Removal of stripped protons produced in low-energy beam transport for superconducting linac

Abstract

Superconducting linear accelerator (SCL) is commonly used to boost the negative hydrogen ion (H^{−}) beam energy above the medium-β range. Stripped proton beam loss in SCL is one of the heat and radioactive source, which could threaten the operation of the SCL. This paper describes a novel technique for removing stripped protons produced in the low-energy beam transport section, the main area of H^{−} beam stripping in the linac. The experiment is conducted at the China Spallation Neutron Source. The H^{−} beam is bent by 1.8° before being focused into the radio-frequency quadrupole (RFQ) entrance. As a result of the differential pumping and optimized beam optics design, the bending magnet effectively removes over 99% of the stripped protons, resulting in a significant reduction of stripped protons captured by the RFQ and downstream linac.