• S. Ghatak, A.S. Dhavale, K.C. Mittal
  BARC, Mumbai

BARC is involved in the development of superconducting cavities for Accelerator Driven Sub-critical System (ADSS). The performance of superconducting RF structure can be greatly affected due to multipacting. Hence 2D and 3D multipaction simulation studies have been carried out for a medium velocity (β=0.49) elliptical Niobium cavity operating at 10⁵⁰ MHz. An in-house code has been developed which uses finite element method based software to calculate electromagnetic field of the structure. Leap frog method algorithm has been used to solve Lorenz force equation for trajectory tracking of electrons which are launched inside from different initial positions. Electron trajectories are tracked until they hit the surface. An interpolation function is used to calculate SEY at different impact energies. By repeating the process at different field level for different primary electrons multipacting field levels are identified. The study revealed that the cavity structure is not multipacting prone up to 17 MV/m average accelerating field. Two point first order multipacting is observed at the equatorial region of the cavity when the accelerating field is between 18 MV/m and 28 MV/m.

• A.S. Dhavale
  BARC, Mumbai
• K.C. Mittal
  BARC-EBC, Mumbai

The performance of superconducting cavity, couplers and ceramic windows is greatly affected due to multipacting. The present paper describes the multipacting simulations carried out on the co-axial coupler. The equation of motion of electron in RF field is calculated numerically. The enhanced counter function (ECF) is calculated to find out whether a particular electron will give rise to the multipacting. The simulation was carried out for a co-axial coupler having the inner conductor diameter of 34.78 mm and outer conductor diameter of 80 mm at a RF frequency of 350MHz, 700MHz and 1050MHz.