EPFL, Lausanne
CERN, Geneva
Crossing transition energy in the CERN PS is critical for the stability of high intensity beams, even with the use of a second order gamma transition jump scheme. The intense single bunch beam used for the neutron Time-of-Flight facility (n-ToF) needs a controlled longitudinal emittance blow-up at the flat bottom to prevent a fast single-bunch vertical instability from developing near transition. This instability is believed to be a Transverse Mode Coupling (TMCI) type. A series of measurements performed in 2009 and 2010 aims at using this TMCI observed on the ToF beam at transition, as a tool for estimating the transverse global impedance of the PS. For this purpose, we compare the measurement results with the predictions of the HEADTAIL code and find the matching parameters. This will allow predicting the stability of the high brightness LHC beam near transition. The final goal is to study the feasability of a possible cure to the fast vertical instability measured on the ToF beam by applying an improved gamma transition jump scheme instead of compromising the longitudinal density.
