It’s Sunday night at 10.05pm, and I’m at work. I am being afforded the chance to update in the blog again (seriously, someone tell me if I’ve posted a bit too much recently and I’ll tone it down) thanks to the beams again, this time though, the lack thereof. I am on shift, but not ATLAS shift. I am in the north area of the CERN prevessin site, situated on the French side of the border, here. That big building is where some of the test beams take place and as a member of the ATLAS 3d-pixel collaboration I am part of a small group testing 3d silicon sensors that could potentially be used in the ATLAS pixel detector upgrade. I won’t go into the details of this side of my work now (although it is quite exciting in my opinion) but just to mention a couple of things. I posted many words about the beam in the LHC late on Friday, November 20th, trying to relay the obvious excitement here at CERN about the first circulating, captured beams in the LHC for over 14 months! The particles contained in the LHC beams don’t appear out of nowhere though, they are the result of a long process, culminating in a machine called the SPS.
You can see the SPS in relation to the LHC on this post. The SPS stands for Super-Proton-Synchrotron and it’s the final injector for high-intensity proton beams for the LHC, accelerating protons from 26 GeV to 450 GeV. This is the energy of the protons in the LHC right now, so the LHC is not accelerating these bunches, only taking what the SPS feeds it and trying to capture and store them. The acceleration will come later.
For the purposes of my current test beam shifts we use the SPS as our source of particles. With the graphic below I’ll try to explain the multi-purpose way in which the SPS serves the CERN site.
The SPS Cycle Explained!
For our test beams we are interested in steps 1, 2 and 3. The protons are injected into the SPS from the PS and then accelerated, they are then sent down beamlines to targets. What happens when the protons hit the target (we have been working at areas called H6 and H8 recently) is that they produce secondary particles, many of which are pions that are focused toward these experimental areas where we have equipment to record their presence and use the beam to test whatever sensors we put “in the beam”. The LHC gets the beam towards the end of this cycle, as the graphic shows.
Tonight though the beam hasn’t beam as spectacular as the other day:
Not every moment is a champagne moment
Given that it’s after 10pm now and the picture tells you that we’re had a vacuum problem for over 2 hours we may be in for a long night. But we keep on trying….
