Dilation x-ray imager a new/faster gated x-ray imager for the NIF

Abstract

As the yield on implosion shots increases it is expected that the peak x-ray emission reduces to a duration with a FWHM as short as 20 ps for ∼7 × 10(18) neutron yield. However, the temporal resolution of currently used gated x-ray imagers on the NIF is 40-100 ps. We discuss the benefits of the higher temporal resolution for the NIF and present performance measurements for dilation x-ray imager, which utilizes pulse-dilation technology [T. J. Hilsabeck et al., Rev. Sci. Instrum. 81, 10E317 (2010)] to achieve x-ray imaging with temporal gate times below 10 ps. The measurements were conducted using the COMET laser, which is part of the Jupiter Laser Facility at the Lawrence Livermore National Laboratory.

Dilation framing camera with 4 ps resolution

“…The temporal resolution is mainly determined by four factors: the PC bias voltage, the gradient of the PC excitation pulse, the drift length, and the MCP gating pulse. 10 In the limit of small accelerating gap and ignoring any birth energy spread, the photoelectron which enters the drift region at times t i will reach the MCP at time 8,9 t…”

“…Moreover, the spatial resolution is measured by imaging the anode mesh onto the MCP. There are two different points in our dilation framing camera compared to the DIXI described by Hilsabeck et al and Nagel et al 8,10 One is that we use a large aperture magnetic lens instead of a coaxially guiding magnetic field to image the electrons. In the DIXI, a spatial resolution of <300 µm for the CsI PC and 510 µm for the Au PC with an image de-magnification of three times is achieved by a large uniform axial magnetic field electron lens.…”

“…The pulse-dilation of the electron signal allows a short duration initial signal captured at the PC to be stretched in time. 10 Therefore, the temporal resolution of the dilation framing camera is better than that of the gated MCP framing camera alone.…”

“…[8][9][10] In the dilation framing camera, the photo-cathode (PC) is pulsed. The electron pulse generated at the PC is accelerated by a time varying electric field between the PC and the anode mesh, which leads to an energy dispersion of the electron signal.…”

“…In the DIXI, a spatial resolution of <300 µm for the CsI PC and 510 µm for the Au PC with an image de-magnification of three times is achieved by a large uniform axial magnetic field electron lens. 8,10 Here, a large aperture magnetic lens is introduced into the dilation framing camera. The magnetic lens has been used to improve the focusing ability and imaging quality of optical electronic in electron microscope and streak camera.…”