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Super-Magnet Sheds Light on Semiconductors
Stony Stevenson writes "A group of researchers at Florida state have demonstrated a magnet design that could shed new light on nanoscience and semiconductor research. 'The Split Florida Helix magnet can direct and scatter laser light at a sample down the centre of the magnet and from four ports on the sides. Due to become fully operational in 2010, the device can generate fields above 25 tesla. The highest-field split magnet in the world currently attains 18 tesla ... The scientists will be able to expand the scope of their experimental approach, learning more about the intrinsic properties of materials by shining light on crystals from angles not previously available in such high magnetic fields.'"
More specifically, this happened at Florida State University's National High Magnetic Field Laboratory. Thanks!
disclaimer - I'm not a physicist.
Having said that... I came across this - http://www.wonderquest.com/extinctions-safetyglass-magnetslasers.htm (Scroll down for pertinent info). Apparently "electromagnetic waves can bend light through an indirect, quantum effect--but to such a tiny degree that we cannot measure it." So, maybe bigger magnet = more bending = measurable?
You are using English. Please learn the difference between loose and lose; they're, there, and their; your and you're.
From what I gather, this magnet isn't able to split/focus light, any more than lesser powered magnets. What makes this one different, is that usually, at such high fields, it is phisically imposible to get any sort of light inside, as the structure of the magnet has no gaps that can be used to shine a light in, ie, 100% enclosed. This magnet is constructed differently, in that even though it attains the highest magnetic fields, the insides are still viewable from outside, and so lasers/etc can be focused from the outside, onto the subject while its in operation.
No, you're right. The summary is just awkwardly worded.
Light is not affected by magnetic (or electric) fields since photons are neutral (no charge). You cannot deflect light with a magnetic field alone (although applying magnetic or electric fields to some materials can alter their refractive index and thereby change the deflection of a light beam passing through that material).
The connection between "light" and "magnets" in this new work is actually that the team found a clever way to build a large (and powerful) magnet that has gaps in it. These ports allow laser light to be directed at a sample sitting in a very high electric field (and allow measurements of the light scattered from the sample).
While it may not seem to be a huge achievement to build a magnet with holes in it, you have to keep in mind that building a 25 T magnet is already a big challenge: doing it with the additional constraint that you want easy physical access to the region of maximum field strength is even harder. This new setup should allow for some cool experiments, since it can probe in real-time (using light) how materials behave under very high magnetic fields.
To put it into perspective:
1 Tesla is about 20000 times the strength of the magnetic field on earth.
Those rare-earth magnets that move the head inside of a hard drive are about 1.25 T.
MRIs in hospitals use about 3 T.
16 T will levitate a frog.
FOXTROT UNIFORM CHARLIE KILO
Yes, of course light is an electromagnetic wave. Light, like all forms of EM radiation (gamma rays, IR, radio waves, etc.) is carried by photons, which are elementary particles that have no electric charge. Since they have no electric charge, they are not affected by electric or magnetic fields.
The reason photons are referred to as "electromagnetic radiation" is not because they are affected by EM fields, but because they are EM fields. The photon is the force carrying particle for the electromagnetic force. What that means is that electric and magnetic fields are in fact "made of" photons: in quantum field theory, their action is in fact described by the exchange of virtual photons.
Since electric and magnetic fields are carried by photons, it would make for a strange universe if the photon had an electric charge, and were affected by those fields. In effect, it would mean that the photon would couple to itself, leading to all kinds of strange effects, like rays of light bouncing off of each other or attracting each other (in vacuum). Such effects are not observed.
Notes:
1. As I mentioned before, it is possible for magnetic or electric fields to affect the propagation of a light ray indirectly through their action on a material. Light refracts through material interfaces because of differences in refractive index. For some materials, a magnetic or electric field can be used to modulate the refractive index, and thereby change the path a light ray takes through the material. But magnetic fields do not affect photons in vacuum.
2. Some theoretical work suggests that the action of extremely intense magnetic fields could polarize the virtual particles that exist in vacuum, and thereby slightly modify the effective vacuum refractive index. This would then be a case of a magnetic field affecting light. Such effects would only occur at massive field strengths (perhaps at the surface of a neutron star), and are as of yet experimentally unverified.
Yes we do know that. We also know that this fact has nothing to do with the ability to bend light using magnetic fields. In the classical view, light is electromagnetic waves. From basic EM theory we know that two electromagnetic fields "crossing paths" will not change each other. If you don't trust me, go back to your introductory book on EM and do the math. In the world of quantum mechanics, light is a particle, photon, and are electrically neutral. Neutral particles are NOT affected by magnetic fields. Again, if you don't trust me, go back to your introductory book on quantum mechanics.
To make really powerful magnets, of course, you need to use some tricks, such as shaping the system to concentrate the field at a particular point. In machines like MRIs and NMRs, the magnet is typically cooled (e.g. to liquid helium temperatures) which makes it superconducting. This allows a very large current to be passed through the coil, which generates extremely large fields at the center.
In this current case, they describe the magnet as: "created by packing together dense, high-performance copper alloys and running a current through them". (See picture here.) The article doesn't say whether they cool the coil to reduce resistance, or whether it is purely the shape of the coil that produces the extremely high field.
The other thing is that experiments sometimes need a certain orientation of the magnetic field. So, if you're using a solenoid (which is what all the highest field magnets are made like), then it's no good sending laser light down the axis of the solenoid, because the field is then pointing either toward or away from the light pulse. Therefore you need a hole in the side of the solenoid, which is when it gets tricky, e.g. keeping the magnetic field quality good etc.
The split magnet mentioned in this story is a purely resistive magnet. This means that it will operate at room temperature and uses copper alloy coils (pretty sure its a copper-silver allow) along with a tremendous amount of current to generate a magnetic field. The resistive magnets at the NHMFL operate at up to 60,000A and at up to 500V which equates to about 30MW. This amount of power is difficult to dissipate and makes these some of the worlds most powerful hot water heaters. The coil technoloy used is known as Florida-Bitter. The tricky part about a split magnet is that you have to take the most efficient portion of the magnet, which are the coils close to the center and effectively move them to the farthest region of the magnet. For comparison, the most powerful resistive magnet at the NHMFL with comperable parameters generates 35T. The most powerful persistant magnets however are the hybrids which have superconducting coils in the low field regions and resistive coils in the high field regions. The most powerful is 45T A lot more information can be found at: http://www.magnet.fsu.edu/