AI 中文总结
本研究通过数值对比发现，螺旋相衬成像（SPCI）相比传统相衬成像（PCI）具有更低的波数响应下限，可为多尺度等离子体湍流研究提供互补诊断信息。
AI 中文摘要
相衬成像（PCI）已被用于研究等离子体密度波动数十年，但其波数响应$k$受相位板凹槽宽度和束腰的限制。带有螺旋相位板的螺旋相衬成像（SPCI）输出信号为二次型，却可能具有更宽的灵敏度，因为除了中心奇点（即$k=0$）外无其他限制。本研究采用两种不同模型对两种技术的波数响应进行数值对比：（i）尺度长度$R$为5至25 mm的静态方形相位物体；（ii）具有类柯尔莫哥洛夫谱的随时间演化的各向异性多尺度湍流场。对于静态方形物体，PCI的下限截止波数$k_{\text{min}} \approx 0.1$ mm$^{-1}$，而SPCI通过梯度谱的自相关可产生低至$k_{\text{min}} \approx 0.007$ mm$^{-1}$的可测量信号；对于类等离子体湍流模型，PCI仍保持$k \approx 0.1$ mm$^{-1}$的下限截止，SPCI则可产生低至$k \approx 0.007$ mm$^{-1}$的可测量信号。这些结果表明，SPCI可提供PCI截止以下的低波数信息，为多尺度等离子体湍流研究提供互补的诊断信息。
英文摘要
Phase contrast imaging (PCI) has been used for decades to study plasma density fluctuations, but its wavenumber response $k$ is constrained by the phase plate groove width and beam waist. Spiral phase contrast imaging (SPCI) with a spiral phase plate may offer broader sensitivity, even though its output signal is quadratic, because it has no constraint except at the central singularity, i.e., $k = 0$. In this work, we numerically compare the wavenumber response of both techniques using two distinct models: (i) static square phase objects with scale lengths $R$ ranging from 5 to 25 mm, and (ii) a time-evolving, anisotropic, multi-scale turbulence field with a Kolmogorov-like spectrum. For static square objects, PCI exhibits a lower cutoff at $k_{\text{min}} \approx 0.1$ mm$^{-1}$, while SPCI produces measurable signals down to $k_{\text{min}} \approx 0.007$ mm$^{-1}$ via the autocorrelation of the gradient spectrum. For the plasma-like turbulence model, PCI retains its lower cutoff at $k \approx 0.1$ mm$^{-1}$. In contrast, SPCI produces measurable signals down to $k \approx 0.007$ mm$^{-1}$. These results suggest that SPCI provides low-wavenumber information below the PCI cutoff, offering complementary diagnostic information for multi-scale plasma turbulence studies.
