Optics Tuning for Beam Collimation in the J-PARC 3-50 Beam Transport Line

Abstract

The Japan Proton Accelerator Research Complex (J-PARC) 3-50 Beam Transport line (3-50BT) is a beam transport line from 3-GeV rapid-cycling synchrotron (RCS) to 50-GeV main ring (MR). The RCS is a high-intensity proton accelerator, where the designed beam power is 1 MW, and has the complex source of space charge effect and beam instability, etc. Therefore, the uncontrolled emittance growth and beam halo increase nonlinearly with the beam power ramp up. Additionally, the physical aperture of 81  mm mrad in the MR is smaller than physical aperture of 486  mm mrad in the RCS. Therefore, the 3-50BT line has the collimators in order to remove the unwanted beam tail or halo from the RCS. The designed collimator aperture is 54  mm mrad. It is required to measure and optimize the optics parameters in the collimator area for taking full advantage of the beam collimation. Especially, it is very important to make the dispersion functions free in the collimator area and optimize the beta function to remove beam tail or halo over predefined transverse emittance. This paper introduces the method of optics measurement and reports the results of the measurement and optimization based on an accelerator model.