Recycling Magnets
July 15, 2013


The cost of a nuclear or particle physics experiment can be enormous, several hundred million dollars for the Large Hadron Collider Experiments, ATLAS and CMS at CERN, several tens of millions of dollars for an experiment like our GlueX experiment in Hall D, being built as part of our upgrade project. Among the expensive components of many experiments is a large magnet or sometimes more than one magnet. Sometimes the magnets have interesting histories.

This article was prompted by the recent sighting of the “g-2” magnet in Hampton Roads. This is a large magnet that generates a very well understood magnetic field that results from a very accurately constructed iron yoke for the magnet. It was built and operated to measure the rotation of the spin of muons in the field. This measurement leads to knowledge of the precession factor, which goes by the label “g-2.” The ability to both measure accurately and to calculate the quantity within the standard model of physics leads to sensitivity to possible new physics. The experiment completed a few years ago at Brookhaven indeed hinted at new physics. In order to increase the sensitivity, the experiment is to be enhanced and installed to run at Fermilab near Chicago. To get from one lab to the other, it is going by barge, round Florida and up the Mississippi and Illinois rivers. Because of bad weather it spent a weekend in Norfolk.

This route, up the Mississippi and Illinois rivers, was also taken by a large superconducting magnet en route from CERN to Fermilab in the ‘80s. In that case, it floated down the Rhine to Rotterdam before crossing the Atlantic. The magnet had been used by the European Muon Collaboration in its NA9 experiment, and became part of the E665 muon scattering experiment. There were also people who crossed the ocean from EMC to E665. The E665 experiment actually had three recycled magnets. The second was the Chicago Cyclotron Magnet. By the time of E665, Bob Kephart (now the director of the Illinois Accelerator Research Center at Fermilab) and his team had transformed that magnet from being conventional, with warm coils, to being superconducting. Even in pieces, the magnet was very heavy, not easily handled by internal cranes in the experimental areas. When I arrived at Fermilab in 1983, the magnet had been lifted into place and stood in the snow in a hole in the ground. The experimental hall was then built around it. The third magnet in E665 had also been in a cyclotron, the Rochester Cyclotron, but we used it as a hadron absorber, cut up, no coils, it stopped all charged particles except muons.

At Jefferson Lab, we have one of the most celebrated travelling magnets. The Hall D solenoid, which we are in the process of commissioning, was first used in the San Francisco Bay area. It started life as the LASS (Large Aperture Solenoid Spectrometer) at Stanford Linear Accelerator Center. There, a team led by David Leith made an extensive study hadron spectroscopy. There are four separate cryostats, each housing several coils that completed the magnet. Once the LASS experiment ended, the magnet components were transported to Los Alamos National Laboratory where, in the ‘80s, several of the coils formed the primary magnet for the MEGA experiment. This experiment sought the decay of a muon into an electron and a photon. Subsequently, about the turn of the century, Jefferson Lab acquired the magnet and refurbished the coils in Indiana and here at Jefferson Lab. The coils are organized in a different order to better match the field to the needs of GlueX, but it’s the same magnet, just a little more mature.

We are just now finalizing a discussion with Brookhaven National Lab that will soon result in the movement of a magnet from BNL to Jefferson Lab for the Super Bigbite Spectrometer being constructed for Hall A. We are also discussing with Cornell University about the magnet used previously for the CLEO experiment. It is desired by the collaboration planning the SoLID experiment.

It would seem that magnet moves are really quite common. But back with the LHC, the ALICE experiment (which concentrates on heavy ion collisions) has demonstrated that a move is not a requirement. ALICE is based on the magnet that was original built for the L3 experiment. L3 operated at the LEP, Large Electron Positron collider, which preceded the LHC in the same tunnel. That magnet stayed where it was, and they built another experiment around it.

Moves or not, recycling magnets is the norm.