The objectives of such measurements can be classified into 3 categories: (ⅰ) The confinement of fusion alphas directly depends on the magnetic field structure. Generally, the loss cone of the configuration should be as narrow as possible to avoid first orbit losses, otherwise alpha particle and auxiliary heating efficiency may be deteriorated. Although alpha particle confinement is expected to be sufficient in a HELIAS reactor (R = 20 m, a = 2 m), alpha particle confinement studies should be performed in W7-X (R = 5 m, a = 0.5 m) with 60 keV protons as a substitute. First orbit losses of ions injected by neutral beam heating (NBI) are caused in cases where the particle sources reside close to the lost/confined boundary in phase space or even are located inside the loss cone. Ion cyclotron heating (ICH) drives mainly perpendicular momentum of the ions, thus a transport into the loss cone is likely, (ⅱ) Even in magnetic fields with perfect ion confinement losses may occur when ions are affected by fluctuating electric and magnetic fields. Shear Alfven modes as an example are accompanied by poloidal and radial electric field oscillations that change the ion orbit trajectory, provided that particle and wave propagation are roughly in resonance. In this case, a subensemble of fast ions suffer from radial diffusion. Such modes can be excited by inverse Landau-damping with either fast ions of auxiliary heating or fusion alphas. In contrast to this, fusion alphas may be expelled from the plasma by fast ion driven modes, which could endanger reactor operation. However, if specific modes are excited in a controlled way, ion-wave interaction may be beneficial for helium ash removal. In this case, fusion alphas have to pass a resonance layer at a certain velocity during their slowdown at which enhanced radial transport is induced, (ⅲ) Knowledge about fast ion losses is also essential to improve plasma performance. Strong fluxes of suprathermal ions are an additional drive mechanism for radial electric fields. Consequently, the lost/confined boundary may changes in a positive way and plasma performance can be improved, at least for thermal ions. The fast ion loss diagnostic provides experimental evidence whether such a drive is caused by fast or thermal ions. Another important issue is the influence of impurities. Enhanced impurity concentration increases pitch angle scattering of fast ions. This leads to an enhanced diffusion in phase space, and subsequently, to increased ion loss rates. Strong ion outward fluxes are not desirable, because they cause strong local heat loads on the first wall, which are not acceptable in a steady state plasma operation. Additionally, new impurity sources are generated by sputtering or by ion impact induced desorption. Thereby, the impurity concentration is. increased and pitch angle scattering gets further enhanced leading to a non-stationary behavior in all plasma parameter.
机译：未来类似反应堆的聚变设备的一个重要问题是限制燃烧等离子体所需的聚变中生的α粒子。像这里建议的那样，快速离子损失诊断可能是研究W7-X的快速离子限制特性的适当诊断工具，因此可以确认参考文献7中给出的7个优化标准中的至少一个。此类测量的目标可分为3类：（ⅰ）融合alpha的限制直接取决于磁场结构。通常，该构造的损失锥应尽可能窄以避免第一轨道损失，否则α粒子和辅助加热效率可能会降低。尽管预计在HELIAS反应堆中将α粒子限制为足够（R = 20 m，a = 2 m），但应在60 keV的W7-X（R = 5 m，a = 0.5 m）中进行α粒子限制研究。质子作为替代。在粒子源位于相空间中丢失/受限边界附近或什至位于损耗锥内部的情况下，会导致中性束加热（NBI）注入的离子的第一轨道损失。离子回旋加速器（ICH）主要驱动离子的垂直动量，因此有可能传输到损耗锥中。（Even）即使在具有理想离子约束的磁场中，当离子受波动的电场和磁场影响时，也会发生损耗。以剪切阿尔夫文模式为例，如果粒子和波的传播大致共振，则伴随着极性和径向电场的振荡就会改变离子轨道的轨迹。在这种情况下，快离子的一个整体遭受径向扩散。可以通过辅助加热的快速离子或聚变α的逆Landau阻尼来激发这种模式。与此相反，可以通过快速离子驱动模式从等离子体中排出聚变α，这可能危及反应堆的运行。但是，如果以受控方式激发特定模式，则离子波相互作用可能会有利于去除氦灰。在这种情况下，聚变α必须在其减速过程中以一定的速度通过共振层，从而引起增强的径向传输。（ⅲ）关于快速离子损失的知识对于改善等离子体性能也是必不可少的。超热离子的强通量是径向电场的另一种驱动机制。因此，至少对于热离子而言，丢失/受限制的边界可能会发生正向变化，并且等离子体性能会得到改善。快速离子损失诊断为这种驱动是由快速离子还是由热离子引起提供了实验证据。另一个重要问题是杂质的影响。增强的杂质浓度会增加快速离子的螺距角散射。这导致相空间中扩散的增强，并随后导致离子损失率的提高。强的离子向外通量是不理想的，因为它们会在第一壁上引起强烈的局部热负荷，这在稳态等离子体操作中是不可接受的。另外，通过溅射或离子碰撞诱导的解吸产生新的杂质源。由此，杂质浓度为。增大并且桨距角散射得到进一步增强，从而导致所有等离子体参数的非平稳行为。

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