EMP

[DougM]

I have done some research but I can't find a simple place to learn about EMPs. Either the info is to basic or it is way to technical.
Basically I am thinking about a few different timeline ideas but not sure how the would work out as I don't have good info to go on. Any ideas were I can get some of the following.
At what point did cars, trucks, and trains become susceptible to emp. Or in other words, would a 1950 or 1960 car get knocked out?
How far would an emp effect from ground zero?
Would our electrical grid from the past survive? If so when did it become vulnerable to emp?
I have read about the one bomb in space over the US taking out most of the country. Is this true?
If so how big a bomb and how high?
Could something similar be done with a few more bombs but inside the atmosphere say in a jet plane?
And how does a natural emp like effect like from the sun compare?

Note I don't expect answers to these questions but if someone can tell me were i can find this info.?
Thanks in advance.

 

[riggerrob]

There are two ways to generate Electro-Magnetic Pulses: capacitors or nuclear bombs.
Since above-ground testing of nuclear bombs was stopped by test ban treaties circa 1960, there was little data published after then.
Meanwhile, both the USA and the USSR developed a variety of EMP simulators to test "hardened" electronic systems. Most of these simulators were based on electrical capacitors that were rapidly collapsed to produce electro-magnetic pulses. They had to collapse so quickly that many EMP simulators used explosives to shove the plates together.
Up until the early 1960s, both the USA and USSR published scientific papers about how to simulate EMPS.

More recently (2014 or 2015), Aviation and Space Weekly leaked news of a new class of EMP generators being tested by the USAF. A&SLeakly hinted at High Pulse Microwaves that could be fired multiple times during one flight. They also claimed that HPM would not damage the drone that was carrying them.

However, high tech, gee wiz gadgets are not needed if you only want to temporarily disable one transmitter site (e.g. a cell phone tower). All you need is a powerful transmitter, transmitting on the correct frequency, close to the victim site.

Difficult to say exactly when civilian cars and trucks became vulnerable to EMPS. My guess would be the mid-1970s, the first oil crisis forced car manufacturers to add electronic components to their engines to improve fuel efficiency and reduce pollution. Electronic fuel ignition replaced carburetors to more precisely meter fuel into cylinders. Electronic ignition replaced points and condensers to reduce maintenance and more precisely time ignition. Electronic (automatic) transmissions shift more precisely, further smoothing loads to engines. Electronic anti-skid brakes reduce the risk of sliding into the ditch. Electronic traction control reduces the risk of spinning out of control on icy roads. Electronic automatic braking reduces the risk of rear-ending another car that the driver is not watching. Electronic lane-keeping systems reduce the risk of side-swipping another car. etc.
Bottom line, modern cars depend upon so many electronic gadgets that they are vulnerable to EMPS.

 

[muskeg13]

How far would an emp effect from ground zero?

I've been told damaging EMP effects are mostly Line-of-Sight, so you need to consider the altitude of the burst, the distance to the horizon (curvature of the earth) and the masking protection afforded by intervening terrain, such as mountains, valleys and possibly the man-made valleys created by very large buildings. In the Army, if an imminent nuke strike was anticipated, we were trained to seek shelter in low spots, like gullies and dry creek beds, lower our radio antennae, and turn off all but the most essential electronic gear.

 

[Saphroneth]

Probably the best test case of a nasty EMP is STARFISH PRIME, which was a nuclear test that resulted in very wide area EM interference.

 

[Tovarich]

It doesn't really matter what you put in your TL.
If EMP so much as affects an early digital watch, the pro-nuke fanboys will be down on you like a ton of bricks, demanding your TL be sent to ASB.
Also, a drop of Factor 50 sunscreen will prevent any flash burns, no problem.

 

[nixonshead]

I looked into EMP some years back, and as I recall nuclear weapons generate EMP when their EM radiation (mainly gamma rays) starts a cascade of electrons getting knocked out of molecules in the air (Compton effect). This flow of electons sets up a current, which generates a powerful, sudden magnetic field, and it's that which goes on to induce large currents in any conducting materials it comes across. It's the huge induced surge of power is what knocks out your electrical systems.

