6 ms·
Magnetic Field Record Set with a Bang: 1,200 Tesla
- jacquesm 8y ago> The resulting current increases at an astounding 40 million amperes per microsecond and tops out at about 4 amperes. Could someone with more understanding of the material explain the above fragment?
- ddebernardy 8y agoThink of the first (current increase) as an acceleration, and the second (current) as a velocity.
- jacquesm 8y ago4A does not seem all that high?
- thomasfedb 8y agoCorrect, but it is the rate of change that is more crucial. Just like 60 mph isn't hugely fast, but we still quote 0 to 60 times.
- jacquesm 8y agoAh now I get it. Thank you very much!
- amelius 8y agoSo when I turn on the light at home, what is the increase in current typically, order of magnitude?
- FPGAhacker 8y agoin America household voltage for lighting is usually 110volts AC RMS. And you could divide that by the resistance of the bulb to get current. Or take the power rating and divide that by 110. So a 100 watt bulb is close to an amp. As to the rate, you could use an oscilloscope or a high speed camera.
- thomasfedb 8y agoDecent question, I'm not sure how to calculate that and a cursory Google didn't find me an answer. Household power is AC, I'm sure that will have an impact. For example, switching on the circuit when the voltage is instantaneous 0V would surely result in no change in the flow of current. All you'd have in that scenario would be the rate of change of AC, which would be 10A at 50Hz = 2000 A/s in Australia (1Hz = +240 to -240 and back in 1s). I'm sure this is hopelessly simplistic though, nothing happens instantaneously - there will be some period of high-resistance arking, etc.
- amelius 8y agoI think this concept explains it: https://en.wikipedia.org/wiki/Parasitic_element_(electrical_networks) https://en.wikipedia.org/wiki/Parasitic_element_(electrical_... So instead of modeling your home wiring as wires, you should model them as wires plus capacitances, inductances and resistances. The loop from light switch to lamp and back is basically one "big" inductor. The challenge is to find adequate values for these parasitic elements. You are right about AC though, didn't think of that.
- danielvf 8y agoPower is Amps x Volts, so I'm guessing the voltages involved are epicly huge. (Even though this paragraph is really talking about the acceleration)
- jacquesm 8y agoMagnetic fields are all about current and rate of change, the voltage isn't nearly as important a factor as long as it generates the required current. So the biggest element in all this is the internal resistance of the supply, hence the use of capacitors to dump all that energy in one go into a very low impedance coil. I mostly missed the microsecond/million factor, that's 10^12 we're talking about.
- danielvf 8y agoDo you know voltage MRI machines work at?
- jacquesm 8y agoMRI machines are expected to continue to work after they are used once :) The idea here is that the field strength is such that if you don't reach it quickly that the machine will self-destruct before you have reached your target field strength. So you have to cheat, taking for granted that the machine will not survive the experiment, hence the ridiculously high rate of current change. Note the the destruction is totally part of the plan and is a major factor in focusing the field even more. Anyway, the typical MRI power supply is pretty beefy, a few KV and 100's of Amps. And that in a way says it all about how impressive those machines are, they get up to serious field strengths without breaking up.
- eigenloss 8y agoThe 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.
- mikeq101101 8y agoCan someone explain what are some consequences and real world applications of this?
- dschuetz 8y agoThere certainly are consequences concerning science and research of electromagnetic fields and radiation, fusion power research and application. Direct real world applications? There are none, really. Where would you need 1000 T which basically makes everything metallic evaporate in it's vicinity?
- paganel 8y ago> Where would you need 1000 T which basically makes everything metallic evaporate in it's vicinity? There are lots of metallic big things on different types of battlefields, like tanks or even aircraft carriers, it would be really helpful for the opposing sides to be able to “evaporate” them. Not sure how close to implementing this as a weapon we are, though, probably not that much.
- dschuetz 8y agoI see, my imagination is lacking weaponry.
- rangibaby 8y ago> There are lots of metallic big things on different types of battlefields, like tanks or even aircraft carriers, it would be really helpful for the opposing sides to be able to “evaporate” them. Not sure how close to implementing this as a weapon we are, though, probably not that much. 70 years ago
- speeder 8y agoWhen I read the first article about his some days ago, the authors of the experiment were happy with the result, and said it is useful for fusion power. Seemly some fusion power reactor designs DO need a temporary very strong magnetic field.
- Jaruzel 8y agoDumb Question: Could this tech somehow be harnessed for space propulsion?
- tim333 8y agoI doubt that particular magnet but there is a YC startup working on a magnets -> fusion -> space drive thing https://news.ycombinator.com/item?id=8178450 https://news.ycombinator.com/item?id=8178450 https://www.nextbigfuture.com/2013/11/john-slough-personally-explains-his.html https://www.nextbigfuture.com/2013/11/john-slough-personally...
- kadoban 8y agoFor a magnet to be used as propulsion, you'd need something for it to pull or push against. Finding a likely target seems impossible. The way magnetism drops off with distance means it would only be useful when you were already there (or just starting out). Also the magnetic field in this case is only lasting a tiny fraction of a second, which would be an issue for propulsion.
- EthanHeilman 8y agoFrom the impractical ideas dept: Could make a magnet strong enough that it would pull apart virtual particles, i.e. Vacuum polarization [0], and based on some asymmetry in the magnetic field created the particles would pull/push you forward? [0]: https://en.wikipedia.org/wiki/Vacuum_polarization https://en.wikipedia.org/wiki/Vacuum_polarization
- mathnmusic 8y agoI guess what OP meant is interaction with earth's magnetic field to get out of its gravitational pull.
- macromaniac 8y agoIf can get to 4 billion tesla I /think/ that's enough to generate electrons from the vacuum of space (see:schwinger magnetic induction) and you could do something akin to magnetohydrodynamics ( see: https://youtu.be/LS3GQk9ETRU https://youtu.be/LS3GQk9ETRU ) which would use the magnetic field to accelerate the electrons away from the ship, I could be incorrect here though
- wumms 8y ago> Bigger magnetic fields have been made before, but they aren’t practical or reliably reproducible, because they rely on rather dangerous amounts of TNT. TNT aside, would one survive a MRI at 1200 T? I estimate the resolution would be around 1/10th of a nerve fiber - would that be small enough to _really_ scan a brain?
- bcaa7f3a8bbc 8y agoCurious about it, too. A quick search got this from the WHO. > For static magnetic fields, acute effects are only likely to occur when there is movement in the field, such as motion of a person or internal body movement, such as blood flow or heart beat. A person moving within a field above 2 T can experience sensations of vertigo and nausea, and sometimes a metallic taste in the mouth and perceptions of light flashes. Although only temporary, such effects may have a safety impact for workers executing delicate procedures (such as surgeons performing operations within MRI units). > Static magnetic fields exert forces on moving charges in the blood, such as ions, generating electrical fields and currents around the heart and major blood vessels that can slightly impede the flow of blood. Possible effects range from minor changes in heartbeat to an increase in the risk of abnormal heart rhythms (arrhythmia) that might be life-threatening (such as ventricular fibrillation). However, these types of acute effects are only likely within fields in excess of 8 T. https://www.who.int/peh-emf/publications/facts/fs299/en/ https://www.who.int/peh-emf/publications/facts/fs299/en/
- sctb 8y agoPreviously: https://news.ycombinator.com/item?id=18092967 https://news.ycombinator.com/item?id=18092967.