HL-2A/2M托卡马克等离子体同位素效应及小尺度湍流的实验研究

There is clear experimental evidence that at comparable plasma discharge parameters deuterium (D) plasmas have improved confinement properties as compared with hydrogen (H) ones.The isotope mass effect has been observed in many different tokamaks under various plasma conditions with a degree of confinement improvement in energy, particle and momentum depending on plasma regimes. Additionally, it has been found that in D plasmas the L-H transition power threshold is lower than in H ones. Understanding the underlying physics of the isotope effect in plasma transport and confinement remains a fundamental open question confronting the fusion community for 30 years of intense research with direct impact in the confinement properties of fusion D-T reactors. Considering that the characteristic step size of collisional transport increases with plasma gyroradius, increasing the mass of the isotope would imply a deleterious effect on transport. Thus, the experimentally observed isotope effect is a counterintuitive phenomenon to our general understanding. In recent experiments at TEXTOR, evidence shows that the isotope effect has a close link to zonal flows which systematically increases during the transition from hydrogen to deuterium dominated plasmas. However, the intimate correlation between the isotopic mass and zonal flows needs further investigation. In order to survey the isotope effect on multi-scale turbulence, such as ITG, TEM and ETG modes, measurements on low-wavenumber range (k<15 cm-1) turbulence, including ITG and TEM modes, have been performed. Experimental findings indicate higher level turbulence in D discharges than in H ones, in disagreement with better confinement in D plasmas. Thus, it is necessary to measure properties of small-scale (high k>15 cm-1)turbulence. In addition, investigation on the nature of small-scale turbulence is also very crucial for understanding core electron thermal transport and the formation of electron internal transport barrier (e-ITB) as well. At present, experimental results reveal that the development of the electron ITB is usually more difficult than that of ion ITB. Assuming that the formation of ITB is significantly attributed to the shearing effects of ErB flows on turbulence, strong ErB flow shearing reduces or even suppresses the transport produced at large scales (ITG or TEM modes), while leaving the transport at small scales produced by ETG almost unaffected.In fusion reactors like ITER, the electron heating is predominant via the interplay between electrons and alpha particles. As a consequence, understanding the nature of ETG modes and electron heat transport is of paramount importance..Therefore, we propose to develop a set of diagnostic at HL-2A/2M, in particular,to measure the small scale (high wavenumber k>15 cm-1) turbulence.

大量实验事实表明托卡马克等离子体能量约束时间随同位素（氢、氘、氚）离子质量增加而增加，而L-H模转换功率阈值随同位素质量增加而降低。这与输运步长正比于拉莫半径、重离子输运高、约束差相违背，因而成为困扰聚变界的难题之一。已有结果表明同位素效应与带状流有关，与理论预言相符，但带状流和同位素效应之间的内在关联，需进一步证实。为了解同位素效应对不同尺度湍流的影响，已有诊断测量低波数范围（k<15cm-1）ITG和TEM模的湍流特性并发现氘放电时密度涨落高于氢，这与氘的能量约束高不一致。为探索同位素效应对不同尺度湍流的作用，有必要对更小尺度的ETG模（k >15cm-1）进行研究。此外，研究小尺度湍流对于理解电子热输运和形成电子内部输运垒也很重要。目前，芯部离子输运垒易形成，但电子输运垒却难形成。鉴于燃烧等离子体中α粒子主要加热电子，研究和控制ETG模和电子热输运对将来ITER的成功运行至关重要。

研究磁约束聚变等离子体中的同位素效应及其对不同尺度湍流和输运的影响关系到未来商用聚变堆的成功运行。深入研究小尺度湍流的物理特征对理解和控制ETG模和电子内部输运垒至关重要。本项目按计划在HL-2A装置上开展了等离子体同位素效应及小尺度湍流的相关实验研究。在硬件方面, 成功研制出一套高时间和波数分辨的二氧化碳激光相干散射诊断系统用于测量等离子体芯部波数范围为k=10-50cm-1的小尺度密度涨落；在物理方面，首先研究了同位素等离子体中带状流与湍流输运之间的相互关联，发现D等离子体比H等离子体具有更强的带状流、并对湍流粒子输运具有更显著的抑制作用，与相关理论和模拟结果相符合。此外，研究了小尺度湍流在电子热输运过程中的作用，首次观测到由芯部大尺度热脉冲激发的小尺度ETG湍流间歇性爆发现象；发现在电子非局域热输运过程中小尺度湍流的极向相关和流剪切增大以及雪崩效应与新经典撕裂模之间的内在联系；在边界湍流基本特征研究方面，首次观测到边界湍流由电阻性气球模（RMB）向离子温度梯度模（ITG）转换的实验证据。上述结果深化了我们对等离子体约束的同位素效应和小尺度湍流物理特性的理解，为控制电子热输运和内部输运垒并实现未来聚变堆的高效运行提供了重要的依据。