Simulation, experiment, and performance of a 4 MV induction voltage adder machine for flash x-ray radiography

A 4 MV flash x-ray radiographic machine based on induction voltage adders has been developed. The configuration and design of this machine are reviewed. A three-dimensional, fully electromagnetic model and a circuit simulation model are established to compare with the experiments. The simulation results are in overall agreement with the electrical measurements. The pulsed power performances and output fluctuations of this machine over successive shot sequences are demonstrated. Among the 54 shots, the average peak output voltage is $4.4\ifmmode\pm\else\textpm\fi{}0.3\text{ }\text{ }\mathrm{MV}$ ($1\text{\ensuremath{-}}\ensuremath{\sigma}$) and the average diode current is $81.6\ifmmode\pm\else\textpm\fi{}4.5\text{ }\text{ }\mathrm{kA}$ ($1\text{\ensuremath{-}}\ensuremath{\sigma}$). Four typical malfunction modes are identified shot by shot including the diode-impedance collapse, insulator flashover, core saturation, and drive mistiming. Some remarkable features from each fault mode are recognized. The first-to-last time spreads of the four drive pluses, ${t}_{\mathrm{spread}}$, are chosen to quantify the drive synchronization and the influences of the ${t}_{\mathrm{spread}}$ on the peak voltages and diode currents are summarized from the almost 100 shots since the machine was commissioned. It is found that, in order to achieve a voltage of up to 4 MV, ${t}_{\mathrm{spread}}$ should not exceed 25 ns, which is approximately twice the time for electromagnetic wave propagation from the first cavity to the last cavity in vacuum. In addition, the rise time and FWHM duration of output voltages varying with ${t}_{\mathrm{spread}}$ are given. The results indicate that the rise time changes little at the beginning but increases exponentially once the ${t}_{\mathrm{spread}}$ exceeds 30 ns. The FWHM duration nearly increases linearly with ${t}_{\mathrm{spread}}$.