Towards optimum material choice for LHC collimation upgrade
The first years of operation at the LHC showed that collimator material-related concerns might limit the performance.
In addition, the HL-LHC upgrade will bring the accelerator beyond the nominal performance through more intense and brighter proton beams.
A new generation of collimators based on advanced materials is needed to match present and new requirements.
Low-impedance collimators for IR7
Low-impedance and robust secondary collimators made of Mo-Gr are planned to replace the present CFC secondary collimators in IR7 to cope with the HL-LHC beams.
The new low-impedance collimators will also have a completely new jaw design and material, which have to be validate throughout extensive simulation studies.
The list below includes inputs from tracking simulations (SixTrack) to be used for energy deposition studies:
- Reference case: 7 TeV, beta*=55 cm, 1-sigma retraction IR7 collimator settings, 500 kW on collimation system
- HL-LHC baseline: 7 TeV, beta*=15 cm, 2-sigma retraction IR7 collimator settings, 1 MW on collimation system
FLUKA maps will provide inputs for mechanical simulations with ANSYS to validate the jaw design for 1 MW scenario at 7 TeV.
Dispersion suppressor collimators in IR7
One of the main limitations to the cleaning efficiency of the present collimation system is posed by losses in the Dispersion Suppressor (DS) magnets downstream of the betratron cleaning insertion IR7. This concern becomes even more relevant in the perspective of the higher intensities of HL-LHC beams.
The mitigation of DS losses will rely on adding one (or two) TCLD collimators per beam in IR7 to clean local losses and reduce the risk of quench of superconducting magnets in the DS. Two staged installation in LS2 and LS3 following availability of 11 T dipoles is foreseen.
According to the present baseline, TCLDs will be made of Inermet-180.
The final settings for these collimators are still under discussion. Futher studies are needed to evaluate whether the loss peak in the DS magnet coils downstream of IR7 would be tolerable or not for the following TCLD configurations:
