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I have an enemy planet with advanced technology and extensive defense infrastructure. All defensive infrastructure relies on electronics. I want to destroy the infrastructure, but leave the people unharmed. To do this, I want to inflict a geomagnetic storm that will render planetside electronics completely unusable, by inducing current in them or by other means. Ideally, this would be accomplished by a starship in orbit using plasma fusion to mimic a coronal mass ejection, just on a larger scale.

My questions are:

  • How much energy might---plausibly---be involved to generate enough magnetic flux to unleash a geomagnetic storm?
  • Would a geomagnetic storm large enough to destroy planetside electronics also cause other effects? For example, should I expect aurorae bright enough to cause vision damage? Seizures? Radiation burns?
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  • $\begingroup$ you might want to look up solar storms. They have the potential to fry electronics on a planet in a large scale. $\endgroup$ Mar 31 at 8:44
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    $\begingroup$ @Fallenspacerock - the OP has already mentioned coronal mass ejections. It's a safe bet they're well aware of solar storms. $\endgroup$
    – jdunlop
    Mar 31 at 9:42
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    $\begingroup$ @Fallenspacerock: An electromagnetic storm which is powerful enough to kill the phone in my pocket with its tiny tiny wires is also powerful enough to kill me. After all, I am a much longer electrical conductor, and I would be expected to couple much better with the electromagnetic storm... $\endgroup$
    – AlexP
    Mar 31 at 16:45
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    $\begingroup$ @AlexP i don't think so. Though probably a powerful enough blast is going to fry the entire planet. You can as far as i am aware not make an electronic pulse powerful enough to surly destroy all electronics with out killing every one that is. But you don't need to as even knocking out civilian infrastructure or satellites leaves your opponent severely at a disadvantage. $\endgroup$ Mar 31 at 16:50
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    $\begingroup$ Ooh, did someone say electronics-destroying electromagnetic effects? $\endgroup$ Apr 2 at 13:02

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First thing first:

I want to destroy the infrastructure, but leave the people unharmed

If you destroy all infrastructure, people are going to die. A lot of people. That's just the nature of technological society. Everyone on life support, almost everyone in an airborne commercial aircraft, anyone in a self driving car... they're all going to be prompt fatalities. Maybe people with pacemakers too, and perhaps various kinds of brain implant. Early fatalities will include anyone having a medical emergency. Delayed fatalities start mounting up as soon as people start getting hungry and thirsty and there's no more food or clean water.

Anyway, that disclaimer out of the way:

Geomagnetic storms are a surprisingly poor way to damage electronics. They can produce effects that can take out country-scale power grids, but that's only because power grids are very large, and as such a country-scale electromagnetic effect can interfere with them, potentially catastrophically. The same field that can take out the power grid will have no effect on your mobile phone, because the conductors in it are too short to develop a significant potential difference. Things between phones and national grids in scale will suffer to varying different degrees I won't go into here.

A more useful thing related to your geomagnetic storm might be a High-Altitude Electromagnetic Pulse. There were a bunch of nuclear tests back in the 60s that caused this effect... the American ones might have a familiar name. Those tests managed ground-level electrical field strengths of 50 kV/m. Proposed specialized nuclear EMP weapons might generate field strengths of over 200 kV/m.

The effects are brief, and will be most notable on things with large conductors. If you stick a meter-long object in a 200 kV/m electrical field, you'll get two hundred kilovolts across it which is probably bad news. Even tiny conductors that are only a millimeter long will experience a 200 V difference from end to end, and the problems that will cause depend very much on the device in question but you may find that your phone might actually survive though your television might not. With sufficient damage to infrastructure though, the smaller devices which survived the initial effects will be significantly less able to function. Sure, solar-recharging and UHF mesh communication might survive, but the equivalent of the internet is rather less likely to hang on when all the datacenters get frazzled and catch fire.

How much energy might---plausibly---be involved to generate enough magnetic flux to unleash a geomagnetic storm?

A Carrington event requires a blob of plasma tens of millions of kilometers across travelling at more than 2000 km/s. You can't really get away with anything smaller than that, because the Earth's magnetic field is rather big and you need a hammer of that sort of size to squish it.

Nuclear EMP is much easier to induce... you could do it with 60s level technology, after all, and can do just as good a job.

Would a geomagnetic storm large enough to destroy planetside electronics also cause other effects? For example, should I expect aurorae bright enough to cause vision damage? Seizures? Radiation burns?

A geomagnetic storm will be associated with dramatic aurorae, but that's about all the visible signs (bar the power grid catching fire). The atmosphere will protect everyone quite effectively. No bright flashes, certainly... the CME will be quite diffuse by the time it hits the Earth.

For the nuclear EMP, you'll get some aurorae, but people will (mostly) be unaffected (though see the first paragraph of the answer). Some research has been done on rats, which showed that strong and repeated EMPs can cause short-lived physiological issues which might increase the risk of certain problems down the line, but on the whole probably aren't an issue.

The atmosphere will do an excellent job of protecting everyone from radiation burns, though it is possible that eye damage could result from looking at the initial blasts.

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    $\begingroup$ "the American ones might have a familiar name" The nerve. $\endgroup$
    – jdunlop
    Apr 2 at 18:40
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You might want to think about ionospheric whistlers, and their discoverer Helliwell. I have wondered if it would be possible to set up a resonance in the ionospheric cavity that beats with the Schumann resonance to create an oscillation deadly to electronics.

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    $\begingroup$ Welcome Clarkman. The automatic system has flagged this for its length and contents. Don't worry about that too much as to me at least, this seems to be the basis of a really good answer (what we refer to as a frame challenge). (I'd never heard of whistlers). Perhaps to please the auto-system, you might expand slightly to tell us something about whistlers, how they occur and how that might relate to the questioner's concern about energy levels. You can edit. Don't be afraid to assert that it's going to be possible, the science-fiction tag on the question closes the possibility-gap. $\endgroup$ Mar 31 at 20:30

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