Truong D D, McKee G R, Yan Z, Jaehnig K, Winz G R, Fonck R J, Geiger B
Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Rev Sci Instrum. 2021 May 1;92(5):053513. doi: 10.1063/5.0043095.
An upgraded detector and several optimizations have significantly improved the Ultra-Fast Charge Exchange Recombination Spectroscopy (UF-CHERS) diagnostic sensitivity to ion temperature and parallel velocity fluctuations at turbulence relevant spatio-temporal scales. Normalized broadband ion temperature and parallel velocity fluctuations down to x̃x∼1% (x = T, v) and up to ∼450 kHz have been measured in a variety of plasmas. The multi-field nature of the CHERS technique also allows measurements of the cross-phase angles of the fluctuating fields. UF-CHERS is optimized to observe emissions from the electron exchange reaction between intrinsic C and hydrogenic neutral beam injected particles near 529 nm. UF-CHERS consists of two chords separated by ∼1 cm radially, less than the turbulence correlation length in DIII-D plasmas, which enables correlated measurements to suppress incoherent electronic and photon noise. The optical components of the spectrometer include a volume-phase-holographic grating with >90% transmission between 528 and 530 nm and f/2 200-mm lenses, selected to maximize the optical efficiency and photon flux. Diffracted light from each chord is collected in eight spectral bins, each with a bandwidth of ∼0.25 nm, and detected and amplified by chilled avalanche photodiodes and custom high-gain, wide bandwidth low-noise preamplifiers to achieve the optimal signal-to-noise ratio. The resulting signals are digitized at 1 MHz, 10-10× faster than the conventional CHERS diagnostics. Spatial coverage is achieved by repositioning a motorized fiber tray between plasmas. UF-CHERS measurements will advance the understanding of turbulent ion transport and contribute to the validation of transport models and simulations.
一种升级后的探测器和多项优化措施显著提高了超快电荷交换复合光谱（UF-CHERS）对湍流相关时空尺度下离子温度和平行速度涨落的诊断灵敏度。在各种等离子体中，已测量到归一化宽带离子温度和平行速度涨落低至x̃x∼1%（x = T, v）且高达约450 kHz。CHERS技术的多场特性还允许测量波动场的交叉相位角。UF-CHERS经过优化，用于观测本征C与注入的氢中性束粒子之间在529 nm附近的电子交换反应所产生的辐射。UF-CHERS由两条径向间隔约1 cm的弦组成，该距离小于DIII-D等离子体中的湍流关联长度，这使得相关测量能够抑制非相干电子噪声和光子噪声。光谱仪的光学组件包括一个在528至530 nm之间透过率>90%的体相位全息光栅和f/2 200-mm透镜，其选择目的是使光学效率和光子通量最大化。来自每条弦的衍射光被收集到八个光谱 bins 中，每个光谱 bin 的带宽约为0.25 nm，并由冷却雪崩光电二极管和定制的高增益、宽带宽低噪声前置放大器进行检测和放大，以实现最佳信噪比。所得信号以1 MHz进行数字化，速度比传统CHERS诊断快10 - 10倍。通过在等离子体之间重新定位电动光纤托盘来实现空间覆盖。UF-CHERS测量将推进对湍流离子输运的理解，并有助于验证输运模型和模拟。
