TMCI for LHC collimators (very preliminary results) Benoit, Elias, Giovanni, Nicolas Thanks to Adriana and the collimation team for the collimator parameters

Context Phase 2 collimation project to replace the existing collimation system. Objectives: divide the impedance by 10 while keeping collimator robustness and flatness Need to give answers to the Phase 2 collimation project, in particular in terms of the impedance of preferred materials. Need to assess the multibunch and single bunch effects of changing materials. Here we look at single bunch effects Integration of the preprocessing and postprocessing steps to obtain the impedance and launch Headtail simulations for a set of collimators.

Example of TMCI for a Phase 1 graphite collimator (gap=6 sigma) in IR7 TMCI between modes 0 and -1 Instability threshold at ~1014 p/b

Changing the collimator resistivity (Here, the thresholds were obtained using the Sacherer formula) - We are quite far from the threshold - Worst case seems to be for resitivity of around 1 Ohm.m

Changing the collimator permittivity (Here, the thresholds were obtained using the Sacherer formula) - We are quite far from the threshold - Worst case seems to be again for resitivity of around 1 Ohm.m

To be continued…