Overview
Sector 20 beamline prior to the FY21 reconfiguration effort is shown schematically below.
The final build (by the end of the 2021 summer downtime) looked like this from final focus down to the dump (with the exception of the turbo pumps for the Differential Pumping System):
Final Focus Rebuild
Final Focus re-build is complete. State prior to May is top image. State by the end of the 2021 summer downtime is lower image.
The three magnets closest to the user area (numbered from right to left: Q0FF, Q1FF and Q2FF) were installed in May 2021 with cans for future differential pumping system also installed. These have BPMs and are hooked up to power.
Upstream of these, Q3FF and Q4FF were installed in the summer downtime and the TCAV was relocated. In November, the TCAV was rotated such that the deflection is in x (rather than y).
Differential Pumping System
Pumps for the downstream side of the sector 20 differential pressure system will be installed by the end of the 2022 winter (January) downtime. The upstream pumps and the small apertures, required for the DPS performance with gas in the user area, will not be installed in this period.
There are four stages of differential pumping upstream of the IP and two stages downstream. Information on this can be found in the engineering specification document.
Ultimate plans for BC20 (sector 20 chicane) rebuild- timeline to be determined
A summary of the reconfiguration can be seen in the below PDF file but a top level overview of the changes is:
1) Reconfiguration from a 6-bend W shape chicane, to a 4 bend standard chicane. This increases the maximal horizontal deflection of the beam from about 25 cm towards the aisle side of the tunnel in the current chicane, to about 45cm towards the aisle side. So overall, the beam will be deflected further from the wall and penetrations than the existing chicane.
2) The chicane is being shortened slightly, with the final bend being moved upstream by 3.5 m from linac Z = 1977.2 to 1973.7 m.
3) The move entails removing 8 quads, 2 sextupoles, and 4 of the current bends and replacing with 2 new dipoles and repositioning everything else between. The position of every beamline element after the first chicane bend at Linac Z = 1929.2 m will change as is shown on the attached PDF.
