US government HAS the ability to simulate EMP or flare blackout.

originally posted by: MysterX
It fried MANY telecommunications systems, left comms blackouts all over the UK..i know, because i was one of the engineers tasked with replacing all the dead switches.

It also affected Quebec's hydro-power plant's transmission system, and caused it to collapse.

I don't need to mention the Carrington event i assume.

And...what do these two things have in common, and why are they affected by geomagnetic heave caused by CMEs, whilst all the other electronics is untouched?

You have to understand WHY certain things are affected. A CME is not an EMP.

Okey dokey, got a few spare minutes. Lessee (tap tap tap is this thing on... on... on... on... (howl!))

First:

Why do you say a solar flare/CME isn't an EMP?

Answer: Because it's not one. They have different causes. And different mechanisms. There's sort of a bit of overlap of effect, but in general, you can consider any solar anything short of a nova to be a small subset of an EMP in types of effects. But a CME has a much BIGGER, more widespread effect in the one or two things they actually do.

On top of which, the term "EMP" can be used for several things, all of which are different in nature, and THOSE have different effects from each other and from a CME. And of course, the MSM can't get it right because they don't have science editors anymore, in favor of spell checkers.

So, unfortunately without the white board which would make this much easier for me, being a visual/drawing sort of guy, I'll try to succinctly (ha) pop down some of this, leaving out the grodier physics and all the math.

a) HAND

This is what the gubmint uses to designate what you most likely first think of when you hear the term "EMP". HAND stands for High Altitude Nuclear Detonation. It's sort of the sui generis of EMP, the thing that the term was designed to fit.

When you pop off a nuke in low Earth orbit, you set a series of events in motion. And right off the bat, I'd like to say "No, the nuke doesn't emit the EMP itself", because it doesn't. What the nuke squirts out is hard x-ray and gamma radiation, in all directions. A portion of this is aimed more or less downwards, a bit less than half typically depending on the trigger altitude. The part that goes away from the ground you can ignore. The part that goes downward and hits the atmosphere is the key for all the festivities.

If you pop a big mother off at about 500km, you'll light up the entire North American continent. Lower, and you can sort of pick the radius of destruction, down to about 100km, less than that and other things start happening instead. 100km would get you about a third of the country. It's also better to pop the nuke off more towards the pole and less towards the equator - an equatorial HAND doesn't do nearly as much. And it also depends on the nuke design, which I can't discuss.

Anyway, off goes your nuke. The parts of the bang that are relevant are the hard x-ray and gammas. The light, heat, and whatnot are irrelevant for this. The radiation squirts out in a more or less spherical shape (again, you can affect this with the design), and hits the ionosphere and upper atmo. This is where the fun starts.

Right off the bat, you get some really nice high energy physics, and this falls into three categories, two of which you can probably ignore for the purposes of this discussion.

The two ignorable effects are photoelectric effect ejection of electrons from gases, and pair production of electrons and positrons. They're definitely there, and you can detect them with instrumentation. But the real workhorse here is the Compton effect. When a very high frequency EM photon whacks into a gas atom, an electron will be shot away like a croquet ball when you 'send' someone. It can depart at relativistic speeds. What's left is emitted as another photon, and it can do the same thing possibly several more times, depending on how things play out.

The flying electrons do a couple of things. One, they tend to travel in the same direction as the gamma ray that caused them to separate from the gas atom, so they head downward, leaving the positive gas atom behind. This produces a dipole, and a resulting electric field. Two, they will spiral like mad along the geomagnetic field lines. This circular motion produces a magnetic field. And eventually, the electrons will whack into thicker air below and make more ionosphere.

The time varying electric and magnetic fields thus produced cause a couple of issues.

The electric field is basically going to expend its energy in the form of a propagating radio wave, aimed at the ground, and in a real mix of polarization and frequencies. This hits the ground in two phases. The first is a transient phase or early pulse, and it hits as a radio blurt about a microsecond long, with energy spread unevenly over the 1MHz to about 250MHz range, but most of the total energy is below 30MHz. The second is a much less destructive event, the intermediate EMP, which lasts for about a tenth of a second and has spectral content mostly below 100kHz. This one doesn't do much.

