【作者】 叶扬；

【导师】 徐国盛；

【作者基本信息】 中国科学技术大学 ， 等离子体物理学， 2018， 博士

【摘要】 1982年ASDEX(德国)装置上第一次获得高约束(H)模式,这一发现成为了整个托卡马克研究中具有划时代意义的突破。H模约束因为其具有相对较高的能量和粒子约束水平以及良好的稳定可重复性,被选为ITER的基本参考运行模式。而边界局域模(ELM)作为H模中最重要的特征之一,由于其带来的严重热负荷问题目前并未得到很好的解决,所以对于ELM的控制方法研究一直都是国际托卡马克研究的热点问题之一。本论文主要依托于EAST全超导托卡马克装置,利用边界高时空分辨的分布及涨落测量手段,主要围绕FEAST上无ELM高性能运行模式、边界相干模式的特征以及参数空间物理开展,包括有诊断搭建和物理研究两部分。(1)在EAST上成功搭建了一径向边界热氦束发射光谱诊断,用LABVIEW语言编写了诊断喷气控制和信号采集程序,使得对边界密度、温度以及静电涨落等重要的物理量高时空分辨测量成为可能。(2)对EAST上自发产生的无ELM运行模式进行了系统的研究,并给出了各自获得参数区间。在EAST上自发产生的无ELM运行,主要分为三种类型:①低功率、高碰撞率、高再循环无ELM运行,显著特征是在进入H模之后边界Dα信号持续上涨,统计发现该运行模式的参数区间为:4.6GHz低杂波加热或者是反向中性束和电子回旋协同加热,当额外的其他加热方式如2.45GHz低杂波、离子回旋或者同向中性束注入都会打破这种无ELM运行。对于等离子体位形的要求:外gap=3.5-5.5 cm及拉长比κ=1.55-1.63等;②低功率、高碰撞率、低再循环无ELM运行,这种无ELM运行模式显著的特征之一是边界Dα信号在进入H模之后会持续下降直到ELM完全消失,需要在非常强的锂化条件或者是实时锂粉注入的条件下获得,此外这种运行还展现出了明显的密度阈值,更易在低密度下获得;③高功率、低碰撞率无ELM运行,该运行模式是EAST上所能取得的最高加热水平下的无ELM运行,但很可惜的是只是暂态的,因为缺少输运通道,所以并不能稳定维持。(3)边界等离子体中存在着相当丰富的模式,本论文较为系统的总结了 EAST上多种边界模式。主要包括有四种比较常见的模式:①静电性质的准相干模(ECM),是低碰撞率、高再循环无ELM运行中的主导模式。并且发现当边界径向电场(Er)增大的情况下,ECM会径向外移并且频谱空间展宽,成为type Ⅱ ELMs以及低再循环ELM H模的主导模式。其磁信号很弱,传播在电子逆磁漂移方向,展现出高环向模数(n～17-19)的气球模特征,研究显示其本质可能是耗散捕获电子模,强烈依赖于碰撞率和压强梯度,ECM被测量到可以带来强烈的粒子和热输运,在边界提供一条关键的输运通道,从而达到抑制ELM效果;②电磁性质的准相干模(MCM),存在参数区间几乎横跨了整个EAST H模放电,目前只在高频类-grassy ELMy H模期间消失,是高功率、低碰撞率无ELM运行条件下的主导模式。其静电信号很微弱,传播在电子逆磁漂移方向,对边界输运贡献不大,但是发现其可以明显改变热流极向沉积分布;③高频电磁相干模(HFM),传播在电子逆磁漂移方向,发现该模式在低场侧中平面附近没有明显的粒子输运,而在高场侧则产生了明显的粒子输运,猜测该模式可能产生于高场侧区域;④电磁先兆、后兆振荡,在type Ⅲ爆发间歇可以观察到一静电先兆涨落,频率在100-200kHz范围内,展现出中等环向模数特征(n～5-10),极向波长大于10cm,径向波长约为1cm。此外在临界ELM间隙(介于typeⅠ和type Ⅲ之间),可以观察到一支频率在50kHz的电磁后兆模,其传播在电子逆磁漂移方向,观察到后兆模可以明显拉长ELM下降时间。等等。(4)对EAST上出现的高频小幅度Type Ⅱ ELM也进行了研究,发现这种小ELMs的出现主要和Er增强有关,Er的增强可以抑制住台基区ECM不稳定性,将ECM峰值位置外移并且同时频率上升,频谱展宽成宽谱涨落特征(BB)。发现BB展现出阵发性特征,阵发频率和ELM频率相吻合,并且阵发频率伴随Er增强而增大,最后还观察到这种小ELM运行模式和内部输运垒以及低扭矩运行相兼容,是未来聚变实验中的一种可考虑的备选运行模式。以上的研究不仅为EAST上小、无ELM实验研究奠定了良好的基础,同时也为预研ITER条件下的ELM控制手段探索提供了重要的参考价值。更多还原

