Design of the Medium Energy Beam Transport (MEBT) line for the Rare Ion Beam (RIB) project at VECC

The design of a 19 m long MEBT line connecting the accelerator LINAC 2 with LINAC 3 of the VECC-RIB project is presented. The design goal is to achieve a robust solution for the transport of heavy ion beams, emerging from LINAC 2 with a fairly large momentum width and transverse emittance with the mean energy of 289 keV/u and q/A≥1/14 so that the beam is well matched both in transverse and longitudinal directions at the entry of the LINAC 3. The limitations of the site necessitate a 90° bending of the beam a few metres downstream of LINAC 2 that adds to the further requirement and complication of dispersion suppression. The skewed position of the RFQ (before LINAC 1) vanes with respect to conventional horizontal and vertical planes complicates the design by requiring the decoupling of the X (horizontal) and Y (vertical) motion before the beam is bent in the 90° dipole after LINAC 2. In the design presented, step-by-step all the requirements, viz, decoupling of X-Y motion, dispersion suppression and transverse and longitudinal beam matching could be effectively met. The robustness of the design with respect to orientation of the initial beam ellipses has also been checked.