There's a really nice analysis of all this with equations that's in DOD-STD-2169(c) but last time I looked it wasn't something you could get, being classified top secret at one point. It may have changed in the time since I was interested in this stuff.

The magnetic field coming off the electrons shoves the Earth's magnetic field lines around something awful. It's sort of like a fat guy doing a cannonball into a deep pool. You get a splash, then the water is thrown away from the entry point, then it snaps back to fill the hole, and big waves go back and forth for a while before the pool settles down again. That happens with the Earth's field, and we call that the late phase or geomagnetic heave. You also get a big chunk of energy that acts about the same way from hot ionized air rising under the bomb site, the upward motion of conductive plasma causes big ass currents in the ionosphere that look like Compton spiraling in terms of the physics. That one lasts from 100 microseconds out to about 1000 seconds, the first part due to the spirals, the end of it due to hot air.

The geomagnetic heave part is what gets power lines and telecom lines that are long copper wires. And it's the part that keeps on giving all over the world, since the geomagnetic heave propagates globally. It's definitely worse right under the bang, but you get a taste of it all over, and it's got another local maximum at the conjugate point. So somewhere on the back side of the globe will eat it as well.

continued in part II...

Ok. So with a nuke, to recap, the bang gives you gamma rays that knock off electrons that head downward toward the ground at near-c speeds, and spiral around the geomagnetic lines, creating their own magnetic field. And then the hot plasma shoots upward and between all that you get a transient phase and an intermediate phase both of which are mostly radio emissions, and a slow phase that's also called the geomagnetic heave, and that one's mostly big ripples and splashes in the Earth's geomagnetic field lines.

I might add, for reasons beyond this post, a high altitude burst will get you both effects, a mid-air burst is almost EMP free, and a ground burst will cause a lot more late-phase geomagnetic heave than prompt radio emissions.

So. The prompt and intermediate radio wave phases hit conductors, and induce high frequency currents in them. This causes a few different types of damage.

One, radio receivers, radars and whatnot are susceptible to the RF input, because they're designed to efficiently pick that sort of thing up. So they get a LOT of it, and the front ends fail. For radios, it's the front end amps that generally eat it. A problem there is that you often have to use unprotected MOS devices or FETs in the front end. The zener diode clamps you'd normally have on the gates of slower speed devices increase the gate capacitance, so you typically don't have them. So what happens is that the gates end up destroyed. So do any small low voltage specialty caps in the tuning circuits of radios, or the circulators/duplexers of radars. Pop goes the weasel. It's not that you can't protect against this at all, but it's definitely a case where the protection lowers your performance. A lot of mil grade radio and radar is designed so that the EMP sensitive bits can be swapped out easily. As a designer for this sort of thing, you have to apply FM to get the equipment past the RF susceptibility tests, which is the nice way of saying it'll hold up to a reasonable bomb.

The two RF phases also cause damage to electronics in other ways. And they can cause it to both tubes and MOS, although the semiconductor stuff is definitely more susceptible. If you've got cables that aren't properly shielded (maybe even if they are) they can act like an antenna and conduct some massive voltage spikes into your equipment. This is also a problem for things where your electronics are both of reasonable size and no good way to shield, primarily LCD displays. The noise spikes coming into the equipment typically cause two types of damage. The first is gate punchthrough. MOS, which is most integrated circuits, use insulated gates, where the insulation is a few microns of some sort of oxide. If the input voltage goes too high, the gate will cease to insulate and become a spark gap. This is bad. The second is single event upset. You get single event upset when you have a circuit with various states (any digital circuit pretty much qualifies) and you end up going from where you want to be in terms of circuit states to something exciting and random which the designer might not have provided for.

For gate punchthrough, you can mitigate this in a number of ways. One is good equipment shielding. If the bay is tight and all the shielding is in place (i.e. the tech hasn't made his life simple and left it off) then it'll likely shrug that off, as you had to pass RF/EMP testing to put it in the plane/bunker/battlefield. You have to address the possibility of letting something in by means of cables. But you can do that as well, up to some reasonable point. Also, most modern digital stuff has clamp diodes on the inputs that can react in picoseconds to divert the spike to ground or the power supply rail. If too much signal gets in, these will pop and the circuit will fail anyway. But it's the designer's job to make sure it doesn't.

