EAST中性束注入束功率爬升关键问题研究

The steady high power neutral beam injection is the most important plasma heating and current drive method for the magnetic confinement fusion device. High power neutral beam as the momentum and energy sources, it is easy to cause all sorts of magnetohydrodynamic instability, and even lead to plasma disruption.This project is aimed at the problem of neutral beam injection process.Through the optimization of technical means, to realize the beam power climbing during the injection process of, make up flexibility defects of the existing neutral beam injection system. The main contents of the study as following:.1）Based on analysis of optical properties of ion extraction system, optimize the matching of electrical parameters for beam extraction process, expand the operating range of the best operating window. Lay the groundwork for achieve slope climbing of the beam power, during one shot..2）Using completed diagnostic system and probe feedback system of arc power, Analyze stability of source plasma, solve the problems source plasma disruption and blackout during the process of climbing. Based on development of the technology of arc power slope climbing, slope climbing of the beam power is realized..3）Based on modulation technology of neutral beam injection, the study on matching of arc power and extraction voltage will be carried out. The step type climbing technology will be developed. Make the ion source to work under the best operating window during each modulation cycle, which will be helpful for achievement of long pulse operation. . The successful implementation of this project can effectively expand the operation window for EAST-NBI neutral beam injection system, give a full effect to the neutral beam injection system in the research of high performance of plasma.

中性束作为动量源、能量源，极易激发各类磁流体不稳定性，甚至导致等离子体破裂；另一方面，高功率的中性束注入到低性能的等离子体时，穿透损失较大，不利于高性能等离子研究的开展。由于EAST-NBI数量较少，基于中性束注入的高参数等离子体研究的多样性受到制约。针对上述问题，拟通过束功率在注入过程的爬升，弥补现有中性束注入系统的不足。主要研究内容是：1）基于离子光学特性的分析，优化参数匹配，拓展最佳运行窗口。2）开展源等离子体稳定性分析，解决爬升过程中源等离子体破裂、熄灭等问题，发展弧功率斜坡爬升技术，实现束功率的斜坡爬升。3）开展调制模式下弧功率与引出高压的匹配研究，发展弧功率与引出高压的台阶式爬升技术，使离子源在每个调制周期都工作在最佳运行窗口，实现束功率台阶爬升下的长脉冲运行。本项目的成功实施可有效拓展EAST-NBI中性束注入系统运行区间，充分发挥中性束注入系统在高性能等离子体研究中的作用。

中性束作为动量源、能量源，极易激发各类磁流体不稳定性，甚至导致等离子体破裂；另一方面，高功率的中性束注入到低性能的等离子体时，穿透损失较大，不利于高性能等离子体研究的开展。由于EAST-NBI数量较少，基于中性束注入的高参数等离子体研究的多样性受到制约。针对上述问题，本项目通过拓展中性束注入系统的窗口，优化系统控制方法和结构，发展了两种束功率爬升方法。首先，项目团队依托中性束综合测试台，对采用菱形等离子体电极结构的离子源进行了性能优化测试。实验结果显示：在第一电极采用菱形引出系统的情况下，其最佳导流系数可由2.3up提高到2.9up，其运行窗口宽度可提高约50%。其次，依托现有控制系统，发展了基于PID算法的单变量弧功率闭环控制回路，解决了弧功率在爬升过程中源等离子体破裂、熄灭等不稳定性问题，实现了弧功率闭环可调控制。然后，基于上述成果，发展并实现了依托宽运行窗口的单次束引出过程束功率爬升的控制逻辑，在束能量30kV的情况下，获得了引出束流强度由8A提高至10.4A的测试结果；发展并测试了依托调制运行模式的束功率台阶爬升控制策略和方法。最后，项目研究中取得的束流光学优化于束功率爬升控制成果应用在EAST中性束注入系统上，通过优化引出电场参数，实现了在相同电压参数下束功率提升20%的目标。本项目的开展使项目团队进一步深化了对强流热阴极离子源的认知，促进了强流热阴极离子源技术的发展。同时，项目的实施有效的拓展EAST中性束注入系统运行区间，优化了系统性能，为物理实验的开展提供了更多的选择空间。