Strategic Headmelter

Presupposing a capacity for briefly (a few seconds will be sufficient) creating arbitrarily large volumes of Plasma (on the order of a hundred cubic kilometers or so at least) while controlling the geometry of that volume with relative precision (via magnetic bottling), it is theoretically possible to create a field of Plasma in any shape one might wish. For example: A Lens several dozen kilometers in diameter. Using one of these plasma-generating/shaping devices (presumably one you've strapped to a missile and shot into low orbit above somebody you really dislike) you create a plasma-lens as described above, and then almost immediately afterward detonate a fairly large nuclear warhead in a slightly higher orbit. The radiations of the blast which fall on the Lens can be focused and directed just like sunlight through a magnifying glass. Despite using nukes as our power source, neither friend nor foe will suffer any impact from fallout or radioactive dust (to say nothing of the fireball and shockwave), because they will either dissipate harmlessly into space or quickly burn up entering the atmosphere and get blown back out into space by solar winds. The Target itself, however, will be hit by a storm of Electromagnetic, Ultraviolet, Visible Light, Infrared, and Microwave Energies of absolutely Apocalyptic intensity.

We can control the parameters of our attack with great precision. First, the points of detonation must be arranged so our both our Nuke and the Target on the planet's surface are aligned with the axis of the Plasma Lens, thus ensuring that greatest possible energy is caught and directed to the right point. Then by adjusting the distance between the Nuclear Blast and the Lens we can optimize the portion of the yield which falls on the lens before it's disrupted by the blast and destroyed (I reckon this will be no more than 15% of the total yield under optimal conditions, which is still overkill even before it's focused). Finally, by adjusting the geometry of and distance from our lens to our Target we can designate the altitude of the focal point, and by altering it adjust the size of the Target Zone and optimize the ratio between AoE vs Energy Saturation.

End Result: Even the most hardened electronics would be fused if not outright melted and all transformers and capacitors would explode. Ferrous Metals with high resistance (like armor, or structural steel) will rapidly heat up and start to slag, and living things within the zone will be blasted with enough broad-spectrum radiation to flash-fry a blue whale. Yet areas adjacent to the blast are relatively safe*, as the energy that would have fallen there has instead been directed away, onto our target. This means the weapon can be used in active-combat zones, near strategic objectives, or populated areas, and even over friendly territory. Also: Auroras, possibly.

One thing I'm not sure about is what happens to the Gamma Radiation, as I can't recall if it's affected by EM Fields, but it's not a great consequence either way. If so, we're just piling Gamma-flavored hurt on top of an already Supreme Pizza of pain. If not, Gamma dissipates so rapidly that, at worst, you're giving everyone on targeted side of the planet the RAD equivalent of walking past a Dentist's office while they're using an X-Ray. Either is acceptable.

* I say "Relatively Safe" rather than "Completely Safe" here because any large reflector within the target area is going to reflect some portion of the energy that falls on it back off, even if only for a few milliseconds before it's vaporized. So if your target is, for example, a relatively large Phased Array such as those used for large Radar installations (just the sort of thing you'd want to hit with an EMP) then you might end up with a reduced but still flesh-searingly intense ricochet careening into whatever. I'll be sure to make a note of this in the Dox, which I'll start writing as soon as DARPA answers one of the several hundred increasingly tear-stained love letters I've sent.

Disclaimer: Filed under "Weapon: Missile" because it's not entirely inaccurate, and because there's no "Product: Weapon: Strategic Headmelters"

tl;dr: Nuke+Plasma = Hell's Gates swing wide and your enemies run in screaming because they are on fire like six or seven different ways. Then you get to see the Aurora even if you're in, like, Texas or wherever.