So the "all devices immediately fail and that's it no more electronics" thing is sort of a myth. Some will, but a lot won't. This goes for consumer stuff as well, I've seen unshielded consumer stuff live through the test chamber when otherwise tight VME or cPCI rigs popped. But a lot of purpose-build military stuff will survive the gate punchthrough.

The single event upset is a bit harder to explain. Basically, designers often don't deal with things that can never happen in real life. So a possible circuit state that turns both transistors on for an output pin just aren't addressed, as the circuit in normal life wouldn't allow that combination to be set. However, it can happen in a SEU. A favorite of mine is that a lot of switching power supplies will happily turn on the top transistor and freeze, leaving the low voltage supply to go to the rail, popping everything on the board. Or you get a mix of some of the switched voltages going to zero and others going to the rail, same effect.

To stop this sort of thing, you just turn the equipment off. Once the bang is over, no more issue. If you design to eliminate don't-care states instead of embracing them to make the circuit cheaper, then you will have much less of an issue. You might have to power cycle to get its attention but you won't lose circuit. And you'd want to make sure you have crowbars on the power supply that turn off the main power feed. So when the bang happens and the board tries to fry itself, you've got a brave little watchdog in there that says "Hey, the CPU voltage ought never go to 3V...kill the power!"

Again, that makes things bulkier and pricier, so you have a hard sell into consumer goods.

continued in part III...

Another recap - nukes at high altitude give you all three phases. A mid-air burst, almost nothing. A ground burst, you get mostly geomagnetic heave.

Of the three phases, the first two are radio signals with mixed frequency at really amazing amplitudes, and they pop circuits by overvolting devices on the front ends of radios and radars, and by causing gate punchthrough and SEUs in digital stuff.

The geomagnetic heave phase is where you take out the power lines and telecom cabling.

In the US, long HV distribution lines are typically wired up in a wye configuration, with a grounded center point. So what you end up with is a long flat loop consisting of the three phase wires for the top part of the loop, and the earth as the bottom part, tied to the middle of the wye at both ends.

This makes for a really nice single turn transformer with a huge aperture, and since the wires are usually pretty high above the ground, you can add in a capacitive couple with the ionosphere.

After the bomb pops off, the prompt phase will cause those Compton effect electrons to head straight down in a big relativistic Zergling rush. This capacitively couples a big voltage spike into the line just for openers.

Once you're past that, the magnetic field starts bucking around. You get that first early buck when the electrons spiral around the field lines. This hits the ground with a big magnetic pulse, which also shoves the field lines from the earth away. Once the pulse is over, the field lines pop back with a vengeance, and then the whole thing oscillates for a while.

All these field changes induce currents into the loop formed by the wires and the ground below. And the bucking takes seconds to complete each way, so it's effectively a DC current that's being induced into the long lines. In addition, you get other ground loops set up so that the earth takes on a different potential at both ends of the wire. This is also bad, and induces its own current in the wire.

The currents in long power lines during a HAND can hit 100A, which is not a good thing.

Now, if you've got copper telecom cables that go for long distances, you'll get the same sort of thing in miniature at the switches or SLAMs. Fiber optics don't care and won't be affected. But high impedance connections at the ends of long copper wires will have a common mode voltage from hell induced on them. If not dealt with, the switch/SLAM will fry due to common mode induction.

The situation with power lines is a bit more complex. The first e-field coupling spike can cause dV/dT failures in transformers by just punching through the insulation between windings, which can ruin your whole day, and will take out a lot of the power line communication system by popping the coupling caps.

Most of the issues, though, will happen with the transformers due to DC currents. Transformers, especially the touchy high voltage ones that drive long transmission AC lines, don't like DC currents at all. The why is a bit complicated, but essentially it's due to saturation.

