Superconducting RF cavities are designed to operate at a specific operating frequency with a very narrow bandwidth. Due to fabrication errors, the frequency and field flatness of cavity may differ from its designed values. Therefore tuning of SCRF cavity is an essential process during cavity development. Manual tuning fixtures and semiautomatic cavity tuning machines have been developed for frequency and field flatness tuning of nine cell 1.3 GHz and five-cell 650 MHz SCRF cavities. Tuning is performed by providing plastic deformations in cavity cells near stiffener rings. The tuning algorithms were developed to evaluate the frequency corrections required for tuning of each cell. Based on tuning algorithm, the cells are either compressed or stretched by motorized tuning jaws to get required corrections. Indigenous development of cavity tuning machine, establishment of tuning procedure and tuning of SCRF cavities are important milestones in the field of SCRF cavity technology development in India for future programs.

Principle of cavity tuning	Manual axial tuners with components	Manual circumferential tuner mounted on cavity
Cavity tuning machine for 1.3 GHz 9 cell cavity tuning	Cavity tuning machine for 650 MHz 5 cell cavity tuning	Field flatness of 650 MHz 5 cell cavity before and after tuning