Validation of prediction capability of operating space for plasma intiation in MAST-U
In order to test the capability of the full electromagnetic DYON to predict the plasma initiation feasibility of individual discharges and thus the operating space in the device, a dedicated experimental database was built in MAST-U by scanning the prefilled gas pressure $p_0$ and the induced loop voltage $V_{loop}$ (3 failed breakdown discharges, 6 failed burn-through discharges, and 15 successful plasma initiation discharges). In the experimental operating space of $p_0$ and $V_{loop}$ the lower and the upper limits of $p_0$ are determined by the plasma breakdown failure and the plasma burn-through failure, respectively. The lower limit of $V_{loop}$ is determined by the plasma burn-through failure. By directly reading the control room data used in each discharge (i.e. currents in the solenoid, poloidal field coils, and toroidal field coils, $p_0$, and gas puffing rate), the full electromagnetic DYON consistently simulated the failed breakdown, failed burn-through, and successful plasma initiation discharges in the experimental database, demonstrating the capability of the full electromagnetic DYON to predict the operating space required for inductive plasma initiation. The Paschen curve calculated with the effective connection length in MAST-U indicates a much higher $p_0$ required for plasma breakdown than the experimental data, indicating that individual field line evaluation is necessary to calculate the quantitative requirements for Townsend breakdown. The demonstration in this paper shows that the full electromagnetic DYON could be a useful simulation tool to assess the feasibility of inductive plasma initiation and to optimise operating scenarios in future devices.