Transcript TMCI for LHC collimators

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…