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首页> 外文期刊>Plasma physics and controlled fusion >Observation of neoclassical impurity transport in ohmically heated plasmas of CDX-U low aspect ratio tokamak
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Observation of neoclassical impurity transport in ohmically heated plasmas of CDX-U low aspect ratio tokamak

机译：CDX-U低纵横比托卡马克电阻加热等离子体中新古典杂质传输的观察

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High beta, good confinement and stability properties of the low aspect ratio tokamaks, or spherical tori (ST), have been predicted theoretically and preliminarily confirmed in several large experiments recently. This paper reports on impurity transport experiments carried out in ohmically heated plasmas of the small spherical torus CDX-U with the aspect ratio of A similar or equal to 1.5. Vacuum ultraviolet and soft x-ray multichannel spectroscopic diagnostics are used to measure intrinsic carbon, oxygen and radiated power radial brightness profiles in plasmas with T-e (0) similar or equal to 60-80 eV and n(e) (0) similar or equal to 2 x 10(13) cm(-3): The measurements are performed in both magnetohydrodynamically dorminated and quiescent phase of the plasmas. The properties of the observed low m / n modes, sawtooth oscillations, and ST-specific reconnection events are discussed in the context of particle transport. The, measured impurity profiles are modelled using one-dimensional impurity transport code MIST and a collisional-radiative package CRMLIN. Impurity diffusion of 0.2 m(2) s(-1) less than or equal to D less than or equal to 0.6 m(2)s(-1) and convection velocity of nu similar or equal to 4-16 m s(-1) are inferred from the modelling. These transport coefficients are very close to the neoclassical theory predictions obtained with the FORCEBAL code,. which uses analytical plasma viscosity expressions valid for an arbitrary aspect ratio geometry. Neoclassical analysis indicates that both carbon and- oxygen are in the collisional regime, and the Pfirsch-Schluter flux is the major fraction of the impurity flux. The causes of the observed strong non-diffusive transport are discussed, and it is concluded that the deln(i)(i) term, resulting from highly peaked ion density profile, makes the largest contribution to the inward pinch. Present analysis suggests that drift wave turbulence is reduced in CDX-U ohmically heated discharges within at least r/a less than or equal to 0.4, however more refined measurements are needed to interpret the results in the framework of ST ion transport. [References: 73]
机译：从理论上预测了低长宽比托卡马克或球形托里（ST）的高贝塔系数，良好的限制和稳定性，这在最近的几项大型实验中已经得到了理论和初步的证实。本文报道了在小球形圆环CDX-U的欧姆加热的等离子体中进行的杂质传输实验，该等离子体的纵横比A等于或等于1.5。真空紫外和软X射线多通道光谱诊断程序用于测量Te（0）等于或等于60-80 eV且n（e）（0）相似或相等的等离子体中的本征碳，氧和辐射功率径向亮度曲线至2 x 10（13）cm（-3）：在等离子体的磁流体动力学稳定和静态阶段均进行测量。在粒子传输的背景下讨论了观察到的低m / n模式，锯齿波振荡和ST特定重新连接事件的属性。使用一维杂质传输码MIST和碰撞辐射封装CRMLIN对测得的杂质分布进行建模。小于或等于D的0.2 m（2）s（-1）的杂质扩散小于或等于0.6 m（2）s（-1）的nu和对流速度nu等于或等于4-16 ms（-1） ）是从建模中推断出来的。这些传输系数非常接近用FORCEBAL码获得的新古典理论预测。它使用对任意纵横比几何形状均有效的分析血浆粘度表达式。新古典分析表明，碳和氧都处于碰撞状态，Pfirsch-Schluter通量是杂质通量的主要部分。讨论了观察到的强非扩散传输的原因，并得出结论，离子峰分布高度峰值导致的deln（i）/ n（i）项对向内收缩的贡献最大。目前的分析表明，CDX-U欧姆加热放电的漂移波湍流至少在r / a小于或等于0.4的范围内减小，但是需要更精确的测量来解释ST离子迁移框架中的结果。 [参考：73]

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