Electromagnetic design optimization studies for βg =0.61, 650 MHz elliptic superconducting radio frequency cavity

For the proposed Indian Spallation Neutron Source (ISNS), an injector linac is being designed at Raja Ramanna Centre for Advanced Technology. The injector linac will comprise of multi-cell superconducting elliptic cavities to accelerate the H- beam in the range 200 MeV - 1 GeV. Two families of such cavities are proposed to be used - βg=0.61 cavities to accelerate the beam in the range 200 - 500 MeV, and βg=0.9 cavities to accelerate the beam in the range 500 MeV - 1 GeV. For the optimization of the geometry of such cavities, we have recently developed a generalized approach and used it for the optimization of βg=0.9, 5-cell cavities. In this paper, we use the approach described in Ref. 1 to optimize the geometry of βg= 0.61, 5-cell cavities to maximize the achievable accelerating gradient. The geometry of the end cells of the cavity have been especially optimized to facilitate the extraction of trapped monopole higher order modes. For the dipole higher order modes, we have performed a calculation to estimate the threshold current for excitation of regenerative beam break up instability. We discuss the details of these design calculations in the paper. (author)