A transformer's core steel works by having lots and lots of little magnetic domains. AC power on the primary rotates the little magnetic domain alignments in the cores, coupling a field into the secondary. That's how it's supposed to work. There are only so many domains in that steel, though. As you apply more and more current in the primary, you flip more and more domains. And eventually you start running out, and more current in the primary doesn't increase the field in the core any more. This is what we call saturation. You just can't put any more magnetic field into the core, because it's taken all the flux lines it's going to. There aren't any more domains to recruit. So more current just creates crappy field lines in the air around the core, but they don't end up coupling power into the secondary.

Saturation is bad. You never design a transformer to operate saturated in a normal world (swinging chokes are a different thing), or even to approach saturation. You can't put a HUGE margin in though, because you have to buy margin between your operating point and saturation by putting in more steel, or better steel, or more windings or whatnot. So you have to pay for that margin, and mostly you can't justify it in a business case for civilians.

More, there's a thing called hysteresis, and that's more than I want to explain, but it's related to the core efficiency. The fatter and less symmetric your hysteresis curve (also called the BH curve), the more of your electrical power goes into warming up the core instead of going down the line.

As you enter the geomagnetic heave phase, the flux changes caused by the heave enter the wire-Earth loop and induce a big current. And there's another loop in the ground itself that changes the ground potential between the ends of the line, which also adds to the fun. The quasi-DC current has a lot of non-optimal effects on the distribution system.

One, it saturates the transformers really well. That 100A+ current recruits all the domains, or most of them, to the DC current flow. As a result, the energy coming into the primary can't make magnetic fields out of the power, at least not in the core. So what you do produce radiates into the area around the core, heats up the transformer casing, induces voltages into the connections and surrounding structures and what not. Also, since the core's not accepting any more flux, the effective AC impedance of the transformer closely approximates to zero, and it turns from a transformer into an expensive short circuit. What power's not going into heating the case red hot just dumps its energy into the primary in the form of I2R losses, the wires turns red hot and becomes what we call a molten puddle.

Also over on the secondary side, that 100A current is more than the secondary is able to tote and IT starts heating up to failure.

If you get less of a hit and don't saturate totally, you get some other effects that are more slowly bad but will still cause a failure. The current raises you on that hysteresis curve, and instead of being thin and tall, it starts becoming fat and distorted. The fatter the curve, the more loss in the core. A lot more loss. Instead of being 90%+efficient, you're down to the 30% point and most of the power is going into burning up the core. And since that hysteresis curve isn't symmetric anymore, you get harmonics. Some of the nice 60Hz power going in is now 120Hz, 180Hz, 240Hz etc, and the currents tend to circulate in the transformer, further heating it, they also cause eddy currents in the core. That asymmetry also starts coupling a lot of magnetic flux into mechanical stress in the core, so you get this organ chord as the thing starts disassembling itself. Harmonics also cause hot spots in the windings, so between heating and shaking the core around and heating up spots on the wiring, you will very shortly get a short and Bob's your uncle.

The good thing, if there is one, is that shorter runs have dramatically less problems, so the local distribution from the power plant next county over will likely safe itself and shut off, leaving the turbines to deal with an unload, which isn't going to be nice either. But it's not necessarily curtains for local power. You will lose the AC links between areas, though.

continued in part IV...

Now, back to - "how's a CME different?"

Well, a CME only has the heave part. You don't get ANY of the prompt or intermediate effects. So it's not an EMP. It's not even really LIKE an EMP. CME's don't have the fast initial heave, and they don't have the e-field coupling due to the Compton electrons. CMEs have a lot of slow component heave, though.

When the CME passes close by or hits, the magnetosphere bucks around in response. That causes classic heave. In the case of the telegraph wires for Carrington, you had cotton insulation (if any) and the voltages induced easily punched through it and set it on fire. So you won't get the dramatic failure you'd get in the 1800's.

However, you still get common-mode voltage hikes in telecom lines. And you'll still get all the geomagnetic heave you'd have gotten with a HAND, only it'll go on a lot longer than 1000 seconds. So even if you're only partially saturated, you've got plenty of time for hysteresis curve flattening and harmonic production to overheat the transformers and cause a failure.

