Zeff is measured by two visible bremsstrahlung diagnostics on HL-2A tokamak, one of which uses a high spectral resolution spectrometer coupled with an electron multiplied CCD (temporal resolution of 100 Hz), and the other uses a filterscope system (temporal resolution of 1 MHz). The bremsstrahlung brightness measured by them coincides with each other very well. Z̅eff is systematically measured under different discharge conditions, such as divertor and limiter configurations, ohmic and auxiliary heating phases, before and after siliconization, and L-H transition. Under ohmic phase, Z̅eff is higher in the limiter configuration than that in the divertor configuration by a factor of ~1.5 under high-density regime. Z̅eff increases in all cases of auxiliary heating scenarios due to enhanced plasma-wall interaction, accompanied by influx increases of low ionization states of impurities such as C2+ and Fe1+ in plasma edge. Siliconization for wall conditioning is prominently effective in lowering the main impurity influxes in plasma edge and thus the impurity level, and a concentration of ~4% for carbon and ~0.2% for iron is roughly evaluated for a typical nonsiliconized plasma. A simple relationship that Zeff is positively correlated with Φin and τp is verified from the Land H-mode features, where Φin is the impurity influx and τp the particle confinement time. A nearly constant Z̅eff evolution is observed during L-H and H-L transition and it seems that Z̅eff is insensitive to L-H and H-L transition under some Zeff(0) threshold. The Zeff profiles are flat/weakly hollow in plasma core region (rho <; 0.7) in case of low Zeff(0) and tend to be peaked when Zeff(0) is larger than 3, which agrees with the neoclassical theory prediction.

中文翻译：

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HL-2A 托卡马克上欧姆、L 和 H 模式等离子体的 Z eff 测量


Zeff 通过 HL-2A 托卡马克上的两个可见轫致辐射诊断仪进行测量，其中一个使用高光谱分辨率光谱仪与电子倍增 CCD（时间分辨率为 100 Hz），另一个使用滤光镜系统（时间分辨率为 1 MHz） ）。他们测量的轫致辐射亮度彼此非常吻合。 Z̅eff 在不同的放电条件下进行系统测量，例如偏滤器和限制器配置、欧姆和辅助加热阶段、硅化前后以及 LH 转变。在欧姆相下，在高密度状态下，限制器配置中的 Z̅eff 比偏滤器配置中的 Z̅eff 高约 1.5 倍。由于等离子体-壁相互作用增强，Z̅eff 在所有辅助加热情况下都会增加，同时伴随着等离子体边缘的低电离态杂质（例如 C2+ 和 Fe1+）的流入增加。用于壁调节的硅化对于降低等离子体边缘的主要杂质流入量以及杂质水平非常有效，对于典型的非硅化等离子体，粗略评估碳浓度约为 4%，铁浓度约为 0.2%。从 Land H 模式特征验证了 Zeff 与 Φin 和 τp 正相关的简单关系，其中 Φin 是杂质流入量，τp 是粒子限制时间。在 LH 和 HL 转换期间观察到几乎恒定的 Z̅eff 演化，并且在某些 Zeff(0) 阈值下，Z̅eff 似乎对 LH 和 HL 转换不敏感。在低 Zeff(0) 的情况下，等离子体核心区域 (rho <; 0.7) 的 Zeff 轮廓是平坦/弱空心的，并且当 Zeff(0) 大于 3 时趋于达到峰值，这与新古典理论的预测一致。