Gentlemen, we have a Deathray.

[Thoth]

We now need sharks.

Fricken' sharks with fricken' laser beams.


"I'm a Shaaaark......."

[Patroklos]

There used to be some video out there from the older chemical laser tests mentioned in the second article. Interesting stuff.

There used to be a lot more talk about a navalized version of this, which makes sense on a lot of levels. I would be very interested on the effective range of this weapon not for use against small boats, but rather cruise missiles and aircraft.

[The Mad Monk]

I remember reading that naval hulls are much thinner than they used to be. If that is so, this could be an effective weapon against larger ships, too -- and maybe bring back naval armor.

[Kuciwalker]

IIUC (and KH/Jon/etc., please correct me here), EMP is caused by gamma rays that induce a magnetic field; one component is direct induction and one is through manipulating the earth's magnetic field. Wiki describes a third kind that I don't really understand (even beyond my limited understanding here).

Close. Gamma rays, being electromagnetic waves, are an induced magnetic field (that induces an electric field, that induces a magnetic field, and so on). The EMP effect involves roughly 3 steps:

1. Nuke goes boom, emitting lots of gamma.

2. Gamma rays spread through the atmosphere. Each gamma ray photon has far more energy than the ionization energy of the atoms and molecules in the air, so it penetrates far through the atmosphere, ionizing lots and lots of atoms.

3. You now have a large volume of ionized air, which allows the free flow of electrons. These electrons form a HUGE amount of current in a short time. A changing electric current generates radio waves. Radio waves induce current in conductors. Effectively, you have a massive antenna blasting a portion of the energy from the nuke into radio waves, causing power surges in nearby electronics. Power surges make transistors unhappy, so your computer fries.

[Patroklos]

I remember reading that naval hulls are much thinner than they used to be. If that is so, this could be an effective weapon against larger ships, too -- and maybe bring back naval armor.

True. Naval hulls are for the most part completely unarmored, with hulls on the order a .25 of an inch think forthe most part. The penetrating power of modern missiles simply made armor obsolete. We do have kevlar "armor" surrounding some spaces to stop shrapnel from moving freely through the hull after taking a hit, but it isn't going to stop a primary weapon.

Carrier decks are armored, but that is to protect the ship from aircraft crashes. There is a bit of talk about bringing back water line armor to protect against suicide boats. They can pack quite a punch but are obviously not armor piercing in nature. Its all a give or take tonnage wise though, is being that much faster or being able to mount one more weapons mount more useful than dead armor weight?

I don't see laser's leading to a revival in armor, as I think their destuctive power will improve much faster than our ability to add armor. Though perhaps some more exhautic armor tech not as crude as just adding more inches or steel could be effective. Materials science is always coming up with new stuff, I am endlessly surprised by what I read about these days.

[The Mad Monk]

That reminds me, I need to build a faraday cage for my computer room at some point.

[Patroklos]

Effectively, you have a massive antenna blasting a portion of the energy from the nuke into radio waves, causing power surges in nearby electronics. Power surges make transistors unhappy, so your computer fries.

I will preface this by announcing I am ignorant on this stuff for the most part.

Is the character of these radio waves remarkably different from the average run of the mill ones we use everyday, or is it just the strength?

[The Mad Monk]

I think it's the strength.

[Kuciwalker]

That reminds me, I need to build a faraday cage for my computer room at some point.

That doesn't work unless you have a really good surge protector

[Kuciwalker]

I will preface this by announcing I am ignorant on this stuff for the most part.

Is the character of these radio waves remarkably different from the average run of the mill ones we use everyday, or is it just the strength?

What TMM said. In principle you could do this without a nuke... it's just a lot easier with one. Especially because if you detonate it in the upper atmosphere you can hit a good portion of the Earth's surface at once.

[The Mad Monk]

I've actually thought about that, and I'm really hoping for enough warning to pull all the cables and button everything up.

[KrazyHorse]

Kuci's is a better explanation. One quibble: the radio emission is due almost entirely to charges spiraling through the Earth's magnetic field. This in turn is almost entirely from the free electrons (liberated by compton scattering with initial gammas). The fact that the air is ionized and allows the free flow of electrons is actually a really weird way to think about it. The air is ionized BECAUSE of the free electrons (which are given enough energy from the initial scattering that power loss due to precession in Earth's magnetic field far outweighs power loss due to secondary scattering with air).

If I toss an electron with kev level energy into the atmosphere it doesn't give a damn whether the air is ionized or not. It will go a significant distance before coming to a halt because it can barrel its way through almost anything it's likely to encounter (other than low cross-section (?) events like inverse beta decay, which have nothing to do with the charge state of the atom containing the target nucleus).

[KrazyHorse]

The fact that the frequency is just regular radio is pretty easy to get at. If the electrons are non-relativistic (this should be the case, I think) then in SI units the cyclotron frequency is eB/m where e is the fundamental charge, B is the Earth's magnetic field and m is the mass of the electron. At B=5*10^-5 T or so the frequency of emitted radiation is ~9 MHz. For comparison purposes AM broadcast radio is ~1 MHz and FM broadcast radio is ~100 MHz (so this sits squarely in the middle; perhaps there's a reason for that i.e. increased interference near here).

EDIT: whoops, mixed up angular frequency and frequency frequency here. Divide that 9 MHz by 2pi and you get ~1.5 MHz in terms of frequency frequency. Not much above the top end of AM broadcast radio (1500 on your AM dial)

Now, the wavelength of radiation at this frequency is in the tens of meters, so (because the efficiency of an antenna is related to its length in terms of the wavelength...can't remember if the most efficient antenna is lambda/2 or lambda/4....goddamn Jackson EM is fuzzy now) I would think that the major damage done would be to devices plugged in to the power grid? Smaller devices have less tolerance for surges but less efficiently capture power from the radio blast due to their minute effective antenna length. Not sure about this part. Can barely remember antenna stuff.

[KrazyHorse]

Kuci's is a better explanation. One quibble: the radio emission is due almost entirely to charges spiraling through the Earth's magnetic field. This in turn is almost entirely from the free electrons (liberated by compton scattering with initial gammas). The fact that the air is ionized and allows the free flow of electrons is actually a really weird way to think about it. The air is ionized BECAUSE of the free electrons (which are given enough energy from the initial scattering that power loss due to precession in Earth's magnetic field far outweighs power loss due to secondary scattering with air).

If I toss an electron with kev level energy into the atmosphere it doesn't give a damn whether the air is ionized or not. It will go a significant distance before coming to a halt because it can barrel its way through almost anything it's likely to encounter (other than low cross-section (?) events like inverse beta decay, which have nothing to do with the charge state of the atom containing the target nucleus).

The other way to say this is that ionization causes conductivity to rise. What is conductivity? It's the sigma in Ohm's law that says J = sigma * E

But there's no applied E field (after the initial compton scattering, of course). These electrons flow because they have so hellacious initial velocity and simply haven't had the good sense to slow down enough to be recaptured yet. Conductivity is a moot concept when your conduction electrons have an average energy much higher than the ionization energy.

[Blaupanzer]

I will play it your way for a moment, KH. Shouldn't the process Kuci described and you amplified be subject to being developed into a beam that could be directed at missiles, planes, etc.? As a fact, the military test name for this weapon is "Directed Energy Beam Weapon," externally appearing as a chassis with an antenna on top. Most generals and military officials are not physicists, so the name is kept generic.