MIT Scientists Demo 150 Ton Magnet For Plasma Research

Dr.Luke writes "The dream of abundant fusion energy just got a step closer to reality. MIT scientists just demonstrated a mammoth 150 ton magnet that could be used to create powerful plasma container needed for a practical fusion power plant. The device produces a magnetic field 260,000 times stronger than that of Earth. Full story here."

Comments

I can see the quotes now...

[stienman]

Scientist, "Yeah, so, like, the fusion reaction can put out, you know, a lot of power - like 10,000 amps or so."

Reporter, "And how much current does the one smaller magnet consume again?"

Scientist, "Uh... 46,000 amps. But it's so cool! I mean, it glows and stuff!"

...

3) Profit!

-Adam

Re:I can see the quotes now...

[stienman]

Given that these are superconducting coils the amperage relates more to power than it does in a situation where the resistance is unknown.

In other words, amperage is simply a measure of the number of electrons passing a cross-section of the wire in a given period of time. In this instance it is enough to give significant measure of the input power.

It is, however, inadequate in measuring the output, but since they didn't give any further info in the article I chose not to expand my narrative further than the nebulous Amp.

Gravity: Not just a good idea, it's the law.

-Adam

Sign on the door

[quintessent]

Warning: Any metal objects in pockets will be confiscated without warning.

A pulsed 13 Tesla magnet and its problems

[kgp]

In the article it says:

A superconducting magnet operated on a constant current, such as those used in Magnetic Resonance Imaging of the body, suffers no dissipation of electrical energy. That is not true, however, when a superconducting magnet is pulsed. And tests of the new magnet in pulsed operation showed that "initially [the electrical] losses were much higher than predicted," Minervini said.

With repeated operation, however, the magnet appeared to correct itself. "With each cycle the losses lessened until they reached a steady value a lot closer to what we'd predicted," Minervini said.

"We think we understand what's happening, at least qualitatively," he continued. "It has to do with interactions between the thousands of wires twisted into cables that in turn are coiled to form the magnet. We are essentially changing the electrical characteristics of the cable in a way that decreases losses over time."

No. That's restating the problem. You don't have the understanding bit here. What is going on that will change the (I presume) I squared R losses in the magnet.

Re:A pulsed 13 Tesla magnet and its problems

[caffeinated_bunsen]

No. That's restating the problem. You don't have the understanding bit here. What is going on that will change the (I presume) I squared R losses in the magnet

Quick bit of advice: Don't casually presume that you know more about the subject of the article than the PhDs who contributed to it. The whole point of a superconducting magnet is that R=0, so there is no I^2 R loss* in the magnet.

But when you build a magnet like this, you can't calculate the magnetic force on every centimeter of superconducting wire in the whole thing. You also can't make the wire stay precisely where you put it. As the field builds up the first time, all the wires move around a little bit, due to the very large magnetic forces on them. This wastes some of the energy put into the field. As you cycle the field, the wires gradually move toward an equilibrium and the mechanical energy loss goes to zero.

I'm sure there are other factors, but this is the only one that I can remember off the top of my head. In fact, I know that there's more than this to the problem, because this is a well-known phenomenon that everybody who designs high-field magnets has dealt with. If it were as simple as this, they never would have mentioned it in the article.

* Of course, there are some losses in type II superconductors due to the motion of flux vorticies. But this doesn't behave quite like an Ohmic resistance, and the loss is really small in good alloys.

Field of the earth is tiny...

[Mt._Honkey]

The device produces a magnetic field 260,000 times stronger than that of Earth.

I don't understand why the news always uses the field of the earth for these kinds of comparison. The earth's field is quite weak, barely enough to point a compas north. An old, weak refrigerator magnet, by comparrison, easily overpowers it from quite a distance. They would be better off using comparisons such as refirgerator magnets or MRI machines, something that people have more contact with and is stronger.

On as side note about public ignorance about science, MRI (Magnetic Ressonanse Imaging) is really NMRI (Nuclear Magnetic Ressonanse Imaging), but because the public is so affraid of anything with the name Nuclear or Radiation or Commie in the name, the word Nuclear is always left off.


Please forgive my spelling

wouldn't this be a bit dangerous?

[moosesocks]

In other news, every CRT located within two miles of the magnet is now in dire need of a degauss.

Meanwhile...

[arban]

Meanwhile, at the conclution of the 34th International Orienteering Competition, no winner could be determined and 5 teams are unaccounted for. Feared dead. Film at 11.