To be most effective, you should detonate your nuke either close to the ground or above the bulk of the atmosphere. If you detonate at medium altitudes, the electron scattering happens in all directions more or less equally, meaning no (or small) net current flow, hence much less magnetic pulse.

Close to the ground, scattered electrons can't travel far downwards, because solid ground doesn't let them travel as far or as easily, meaning a net current flow up into the air. However, line of sight is restricted, so their's less air visible to generate the pulse, and the pulse itself is not seen by anything below the horizon.

By detonating above the atmosphere, there's nothing above the bomb to scatter, so all the scattered electrons are travelling downwards, giving a strong net current. Also, the amount of air subject to scattering is increased, as there's a lot more air visible from the detonation point. Because such a wide area is generating the scattering, the resulting pulse also covers a huge area. IIRC, the talk was of megaton warheads at a couple of thousand kilometers being able to blanket a continent.

A related effect from high altitude nuclear explosions (HANE) is those scattered electrons energising the ionosphere, reflecting radio signals away rather than letting them pass. IIRC, one of the first HANE tests in the 1960s knocked out radio over most of the Pacific ocean.

I found the Federation of American Scientists as a useful resource for this.

 

[altamiro]

EMP radius of a nuke itself is only slightly larger than the destruction radius. a nuclear warhead on a plane will affect a small area immediately below the detonation point, or not at all.

The way to get a massive EMP is to have the bomb's primary radiation interact with very, very thin gas where the molecules have no way to get rid of the excited states energy in a radiationless way (by impacting each other), which pretty much sets a hard upper and lower limits on altitude. Charging up the Van Allen radiation belts further increases the EMP potency. This is what happened with STARFISH PRIME - and Honolulu is still standing.

The electricity network will not be per se damaged by the EMP, but some of the equipment attached to it will be. I am not at al sure that cars will be as affected as most layman writers assume; electronic in a car that is turned off may not be affected at all (the circuits are interrupted), and the fact that a car is a Faraday's cage may protect even electronics in a running car.

The major effects are actually on anything running and connected to a power line - the longer the wire is, the more energy it takes up from the EMP, and the more devastating the surge is. However even then a surge can only go through closed circuits; everything that has been turned off "hard" (with circuits interrupted) is largely safe.

 

[altamiro]

Close to the ground, scattered electrons can't travel far downwards, because solid ground doesn't let them travel as far or as easily, meaning a net current flow up into the air. However, line of sight is restricted, so their's less air visible to generate the pulse, and the pulse itself is not seen by anything below the horizon

You have to take in account that air at sea level is largely intransparent to electron radiation - the intensity fall-off for electron radiation goes down with r^3, while the shockwave effect goes down with r^2 - so basically if you detonate a Davy Crockett near the ground you can actually knock out some equipment by EMP that is uneffected by the explosion, that means maybe a few hundred meters out of the epicentre, but if you take a Tsar Bomba everything that is taken out by EMP will also set on fire by thermal pulse and be pulverized by the shockwave immediately afterwards.

 

[Tovarich]

Serious reply (to make up for my earlier sarky one):

I just stumbled across this on a wiki-walk.
http://www.empcommission.org/
The pdfs seem to be the kind of stuff you're looking for.

 

[bsmart]

The question about effects on vehicles comes down to the type of ignition system. Older cars with conventional distributers (rotating shaft using a gear off the crankshaft) that physically opened and closed contacts to route the spark to the appropriate sparkplug are pretty much immune to EMP results for basic operation. Older diesels should also be immune if they do not have electronic controls for fuel and air metering.

Which year cars went to electronic ignition varied by make and model but was generally from the late 60s thru the 70s.

 

[marathag]

At what point did cars, trucks, and trains become susceptible to emp. Or in other words, would a 1950 or 1960 car get knocked out?.

Chrysler was the first to use alternators in some models in 1960, while GM and Ford didn't have them thru the lines till 1965, relay based voltage regulators thru 1968 or so. Chrysler was the first to replace points with transistorized ignition in 1971, I think

Now solid state radios were in by most makes by 1963

Trains were late '60 for radios, and diesels were mechanical, as were the generators. AC wasn't in for decades