FSU Sets 7 World Records In High Magnetics Research

spence calder writes "FSU's High Magnetic Field Lab, more specifically my Kenpo teacher, just broke 7 world records, and brought the record for a superconducting magnet to 25 Tesla. Check it out at FSView and a more detailed article here. Now if only our football team was that cool." And if you'd like your magnetic toys to shoot metal bits, Jason Rollette points to his railgun project, which looks like good, clean, high-voltage fun.

Another railgun link

[DarenN]

is railgun.org [railgun.org]

They have a detailed overview of the physics involved, too.

Re:Congratulations

[DrLudicrous]

Yes and no. Most MRI systems for humans operate at about 1.5 Tesla. I know of at least one 8 Tesla system, but that is experimental. The higher the static field (i.e. the 25 Tesla), the better the resolution of your system can be.

No one knows the effects of an 25 Tesla magnet on biological tissues. In addition, in order to get useable information out of an MRI system, one must hit it with radiofrequency (RF) waves. The higher the static field is, the higher these frequencies are going to be. A 7-tesla magnet uses frequences around 300 MHz. Therefore, by extrapolation (which I believe is right, since I know that a 9T system uses about 383 MHz), a 25 Hz system would need about 1.1 GHz. This might very well be extremely detrimental to biological tissue. In other words, to do MRI, you'd have to cook your sample.

Finally, to truly achieve a resolution advantage, you will need very powerful gradients. The gradients one would need to take advantage of such a system would be gigantic, at least tens if not hundreds of Tesla per meter. This would be very difficult to design for samples as large as a human body, if not impossible with today's technology, and at the very least extremely expensive.

Personally, I can see a 25 Tesla magnet being useful, just not for MRI. Perhaps for NMR being using not for imaging purposes, but in the study of non-soft condensed matter systems (i.e. not biological or organic, but solid state). It would be useful for examining superconductivity also.

Re:25 Tesla

[DrLudicrous]

The charge is not static. It says "velocity of one meter per second". That means it's moving- if it wasn't moving, there would be no force on it, despite the magnetic field.

One electron has a charge of 1.6E-19 Coloumbs, so you are talking about the equivalent of 6.7E18 electrons moving at 1m/s. One coulomb is the amount of charge that passes through a point in a wire in one second which is carrying one Amp of current.

The instantaneous force being described would be perpendicular to both the motion of the particle and that of the magnetic field. Make a gun with your right hand, let your index finger point in the direction of the charge, let the field point in the direction of your thumb. Stick out your middle finger so it makes a right angle with both digits, and that is the direction of the force.

Re:Congratulations

[DrLudicrous]

MRI is all about pulses my friend. Good point. The reason for the pulses is not to protect the tissues- basically it is a timing issue that allows for nuclear spins to reach certain alignments which are favorable to making measurements that can lead to making an image, hence magnetic (the field) resonance (nuclear spin resonance of the hydrogen [most common] atoms in your sample), imaging (after data analysis of RF signals, you get a pretty picture).

BTW, at smaller scales, things work a bit differently- it is much easier to make powerful gradients over a small distance (say a few millimeters, or hundreds of microns) than it is over larger ones (say a human torso, or even a forearm). I wish I could be more specific about this, but my theory background on MRI is still a work in progress- I hope I didn't screw anything up in my post above. Any MRI geeks out there, feel free to correct or add anything I missed.

Re:Huh?

[DrLudicrous]

The magentic field in these magnets is very localized. They have tiny "bores", i.e. the area inside the magnet where there is actually high field. The earth on the other hand, has a much larger volume of magnetic field, even though it is smaller in magntiude.

So it is kind of a matter of concentration. Your keys aren't going to flying out of your pocket b/c these magnets get turned on, nor will they affect your compass because you are too far away from the space that they affect. The earth on the other hand will affect your compass, because you are in its (fields) area of affect.

Re:Silly question from the ignorant

[DrLudicrous]

No. They are very localized spatially. You would not be able to feel their effects until you got within about 20-30 meters (that is a complete eyeball estimate, probably need to get closer). The Earth's magnetic field, while smaller in magnitude, is not as localized, hence a compass will work pretty much anywhere (except for the poles, where it just spins wildly while you walk in circles waiting for the arctic wolves to devour you).

Re:The problem with railguns

[imsabbel]

The problem is that you cant levitate your object because you need it touching the rail to conduct the drive current.

Thats the main problem. Else you could just throw a bagload of teflon on the slug and fire away.

The main problem is not physical abrasion, but the fact that even if the projectile fits perfectly, the current density creates arc discharges between rail and slug, vaporizing the top layers

Re:World record? Where?

[wakaranai]

I think FSU are only claiming the record for a *superconducting* magnet, not for the highest continuous magnetic field generated using a hybrid magnet.

So yes... relatively speaking, I'm not so sure the FSU's world record is so impressive. Guess this advance could lead to advances in hydrid magnets though...?

Re:25 Tesla

[DrLudicrous]

Well, that is a good try. The equation you have is one of the first taught in electroSTATICS. We are talking about electroDYNAMICS, ie moving charged particles, versus arrangements of particles that aren't moving.

In that case, the equivalent of Coulomb's Law becomes

F=q(E+v x B)

Here, F is force, q is the charge that is moving, E is the electric field (if present, you may remember something like E=kq/|r|, which is basically the force law you listed divided by a charge, giving units of Newtons/Coulomb), v is the velocity of the moving particle. All quantities in bold refer to vectors, so they not only have magnitude, but direction. In the case of the weber definition above, there is no electric field, so that part has no contribution. We are then left with:

F=q(v x B)

Here, the x does not just mean normal scalar multiplication but vector multiplication. All this means is to take into account the angles between the directions of the velocity and the magnetic field. Either way, the force will be perpendicular to both, so if you can imagine drawing lines indicating the velocity and magnetic field lying in a plane, the force the particle experiences points straight out of that plane. The more in line the velocity and field are (i.e. the smaller the angle they make relative to one another in that plane) than the smaller the force will be. If the particle is moving in the direction that the magnetic field points in, then it will experience no force- again, this is a result of the vector multiplication (better known as the cross product, where A x B=|A||B|Cos[theta], where theta is the angle between A and B.

Make sense? If you have questions, post them here.

Re:new MRI application?

[n0mad6]

Perhaps if you were only in the business of scanning plastic containers for contraband...and sort of ferromagnetic material that you would "scan" using a magnet in the multi-tesla reigon would be subject to becoming deadly projectiles.

clarification

[GarbanzoBean]

This is a record field for the superconducting magnet, not for the whole system. FSU magnet lab does hold the record for hightest DC (constant) magnetic field 50T. This is achieved by putting a resistive magnet inside a superconducting magnet. Resistive magnet burns a lot of energy (10MW), but one cannot use superconducting alone; once the current (magnetic field is proportional to it) reaches a certain value, the superconducting material becomes normal. The record up to now has been something like 14T for superconducting magnet (outsert), the new outsert will allow the DC fields in that lab to go up to 60T.

Some tidbits of info...

[Equuleus42]

As someone who works next door [yahoo.com] to the FSU Mag Lab, and has taken a tour of the facilities, I have heard a couple things about it that boggle the mind... First, if they didn't contain the magnetic field that they are producing, they claim that it would erase everyone's floppies, hard drives, and credit cards in the entire city of Tallahassee. Second, they consume one quarter of the entire power consumption of Tallahassee to create the fields they are creating. The city of Tallahassee had to install a power generation station nearby just to get power to them easily. They apparently ramp up the magnets while everyone else is sleeping, in order to prevent brownouts during the day.

Out of curiosity, I just looked up their electric bill online [talgov.com], but it lumps the Mag Lab's usage with multiple other FSU buildings... The total bill was $500k this month, so it must be an amount less than that.

Yes there is a breakthrough here

[pliny3]

This is not just "bigger is better." Here's why.

The wire used for helium-cooled supercon magnets (Nb-Sn or Nb-Bi alloys) has performance envelope that limits the conditions under which it will superconduct. The factors describing this envelope are

• the temperature
• the current
• the magnetic field

Getting to 20T was accomplished by

• better alloys -- mainly higher Nb content iirc
• lower temperature -- achieved by cryopumping the liquid helium (LHe)
• more turns in the winding, allows higher magnetic field without increasing the current

Unfortunately, the critical field (the field at which the material goes non-superconducting) is around 20T. Since the innermost coils are sitting in a field near the field at the bore (these are toroidally wound magnets), you need to use a different material. In this case, that material is HTSC wire. This poses some big engineering problems, including making a sufficient length of the wire (measured in km), and making superconducting joints between the HTSC coil and the LTSC coils. It appears that this team has solved these problems, congrats to them.