Transfer line tests take centre stage

Last weekend, proton beams came knocking on the LHC's door. Shooting from the SPS and into the two LHC transfer lines, the proton beams were dumped just short of entering the accelerator.


The upper plot shows the trajectory of the first TI2 beam, which reached the end of the transfer line in a single attempt after 18 months of technical stop. Below, a smoother beam trajectory in TI2 after some corrections.

For the first time since Run 1, the SPS to LHC transfer lines (TI8 and TI2) transported proton beams just short of the LHC. "We tested the beam instrumentation, the devices that measure the beam intensity, transverse beam profile, position and losses, as well as the beam collimators along the transfer lines," says Reyes Alemany Fernandez, the engineer in charge of the LHC. "We were also able to spot possible bottle necks in the beam trajectory and to perform the first optics measurements."

Once the beams arrived at the transfer line beam dumps, they generated offshoot particles - primarily muons - that are usually considered background events for the ALICE and LHCb detectors. During the weekend’s tests, however, these muons were used to calibrate the ALICE and LHCb detectors. "The experiments were given the precise timing of each beam dump, which allowed them to tune their detectors and trigger to the LHC clock," says Verena Kain, SPS supervisor. Click here to read more about the tests performed by LHCb.

The weekend also saw action in the LHC itself, with the first direct tests of the LHC equipment. The Operations team looked at the timing synchronisation between the beam and the LHC injection and extraction systems: "We were able pulse the LHC injection kicker magnets and trigger the LHC Beam Dump System in Point 6, even though neither saw beam," explains Reyes. "These are key systems for the machine, so being able to successfully commission them prior to beam tests in February was invaluable." The injection lines were also primarily driven by the LHC control system. Although this could have been done using the SPS, it was a great opportunity for the Operations team to test the LHC timing system as well as the complex protocol that allows the LHC to request a beam from the injector chain.

The transfer line tests were very successful thanks, in part, to careful preparation carried out since the beginning of the year. Regular “dry runs” were organised during the year by the LHC Operations team, together with the different equipment experts, to test and debug the accelerator sub-systems from the CCC control applications.

by Katarina Anthony