High performance imaging streak camera for the National Ignition Facility

Abstract

An x-ray streak camera platform has been characterized and implemented for use at the National Ignition Facility. The camera has been modified to meet the experiment requirements of the National Ignition Campaign and to perform reliably in conditions that produce high electromagnetic interference. A train of temporal ultra-violet timing markers has been added to the diagnostic in order to calibrate the temporal axis of the instrument and the detector efficiency of the streak camera was improved by using a CsI photocathode. The performance of the streak camera has been characterized and is summarized in this paper. The detector efficiency and cathode measurements are also presented.

Absolute Equation-of-State Measurement for Polystyrene from 25 to 60 Mbar Using a Spherically Converging Shock Wave

“…To track the shock velocity and the compression at the shock front we use a streaked x-ray radiography platform that was originally developed for ICF capsule implosion velocity measurements [31,32]. Here, the 100-µm-high, horizontal slice of the solid sample at the center of the hohlraum is backlit with a Zn He-α (9.0 keV) area backlighter.…”

Diagnostic Instrument Manipulator (DIM) upgrades for reliability and operational efficiency in a radiological contamination environment at the National Ignition Facility (NIF)

“…See Ref. [3], [4], and [5] for discussion of sample diagnostics such as GXD, hGXI, and DISC. A snout assembly -portrayed in Figure 2 as the nose cone on the Z2 DLP -may be attached to the front of the diagnostic through a side port in the DIM, which gives even greater flexibility for interchanging pinhole arrays or filter assemblies at various magnifications without having to remove the entire diagnostic from the DIM.…”

Recent Progress in Research on CsI Thin Film Photocathodes

“…在 CsI 薄膜光阴极的研究与应用中, 稳定性始 终是研究者面临的一个重要技术难题。由于某些设 备的实际应用与操作使 CsI 光阴极不可避免的接触 空气, 由此导致的性能不稳定制约了其应用 [25,47] 。 另外, CsI 光阴极在一定强度的 X 射线或紫外光中工 作, 辐照环境也会导致 QE 下降。目前, 人们对 CsI 图 2 (a) CsI/ MgO/ MWCNTs/ Si 结构光阴极的 SEM 照片 [45] ; (b)等离子体刻蚀过的 Si 基底的 SEM 照片; (c)Si 基底上 CsI 薄膜暴 露于空气前的 AFM 照片; (d) Si 基底上 CsI 薄膜暴露于空气 24 h 的 AFM 照片 [41] Fig. 2 (a) SEM image of the CsI/ MgO/ MWCNTs/ Si photocathode [45] ; (b) SEM image of the Si substrate patterned by colloidal lithography after lift-off process; (c)AFM image of the fresh CsI film evaporated on the Si patterned substrate; (d) AFM image of the CsI film on the Si patterned substrate exposed to ambient air for 24 h [41] 无 机 材 料 学 报 第 CsI 薄膜光阴极的效率下降, 在极端潮湿的环境中 (如呼吸), CsI 薄膜表面会变为乳白色 [6,48] , 效率完 全被破坏。图 3 为刚制备、在空气中暴露后、极端 潮湿环境中的 CsI 薄膜的 SEM 照片以及 NIF 使用的 X 射线条纹相机上的透射式 CsI 光阴极信号下降与 空气暴露时间的关系 [47,49] 。 目前人们对受潮导致光阴极 QE 下降有几种解 释。Hoedlmoser 等 [23] 认为潮湿空气中 CsI 薄膜表面 吸附的水层(溶液层)使到达薄膜表面的光电子能量 降低, 并将热处理对长波段 QE 提高更明显的原因 归因于表面吸附水层厚度的影响。Triloki 等 [50] 认为 QE 下降是水扩散进入 CsI 薄膜内部产生的缺陷影 响了电子的传输。一些研究者 [6,37] 发现受潮后薄膜 表面 Cs 含量偏高, 将原因归于 CsI 与水的反应和…”

“…Xie 等 [6] 认为这可能是 QE 下降的原因之一。 图 3 (a)刚制备、(b)在空气中暴露后、(c)在极端潮湿环境中 暴露后 CsI 薄膜的 SEM 照片 [49] ; (d)NIF 采用的 X 射线条纹相 机上 200 nm 厚的 CsI 透射式光阴极信号下降与空气暴露时间 的关系 [47] Fig. 3 SEM images of as-deposited (a), aged in ambient air (b) and extreme moisture exposed CsI films (c) [49] ; Percent degradation in the yield signal of streak camera used at NIF from a 200 nm thick CsI cathode as a function of air exposure time [47] Kumar 等 [39,51] 的实验结果表明 Cs 的含量仅在部分 微区域偏高, 他们认为 Cs 含量在真空热蒸发一开 始就出现增加, 原因为 I 的升华和色心聚集与析出。 一些研究者认为受潮导致的薄膜形貌及颗粒尺寸的 变化对 QE 也有影响 [2,11,18,35] , 其中 Nitti 等 [18] 认为这 是 QE 下降的重要原因。 几乎所有对 CsI 薄膜光阴极受潮的研究都发现薄 膜中颗粒尺寸变大, 但对颗粒生长的动力学过程有不 同的描述: Xie 等 [6] 认为, 薄膜中较小颗粒在颗粒顶端 岛状水溶液重力、静电引力及表面张力作用下发生合 并形成大颗粒; Triloki [50] 和 Boutboul [28] 等认为颗粒长大 源于薄膜表面溶液相中水分挥发所引起的再结晶;…”