The dynamic behavior of a test sample during and shortly after it has been irradiated by an intense relativistic electron beam (REB) is of great interest to the study of beam energy deposition. Since the sample densities are far beyond the cutoff in the optical region, flash x-radiography techniques have been developed to diagnose the evolution of the samples. The conventional approach of analyzing the dynamic behavior of solid densities utilizes one or more short x-ray bursts to record images on photographic emulsion. This technique is not useful in the presence of the intense x-rays from the REB interacting with the sample. We report two techniques for isolating the film package from the REB x-ray pulse.
One arrangement employs a microchannel plate electron multiplier array (CEMA) to convert the incident x-ray linage to an amplified electron “image,” This image is proximity focused onto an aluminized plastic scintillator held at 5-10 kV relative to the CEMA output face. A streak camera shielded from the x-rays is used to record the time varying image on the 2 ns persistence scintillator. The resolution limitation is primarily that of the image converter, i.e., 5 ns and 5 line pairs/mm.
To achieve higher sensitivity and resolution, an arrangement employing two microchannel plates has been developed. In this device, two channel plates are immersed in a long uniform solenoidal magnetic field; the electrons generated by the first plate are guided by the magnetic field lines to the second plate which increases the system gain by > 103. Placed a few mm behind the second plate is a phosphor screen which in turn is directly connected to film via a fiber optic face plate. In this way, isolation of the x-ray burst from the long persistence phosphor and film is achieved by using a long solenoid. The temporal resolution (approximately 3 ns) can be gained by the appropriate gating of the channeltron plates and/or grids. The spatial resolution is governed by the channel plate “pores” size, by electron orbit characteristics in the solenoidal magnetic field, and by the effective x-ray source geometry.
By using these two methods, nanosecond time resolved x-ray pinhole photographs and flash x-ray radiograph of REB initiated events have been achieved.