Speakers
Description
Reliable operation of high-gradient superconducting RF (SRF) cavities in pulsed proton and electron linacs requires precise control of the intra-cavity electromagnetic field against three interacting perturbations: Lorentz force detuning (LFD), microphonics, and transient beam loading. Conventional Low-Level RF (LLRF) systems address these perturbations through feedforward tables and model-independent feedback; however, incipient cavity faults — quenches, multipacting, and mechanical instabilities — often precede the LLRF trip by only tens of microseconds, leaving insufficient time for corrective action.
We present a physics-informed virtual accelerator framework that simulates the time-domain electromagnetic field dynamics of a single TESLA-geometry 1.3 GHz nine-cell SRF cavity in the rotating-frame baseband IQ representation. The model couples the standard cavity envelope differential equation to a second-order mechanical oscillator driven by the ponderomotive Lorentz force on the cavity walls, and includes deterministic multi-tone microphonics and a complex beam loading current phasor with a programmable phase step. The simulation is implemented using an adaptive Runge-Kutta integrator, which is essential for correctly resolving numerical stiffness near beam turn-on where fixed-step methods diverge spuriously. Three instability scenarios are systematically characterized. In the baseline stable scenario, the cavity field reaches a peak of 1.78 MV with a total detuning swing of plus or minus 10.6 MHz — approximately 49,000 times the cavity bandwidth — demonstrating the severity of LFD in high-gradient operation while remaining fully controllable. In the LFD quench scenario, an aggressive LFD coefficient combined with near-zero mechanical damping drives a positive-feedback instability that produces a confirmed cavity trip 71 microseconds after beam turn-on. In the microphonics-dominated scenario, with LFD disabled and microphonics amplitudes doubled, the field remains stable with a phase jitter of 4.7 degrees, confirming that a pure microphonics-induced trip requires perturbation amplitudes roughly 25 times the baseline to exceed the cavity half-bandwidth.
| Working group | WG5 |
|---|