Tuesday, January 21, 2014

Electro Magnetic Pulse EMP

EMP, something discovered in the late 1950s.   Consider a nuclear bomb.  Several tons of uranium or plutonium and casework  and whatever.  Detonate it.  The furious energy of the atomic detonation blows all the electrons off the atoms comprising the bomb, and immediate surroundings.  Turns them into charged ions, and blows them away at supersonic speed.  This is a massive moving electric charge, which creates a massive magnetic field that spreads out from the detonation site at the speed of light.  Such a field will induce massive electric currents into any conductor that it encounters.  Other doomsayers worry that solar flares or "coronal mass ejections" can do the same thing.  They point to the 1850's Carrington event, a solar flare so strong that telegraph wires sizzled and crackled with sparks in telegraph offices, scaring the bejezus out of telegraph operators.
   The fear is, that such currents will melt wires, arc over insulators, trip circuit breakers, melt transformers and destroy alternators.  Wreaking the electric power grid, the internet, the wired phone system, the cell phone system, stereos, TVs, Ipads, everything electric or electronic and hurl our civilization back into  a dark age, lit only by fire.
   Not to worry.  The millions of miles of wire hanging from poles, all across the continent, get struck by lightning, every minute of every day.  A single lightning strike stresses electrical systems to the limit.  Lightning will arc over any insulator, and fry anything.  Half a century ago, every summer lightning storm would knock out the electric power.  Well, over the half century since then, the power companies have hardened their systems.  My lights stay on, unless a windstorm drops a tree on the wires and breaks them.   Local damage, sure.  My mother's home took a lightning hit a few summers ago.  Blew out her satellite receiver, her DVD player, and few other things.  But the electric lights survived, along with the furnace, the hot water heater, and the electric stove.
   I don't believe any EMP event will ever be as bad as a  lightning strike.  We have hardened every thing against lightning strikes.  They are probably safe against EMP events, be they hostile nukes, or solar flares.


Anonymous said...

A solar EMP would have a much longer impulse potential compared to a quick lightning strike. Long transmission lines would be highly vulnerable and we don't have nearly enough replacement components to deal with a region wide outage caused by equipment failures.

Dstarr said...

It's the total energy delivered to the system that zaps things. In this respect, lightning bolts deliver a LOT of energy. I seriously doubt that a solar flare or "coronal mass ejection" will deliver anywhere near as much energy as a lightning strike.

DCE said...

There are huge differences between EMP and lightning strikes. It is true that lightning is a local phenomenon and its electrical effects are localized. EMP is as you stated, a wide coverage electromagnetic event.

But EMP can cause a lot more damage than a lightning strike for two reasons: The pulse is of very short duration, on the order of nanoseconds, while lightning takes place over milliseconds. If the EMP is caased by a high altitude nuclear detonation, then much of the energy from the blast is converted into an EMP pulse in the gigawatt or terawatt range. In those few nanoseconds all of the energy from the EMP is released giving a peak output in the terawatt or petawatt range. (Remember, while the total energy released may be relatively low, because it is released in a very short period of time, the energy density - for a lack of a better term - can be multiplied by a few orders of magnitude.) Most terrestrial systems can't handle that amount of energy over such a short duration. In fact, most filtering on power lines would be totally ineffective because the filter response is so slow compared to the energy pulse. And as you mentioned, with all of the power lines acting as antennas, along with the difference in propagation speeds (the pulse moves faster through free space than through wires), the effective energy can be multiplied and very few electrical or electronic devices will survive that kind of spike.

CME's on the other hand, tend to generate long term EM disturbances and at relatively low frequencies. They can cause electrical grids to trip their protection circuits due to over-current or over-voltage faults, creating blackouts, but the chance of widespread damage is much lower. Once the effects of the CME passes most electrical systems can be brought back on line.

Dstarr said...

Where does that nanosecond pulse time come from? I find that figure a little hard to believe. In those movies of nuclear bomb tests, all the mushroom clouds expand and expand for tens of seconds. The vaporized and ionized bomb casing, stuffing, and fissionables, spreads out as long as the mushroom cloud keeps expanding, clearly a matter of tens of seconds. A long as the ions keep moving, they constitute an electric current, which creates a magnetic field. Now the ions will grab loose electrons from everywhere and thus deionize, faster than that. Once the ions turn back into normal atoms, they cease to be a moving charge, otherwise known as an electric current. But I think it will take a second or two before the ion current dies out. That's a lot of nanoseconds.
Systems are damaged by heat, melting things. The things don't care whether they get heated to their melting point in nano seconds or microseconds. Melted is melted. So an EMP of the same energy ought to do the same amount of damage whether the pules lasts nano seconds or microseconds.

DCE said...

There are differences when a nuclear device detonates in the atmosphere versus above the atmosphere.

In-atmosphere detonations greatly attenuate the EMP as a lot of the energy from the blast is absorbed by atmospheric gases, most of which become hot plasma (that's what most of the fireball seen in films of ground/air detonations consists of: nitrogen, oxygen, water, and a host of other gases, including vaporized ground material). There still is an EMP, but it's highly localized, usually within a few hundred square miles.

An out-of-atmosphere detonation generates little plasma but a lot of electromagnetic radiation. As it impinges upon the upper atmosphere, specifically the ionosphere, much of the shorter wavelength EMR is converted to longer wavelengths as the ionosphere absorbs the shorter wavelengths and re-emits them as longer wavelengths. The EMP generated covers a huge swath of the Earth's surface. Because there was no attenuation effect of the atmosphere at the detonation point, the magnitude of the EMP is orders of magnitude higher and the duration of the EMP is much shorter, again on the orders of magnitude shorter. Between the higher energy and shorter pulse duration, the effects of EMP are more dramatic and wider ranging. That's what scares the bejeezus out of a lot of the Defense wonks - a rogue nation or terrorist group will launch a nuke and detonate it high above the US and damage/destroy a lot of our electrical/telecommunications infrastructure.