Energy distribution and dissipation characteristics in a 12-stage linear-transformer-driver facility.

Abstract

Linear transformer driver (LTD) is one of the promising technologies for the next-generation petawatt Z-pinch facility. Mismatch between the driver and load can cause energy reflections, resulting in more energy being dissipated in the LTD and causing damage to the devices. An equivalent circuit model based on a 12-stage LTD facility under different operating conditions was established and validated through experimental results over a relatively long time (∼2 μs). Then, circuit simulations were carried out to explore energy distribution under various load impedances, particularly focusing on the reflected energy to the LTD. The simulation results were used to predict capacitor lifetimes in discharge bricks, analyze output gap electric field strengths, and evaluate protective measures for LTD devices. The results with constant load impedance indicate that a near-matched load impedance can dissipate over 83% of the energy in the load region upon its first arrival, significantly higher than that in short-circuit or open-circuit scenarios (less than 1%). However, in practical experiments, the dynamic load is often closer to a short-circuit condition, resulting in LTD devices operating under more strenuous conditions. This is characterized by faster discharge frequencies (f > 1 MHz), higher voltage reversal factors (Q > 2), and stronger electric field strengths across output gaps (>40 kV/cm), all of which may lead to insulation failures or reduced lifetime of LTDs. Increasing the length of the coaxial water transmission line is expected to enhance device longevity and reduce insulation failure risks, offering valuable insights into optimizing design of LTD-based facility.