【Abstract】 The first High-confinement(H)mode was obtained on the German ASDEX installation in 1982,and this finding became an epoch-making breakthrough in the entire Tokamak research.The H-mode confinement was selected as the standard reference operating scenario for ITER,since its relatively high energy confinement and particle level,as well as good stability repeatability.One of the most important features in the H-mode operation is the edge localized mode(ELM)eruption.Because of the transient giant heat flux problem caused by ELMs has not yet been well solved,the control of ELMs is still a hot issue in the international tokamak research.This paper research relies on the EAST superconducting tokamak device,and utilizes the high spatial-temporal resolution methods for the edge profiles and fluctuations measurements.It mainly revolves around the characteristics of high-performance no-ELM operation scenarios,edge coherent modes,and parameter space of them.There are two main parts included:Diagnostic setup and physical research.(1)A radial edge Helium Beam Emission Spectroscopy(He-BES)diagnosis is successfully established on EAST.Diagnostic gas injection control and signal acquisition procedures are written in the LABVIEW language,which make it possible to obtaine the high spatial-temporal resolution measurements of important physical quantities such as boundary density,temperature,and electrostatic fluctuations.(2)A systematic study of the spontaneously generated no-ELM operating regimes on EAST is performed,as well as the respective parameter space.The spontaneously no-ELM operation produced on the EAST can be simply divided into three types:① Low heating power,high collisionality,and high recycling no-ELM operation.Significant feature is that the edge Da signal continues to rise after entering the H-mode.The parameter space of the scenario is:4.6GHz low hybrid current drive(LHCD)heating or synergistic heating of the counter neutral beam injection(Ctr-NBI)and electron cyclotron resonance heating(ECRH),when additional heating power form 2.45GHz LHCD,ion cyclotron resonant frequency(ICRF)or Co-NBI will break this no-ELM operation.For the plasma configuration:outer gap = 3.5-5.5 cm and stretch ratio κ= 1.55-1.63 and so on;② Low heating power,high collisionalitv.low recycling no-ELM operation:One of the outstanding features of’ this no-ELM is the continuous decreased edge Da signal after the L-H transition until the ELM completely disappears.The experimental conditions needs in this scenario is extensive lithium coating or real-time lithium powder injection conditions,in addition,this operation also shows a clear density threshold,and it is easier to be obtained at low density;③ High heating power,low collisionality no-ELM operation:This scenario is the highest heating level attainable on the EAST nowadays,but unfortunately it is just transient since of the lack of transport channels,so it cannot be maintained for steady-state.(3)There are quite a lot of fluctuations in the plasma edge.This paper systematically summarizes the multiple edge modes on EAST.It mainly includes four common modes:① Edge Coherent Mode(ECM)with electrostatic properties,which is the dominant mode in low collisionality,high recycling no-ELM scenario.When the edge radial electric field(Er)increases,ECM will radially shift and spectrum space broaden,then it become the dominant mode for type II ELMs and low recycling no-ELM H-modes.The magnetic signal is very weak,and the propagation is in the electron diamagnetic drift direction.It is a balloon mode feature with a high toroidal mode number(n～17-19).Studies have shown that it may share the nature of dissipative trapped electrons mode,strongly depending on the collisionality and pressure gradient.ECM is measured to bring strong particles and heat flux,provide a key transport path at the edge,so as to suppress the ELMs;②Magnetic Coherence Mode(MCM):The MCM existing parameter range spans almost the entire EAST H-mode discharge,and is currently only lost during the high-frequency grassy-like ELMy H mode.MCM is the dominant mode under high heating power,low collisionality no-ELM operating conditions.Its electrostatic signal is very weak,and its propagation in the electron diamagnetic drift direction.In contrast to ECM,MCM are thought to contribute little to the edge transport,while it is found that it can significantly change the poloidal distribution of heat flux;③ High-Frequency electromagnetic coherence Mode(HFM),which propagates in the electron diamagnetic drift direction.It is found that this mode has no obvious particle transport near the mid-plane of the low field side,while there is obvious particle transport at the high field side,and it is guessed that this mode may be generated in the high field side area;④ Electromagnetic precursors and post oscillations.An electrostatic precursor fluctuation can be observed during the type III ELMs interval.The precursor frequency range is about 100-200 kHz.It exhibits moderate toroidal modes nature(n～5-10),and the poloidal wavelength is larger than 10 cm.The radial wavelength is about 1cm.In addition,in the critical ELM gap(between type Ⅰ and type Ⅲ),an electromagnetic post mode with a frequency of 50 kHz can be observed,which propagates in the direction of the electron diamagnetic drift and observes that the post mode can be significantly elongated the ELM fall time.(4)The high-frequency and small-amplitude Type Ⅱ ELMs appearing on the EAST is studied.It is found that the appearance of such small ELMs is mainly related to the enhancement of pedestal Er.The enhancement of Er can suppress the instability of the ECM in the pedestal region,and shift the ECM peak position outwards.At the same time,the ECM frequency rises and the spectrum broadens into a wide spectrum fluctuation feature(called BB).It is found that BB exhibits burst characteristics,which the burst frequency is coincided with the ELM frequency,furthermore the burst frequency increases with Er enhancement.Finally,it is observed that this small ELM operation mode is compatible with Internal Transport Barriers(ITB)and low-torque operation.It is a possible alternative operating scenario for the next-step fusion experiments.The above research are not only lays a good foundation for small or no ELMs operations research in EAST,but also provides important reference for the exploration of ELMs control methods under the ITER conditions.更多还原