Koga M, Shiraga H
Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280, Japan.
Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka 565-0871, Japan.
Rev Sci Instrum. 2017 Aug;88(8):083514. doi: 10.1063/1.4999757.
X-ray imaging is very useful to investigate imploded core plasma in inertial fusion experiments. We can obtain information from X-ray images, such as shape, density, and temperature. An X-ray framing camera (XFC) capable of taking two-dimensional, time-resolved X-ray images is used to capture the images. In previous work, we developed a numerical model of an XFC to analyze its X-ray image. The calculated results agreed qualitatively with experimental results. However, it was not accurate enough to determine the absolute value of the signal. We thought this discrepancy was caused by gain depletion. In high energy laser experiments, high photon flux may cause gain depletion. This is a problem for accurate X-ray measurement. In this paper, we report our new model, including gain depletion. The new model is evaluated by tabletop laser experiments and high energy laser experiments. The results calculated using the new model agree quantitatively with our experimental results. Furthermore, we confirmed that gain depletion occurs in our high energy laser experiments. For quantitatively accurate X-ray intensity measurements, the XFC should be used with limited incident photon flux such that the gain linearity is guaranteed.
X射线成像对于研究惯性聚变实验中内爆核心等离子体非常有用。我们可以从X射线图像中获取诸如形状、密度和温度等信息。一种能够拍摄二维、时间分辨X射线图像的X射线分幅相机（XFC）被用于捕捉图像。在之前的工作中，我们开发了一个XFC的数值模型来分析其X射线图像。计算结果与实验结果在定性上是一致的。然而，它还不够精确，无法确定信号的绝对值。我们认为这种差异是由增益耗尽引起的。在高能激光实验中，高光子通量可能会导致增益耗尽。这对于精确的X射线测量来说是个问题。在本文中，我们报告了我们包含增益耗尽的新模型。新模型通过桌面激光实验和高能激光实验进行了评估。使用新模型计算的结果与我们的实验结果在定量上是一致的。此外，我们证实了在我们的高能激光实验中会发生增益耗尽。为了进行定量准确的X射线强度测量，应在保证增益线性的有限入射光子通量条件下使用XFC。
