Design of a radiographic integrated test stand (RITS) based on a voltage adder, to drive a diode immersed in a high magnetic field

摘要

Recent experiments have adapted existing magnetically insulated induction voltage adders (Sabre, Hermes III) to drive a 10-MV diode immersed in magnetic fields as high as 50 T. In such a diode, an electron beam of tens of kiloamperes can be confined by the magnetic field to a diameter of about 1 mm, and when it strikes a high-Z anode, it can create a bremsstrahlung X-ray source intense enough to radiograph massive objects with high resolution. The radiographic integrated test stand (RITS) is an adder system designed specially to drive such diodes, and it will be used to develop and exploit them. As in other adder-based pulsers, such as Sabre, Hermes III, and Kalif-Helia, the induction cells have amorphous-iron cores, and the pulse-forming system consists of water dielectric pulselines and self-closing water switches that are pulse-charged from Marx-charged intermediate water capacitors through laser-triggered Rimfire switches. An oil prepulse switch in series with each pulseline is designed to reduce cathode prepulse to less than /spl plusmn/5 kV, and a means is provided to bias the cathode and avoid negative prepulse entirely. The RITS pulse-forming system consists of two modules. Each module has one Marx that charges two 3-MV intermediate stores, each of which charges three 7.8 /spl Omega/ pulselines, making six pulselines per module. The two modules in concert can supply 1.35-MV, 50-ns pulses to a 12-cell adder and thus drive a 16-MV diode with a single pulse. The 1,35-MV induction cells each have a single-point feed, from which a single, slotted azimuthal oil transmission line distributes energy uniformly around the cell. The modules can also be pulsed separately at different times, either to power two 8-MV adders that each drive one of two closely spaced cathodes immersed in a common magnetic field or to provide two separate pulses to a common six-cell adder and a single 8-MV diode; in these two-pulse modes, the spacing of the two 50-ns pulses may be chosen to be anything from a few hundred nanoseconds upward. The use of only one pulseline per cell has been shown to increase the extent to which the cell voltages can vary with the timing of closure of the water switches. This and all other functions of RITS have been simulated in detail, and a conservative electrical design has been developed. This will be illustrated, along with the conceptual design of a pulse sorting network that can couple two pulselines efficiently to one cell when the two RITS modules drive a common adder in two-pulse mode.