Author: Suetsugu, Y.
Paper Title Page
TUOBC02 Small-Beta Collimation at SuperKEKB to Stop Beam-Gas Scattered Particles and to Avoid Transverse Mode Coupling Instability 1104
  • H. Nakayama, Y. Funakoshi, K. Kanazawa, K. Ohmi, Y. Ohnishi, Y. Suetsugu
    KEK, Ibaraki, Japan
  • H. Nakano
    Tohoku University, Graduate School of Science, Sendai, Japan
  At SuperKEKB, beam particles which are Coulomb-scattered by the residual gas molecular change direction and will be eventually lost by hitting beam pipe inner wall. Due to large vertical beta function and small beam pipe radius just before IP, most of Coulomb-scattered particles are lost there and are very dangerous for the Belle-II detector. To stop such particles before the IP, vertical collimators are installed in the ring. However, such vertical collimators should be placed very close (few mm) to the beam and therefore induce transverse mode coupling instability. To avoid beam instability and achieve collimation at the same time, we need to install vertical collimators where vertical beta function is SMALL, since maximum collimator width determined by aperture condition is proportional to β1/2, and minimum collimator width determined by instability is proportional to β2/3. We present our strategy to stop beam-gas scattered particles and simulated loss rate in the interaction region. We will also show dedicated vertical collimator design to achieve less instability.  
slides icon Slides TUOBC02 [2.196 MB]