LS1 Report: antimatter research on the starting blocks

The consolidation work at the Antiproton Decelerator (AD) has been very intensive and the operators now have a basically new machine to “drive”. Thanks to the accurate preparation work still ongoing, the machine will soon deliver its first beam of antiprotons to the experiments. The renewed efficiency of the whole complex will ensure the best performance of the whole of CERN’s antimatter research programme in the long term.


The test bench for the new Magnetic Horn stripline. On the left, high voltage cables are connected to the stripline, which then feeds a 6 kV 400 kA pulse to the Horn. The Horn itself (the cylindrical object on the right) can be seen mounted on its chariot.

The consolidation programme at the AD planned during LS1 has involved some of the most vital parts of the decelerator such as the target area, the ring magnets, the stochastic cooling system, vacuum system, control system and various aspects of the instrumentation. In addition, the programme also included the installation of a brand new beam line for the new BASE experiment. “The programme has been prompted by the starting of the Extra Low ENergy Antiproton ring (ELENA) project – the upgrade that is planned to be operational in 2017,” explains Tommy Eriksson, member of CERN’s Beams Department and expert in charge of the AD Operations. “Because ELENA is coming up, we have to make sure that the AD will also be able to operate efficiently for the 20 years to come! LS1 was the first period during which we could carry out major consolidation work although urgent consolidation work had already taken place in recent years.”

A lot of work was carried out in the target area. The AD target area is a secondary beam production zone, where antiprotons are produced, collimated and momentum-selected to prepare for their injection into the decelerator, where their energy is reduced to the level requested by the experiments. The antiprotons are produced by using the 26 GeV/c proton beam extracted from the Proton Synchrotron (PS). “The AD target area was designed 30 years ago for a high repetition rate of one proton pulse every 2.4 seconds,” says Eriksson. “Presently, we use it at a repetition rate of 90 seconds and this has meant that the components have worn out more slowly. Although the target has been running extremely well since installation, at the beginning of LS1 we found a very serious problem in the transmission line for the electric pulse that goes into the magnetic horn – a device used to focus the diverging anti-proton beam.” As a result, an urgent repair programme was established by TE, EN and BE department specialists, to replace the transmission line and magnetic horn chariot. While repairing the damaged components in the target area, the teams also renovated and improved the transport system including remote manipulation and monitoring.

One of the 24 main bending magnets in the AD ring. The lower coil is here being lifted out of the lower half of the magnet yoke.

Installed right in the heart of the decelerator ring, the dipole magnets also required a lot of attention from the experts in charge of the AD consolidation programme. “One of the 20-tonne bending magnets was taken out of the ring and opened up for the first time in thirty years. The coils were in good condition but the shimming that holds the coils had been completely transformed into dust. Of course, this meant that we had to rebuild it all,” says Eriksson.

The consolidation programme for LS1 was completed at the end of July and the first beam was sent to the target on 5 August. Debugging, adjustments and fine-tuning are being carried out to deliver antiproton beams to the experiments. While they will be running, the technical teams will continue to work on the upgrades planned during the machine shutdowns and the future LS2.

Did you know?

Although it started operations for the antimatter programme in 2000, the AD has almost 30 years of running as it reuses almost entirely the components and configuration of an older machine - called the Antiproton Collector (AC) – built in 1986. The collector was converted into the decelerator we have today in order to deliver lower energy antiprotons, as required by the present experiments.


Meanwhile, elsewhere...

At the LHC, the electrical quality assurance (ELQA) tests being carried out before cooling are almost complete in all sectors, with the final stages in sector 4-5 on course for completion next week. These tests have allowed non-conformities to be identified in two sectors, which have now been corrected.

Sector 6-7 is at the nominal temperature of 1.9 K and five other sectors are now being cooled; they are currently at various different temperatures. In accordance with the new schedule, all sectors will first be cooled to 20 K for the CSCM (Copper Stabilizer Continuity Measurement) tests, which allow the performance of the circuits to be checked when they are not superconductive.

Also in preparation for the arrival of the beam in the LHC, expected in March 2015, experts will soon begin current tests, starting with sector 5-6.


by Antonella Del Rosso