LHC Report: Rehearsing the LHC accelerator systems for the Run 2 start-up with beam
While the commissioning of the superconducting circuits is ongoing, great care is also being taken to make sure that the other key LHC accelerator systems are qualified for beam.
Since spring 2014, small-scale integration tests on the accelerator systems have been scheduled and carried out successfully to exercise them fully and thoroughly debug their multiple interfaces. The LHC Operations team leads this activity in tight collaboration with the equipment experts and the essential support of the Accelerator Controls group. The tests start once individual system qualification has been performed by the equipment owners and they are ready to be handed over to operations. These tests performed by Operations are called dry runs – dry because they are performed without beam – and they are carried out from the CERN Control Centre (CCC) using the same high-level software applications that will be used during beam operation.
The dry runs are the first step towards a global integration test that involves all the accelerator systems including the superconducting circuits. In this global test, all systems are driven together through the nominal LHC cycle and will be carried out during the machine checkout phase.
For example, the integrated test of the LHC injection kickers, the LHC timing system, the injection protocol and the beam dump system is one of the most important dry runs. First of all, each system is dry run individually, i.e. the Operations team checks that it can be controlled remotely from the CCC with the right configuration. When all the individual tests have been completed successfully, they are done together: in this particular example, they are exercised together using the operational sequence called “inject and dump”.
The test is done without taking beam to the LHC, although the beam is requested by the LHC as the master of the injection protocol. Next, the beam is produced in the pre-accelerator chain, injected into the SPS and finally dumped in the SPS dump. Throughout this process, all the timing events are generated to allow the LHC injection kickers to be pulsed in synchronisation with the SPS beam. In addition, the radiofrequency (RF) systems of the LHC and SPS are automatically synchronised - a crucial condition to make sure the beam will, eventually, be injected into the requested LHC RF bucket. In parallel, all the relevant beam instrumentation for the injection qualification is triggered and analysed by the Injection Quality Check system. A few microseconds after the “virtual” injection, the beam dump kickers trigger to simulate a programmed dump. If this rather complex exercise is successful, we can claim that there is a good chance that we will be able to inject real beam in the LHC. The “inject and dump” sequence has been tested several times already for both beams, and it was the sequence used during the TI2 and TI8 transfer line test that took place in November 2014.
Many other tests have been carried out in recent months, addressing other systems like: beam instrumentation; the interface with the LHC experiments; the dedicated magnets for optics, aperture and tune measurements; collimators, etc. Other systems coming up are the Transverse Damper and the RF cavities, which will be soon handed over to operations. Also under way are critical tests concerning the machine protection systems of the LHC.
The LHC is a very complex machine. Dry runs are part of a staged approach towards beam commissioning that aims to solve problems before the beam arrives, and they are an important part of the overall strategy. Within this staged approach, dry runs and the powering tests of the magnets are two complementary activities that prepare the machine for a successful start-up with beam.
Meanwhile, on the powering test front, four sectors are now fully trained for 6.5-TeV operation with another well into its training program. Important preparatory work has finished in all sectors and the final push is under way to have all magnet circuits ready for beam commissioning.
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