Fast-framing x-ray camera for beam propagation experiments

A practical, hard x-ray (greater than or equal to 50 keV) framing camera has been constructed with sealed microchannel plate (MCP) image intensifier tubes to image bremsstrahlung produced by intense relativistic electron beams. The camera is much simpler in design than its predecessor because it does not require a vacuum system or a toroidal magnetic field for operation. Time resolution is obtained by gating the MCP of each tube; since standard tubes are used, the shutter time per frame is limited to approx. 2 ns. The response time of a standard tube is restricted by the highly inductive wire leads which connect to the MCP electrodes, and the resistive (approx. 60 ohms/square) input and output surfaces of the MCP. To obtain better time resolution a prototype subnanosecond imaging tube has been designed with flat parallel plate stripline connections to the MCP electrodes and a 500 A gold coating on the MCP surfaces. Subnanosecond framing times are essential for the observation of beam front dynamics since a 1 ns shutter integrates over a 30 cm length for relativistic electron energies. The shutter time of the prototype tube has been experimentally determined with an optical sampling system to be < 850 psmore » at the 10% level. Details of the subnanosecond gating results are discussed. New imaging tubes have been fabricated with 3000 A of gold deposited on the MCP surfaces and with a more uniform internal contact arrangement with which we hope to demonstrate a 200 ps shutter. A six-frame camera is being assembled with the new tubes for RADLAC II beam propagation experiments.« less