Study of electrostatic-magnetic deflector for CEPC

Purpose As the key component for the Higgs operating mode of Circular Electron-Positron Collider (CEPC), the electrostatic-magnetic deflectors are required by the double ring collider to separate the electron and the positron beams horizontally in the RF regions. The electric field is required to reach 2 MV/m with the vacuum pressure of less than 2 × 10^-10 Torr. The deflectors make use of both electric and magnetic fields to deflect the beams. The incoming beam gets zero deflection, but the outgoing beam is deflected by the combined effect of the electric and magnetic forces. W and Z modes use the same cavities with H mode to save budget. The deflectors are large contributors to the overall beam impedance which is necessary to be reduced as much as possible.
Methods The electric and magnetic field optimization has been performed by the Opera. The beam impedance study has been carried out using the Computer Simulation Technology (CST) particle studio.
Results The shape of the electrode is optimized for a good electric field homogeneity (± 0.05%) in 46 mm × 40 mm region. The electric field and the magnetic field could be matched perfectly in the main body of the deflector by bending the electrodes and introducing magnetic field clamps and mirror plates. The beam loss factor decreases by about 20% via the introduction of ground electrodes and tapering ends.
Conclusions The design results successfully meet the physical requirements, and the mechanical design has been finished.