| Summary: | In this study, a dynamic pumping model was established for a vacuum-sealed, gigawatt-class, repetitively operated transit-time oscillator (TTO) based on the direct-simulation Monte Carlo (DSMC) method, and the pressure distribution of the model at different times and locations was analyzed. The simulation results showed that the maximum pressure at the diode was an order of magnitude larger than the equilibrium pressure, and the pressure recovery time was three times the duration of a single pulse. To verify the accuracy of the simulation results, experiments were conducted in a vacuum-sealed hard-tube TTO structure with a repetition rate of 10 Hz and the pressure was monitored at the vacuum diode. The diode voltage was about 500 kV and the beam current was 8 kA. Further, the average microwave power was 1 GW with a pulse width of 40 ns. The experimental results revealed that the equilibrium pressure at the vacuum diode was 4.0 × 10<sup>−3</sup> Pa, and the pressure recovery time was three times the duration of a single pulse. These results were consistent with the simulation results, which indicates that the proposed model can provide technical support for subsequent vacuum-maintenance experiments.
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