Design of a 200 MHz CW He2+ RFQ for 211At production

Abstract

Short-lived alpha-emitting radiopharmaceuticals are promising for targeted cancer therapy, providing high linear energy transfer and localized cytotoxic effects while minimizing damage to healthy tissues. To ensure a stable and high-purity supply of these isotopes, a dedicated radiopharmaceutical injector is required, integrating advanced accelerator technology for efficient isotope production. This study presents the design and analysis of a 200 MHz CW He²⁺ RFQ accelerator as a key component of such an injector for ²¹¹At production, ensuring high transmission efficiency (99.5 %) and minimal emittance growth. A four-vane structure with optimized cooling channels was adopted, achieving a stable temperature profile. The implementation of Pi-mode stabilizing loops (PISLs) improved mode separation (7.9 MHz), reducing dipole mode interference. The undercut design ensured a longitudinal field flatness deviation of less than 3 %. Sixty tuners were designed, providing a tuning range of [-1.5 MHz, +2 MHz], sufficient to compensate for frequency shifts caused by machining and assembly errors. Multi-physics analysis showed that thermal deformation of the cavity resulted in a frequency shift of +20 kHz, while the maximum cavity stress was 38.2 MPa, well below the copper material limit of 70 MPa. These results confirm the feasibility of using CW RFQs for high-current alpha radiopharmaceutical production.