Tuesday, February 24, 2009

The Strobist goes to the LHC

Here's the gist of a conversation that went down last October-ish:

DH: The Googleplex may have just moved to #2 on my best-ever lighting seminar destinations.
Me: (bristling at the insult) How so?
DH: Received an invite to do one at CERN. The LHC is currently down and can be toured. And lit. And shot.
Me: HAH!, but do they have strawberry mojitos? And, um, holy shit. Need an assistant?
DH: I am sure they would have no problem. Even if he never did seem to do any work.
Me: engfeh... {wobble}... {THUD}

So that's where we were last week. Touring and shooting all four major detectors at the LHC, and getting better treatment than even nibs like the King of Belgium did (who, I'm told, got to tour a mere one experiment --- pah!).

So here's a brief rundown of the fun at CERN:

Day 1: ATLAS and CMS

Started off the day getting retina scans for our biometric passes into the detector. Now since my right retina is currently being held in place with some chewing gum and gaffer tape, I was all prepared for hilarity to ensue: "Please center your eye in the rectangle". "No, your *eye*"... but I was pleasantly surprised when the system actually worked pretty well.

The ATLAS detector was our first stop. As an aside, ATLAS is an acronym for "A Toroidal LHC ApparatuS". Uh-huh. I'm thinking someone was fishing really hard, and should've just gone with the first choice: "A Thingy Like an Awesome Stargate".



Interesting fact: The ring is an average of about 100m below ground, but it's at a slight angle to the earth's surface so that it all remains within the same geological plate. The engineers that built it thought long-term, and knew that if it straddled different layers, then shifts in the earth's crust over a 50 year period would deform the ring. If only we could write software with that amount of forethought :)

From our vantage point, we could see the ends of the huge superconducting magnets that focus the beam and collision debris. They're the orange-striped bits you can see if you click through to the picture above. It's fascinating to hear about how fragile the superconducting state really is; the currents in these magnets are of the order of 7000A, so a tiny loss of superconductivity in the coil would immediately shove a resistor in the path of that current, which would generate an enormous amount of heat, and cascade the loss of superconductivity to its surroundings.

While I went giddy over the machinery, David was busy scoping out the area and setting up a couple of lights... resulting in these shots of Xavier and Doris.

CMS (Compact Muon Solenoid) was the next stop. You know physicists have a sense of humor when they use the word "compact" in connection with anything resembling such a behemoth.



Michael Hoch was our physicist guide (and model). He pointed out another cool engineering trick: If you shoot the detector using an on-axis flash and nuke the ambient with a fast shutter speed, you'll see a cool pattern produced by little reflectors.



Photographing that pattern from many different vantage points allows them to precisely model thermal expansion/contraction of parts of the detector (which, y'know, you have to think about when cooling the blighter to a nippy -270C).

ATLAS and CMS are twins, in the sense that if the Higgs boson is found by either one, it will have to be verified by the other (The EU member states that fund CERN, and indeed the physics community in general, would turn a fairly jaundiced eye towards anyone making an ass of themselves by announcing a false positive).

Day 2: LHCb and ALICE

If matter and antimatter were created in equal measure at the time of the big bang, then how come most of the observable universe only contains "regular" matter? One of the goals of the LHCb (Large Hadron Collider - beauty --- since it's designed to study beauty-quarks/antiquarks) is to understand the asymmetries that caused matter to win out over antimatter within just a couple of seconds of the big bang.



Since most of the interesting traces for these particles happen in a thin cone around the beam direction, LHCb is constructed like a giant view camera, with planes of detectors perpendicular to the beam. Each of the vertical slices is separate detector, and can slide out on rails for maintenance.

The ultra-cool part? Niko took us to within spitting distance of the section of the beam-pipe that sees the actual collisions:



Most of the beam pipe that runs around the tunnel is made of stainless steel (which is pretty cheap to manufacture) and can handle the pressure differential of the near-vacuum that the beam must travel through. Steel however would cause too much scattering of the collision debris, so this bit (at the collision point) is actually made of beryllium. This is a bit more problematic to acquire since there are only a couple of places in the world that can machine beryllium (being quite fragile and a strong carcinogen in dust form). Right now, while the repairs are under way it's in its protective plexiglass casing, and is pressure-balanced by being filled with neon.

Here's our intrepid chaperon Niko, caught from my vantage point where I leeched off David's light setup. David's shots are here.



Our last stop was ALICE (A Large-Ion Collider Experiment). Besides being able to analyze proton-proton collisions, ALICE can also analyze collisions between much heavier lead-ions. Our crazy kart-racing, horse/jellyfish-eating friend Fons likened it to the difference between smashing a couple of tennis balls together versus a couple of Steinways. There's a lot more debris to analyze in the latter, and part of his work is building out the software infrastructure that can make sense of it all.



Some more pictures from ALICE:




The next day (Saturday), David did the Strobist seminar, and I got to hang out with a bunch of awesome people from all over the place. And on Sunday, Péter & András (the organizers of this entire trip) gave us a choice of driving up a stunningly beautiful mountain, or visiting CERN's compute-center and taking more cool pictures. So, of course we chose the compute-center (besides, it was snowing like crazy).

As of this writing, they have about 15PB of spinning disk storage that is used as a cache for 18PB of tape storage. It was cool watching the little robotic arms shuttle tapes around, so we had to stop and take a shot of that as well.



Huge, huge thank you to Péter, András, Fons, Doris, Niko, Michael, and all the folks at CERN who gave us the unprecedented access. Péter, thanks especially for all the early mornings you had to endure. You can now go back to your regular schedule waking up at the crack of noon :)

DH, I owe ya big time for letting a drooling geek tag along, although I know the really hard bit was parting with half your last 5-hour-energy shot ;)

3 comments:

Johannes said...

Good job escaping from the black hole with your camera and these awesome photos! Stargate and Caught on Tape are my favorites.

Mark H. said...

Brilliant stuff, way to go Aaron and David!

mundhenk666 said...

Wow, that is totally sweat!