Status of the different simulation models for the future collimators in the Dispersion Suppressor (DS).
(Extract from HiLumi report D5.3, courtesy S. Redaelli)
The losses in the IR7 DS and downstream arcs consist of particles that have scattered out of
the collimators with large momentum offsets, but not large enough betatron amplitudes to hit
the downstream collimators. They do not get large transverse offsets until they reach the DS,
where the dispersion starts to rise.
A possibly very efficient way of intercepting them is thus
to install additional collimators in the DS itself, where the dispersion has started to rise.
We call these collimators TCLD. The TCLD locations must be upstream enough to intercept the
losses, with the important peaks starting in cell 8 (results in Halo simulations).
At the same time they have to be
downstream enough where the dispersion is already important. This constrains the possible
locations to places where the available space is presently insufficient for installation.
The preferred solution to create space for a TCLD is therefore to remove one existing dipole magnet and replace it by two shorter magnets with a higher field of 11 T, as shown below. Between the two new magnets, there is enough space for a collimator of about 1m. In order to introduce the DS collimators into the SixTrack simulation setup in a flexible way, a script (see below, "Particle Tracking Simulations") was implemented to replace in MAD-X any existing dipole, identified by name, by two shorter ones with a collimator in between.
Preferred layout of the assembly, consisting of two shorter dipoles with a collimator in between, which can replace an existing LHC dipole.
Taken from V. Parma's presentation pdf pptx at the LHC Collimation Review 2013.
Different particle tracking simulations (SixTrack) were performed with extra DS collimators.
The MadX sequences (used to generate SixTrack inputs) were modified to include the extra collimators.
The first modifications simply consisted in adding "thin" markers for the collimators to the sequence, next to the Q8 and Q10 (results in Halo simulations).
| MadX script, thin TCLD |
Then, the sequence was modified further. In cell 8 and 10, one 8.3T dipole was replaced by two smaller 11T dipoles, keeping the optics unchanged, and a collimator in the newly available space between these two dipoles (R. Bruce).
| MadX script, 11T dipoles |
