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Posts Tagged ‘magnet’

Ramping up to Run 2

Thursday, March 19th, 2015

When I have taught introductory electricity and magnetism for engineers and physics majors at the University of Nebraska-Lincoln, I have used a textbook by Young and Freedman. (Wow, look at the price of that book! But that’s a topic for another day.) The first page of Chapter 28, “Sources of Magnetic Field,” features this photo:


It shows the cryostat that contains the solenoid magnet for the Compact Muon Solenoid experiment. Yes, “solenoid” is part of the experiment’s name, as it is a key element in the design of the detector. There is no other magnet like it in the world. It can produce a 4 Tesla magnetic field, 100,000 times greater than that of the earth. (We actually run at 3.8 Tesla.) Charged particles that move through a magnetic field take curved paths, and the stronger the field, the stronger the curvature. The more the path curves, the more accurately we can measure it, and thus the more accurately we can measure the momentum of the particle.

The magnet is superconducting; it is kept inside a cryostat that is full of liquid helium. With a diameter of seven meters, it is the largest superconducting magnet ever built. When in its superconducting state, the magnet wire carries more than 18,000 amperes of current, and the energy stored is about 2.3 gigajoules, enough energy to melt 18 tons of gold. Should the temperature inadvertently rise and the magnet become normal conducting, all of that energy needs to go somewhere; there are some impressively large copper conduits that can carry the current to the surface and send it safely to ground. (Thanks to the CMS web pages for some of these fun facts.)

With the start of the LHC run just weeks away, CMS has turned the magnet back on by slowly ramping up the current. Here’s what that looked like today:


You can see that they took a break for lunch! It is only the second time since the shutdown started two years ago that the magnet has been ramped back up, and now we’re pretty much going to keep it on for at least the rest of the year. From the experiment’s perspective, the long shutdown is now over, and the run is beginning. CMS is now prepared to start recording cosmic rays in this configuration, as a way of exercising the detector and using the observed muon to improve our knowledge of the alignment of detector components. This is a very important milestone for the experiment as we prepare for operating the LHC at the highest collision energies ever achieved in the laboratory!

Dan Yocum, left, formerly of Fermilab, shakes hands with Google's Brian Fitzpatrick in front of a quadrupole magnet at its new home in Google's Chicago offices. Photo: Troy Dawson

Dan Yocum, left, formerly of Fermilab, shakes hands with Google’s Brian Fitzpatrick in front of a quadrupole magnet’s new home in Google’s Chicago offices. Photo: Troy Dawson

Fermilab does a good job of recycling — from the ubiquitous blue trash cans to electromagnets to — in my case — employees. I myself left Fermilab in 1999 only to recycle back to the Experimental Astrophysics Group in 2000 to work on the Sloan Digital Sky Survey before leaving again in 2012.

When news of the Tevatron’s decommissioning reached Brian Fitzpatrick, head of software engineering in the Chicago offices of Google, he sent
me a short email lamenting the Tevatron closure. He included a request for a souvenir to display in Google’s Chicago offices. Brian and I met when he came to Fermilab to give a computing seminar talk on MapReduce and BigTable several years ago. We have remained in touch ever since, so I gladly accepted the challenge.

My next stop was the office of Accelerator Division head Roger Dixon. We discussed the possibility of acquiring something from the Tevatron for Google and conferred briefly with scientist Todd Johnson. We settled on a quadrupole steering magnet.

But getting a magnet out of the Tevatron was out of the question since the magnet would be slightly radioactive. As a rule, Fermilab’s safety section and the Department of Energy never let even slightly activated material leave the site to be recycled. But hope was not lost, and Roger suggested I speak with Dave Harding, then deputy head of the Technical Division, to see if there were any spare magnets in storage. Off I went to find Dave.

Dave determined that there were indeed several magnets that were clean and in storage because they had been determined to be flawed during post-manufacture testing. One man’s trash is another man’s treasure. I had hit pay dirt!

