Chapter 8: Plasma operation and control

摘要

Wall conditioning of fusion devices involves removal of desorbable hydrogen isotopes and impurities from interior device surfaces to permit reliable plasma operation. Techniques used in present devices include baking, metal film gettering, deposition of thin films of low-Z material, pulse discharge cleaning, glow discharge cleaning, radio frequency discharge cleaning, and in situ limiter and divertor pumping. Although wall conditioning techniques have become increasingly sophisticated, a reactor scale facility will involve significant new challenges, including the development of techniques applicable in the presence of a magnetic field and of methods for efficient removal of tritium incorporated into co-deposited layers on plasma facing components and their support structures. The current status of various approaches is reviewed, and the implications for reactor scale devices are summarized. Creation and magnetic control of shaped and vertically unstable elongated plasmas have been mastered in many present tokamaks. The physics of equilibrium control for reactor scale plasmas will rely on the same principles, but will face additional challenges, exemplified by the ITER/FDR design. The absolute positioning of outermost flux surface and divertor strike points will have to be precise and reliable in view of the high heat fluxes at the separatrix. Long pulses will require minimal control actions, to reduce accumulation of AC losses in superconducting PF and TF coils. TO this end, more complex feedback controllers are envisaged, and the experimental validation of the plasma equilibrium response models on which such controllers are designed is encouraging. Present simulation codes provide an adequate platform on which equilibrium response techniques can be validated. Burning plasmas require kinetic control in addition to traditional magnetic shape and position control. Kinetic control refers to measures controlling density, rotation and temperature in the plasma core as well as in plasma periphery and divertor. The planned diagnostics (Chapter 7) serve as sensors for kinetic control, while gas and pellet fuelling, auxiliary power and angular momentum input, impurity injection, and non-inductive current drive constitute the control actuators. For example, in an ignited plasma, core density controls fusion power output. Kinetic control algorithms vary according to the plasma state, e.g. H- or L-mode. Generally, present facilities have demonstrated the kinetic control methods required for a reactor scale device. Plasma initiation - breakdown, burnthrough and initial current ramp - in reactor scale tokamaks will not involve physics differing from that found in present day devices. For ITER, the induced electric field in the chamber will be ～0.3 V·m~(-1) - comparable to that required by breakdown theory but somewhat smaller than in present devices. Thus, a start-up 3 MW electron cyclotron heating system will be employed to assure burnthrough. Simulations show that plasma current ramp up and termination in a reactor scale device can follow procedures developed to avoid disruption in present devices. In particular, simulations remain in the stable area of the l-i-q plane. For design purposes, the resistive V.s consumed during initiation is found, by experiments, to follow the Ejima expression, 0.45μ0 RI_p. Advanced tokamak control has two distinct goals. First, control of density, auxiliary power, and inductive current ramping to attain reverse shear q profiles and internal transport barriers, which persist until dissipated by magnetic flux diffusion. Such internal transport barriers can lead to transient ignition. Second, combined use poloidal field shape control with non- inductive current drive and NBI angular momentum injection to create and control steady state, high bootstrap fraction, reverse shear discharges. Active n = 1 magnetic feedback and/or driven rotation will be required to suppress resistive wall modes for steady state pla

机译：聚变装置的壁调节涉及从装置内部表面除去可吸收的氢同位素和杂质，以实现可靠的等离子体操作。当前装置中使用的技术包括烘烤，金属膜吸气，低Z材料薄膜沉积，脉冲放电清洁，辉光放电清洁，射频放电清洁以及原位限制器和分流器泵浦。尽管壁调节技术变得越来越复杂，但反应堆规模的设施将面临重大的新挑战，包括开发适用于存在磁场的技术以及有效去除掺入面对等离子体的组件上共沉积层中的of的方法。及其支持结构。审查了各种方法的现状，并总结了对反应堆规模装置的影响。在许多目前的托卡马克中已经掌握了成形和垂直不稳定的细长等离子体的产生和磁控制。反应堆规模等离子的平衡控制物理原理将基于相同的原理，但将面临其他挑战，例如ITER / FDR设计就是例证。考虑到分离线处的高热通量，最外侧通量表面和偏滤器撞击点的绝对位置必须精确可靠。长脉冲将需要最少的控制动作，以减少超导PF和TF线圈中交流损耗的累积。为此，设想了更复杂的反馈控制器，并且在其上设计了等离子体平衡响应模型的实验验证令人鼓舞。当前的仿真代码提供了一个可以在其上验证平衡响应技术的适当平台。除了传统的磁性形状和位置控制外，燃烧等离子体还需要动力学控制。动力学控制是指控制等离子体芯以及等离子体外围和偏滤器中的密度，旋转和温度的措施。计划中的诊断程序（第7章）用作动力学控制的传感器，而气体和颗粒燃料，辅助动力和角动量输入，杂质注入和非感应电流驱动则构成控制执行器。例如，在点燃的等离子体中，芯密度控制聚变功率输出。动力学控制算法根据等离子状态而变化，例如。 H或L模式。通常，现有设施已经证明了反应器规模装置所需的动力学控制方法。反应堆规模托卡马克中的等离子体引发-击穿，烧穿和初始电流上升-不会涉及与当今设备中发现的物理不同的物理现象。对于ITER，腔室中的感应电场将为〜0.3 V·m〜（-1）-与击穿理论所要求的相当，但比目前的器件要小。因此，将采用启动的3 MW电子回旋加速器加热系统来确保烧穿。仿真表明，反应堆规模设备中的等离子电流斜升和终止可以遵循为避免当前设备中断而开发的程序。特别地，模拟保留在l-i-q平面的稳定区域中。出于设计目的，通过实验发现在引发过程中消耗的电阻V.s遵循Ejima表达式0.45μ0RI_p。先进的托卡马克控制有两个不同的目标。首先，控制密度，辅助功率和感应电流的斜率，以获得反向剪切q分布和内部传输势垒，这些势垒一直持续到磁通量扩散消散为止。此类内部运输壁垒可能导致短暂着火。第二，结合使用极向场形状控制与非感应电流驱动和NBI角动量注入，以创建和控制稳态，高自举率，反向剪切放电。需要有效的n = 1磁反馈和/或驱动旋转来抑制稳态pla的电阻壁模式

Chapter 8: Plasma operation and control

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