Design and performance study of a dielectric-filled cavity beam current monitor for HUST-PTF

To guarantee the exact proton dose applied to patients and ensure treatment safety while disrupting and destroying tumor cells, it is essential to accurately monitor the proton beam current in real-time during patient treatment. Because clinical treatment requires a proton beam current in the ~nA range, nondestructive beam current monitors (BCMs) are preferred to minimize the degradation of beam quality. However, this poses significant challenges in accurately monitoring such extremely low beam intensities. This study proposes a cavity-type BCM equipped with a dielectric plate to reduce its dimensions and achieve sufficient measurement sensitivity for practical requirements. A prototype cavity BCM was fabricated, and offline testing was performed using a metal wire to simulate the beam to study its performance. Both the simulation and experimental results showed that the cavity BCM could measure ultralow proton beam currents with a resolution up to 0.03 nA.