Development of Pepper-pot Emittance Monitor for High-intensity Ion Beam Accelerated by RIKEN AVF Cyclotron

At the Center for Nuclear Study of the University of Tokyo, the measurement of Electric Dipole Moment of Francium (Fr) is underway with the world highest precision. Fr is generated by nuclear fusion reaction by irradiating gold with oxygen ion beam accelerated by RIKEN AVF Cyclotron. The required beam intensity is 18 eµA or more. However, the average beam transport efficiency drops to be around 66 % as the beam intensity exceeds 10 eµA. To solve the problem, a pepper-pot emittance monitor (PEM) for high-intensity beams has been developed. Referencing the PEM used for the injection beams of AVF Cyclotron, we have developed three additional items. The first is reducing the radiation damage to a camera, which is placed away from the beamline. The distance between the camera and PEM is 2.2 m, and the average image position accuracy of 0.15 mm is achieved. The second is the angular accuracy suitable for the accelerated beam. The required angular accuracy is estimated to be less than 0.3 mrad. A beam test for the first and second items is planned. The third is a beam shutter system to prevent PEM from heating due to beam. The measurement time by the system reaches 0.27 seconds now.