Knocking at the LHC’s door

Less than 24 hours before the annual shutdown of the accelerators, the I-LHC teams dispatched a beam of lead ions towards the LHC.

A digital image of the ion beam extracted from the SPS into the TT60 transfer line at 5 p.m. on Monday, 12 November.

There was jubilation in the CERN Control Centre in the late afternoon of Monday, 12 November. Only a few hours before the annual shutdown of the accelerators, the I-LHC teams saw on their monitoring screens a beam of lead ions dispatched from the SPS reach the very threshold of the LHC. The beam was extracted in an area very close to the LHC for the first time: the TT60 transfer line. "This marks a new and important stage in the commissioning of the lead ion injection chain", observes Django Manglunki, who is in charge of the operation.

Members of the teams that have contributed to the success of the operation celebrate their achievements.

Since the installation of the low-energy ion ring LEIR in 2005, the I-LHC project headed by Stéphan Maury has been focussing all its energies on the injector chain in order to supply ion beams to the LHC in optimal conditions. This time last year, the ions accumulated in LEIR and sent to the PS were ejected at the threshold of the SPS for the very first time. This latest achievement marks a further milestone towards the teams’ target: circulating lead ions in the LHC to produce collisions.

The suspense had been mounting to fever pitch over recent weeks. Ions had been successfully injected into the SPS since the beginning of September. After many adjustments and targeted studies, the beam had been accelerated with a view to its extraction into one of the two transfer lines linking the SPS and the LHC. But technical problems had arisen, including a vacuum leak detected in the PS at the beginning of November. By increasing ion losses, this leak had resulted in a reduction in the intensity of the ion beam, placing the success of the operation in jeopardy. At about 5 p.m., thanks to an increase in beam intensity to 20 million ions per bunch, the long-awaited beam finally made its appearance on the control room screens as a tiny blue speck with a bright halo barely 1 mm in diameter.

This was a welcome reward for all those taking part in the operation and is the result of close collaboration between a large number of teams (Linac 3, LEIR, PS, SPS, Radiofrequency, Beam Transfer, etc.). "We have not yet reached the stage of filling the LHC, but we have good reasons to be satisfied, even if we still have a long way to go and many studies and adjustments to carry out", admits Django Manglunki.

The next stage will be to refine and optimise the beam to reach the nominal intensity of 100 million ions per bunch, five times higher than that recently obtained, so that it can be injected into the LHC and produce the much awaited collisions.