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Single and multi-frame gated x-ray images with time-resolution as fast as 150 psec are described. These systems are based on the gating of microchannel plates in a stripline configuration. The gating voltage comes from the avalanche breakdown of reverse biased p-n junction producing high power voltage pulses as short as 70 psec. Results from single and four frame x-ray cameras used on Nova are described. There has been much recent interest in gated x-ray cameras and spectrometers with gate times as short as 100 psec. In the ICF field, this time resolution is necessary to freeze implosions with velocities of 107 cm/s and resolutions of 10 μm. There are two different techniques for gating, shuttering electro optic tubes and voltage gating of a proximity focussed device. Several schemes have been proposed for subnanosecond shuttering of electro-optical tubes. Such approaches are attractive in that several frames can in principle, be achieved, there is little problem from x rays that are transmitted through the cathode, and a uniform response can be obtained over a large photocathode area. However, these schemes are complex and to date have found little practical application. Gating a proximity focused device is much simpler. A voltage pulse is applied across either photocathode-phosphor gap, or across a microchannel plate. There are several disadvantages to this approach: a fast, high voltage drive is required because a large detector area implies a high capacitance, it is inherently a single-frame device, straight through hard x rays can cause problems, and the response across a large sensitive area will be non-uniform due to the finite propagation velocity of the gating voltage wave. Until recently, fast high voltage pulses for the electrical gating could only be generated by photoconductive switches with the concomitant complexity of a short pulse laser. However, the well known phenomenon of avalanche breakdown/ has now been developed so that high power electrical pulses as short as 70 psec can be produced by purely electronic drivers. These voltage pulses are applied to a strip transmission line with a microchannel plate as the dielectric. The temporal and spatial resolution are described in Sec. II. Using a voltage doubling scheme sufficient voltage from four paralleled reverse biased diodes can be produced to gate four microchannel plates arranged in the four corners of a rectangle. The field uniformity and gain width variation of this configuration are described in Sec. II. For use on Nova, these microchannel plates are gated at different times and detect four gated images from an array of four pinholes. The system and its timing fiducial are described in Sec. III. Representative results from direct-drive implosions are described in Sec. IV.
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