Speakers
Description
An RF driven negative hydrogen source is under development for the upgrade of China Spallation Neutron Source (CSNS), which requires an H$^-$ beam current more than 50 mA, and a duty factor of 1.5%$\sim$2%. The ion source produces an H$^-$ beam of 20 mA without cesium injection. After it is cesiated, about 47 mA H$^-$ beam is extracted. The emittance of the ion beam is measured both with a double-slit scanner and a pepper-pot device. It gives a normalized root of mean square emittance of more than 0.4 $\pi\cdot$mm$\cdot$mrad at a beam current of 27.5 mA, which is much lager than the acceptance of Radio-frequency Quadruple (RFQ) accelerator located downstream. To find the reason, the magnet field distribution of the extraction system is measured. Based on the measurement, the trajectories of the H$^-$ beam and the co-extracted electron beam are simulated with CST program.
