Life as a Physicist

Wow – I didn’t realize how many meetings there were going on this week! In ATLAS there is the trigger workshop I’m attending in Beatenberg. I know of a Liquid Argon Calorimeter week going on in Marrakesh (lucky bastards!). The Chamonix meeting, however, is the one where everyone wishes they could be a fly on the wall at.

Every year for years and years (going back more than 20 years, I’m given to understand) the CERN accelerator folks decamp to Chamonix to discuss all things CERN accelerators (perhaps to do a bit of skiing to!?!?). CERN is large and quite active – with more than the LHC going on, so they have a lot to discuss! Of special interest, of course, is how they will manage the startup for the LHC.

The current date for startup is this summer — July. That is subject to change, of course, if they find a problem with the ongoing repairs. The news I’ve heard of the repairs has been quite smooth – though I’m not really plugged into the rumor mill. So perhaps that July date will stand – which would be great.

But there is a lot more to decide than the start up date. What energies will they try to run at? How many protons will they put in the machine: how intense will they make the beam? How fast will they ramp the energy and intensity up? Heck, how long will they experiment with single beams before they try colliding beams?

From the experiments point of view, the most important a few collisions (at least in my opinion). It almost doesn’t matter what energy they are at. Even just a few days would be a huge help to commission the detectors. We’ve taken 100’s of millions of cosmic rays now – we know a lot about the basic performance of a substantial fraction of the detector. But the trigger and timing ourselves to match the LHC’s collisions is hard! We all guess there is a lot of work there. And any data at all would be a huge help. The process is sort of like diminishing returns: the first dollop of data lets you get the big things right, the next the next most important things are tuned up, etc. And what is worse is those first fixes are usually the largest and require the most time – imagine if we’d had a few days of collisions last September. Wow – we’d be so much further along than we are today (or we know that we were so much further along if everything had worked)!

Of course everyone wants to do physics as well. There the experiments will probably push for higher energies – if the LHC will accumulate only a small amount of data those higher energies are required to give any competition at all to the Tevatron. Of course, the LHC may want to operate at lower energies to keep things safe.

We’ll see what they say…

Robert Aymar is the outgoing Director General of CERN. He gave a recent update of CERN accelerator activities at the ECFA conference. It is a complete update, but there are a few pages in the middle with information on the current state of the LHC. And – lo!!!!! – pictures. Just two. And no ice is visible. I’ve extracted one of the pictures and put in here. That is the link between two magnets – normally the two magnets should be totally lined up.

There are three mitigation strategies that he lists in this talk:

• Improve the quench detection system. The improved sensors will help better localize problems as well as detect them a bit faster.
• Add relief valves all around the accelerator. If such a disaster occurs again then these releif valves should prevent the violent pressurization that occurred and caused such a lot of damage (like the moved magnets shown above).
• Better anchoring of the magnets. So if there is another pressure build up the magnets are less likely to move!

He also mentions two other inter connects similar to the one that failed that have an abnormal resistance – but their resistance is thought to be much less than the interconnect that failed. In ATLAS we’ve been having to evacuate the cavern due to numerous electrical tests of the LHC when they were localizing these. Nanohoms. So small!

Unfortunately, there is no real mention of schedule in this talk. It is nice to see something that is officially public. This matches the talk I saw on Monday, but, of course, it looks like CERN has made it officially public. It would be nice if they would do the same thing to that other talk too.

What is sad about this is I found this out from a news posting in DZERO, which was linking to a USLHC blog. Why did it come to me that way!? They can do a little better!!

Last week there was a talk at an ATLAS meeting that got wide coverage in the blogosphere. The talk, by Jorg Wenninger, was full of detail, and Not Even Wrong did an excellent job of summarizing the talk.

One thing that worried a lot of us was picked up by Peter in his posting:

There is also a plan is to add pressure release valves on every dipole cryostat, but this is highly problematic since it will require warming up all the sectors and likely would not allow the LHC to run with beam during 2009.

As we saw in a meeting here at CERN earlier this week, that turns out not to be entirely true. They can actually add pressure relief valves to the LHC magnets while they are cold. They can do more to the warm sections, but they can do enough to the cold sections to make it capable of withstanding a massive quench like the one on September 19th.

This extra information is nice because it means that when CERN talks about starting to run in summer 2009 it doesn’t mean the accelerator will be in danger of a similar disaster. My impression is sometime in early February there will be a final discussion on exactly what the run parameters will be, along with a startup date more precise than July 2009. I also suspect there won’t be any further news before then. BTW, during this talk it was commented that they have already started to replace the damaged magnets. Nice to see them working so fast, though I suppose they have to in order to meet the fairly aggressive schedule of startup next summer!

Well, I may not be getting my gossip from blogs right now, but my email still renders it. I’m given to understand that Lyn Evans, head of LHC operations, said that they will finally have access to the tunnel this weekend at the LHC conference in Split – so they can figure out exactly what went wrong. He gave a talk there, but this information came during the Q&A session. Further, from their preliminary examination they have enough magnet spares to replace everything that looks like it might have been damaged. That is very good news. Next week is ATLAS week and Evans is scheduled to give another talk there – perhaps he will have more details by then. Sadly, that meeting isn’t public so even if he does post slides I can’t point everyone to them!

When I searched for “Large Hadron Collider” on google the other day it told me:

I suppose any press is better than no press!