Design and implementation of high-current pulse measuring device for real-time FLASH electron beam monitoring

A FLASH beam is a beam with a short irradiation time and an ultrahigh dose rate of more than 40 Gy/s. FLASH beams are known to increase the effectiveness of radiation therapy and are currently being studied in the field of radiobiology. These types of beams can be generated using an electron linear accelerator and are being used in many biological experiments using cells. For beam irradiation during experiments, the total dose must be monitored in real-time. However, when monitoring FLASH beams using a typical transmission-type monitor chamber, the charge density generated in the chamber cavity is too high to monitor the beams due to the overflow of the electrometer. For 6-MeV FLASH electron beams with a pulse width of 2.5 μs, the pulse current per unit chamber volume and unit dose is estimated to be approximately 14 mA/(cm 3 Gy). Conventional electrometers do not support such high input currents. In this study, we fabricate a device that can measure the pulse current for monitoring 6-MeV FLASH electron beams using a PTW-7862 ionization chamber. The capacitor voltage is measured directly without an operational amplifier (opamp)-based integrator circuit. The device consists of a polarization voltage generator, current integrating capacitor, high-input-resistance buffer amplifier, and digital voltmeter. Measurements using the prototype device were performed on 6-MeV FLASH electron beams, and voltage signals proportional to the number of pulses were obtained. In the future, signal processing research will be conducted to assess the practical use of the device.