Development and Commissioning of the Beam Diagnostics for CIAE Proton Therapy Beamline System

A superconducting cyclotron-based proton therapy (PT) system, featuring a high dose rate, fast energy varying, compact size, and low energy consumption, is developed at the China Institute of Atomic Energy (CIAE). From the cyclotron to the nozzle, the beamline is equipped with 51 magnets, including six 30°, one 60°, and two 75° dipoles. Its strict symmetry ensures better beam optics, such as achromatic aberration for a wide energy range beam. The beam diagnostics system has been developed in-house to meet the beam commissioning needs of those high-quality beamlines. Along the beamline, the system includes: 1) seven standardized comprehensive diagnostic units (a combination of Faraday cup, dual-wire scanner, and optical beam profile monitor); 2) four pairs of X-Y slits for energy selection and emittance redefinition; and 3) several separate circular collimators, fast beam cutoff devices, and online monitoring ionization chambers for beam position, as well as Faraday cup for measuring beam intensity in the air section for flexible use. In this article, the design of the diagnostic system, the specialized electronics, and the electromagnetic compatibility (EMC) consideration were introduced. The dual-wire structure for the pA-level low-intensity beam was depicted. The cerium-doped yttrium aluminum garnet (Ce: YAG), an essential photonic material used as a yellow phosphor for white light-emitting diodes, with a very low-intensity threshold for proton beam profile measurement, was also presented in detail.