Roger had also warned that I would have to walk through a labyrinth of people in the Directorate, Business Services, Environmental Health and Safety and DOE before the magnet could be released. Over several months I proceeded to meet and speak with many folks. I list them here so they know how much I appreciate them: Gerald Annala, Dave Augustine, Jose Cardona, Debra Cobb, Shannon Fugman, Jack Kelly, Scott McCormick, Dean Still and John Zweibohmer.

After many emails of clarification, justification and negotiation, everything was signed off and the plan was approved.

Success! Or so I thought. I was already starting to feel a bit like Odysseus trying to get home after the Trojan War when I spoke with Jack Kelly in the Property Department: We had one more bit of stormy water to navigate. Luckily, Jack was an able guide, shepherding the paperwork and the magnet through not one but three online auctions for the DOE labs, the universities and, finally, eBay. He put the big shiny blue “Buy it Now” button on the final eBay page, where Google’s Brian Fitzpatrick clicked and paid $150 for a piece of Tevatron history. How did they come up with the price? That figure was based on the magnet’s estimated scrap metal value. But instead of being turned into scrap, it now proudly resides in Google’s Chicago offices.

On September 28, 2012, after 349 days of navigating a quagmire of paperwork, we had recycled a Tevatron quadrupole magnet and found a new home for it.

The magnet is the centerpiece amongst a myriad of historical scientific and computing items at the Google office. There’s even an Sloan Digital Sky Survey spectroscopic plug plate to keep it company.

Former Fermilab employee Paul Rossman, who works at Google, says, “It’s nice to pass an awesome piece of technology like the quadrupole magnet on the way to my desk. It’s almost like I got to take a little something with me from Fermilab.” Nice, indeed.

I’d like to express my sincerest appreciation to all the people named in this article. You are some of the best of Fermilab. Thank you.

Dan Yocum


Magnet’s ramping!

Friday, August 29th, 2008

Just a quicky-the CMS magnet ramps have started in the last few days – this is critical for us, since the last time we really turned on this magnet it was on the surface, about 2 years ago (nearly to the day!). Here’s the plot of the current (in Amps) versus time for the last few days – last night they reached 10 kA, about half of what they eventually plan to get to, but one does these sorts of things pedantically and carefully.  Keep in mind your house probably has 100 A service – so 10 kA is 100 Houses!  That’s a lot, but that’s the beauty of superconductivity.

The CMS magnet ramping up in the collision hall

I believe the plan is to go to 3/4 of full field this evening.   Soon all those event display pictures with tracks will be curving!


Magnet Tests

Tuesday, June 17th, 2008

Who doesn’t love magnets. I remember as a kid having these two bar magnets and spending hours trying to move them around the kitchen table without actually making them touch (yes, this classifies as fun when you grew up in a small farming town that was 30 miles from the closest movie theater). The ATLAS magnets inspire the same feeling except now these magnets are superconducting and the size of a building (and we generally prefer it when they stay in one place).

ATLAS has two separate magnet systems used for bending the tracks of charge particles in the detector. The magnet surrounding the inner detector is a solenoid (the magnetic field points along the beam pipe). And the magnet for the muon system is a toroid (the magnetic field is circular around the beam pipe). The toroid magnet itself is in three sections: the barrel and two end-caps. And for a sense of size, here is one of the ‘little’ end-cap toroids being transported to the pit many months ago.

End cap toroid

Now that we are in the last steps of closing the detector, the final commissioning of the magnets has begun. The plan of the magnet commissioning is to test each of the four magnets separately (the two endcap toroids, the barrel toroid and the solenoid in that order) and then do the full combined test. And since you can’t have people working on other parts of ATLAS when there are large magnetic fields, all the testing is done at night. Over the past few weeks, the tests on one of the end-cap toroids have concluded (successfully!). Unfortunately in the second end-cap toroid, a helium leak was discovered (helium being used to cool the magnets). As a result, tests with this magnet had to be stopped in order to repair the leak. This does not delay us any but it does involve some reshuffling of the magnet commissioning schedule. Tonight will be the first test of the barrel toroid. Fingers crossed that it goes well!

Oh and Spain in an absolutely, spectacular goal in the last minute of injury time beat Sweden to secure their position in the quarter finals!! One step closer to Euro Cup glory!