The Control Room is a hive of activity while the electrical tests are carried out.
The quadrupole and main dipole circuits have been powered up to 10,200 amps in Sector 4-5. Sector 5-6 is currently being cooled and will be the next to undergo electrical tests, which will be stepped up over the next few weeks.
Numerous electrical tests were carried out in Sector 4-5 during the period from November to mid-February. Once the temperature had been stabilised at around 1.9 K (-271°C) at the beginning of December, the circuits were initially powered up to 8,500 amps. The main dipole circuit was then gradually brought up to 10,200 amps during the last week of January, then the main quadrupole circuits to 10,800 amps in February. At this intensity of current the magnets are capable of guiding a 6 TeV proton beam. During this process, for both the dipole and the quadrupole circuits, a number of training quenches occurred.
138 superconducting circuits ramped in unison at an equivalent beam energy of 5.3 TeV.
"Given the limited time at our disposal, we decided to stop at this energy, which is very close to the target, and start to commission the numerous circuits (each sector has 200) before Sector 4-5 was warmed up again. The mechanics have to connect the triplet (the focussing magnet on both sides of each experiment). We have scanned all the circuits to check that they are working properly. Today we know that the electrical circuits in this sector require no major corrective action", says Roberto Saban, responsible for coordinating the commissioning of the LHC technical systems.
"The experience we gained in Sector 7-8 has already allowed us to validate and improve the procedures, the tools and our understanding of the phenomena we encounter. This is invaluable for the sectors to follow, as confirmed by the commissioning of Sector 4-5, which was a lot quicker and more efficient", he continues. The teams who carried out the work and those responsible for the equipment from the AB, AT and TS Departments worked flat out to optimise the tests. Their task was facilitated by the existence of special tools designed to help with carrying out tests and analysing the results.
The commissioning of the LHC began with Sector 7-8 in June 2007. During the summer, the quadrupole circuits in the sector were powered up to 6500 amps (see Bulletin 30-31/2007 of 23 July 2007). The next sector to cross the 10,000 amp threshold will be Sector 5-6, which is currently being cooled down. It is scheduled to reach 1.9 K by the end of March, when it will be subjected to the same tests as Sector 4-5. Thanks to the experience gained, the commissioning should proceed even faster.
From late April onwards, the LHC commissioning teams will have a new sector cooled to 1.9 K and ready for testing every two weeks.
"We are working on unique and magnificent hi-tech facilities with sophisticated tools. I have every confidence in the professionalism and motivation of the teams involved and think we will be able to meet the challenge of completing the commissioning procedure for the summer", concludes Roberto Saban.
More from LHC
Warm reception for warm magnets
A celebration marking the successful completion of the installation of all the normal conducting magnets in the LHC was held on 19 February.
A celebration making the successful completion of the installation of all the normal conducting magnets in the LHC was held on 19 February
You often hear the LHC described as a super-conducting particle collider. However, that’s not 100% true. In fact, there are 154 normal conducting or ‘warm’ magnets in the collider, about 12% of the total number, which will be indispensable in shaping the course of the proton beams when the LHC is switched on.
A celebration organised by the AT/MCS (Accelerator Technology/Magnets, Cryostats and Superconductors) group commemorating the installation of the last warm magnet was held on 19 February in Hall 867 – the location where each of the magnets, plus many spares, have been tested over the past 10 years.
The LHC is not a perfect circle and in some places it’s almost straight. In these sections, the magnetic intensity required to bend the proton beams is not as high as elsewhere. In these few parts of in the accelerator, for instance on each side of the four big experiments and where there are the so-called long straight sections, the magnetic intensity delivered by warm magnets is sufficient, hence their use.
Another advantage of warm magnets is their robustness when exposed to radiation. In the locations where the proton beams interact there are a greater number of secondary particles. An example is in the long straight sections LLS3 and LLS7, where collimators clean the beam by removing particles that are located far from the central distribution of the proton bunches. Using superconducting magnets here would be hard, as senior physicist and previous head of the Normal Conducting Magnet section, Willi Kalbreier, explains: "Collimators take away the secondary particles, but they are not stopped immediately and reach the magnets. If they heated a superconducting magnet above a certain point the magnet would quench," – therefore losing its superconducting ability and stopping the whole accelerator.
Nearly all the warm magnets were made especially for the LHC and travelled vast distances to reach CERN. 48 magnets have come from Vancouver, 40 from Protvino near Moscow and 65 from Novosibirsk in Siberia (travelling a staggering 5,000 miles to reach CERN). That leaves just one magnet that was not built from scratch for the LHC. Originally built for the ISR in the 1970s, it has now been recycled for use in ALICE.
Apart from being able to withstand relatively high radiation loads, warm magnets also have the advantage of being more affordable than superconducting magnets and easier to make and install, due to their comparative simplicity. The head of the Magnets, Cryostats and Superconductors group, Lucio Rossi, believes that this is where warm magnets come into their own. "This is the new challenge – to do something that is affordable. It is not impossible," he said.
At the celebration Rossi gave a speech thanking all the contributors for their hard work. "This has been the fruit of collaboration between CERN and many countries which have contributed financially and via their national laboratories which designed and made these magnets for the LHC", he said. "Today we are very happy".
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