The Super Proton Synchrotron (SPS) is undergoing an overdue overhaul. Its beam dump, which was previously at point 1 of the SPS, will be replaced by a new one located across the ring at SPS point 5. The new beam dump being constructed requires extensive civil-engineering work to house and operate it, which is one of the primary tasks for the SPS team during the second long shutdown (LS2) of CERN’s accelerator complex.
When a beam of protons or heavy ions accelerating through the SPS needs to be brought to a stop, it is redirected into a beam dump that absorbs the particle beam, terminating its flight. “We need a bigger dump for the SPS due to the higher energies of circulating particles following the LHC Injector Upgrade (LIU) project,” explains Jonathan Meignan, who is coordinating the project to replace the SPS beam dump. After scouting for a suitable location, it was decided to install the new beam dump at an opposite point in the SPS ring, where there is sufficient space for the dump and the additional infrastructure it needs.
The task is however a difficult one, involving several related works. The underground cavern that will house the new beam dump, known as ECX5, was the location of the erstwhile UA1 detector, which discovered the W and Z bosons in 1983 when the SPS was operated as a proton–antiproton collider. It will need to be drastically modified to incorporate the services needed for the modifications to the SPS. For example, the transport zone next to the SPS tubes, which is used by both personnel and equipment, will have to be rerouted so it skirts the voluminous beam dump and its large shielding. The SPS tunnel will therefore undergo digging to widen a section of it by about one metre to accommodate the new shape of the transport zone.
Kicker magnets, which are responsible for deflecting the travelling particles into the dump-bound trajectories, have to be installed in Long Straight Section 5 of the SPS leading up to the beam dump. “To prepare for this installation, the beamlines within LSS5 had to be completely removed,” remarks Meignan. Simultaneously with this removal, an intense decabling campaign was conducted to free space for the new cables. More than 135 km of obsolete cables were removed, notes Meignan. New cables, including high-voltage cables for the kickers, have been installed, snaking all the way from LSS5 to the service cavern adjacent to ECX5, where their instrumentation and control systems will be located.
The crane suspended from the roof of ECX5, which can be used to move the large blocks making up the beam dump, has been upgraded as well. “The crane was fitted with cameras during the last year-end technical stop,” says Meignan, “and equipped for remote control from the service cavern, to minimise the radiation exposure of the operators.”
As of early April, ECX5 has been isolated from the rest of the SPS to conduct these civil-engineering activities, which are expected to be finished in December. At the same time, the dump and its shielding, which is made of steel, concrete and marble surrounding the inner core, is being assembled on the surface above its future home. In the new year, the beamline will be reconnected and the dump will be installed before being commissioned.
We will return to the SPS and its many LS2 activities in a future report.