Knocking on the LHC’s door
On 24 May, a proton beam knocked on the door of the LHC. This is only the second time since 2004 that the beam has crossed from the SPS into the TI8 transfer line.
Screen shots from the Control Centre before (below) and after (above) the beam appeared in transfer line TI8.
Thanks to a huge collaborative effort the final commissioning of the transfer line TI8 has been successful. There was both excitement and relief as, after some unforeseen delays, the beam burst onto the monitors in the Control Room on Saturday 24th May. Although the beam is less intense (at around 5 thousand million protons per bunch) than will eventually be used in the LHC, this test represents an important milestone in the run-up to the switch-on of the accelerator.
The TI8 transfer line runs from the SPS towards the LHC, where it intersects just before point 8. The beam was extracted from the SPS, sent down the 2.8km transfer line and stopped just 15m or so from the LHC tunnel. This is done with a TED or ‘beam stopper’ that is physically placed in the path of the beam line to prevent the beam from taking the last step into the LHC.
Paul Collier, Head of the Operations Group, was satisfied with how the day went, and explains the delays: "Everything went to plan in the sense that we are more or less on time for our programme. We had some significant difficulties. For example, some of the elements that are there for safety were in a position where they were locked and they had to be released before we could withdraw them in order to send the beam."
The injection of the beam from the SPS to the transfer line requires extreme precision at very high speeds. The beam is travelling at essentially the speed of light and so the passage from one accelerator ring to the other has to be done in a matter of microseconds. In this case the deflection out of the SPS is principally achieved using ‘kicker’ magnets. "These are magnets where we can go from zero to maximum field very very quickly and in the case of the kickers in the SPS we are talking about a rise time of about 1 microsecond. As the beam is circulating in the SPS at a certain point you fire this kicker to make it go to the maximum field. When the beam passes it will see this field and it will be deviated out of the ring of the SPS and into the transfer line," says Paul Collier.
What comes next for the commissioning team? First, the second transfer line, TI2, will go through the same process in a couple of weeks’ time before the injector complex and the transfer lines are ready. After that is completed all the next steps are in the LHC. "At this point we have to continue the present activity of hardware commissioning in the sectors, but most importantly we have to finish the cool-down of the last two sectors," explains Paul.
Soon then, we hope, the LHC can open the door to its eagerly awaited guest.
