实验研究EAST电子加热占主导的L-模等离子体中电子热输运的阈值现象

Understanding transport of different channels (heat, particles and impurities, toroidal momentum), is essential to predict and optimize future fusion reactors based on magnetic confinement. Electron heat transport is of particularly importance because of the dominant electron heating by the fusion-generated alpha particles in ITER and future reactors. The theory of heat transport indicates that electron heat transport may be driven by turbulence excited by TEM and/or ITG modes and/or by ETG modes. These modes have in common to be unstable above a threshold in normalized temperature gradient: Transport driven by an instability is zero below the corresponding threshold and increases above it with increasing gradient. While the ion thermal transport is now well understood, the electron thermal transport is relatively less understood..The Experimental Advanced Superconducting Tokamak (EAST) is the first full superconducting tokamak with a noncircular cross-section vacuum vessel around the world. A scientific research platform has been established based on comprehensive diagnostics and auxiliary heating systems which have been commissioned in the past few years or will be implemented soon, and it lays a foundation for plasma physics studies. The experimental study on the relationship between the electron heat diffusivity and the normalized electron temperature gradient R/LTe in electron.heating dominated L-mode plasmas on EAST, is proposed. Diagnostic based on electron cyclotron emission (ECE) measurements is an ideal tool for the electron heat transport study, since it provides the information of the local electron temperature evolution with a fairly good spatial and temporal resolution. Presently, there are 4 ECE measurement systems on EAST: a 32-channel heterodyne radiometer, a 16-channel heterodyne radiometer, a Michelson interferometer and a 20-channel grating polychromator. The ECRH power modulation method, will be employed to obtain the perturbative electron heat diffusivity coefficients, and to change the normalized eletron temperature graident R/LTe via off-axis electron heating.

电子热输运是聚变研究的关键性物理问题；对电子热输运机制的研究，可以指导未来的聚变装置自持燃烧运行模式的探索。目前的理论预言等离子体芯部的电子热输运主要是由捕获电子模(TEM)，离子温度梯度模(ITG)和电子温度梯度模(ETG)驱动的，且它们都存在归一化温度梯度的阈值。但目前对这几种不稳定性的特性的相关实验研究还很少，不同装置上的独立研究对理解和验证现有理论有着重要的意义。.经过几年的发展，EAST 上已经建立了比较完备的诊断和加热手段，已经可以为各种物理研究提供实验平台。申请人在本申请项目中，提出了结合EAST 上的高性能电子回旋辐射诊断和即将建成的ECRH（电子回旋共振加热）辅助加热；用ECRH 功率调制的方法，测量电子热扩散系数；同时通过ECRH 离轴加热改变R/LTe,研究电子加热占主导的L-模等离子体条件下电子热扩散系数与R/LTe 的关系；研究电子热输运的阈值现象。

电子热输运是聚变研究的关键性物理问题；对电子热输运机制的研究，可以指导未来的聚变装置自持燃烧运行模式的探索。目前的理论预言等离子体芯部的电子热输运主要是由捕获电子模 (TEM)，离子温度梯度模(ITG)和电子温度梯度模(ETG)驱动的，且它们都存在归一化温度梯度的阈值。但目前对这几种不稳定性的特性的相关实验研究还很少，不同装置上的独立研究对理解和验证现有理论有着重要的意义。.本项目完成了用于电子热输运的关键诊断——电子回旋辐射诊断的完善，包括：(i)扩展了测量系统的径向覆盖范围，降低了相邻测量位置的间距，升级后的外差系统可以适用于EAST纵场电流大于7.5kA的放电；(ii)建立了基于高温黑体源的原位强度绝对标定系统，掌握了微弱信号探测技术，并在EAST上首次成功实施了电子回旋辐射诊断的强度绝对标定。在诊断工作圆满完成的前提下，开展了ECRH功率调制实验，分别利用功率平衡方法和扰动方法得到了电子热扩散系数；研究了不同放电参数下的电子热扩散系数的特征。这些工作为在EAST上深入开展电子热输运研究打下了坚实的基础。.基于已经完成的工作，项目组成员已发表SCI论文5篇，另有一篇论文在投(Electron Heat Transport Study by Using ECRH Power Modulation in the EAST Tokamak)。申请国家发明专利两项。