LABORATORI NAZIONALI DI LEGNARO
Inter University Accelerator Center (IUAC); New Delhi is equipped with 15UD Pelletron, which is capable of producing energized ion beam of the entire periodic table. To increase the energy of the ion beam from Pelletron accelerator, a superconducting booster linear accelerator (linac) is under construction. Quarter wave resonator (QWR) made by niobium has been chosen as the accelerating unit of the Linac. Initially, the first twelve resonators were fabricated in collaboration with ANL, USA. Recently eight resonators along with a superconducting solenoid had been installed and aligned in the first linac cryostat at IUAC. In the first on-line beam acceleration test, a pulsed beam of 28Si+7, 90 MeV, 1.5 ns FWHM was injected into the superbuncher which produced a beam of 300 ps FWHM at the entrance of Linac. By turning on resonators one by one in linac cryostat and carefully adjusting their reference phases, a total energy gain of ~ 6 MeV was measured at the exit of linac. However, the energy gain from the five resonators was a factor of three less than what was expected from the design value of the resonator. The reason behind the poor performance of the resonator was identified as the metal coating on the inside surface of the power coupling port of the resonators. The most probable reason behind this metal coating is the usage of excessive RF power to lock the resonator at a given field. The problem of usage high RF power was attacked by cooling the drive coupler and most importantly, by damping the lowest mode of the mechanical vibration of the resonator by using simple SS-balls. This simple, inexpensive mechanical damper had reduced the RF power by ~50% or more when the resonator was phase locked in Linac cryostat. In a parallel path, fabrication of more niobium resonators has been going on in house. After the successful completion of the first niobium resonator at IUAC, the fabrication of a couple of resonators is finished and production of another fifteen resonators is going on right now. The seminar will cover the first beam acceleration by the first linac module, its associated problems and their solutions including the novel damping mechanism. The fabrication facility to produce niobium resonator at IUAC will also be discussed in the presentation.

DATA: 26-10-2005