Dipole-mode-free and kick-free 2-cell cavity for the SC ERL injector

For the ERL injector, superconducting cavities are needed to deliver to the beam a 100 kWCW RF power. With a beam current of 100...33 mA, gap voltage of 1...3 MV, the coupler must have an external g-factor in the range of 4.6×10⁴...4.1×10⁵. The cavity shape and coupler design presented provide the possibility of working in the range of parameters without substantial transverse kick to the beam and HOM-losses in the system. In order to preserve field flatness while the dipole mode is driven out, the 2-cell cavity has a protruding iris between the cell and the larger beam pipe. A twin-coaxial coupler has high coupling but low kick because of its symmetry. Calculation and optimization of the coupler-cavity system are performed with a 2D SLANS and 3D Microwave Studio^® codes.