Development of ceramic vacuum chamber for collider ring kicker of Circular Electron Positron Collider (CEPC)

Abstract

The fast-pulsed kicker of the collider ring of Circular Electron Positron Collider (CEPC) uses a ceramic vacuum chamber to reduce eddy currents and maintain the magnetic field waveform at the beam's track. But the image charges induced by beams will accumulate on the insulating ceramic to increase the beam impedance. Eddy current shielding and beam impedance are traded off by coating a discontinuous “pattern” of TiN (titanium nitride) film on the inner wall of the ceramic vacuum chamber. Several potentially effective coating patterns are proposed. The eddy current shielding effect and the beam impedance are analyzed by simulation software. The simulation results show that coating in a ladder-shaped pattern maintains the magnetic field waveform well and helps to reduce the impedance. Properties such as electrical conductivity and SEY (secondary electron yield) of the films are improved in coating experiments and the technical feasibility of coating in a racetrack-shaped ceramic vacuum chamber is verified. Finally, the impedance of a 1200 mm-long ceramic vacuum chamber coated with ladder-shaped pattern film and the effect on the kicker magnetic field are measured.