Optimum phase focussing on the superconducting LINAC of IUAC

The superconducting linear accelerator at Inter University Accelerator Center (IUAC) is operated routinely to boost up the energy obtained from 15 UD Pelletron and the energised ion beam is delivered for scheduled experiments that extends for several months. Conventionally, the accelerating phases of the resonators are kept at 70 (or 80) degree and the time focussing at the experimental station can be achieved by operating the re-buncher resonators installed after the linac accelerating modules. As the time width of the beam bunch beyond ∼ 1 ns is not acceptable in many Nuclear Physics experiments, the use of rebuncher resonators became inevitable in the past. A method to reduce the longitudinal emittance of the energised ion beam is adopted by selecting the accelerating phase of about ≤ 50% resonators from 70° (or 80°) to 110° (or 100° ) respectively. This method, named as Optimum Phase Focussing (OPF), determines the combination of the accelerating phases of the resonators with the help of an in-house developed simulation program. During the recently concluded beam acceleration through linac, the phase combination on the resonators calculated by the OPF program was applied and a significant reduction of the time width and the energy spread of the beam bunch were measured along with a substantial enhancement of the beam transmission from linac to the experimental chamber. (author)