3 ms·
The current in question increased from 0 to 4 amps in approximately 100 femtoseconds (10^-13 seconds). When generating fields this large, the coil's destruction
by eigenloss 8y ago
The current in question increased from 0 to 4 amps in approximately 100 femtoseconds (10^-13 seconds). When generating fields this large, the coil's destruction is guaranteed, so to create a large maximum field magnitude, you have to ramp the current faster than the coil can vaporize/disintegrate. 40 trillion amps per second is pretty fast.
For reference, a back-of-the-envelope calculation puts the current ramp rate for the LVDS data lines coming from your phone's camera around a few hundred thousand amps per second (-1 to 1 mA in a few nanoseconds).
- dschuetz 8y agoAccording to Maxwell's Equations: faster changes in the current generate stronger magnetic fields. 40 trillion A/s is insane!
- kmm 8y agoMagnetic fields are generated by currents, not by changing currents. The current only needs to rise that fast to outpace the imminent destruction of the coil from resistive heating.
- eigenloss 8y agoCommon misconception. It is mainly not resistive heating that destroys the coil; before resistive heating of a significant degree can occur, the coil physically implodes from the force, and this is gainfully used to further concentrate the magnetic flux. Please see the sixth paragraph of the linked article.
- jacquesm 8y agoExactly, the whole point of the rate of change is to get the field up to strength before the materials give way. Which makes me wonder whether there is a highest magnetic field that you could create given 'ordinary' matter.
- kmm 8y agoInteresting. During my BSc in physics, I did some experiments with single turn coils, and they certainly formed plasma. One of the most interesting phenomena we noticed was plasma conduction, where the metal vapor of which the coil previously consisted started to conduct, giving two distinct peaks of the magnetic field. The setup described in the article is different, with a secondary coil, so I was mistaken.
- amelius 8y ago> When generating fields this large, the coil's destruction is guaranteed Is this due to resistive dissipation (heat)? I was under the impression they used superconductors, for which this problem does not exist, but I'm probably wrong.
- eigenloss 8y ago> Is this due to resistive dissipation (heat)? No: > The two currents produce magnetic fields that repel each other. However, the main coil is a relatively thick and heavily reinforced ring of copper-lined steel, and the liner is practically foil. You can guess which wins this fight. “Because of the difference in the mass inertia, the liner implodes inwards” at a rate of about 5 kilometers per second, explains Takeyama. As it does so, it compresses the 3.2 T field so that when the liner is at its smallest, the magnetic field inside it reaches 1,200 Tesla. Unable to be compressed any further, the liner rebounds at about the same rate it imploded, destroying itself and the main coil.
- akiselev 8y ago> The current in question increased from 0 to 4 amps in approximately 100 femtoseconds (10^-13 seconds). When generating fields this large, the coil's destruction is guaranteed, so to create a large maximum field magnitude, you have to ramp the current faster than the coil can vaporize/disintegrate. 40 trillion amps per second is pretty fast. Coincidentally, it's the same technological challenge in building an EMP (plus or minus some explosives).