<title>Two-Frame Flash X-Radiography System For The Study Of Particle Beam Fusion Target Implosions</title>

Abstract

A two-frame flash x-radiography system has been developed for studying the implosion hydrodynamics of particle beam driven inertial confinement fusion targets. This system consists of two micro-point flash x-ray (FXR) sources, two micro-channel plate (MCP) x-ray sensitive cameras, and a space frame. The sources and cameras are arranged in pairs on the space frame to secure rigid registration of the sources with the cameras and to provide ease of alignment with the target. The micro-point FXR sources have an output spectrum characteristic of a tungsten bremsstrahlung source with an end point energy of 600 key, a source intensity of 8 mRad at 46 cm, and a spot size of approximately 100 μm. A direct 4x magnification of a 3 mm gold target was achieved by using this source in a backlighting arrangement with an overall system resolution of 4 1p/mm. This system has been used successfully to observe relativistic electron beam driven ablative pusher target implosions. In the inertial confinement approach to controlled thermonuclear fusion, ignition is to be achieved via heating, compression, and confinement of the fuel by an imploding shell. Since the confinement time improves with increasing pusher pR, target design calculationsl achieving gain > 1 require a pusher pR > 1 g/cm2, where p and R are the mass density and shell thickness of the pusher, respectively. For such targets, the pusher can, during its acceleration by the driver and during subsequent deceleration by the compressed fuel, be unstable which can lead to reduced compression, fuel heating, and confinement time. An experimental study of this problem is very difficult because of the pusher thickness and requires a technique such as flash x-radiography (FXR) to directly observe the hydrodynamic behavior of the interfaces between the target ablator and the pusher and between the pusher and the fuel. To make these studies, a two-frame FXR system has been developed. This system consists of two micro-point FXR sources (each having a spot size of 100 pm), two gated microchannel plate x-ray sensitive cameras, and a space frame which holds the FXR source and camera pairs in rigid alignment. A schematic representation of this system is shown in Figure 1. Two 3 ns FXR radiographs of an imploding target can be made with this system with arbitrary interframe separation and with a system spatial resolution of 125 μm.*