Performance measurements of the DIXI (dilation x-ray imager) photocathode using a laser produced x-ray source

Abstract

DIXI (dilation x-ray imager) will be used to characterize ICF (inertial confinement fusion) implosions on the NIF. DIXI utilizes pulse-dilation technology 1 to achieve x-ray imaging with temporal gate times below 10 ps. Time resolved x-ray measurements were conducted using the COMET laser facility at the Lawrence Livermore National Laboratory. Here we focus on some of the challenges faced by the large aperture photo cathode of the instrument and report on how to maintain a flat photo cathode as well as how the required spatial resolution of the instrument is achieved.

Design and implementation of Dilation X-ray Imager for NIF "DIXI"

“…The flatness of the DIXI photocathode is critical and can only be controlled by ensuring the kapton membrane is taught. Any wrinkling or wave in the plane of the photocathode results in distorted images, Figure 9 and [2]. Additionally the strip lines on the photocathode are aluminum and it was difficult to make good electrical contact at all four strip lines simultaneously.…”

“…While the electrons travel along the drift space the 4 electromagnetic coils generate a longitudinal Bfield that guides the electrons and the signal stretches as the higher energy electrons are traveling at a faster velocity. By stretching or dilating the signal the effective gating at the MCP is reduced by a factor of 7 over conventional gated imagers and provides <10ps temporal resolution, Figure 12, [1][2][3][4]. Figure 12.…”

“…DIXI (Dilation X-ray Imager) is a new fixed base diagnostic that has been developed for use in the National Ignition Facility. The DIXI diagnostic utilizes pulse-dilation technology [1,2,3,4] and uses a high magnification pinhole imaging system to project images onto the instrument. DIXI is located outside the NIF target chamber approximately 6.5m from target chamber center (TCC).…”