Friday, December 15, 2006

In a spin

After a year in China I still haven't worked out which teas will send me to sleep and which will get me buzzing (and some have a much stronger effect on me than coffee). Unfortunately on Wednesday evening during my English lesson I opted for pu-er in the hope that I would rest peacefully ready for the next day's talk at IHEP.

One night but just three hours sleep later I took myself across to the theory group in the institute for high energy physics where Beijing's particle accelerator is stationed. Security was rather higher than I'd expected and gates were cordoned off with policemen all over the place. I was informed that it was for a special international visitor who was coming to give a talk. Sadly they were not talking about me but in fact I had a parallel billing with George Bush Snr. It also transpired that he hadn't bothered to rearrange his talk in order to come and hear about the wonderful world of the AdS/CFT correspondence. Along with a Sino-French conference on the LHC and a talk by Steven Chu I was pleased to have as many people as I did in the audience, though I was told that on a normal day I would have had a few more. With some luck, some skill and fine hospitality on the part of my hosts I managed to get in a quick hit of caffeine before the seminar and the hour and a half talk was a pretty enjoyable one for me at least. Lots of good questions and a generally enthusiastic audience.

Post seminar and large Beijing duck meal, complete with sea cucumber and duck's feet, we went to have a look at one of the control rooms for the accelerator. It's a hive of activity with perhaps ten people milling around and monitoring the 20 or so screens watching the histograms come up and coding up for data analysis and beam control.

When you are running a particle accelerator you don't simply press go, get the particles up to speed and then crash them together. A lot of the time is spent in tuning the machine such that you have good control on the bunches of particles you're accelerating to near the speed of light - getting a smooth profile and getting as many as possible to increase the luminosity of your equipment. The more controlled bunches, the more you can study in a shorter time. This isn't an easy job and the 240m circumference ring is no exception. (Have a read of Joanne's recent detectors masterclass for a good overview of the complementary subject).

The spectrometer attached is primarily built for precision measurements of the J/psi resonance and BES has accumulated the largest number of J/psi events of anywhere in the world.

On top of this is a large proportion of time set aside for studying and using synchrotron radiation for a variety of purposes. Synchrotron radiation is radiation given off when you accelerate a charged particle. Some of the time this happens because your electrons have to go round a corner and some of the time it's because of the wigglers, magnets in your system specifically used to wobble the beam. There are 13 stations around the beam where they use this radiation for medical purposes and/including imaging techniques. A great deal of groundbreaking work has been carried out here in the realms of protein imaging and in areas from archeology to nanotechnology.

Currently BES is being upgraded but the accelerator is still in use so we chatted with one of the scientists on duty. I was interested to see the control room and find out what goes on but I do have a bit of a thing about spending too much time in such places. I spent a week at SLAC a couple of years ago on shift for the Babar detector. The idea is that at all times there must be a couple of people monitoring the huge number of graphs telling you how the detector is functioning and how the data is coming out. If anything goes wrong there are a sequence of strict protocols to go through from flicking a switch, to waking an expert who has to rush in to look at the problem. At some point I will explain why as a theoretical physicist I was performing distinctly experimental duties.

These shifts last for eight hours and I was lucky enough to have shifts ranging from 8pm-4am to those going from 4am-12am (I seem to remember - there may be a four hour slippage somewhere in there). With jet-lag and a schedule of 5 or 6 shifts to complete in a week this is the most confused my body clock has ever been. What is worse than sitting in the control centre monitoring the data is sitting in the control centre when there is no data. Sometimes the beam is lost, literally falling out of the correct trajectory and breaking up and so those in the detector room have nothing to do. At 2 in the morning with nothing to do but a need to stay awake I vaguely remember sending some rather bizarre e-mails that probably appeared drug induced to those on the other end. I also have memories of cycling back to the guest house at four in the morning through the rather eerie undulating Californian roads getting into the realms of the hallucinatory.

Anyway, I'm firmly at the other end of things at the moment sitting precariously in extra dimensions. The weekend beckons...

2 comments:

Trumpers Cornichon said...

Fights - check. Visa - check. Bobble hat - check. I'm all kitted up! And I come bearing gifts...

Jonathan Shock said...

Good news, though you can leave the fistycuffs at home and replace them with a stout pair of longjohns.

Extra good news is that the department's weekend has moved such that I will have a couple of days completely clear after you land so I shan't have to send you off into the unknown straight away.

See you shortly,

J