HellstormOP
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Usage of magnetized NdFeB in flash powders/explosives? EMP effect?
Hello,
recently I got the idea, that it might be possible to use NdFeB powder or magnets in different ways to achieve interesting effects.
The first way I could think of, is to stack a few magnets of this material, that have a hole in the center and to fill that holes with a (preferably
fuel-rich) explosive.
The second way, would be to demagnetize a such magnet using heat, then powder it, obviously taking all precautions against self-ignition, and then
either mix it into a powder-based explosive/flash powder, then press it into a suitable form, or add it to a plastic explosive and shape it into a
such form. After that, the resulting "pellet" should be magnetized by a strong magnetic field, e. g. using a larger NdFeB magnet.
Firstly, neodymium in its powdered form, is highly flammable and pyrophoric and I suppose that the Nd in the NdFeB alloy will either act as a powerful
fuel in an fuel/oxidizer explosive or in a flash powder-like composition and will also ignite the Fe and maybe the boron part of the alloy, or when
arranged around an explosive and pulverized by the explosion, self-ignite and combust with the surrounding air.
Secondly, during the explosion the magnetic field should vanish instantly, due to the heating and combustion of the NdFeB. This would cause a strong
change of the magnetic field strength in a very short time, which should induce strong currents in the plasma component of the explosion gases. This
could, on the one hand, further heat up the already very hot plasma, and on the other hand, the plasma which the currents would flow through will
expand, which might convert some of the chemical energy of the explosive into electrical/magnetic energy, which would be released when the plasma
cools down. Additionally, in case of magnets arranged around the explosive, they will be shattered and the powder cloud will expand, which could add
potential energy to them, as the particles are pulled apart against the magnetic force that attracts them to each other. This energy will be
eventually released, as the powder should self-ignite or be ignited by the explosion gases.
All these effects may lead to an EMP.
I have a few questions:
- Is there already any information about this kind of idea?
- Is it possible, that some chemical energy of the explosion is converted into electromagnetic energy, or is the maximum output of EM energy limited
by the amount of magnetic energy stored in the NdFeB magnetic field?
- Are there any other flaws in my idea?
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Wizzard
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Neo magnet dust is not very pyrophoric.
Exploring a magnet will result in the same thing as exploding a chunk of most sintered metals- Just a spray of hot, small fragments. Nothing special.
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Fusionfire
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It is a nice idea. I would agree that after the demagnetisation of the NdFeB you will get induced currents that try to oppose the change (Lenz' Law).
However from an outside perspective the magnetic field from the magnets were very weak so the induced currents upon demagnetisation will yield a weak
external field. Furthermore to start with, your magnetic field strength from a NdFeB powder isn't great, because a magnet's strength is proportional
to the length of the dipole. As a dust the dipole length is of the order of your dust size, so it is tiny.
The tried and tested non-nuclear way of generating EMP is through an explosively pumped flux compression generator.
http://en.wikipedia.org/wiki/Explosively_pumped_flux_compres...
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Wizzard
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Simple demagnetization will not induce currents- You need AC, a compression (hard-core) followed by release.
You'd be far better off condensing a highly charged wire (short circuit electromagnet), then exploding it.
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Fusionfire
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Quote: Originally posted by Wizzard  | Simple demagnetization will not induce currents- You need AC, a compression (hard-core) followed by release.
You'd be far better off condensing a highly charged wire (short circuit electromagnet), then exploding it. |
Let's say you have a series of stacked ring magnets arranged along an axis so that the magnetic flux passing through their hole.
Around that you have a larger solenoid coil (not a plasma as has been originally suggested).
What happens if you send a shockwave through the ring magnets and demagnetise them?
Surely you will get induced currents in the coil.
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HellstormOP
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The length of the dipoles should add up as a larger pellet of the mixture is formed, shouldn't it?
Assuming that currents will be induced in the plasma of the explosion, wouldn't the currents increase as the plasma expands against the constrictive
force of the magnetic fields induced by the currents?
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Fusionfire
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The magnetic moments from little dipoles can add up, but due to the heat from the combustion the tendency is to maximise entropy/chaos so they won't.
Heat is the enemy of order (2nd law of thermodynamics, paraphrased  )
As the plasma is expanding it is also cooling. Therefore its resistance is going up and eventually it will lose its plasmatic state.
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HellstormOP
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Actually, I've meant that as long as they stay as a pellet, they will add up, and then instantly demagnetize during the combustion. This should induce
currents in the plasma.
Of course the plasma will cool, but as long as it's hot and conductive, there should be currents, shouldn't they? And as soon as it cools to a point
where it's not plasma anymore, the currents should be released as electromagnetic radiation?
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franklyn
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There will not be any enhanced effect without specific channeling of energy for the
desired transduction. You could for example fire a magnet in a gun and capture an
electrical pulse from it with a surrounding coil. The extent of effect is limited by the
magnet's gauss rating. Rare earths as this peak at near 15 kilogauss. The effect
from demagnetising is similar to shorting a solenoid of equivalent magnetic field
strength. In comparison a conventional exploding magnetic flux compression
generator develops many tens of megagauss.
To produce EMP effects on small nearby objects , requires good coupling with
enormous transient fields. Exploding a magnet , dispersing the ferromagnetic
material de-rates the gauss rating by 1/(r^2) the opposite of what flux compression
does. The energy of the system is constant , ending as residual heat. Microscopic
effects at the particle level will not be manifest at a large scale unless there is already
a strong applied external field covering the blast area. Any effect will be feeble since
plasma is diamagnetic and the domains will couple ending the external field they can
produce when aligned.
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Fusionfire
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^ What Franklyn said.
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niertap
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Apparently explosively driven ferromagnetic generators are somewhat similar to the concept you raised. They seem to be able to generate a reasonable
amount of pulsed power by placing coils around the device, in order to couple the flux in a not completely inefficient way.
However, they likely come nowhere close to the efficiency and power of explosively compressed flux generators. Aluminum or copper has less inertia
and can be compressed much easier than expanding ceramic magnetic material. This means a reasonable efficiency.
Also it occurred to me that the magnetic effects would probably add an interesting inertial/electrodynamic confinement. A magnetic primary explosive
could possibly be very insensitive to everything but a flame and cross the DDT quite interestingly.
http://en.wikipedia.org/wiki/Explosive-driven_ferromagnetic_...
http://en.wikipedia.org/wiki/Explosively_pumped_flux_compres...
"An EPFCG can be used only once as a pulsed power supply since the device is physically destroyed during operation. An EPFCG package that could be
easily carried by a person can produce pulses in the millions of amperes and tens of terawatts, exceeding the power of a lightning strike by orders of
magnitude."
Ignorance is bliss
Outliers in life are modeled by chemical kinetics
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AndersHoveland
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I really do not think permanent magnets propelled by explosive force would make a powerful EMP. In a typical EMP bomb, the explosive force generates
extremely high currents that go back to strengthening the magnetic field. The short-lived magnetic field in the coil will be much stronger than any
permanent magnet, and so will also be more efficient.
The other problem is that an explosive would be likely to shatter the brittle neodymium alloy magnet, and the tiny pulverised pieces might have a
tendancy to realign before they have been pushed all the way outward.
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