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Green is a Relative Thing December 23, 2008

Posted by gordonwatts in D0, Fermilab.
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I’m ending a series of 3 owl shifts at DZERO right now. The Tevatron, the accelerator at Fermilab, has been going great guns all week. It finally broke today. You know it is bad when the post to Channel 13, the web page that tells you the status of the machine, “Experts working on LRF3; no estimate.” The Linac is busted. That means no data for a while.

Looking at the accelerator’s log book (not accessible from outside fermilab) we found an interesting entry (we means myself and the other 3 people here on shift):

An energy-conservation timeline has been loaded

We called to find out what that means. Mike, from the Main Control Room, told us that is is like putting your car at idle. The Main Injector normally is constantly ramping protons up to 150 GeV energy and slamming them into a target. It does this once about every 2 seconds. With the Linac broken, however, there are no protons to accelerate – so why ramp every 2 seconds. It takes energy to ramp… The effective equivalent of putting your car as idle when you are at a stop light rather than keeping it revving at 4000 RPM’s.

Fermilab uses a lot of power – in 2007 the power consumed was about that required to run 45,000 homes. A lot!! As you can imagine this has impacts both on operating costs and general “greenness” (pollution, etc.). There is a broad effort to reduce power at Fermilab, but this is the first one I have seen in the science program. Very cool.

You might ask – since there is no beam, why run the Linac at all? Why not just shut it off. I will point you to a previous posting of mine:

On Tuesday I decided to shut down my home computer. I’m not sure why I decided to do that – I almost never do. … When I hit the “power” button on the 2.5 year old Dell XPS/200 machine the power light briefly flickered yellow… and that was it.

The accelerator is so large and so complex and there are so many different parts (and computers!) that shutting it down and then turning it on is something that is only done when a very long shutdown is planned. Very long means months. Otherwise things fail and then it takes much longer to get back to doing the science.

For those not familiar with the operation of the Tevatron, the “no estimate” isn’t as bad as it might sound. It just means the experts who have looked at the problem scratched their collective heads and said “Hmmm, I don’t recognize this!”. Usually that means it will take several hours to get things going again. Experiments treat it as an opportunity, actually. The machine has no protons circulating and so we can take special calibrations. Or sometimes we can get access to the detector and fix things.

Tomorrow I jump on a plane and my actual Christmas break starts! Happy holiday’s everyone!

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1. tim head - December 23, 2008

I found it odd that after the no beam time in November it took the Tevatron “ages” to get going again. I would have thought after a power outage its just a question of going through all the procedures and “poof” beam is back.

Has anyone ever investigated how many components never come back after a switch off? Similar to Google and Cerns investigation into how often there is a problem with a hard disk?

merry christmas to you too.

2. The Start Of The Internet « Life as a Physicist - December 24, 2008

[...] Start Of The Internet December 24, 2008 Posted by gordonwatts in computers. trackback While waiting for the Tevatron to come back, I stumbled across this article on the web with the following quote: [...]

3. gordonwatts - January 4, 2009

Sorry it took me so long to get back to you Tim.

I imagine there are lots of reasons. The first is that during those long shut downs they pull lots of stuff apart. Re-adjust the positions of magnets. Add new upgrades. The result is when they start up it takes some time to get everything working together again.

There is actually a lot of “tuning” that goes on to make the beam work. I’m not sure how many parameters there are, but imagine you can adjust the current though every magnet, you have some focusing magnets which probably have even more optorutnities to tune, and then each time the beam has to move from one machine to the next… well – all of those parameters have to be set correctly for it to work. I would imagine getting just a few protons through the Tevatron wasn’t that “hard” – however, no one at Fermilab would call that a success anymore. Perhaps on the first day the Tevatron started working. :-) Now, it doesn’t work unless it is working as well as it was when it shut down….


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