1 August 2010

Partners in pulse: The MagLab at Los Alamos

Like so many things in life, there are tradeoffs in creating high magnetic fields.

By Susan Ray, This email address is being protected from spambots. You need JavaScript enabled to view it.

During tours of the Mag Lab's headquarters in Tallahassee, we sometimes brag about having our own utility substation; you need a dedicated substation when your facility's capacity is 56 megawatts. To put that number into perspective, one megawatt is equal to one million watts — enough electricity to power about 600 homes!

LANL power generatorThis power generator dumps massive, instant bursts of energy into pulsed magnets.We may follow that up with details about our astonishing electric bill ($6.4 million a year) and energy consumption (7 percent of the city's total power capacity when the magnets are running at full field).

All that power is needed to run our resistive magnets. Impressive as those statistics sound, though, they are dwarfed by the lab's Pulsed Field Facility in Los Alamos, New Mexico, which boasts a 1.4 gigawatt generator and a 2.6 megajoule capacitor bank, which stores electrical energy. (A joule is a unit of energy.)

In fact, that generator and capacity bank setup used to run the lab's large magnet program is the reason the lab's Pulsed Field User Program is located at the Los Alamos National Lab.

"Our large magnet program is second to none and it includes the 100-tesla magnet program, which currently is enabling us to deliver 85-tesla pulses to users," said John Betts, director of the Pulsed Field User Program at Los Alamos. "And, as time goes on, we will bring this up to 100 tesla. We could not do this without the support of Los Alamos National Lab."

Tesla is unit of magnetic field, and 85 tesla is a lot when you consider that a junkyard magnet capable of picking up huge cars is a mere 2 tesla. When turned on, the 85-tesla magnet contains the energy of more than 100 sticks of dynamite.

Like so many things in life, there are tradeoffs in creating high magnetic fields. The highest continuous field strength is 45 tesla, a world record held by the Mag-Lab built 45-tesla hybrid magnet (we have the Guinness certificate to prove it). Researchers love this magnet, but a lot of the coolest physics happens at fields much higher than that. This is where pulsed magnets — and the tradeoff — come in.

"A pulsed magnet is designed to produce magnetic fields so large that the magnet can't be energized for more than a very short period of time without destroying itself," explains Al Migliori, a scientist in the lab's Pulsed Field program. "Instead of hooking up the magnet to power supply terminals as we do in Tallahassee, we hook it up to an energy storage device, either a capacitor bank or a generator, and we dump all the energy into the magnet in the course of a short period of time, from microseconds through milliseconds to a fraction of a second."

All that energy creates incredible stresses and heat inside the magnet, which is essentially trying to tear itself apart during operation. The tremendous magnetic forces produce enormous pressure: around 200,000 pounds per square inch. Now you understand why pulse magnets operate so briefly. Left to run any longer, the magnet would either rip itself apart or melt from the heat generated by the power. But for researchers, exchanging time for higher field is worth it.

"Many physics phenomena depend on the square of the magnetic field," said Migliori. "So even a little boost in the magnetic field buys you a lot of physics."