But without the two prompt phases, you don't get widespread destruction of semiconductors. That's why a CME isn't like an EMP caused by a nuke. The things that are damaged will be devices connected to wiring long enough to pick up enough flux lines to induce a voltage spike sufficient to damage the equipment. But not your PC. Typically, it'll be telecom.

E-bombs, flying CARMs and whatnot are sort of the exact opposite of a CME. You get a very high power radio emission but no heave at all. So an e-bomb can't cause a saturation upset of a power system. It CAN cause, in some circumstances, winding damage in local pole transformers. But not on long lines.

The target for these things (the op's original misstatement) is local electronics. A good e-bomb might fry up a few hundred meters of ground electronics. But it's not going to knock out the power for the entire US. These devices also don't radiate a wide swath of HF power like a nuke would, either. Typically, it's one frequency and that's usually in the UHF or microwave part of the spectrum. So it's also generally easier to defend against.

You see all three things lumped inaccurately into the "EMP" label. They're not alike at all. All of them can be defended against to an extent, not all devices will instantly die. A flying CARM will damage different types of things in a different way than a HAND, which is still different from a CME. So when you see the EMP doom porn a-flyin', you have to distinguish what sort of thing you're talking about and if it will, in fact, cause that sort of damage. A lot of times you see what happened on the first page or two, someone claiming that this or that device will cause all this widespread havoc because it's an EMP, and by golly I've read that EMP does this and all EMP is the same, therefore, destruction.

The problem is, that's not true. The term is a bit diluted, and most people don't make the distinction. Even people who should know better, including a couple of think tanks who make their money off of EMP doom porn. I would like to assume they DO know better, and are simply trying to be misleading to make more money off of speaking engagements, but it's at least possible they're all accountants and upper management types and DON'T understand.

And that's pretty much enough beating that horse.

Oh, yeah. PS.

The first one that goes off is all that matters. Back to part 1 or so, the electrons and gammas are all flying around and when they get done doing that, you've got an absolutely huge ionosphere. Incredibly deep. And it's going to be "hot" as hell in terms of electron temperature.

It's also going to be rippling and bouncing around like mad.

This does several things. One, any late-coming HANDs are not going to have a big effect, because the new ionosphere will tend to shield against any further e-field incursions. And the geomagnetic field is going to be really screwy, so you don't get that nice line spiraling thing you got on the first one. So subsequent bangs don't do a lot.

It also cuts off your communications with satellites. The new, superduper ionosphere is going to be reflective way way up into the microwave spectrum. So before the bang you could use anything above maybe 80MHz to do space comms with, but now you can basically forget it for a while. It'll take a laser link to a satellite that can relay signals for you.

The other thing is that the ionosphere is a lot lower and a lot more opaque after, and it'll be rippling and bounding like mad, so you can also sort of give up on most radio communications until that stops. GWEN was designed to work in that environment by not interacting with the ionosphere at all (hence the GW part of GWEN). Now we just plan to use fiber optics.

And last but not least, all the left over high altitude really high speed electrons will whiz around in loops between the ionosphere and inner magnetosphere for weeks and weeks. When they hit a satellite, they emit x-rays and fry up the electronics. We have ways to stop that that were designed at Gakona, so instead of losing all the orbital assets, we can clean up near space using something we figured out at HAARP. So you got THAT for your tax money, if nothing else.

a reply to: Bedlam

*submits "white board presentation" feature to ATS suggestion box*

Thanks for the write up. The DOD citation is still classified unfortunately; only found something on protecting equipment and such from the events. But, hey cleaning up after a HEMP you say? A lot better than rattling our brain stems lol

a reply to: Barkowsky

I imagine a grounded Faraday cage, portable if possible, would offer sufficed protection against an EMP attack regarding our normal everyday electronic devices and storage mediums. Then again if our power grid and/or info-structure sustained enough damage there's not much point considering we would essentially see a return to 1700s-1800s society. Worst case scenario your better off with a sharp axe than an IPhone, semi functional or otherwise.

originally posted by: Barkowsky
The DOD citation is still classified unfortunately; only found something on protecting equipment and such from the events.

A pity, it's got drawings and examples with math. I can see why you might not want it out, though.