Things are happening pretty quickly, after all! Six hours ago, protons were injected into the main LHC ring and they travelled several meters before (presumably) crashing into a deliberate beam dump. I had heard about an upcoming test in which the beam would be injected into one sector only (Sector 1-2, near ATLAS— the ring is divided into eight sectors). This must be the beginning of that test.
Here is a “Beam TV” image captured from the monitors and passed around to everyone in US-CMS. The blob must be the not-very-well-centered beam.
To try to figure out what it is we’re looking at, I found the following paper: A Large Scintillating Screen for the LHC Dump Line by T. Lefèvre et al., which has this figure:
Apparently, the beam is spattering through an alumina ceramic screen which lights up due to the radiation, and the image is captured by a CCD camera. I strongly suspect that this configuration is only used for tests: ordinarily, we wouldn’t want any obstructions to the beam (and that makes it hard to image).
According to the LHC e-log:
Protons were injected into the LHC (clockwise/Beam 1) today at about 6:30 PM, CET. The injection kicker fired and the beam appeared on the TDI (internal target)–this is a few meters into the LHC. Now, they are working on the kicker that needs to fire to keep the beam in the ring.
And this blog shows celebrations in the LHC control room. They have a picture of a beam which is even less-well centered (probably the very first).