Originally posted by Gormagon
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Cold plasma and hot plasma are the same thing essentially. The main difference is that cold plasma is room-temperature and atmospheric pressure, while hot plasma can be thousands to millions of degrees at less than a hundredth atmosphere.
Secondly, it may be possible to design such a shield. It required some additional reading. Well i doubt it's in the form of the shield you mentioned but still.
The idea of such a plasma shield is identical to the one i mentioned earlier. By tuning the plasma it becomes possible to turn it into an energy mirror. This is similar to how radio waves bounce off the ionosphere. That's also where the problems come in. First of all, you need a sufficiently strong plasma shield to counter the enemy's EM. So far i see radar being mentioned, that's very far down the wavelength range. The earlier mentioned idea of plasma shields thus still applies: a weapon of sufficient wavelength will cut through the shield like butter. if you have an IR mirror you can cut through it with a visible light laser. If you have a UV mirror you cut through it with X-ray. Even UV, IR and X-ray are a spectrum of energy states and so, an IR shield does not necessarily protect from another IR laser.
The plasma that makes up the shield needs to have a higher frequency (i am not sure how that works, but i assume it's tied to the AC current source) for a higher frequency lightwave. Almost inevitably that leads to a hotter shield. So, if you need to defeat a Gamma Laser you're probably moving a fusion reactor around on your hull.
As usual there is a possible exploit, which is what your source mentioned. If you tune the inner shield and outer shield to reflect the hot shield's own heat, you keep it trapped. Keep hot iron in mind. If you heat it, you can feel the heat radiating off it. That's IR. Increase the heat until it becomes red hot. It's now radiating visible light. Make it hotter and hotter and it'll glow white-hot. That's the entire visible spectrum. Now if you keep heating it further, it will go up in the spectrum and start emitting UV. I am not entirely sure how this works for a random kind of plasma, but as you get hotter you can use a less energetic shield to protect from that emission.
Obviously such an emission isn't perfect and a UV-radiating plasma will still radiate some visible and IR light. So heat loss is there anyway.
There is one very, very, very big IF. Modern plasma generators still rely on big magnetic coils. Erecting a single shell is going to be a massive feat of engineering. Erecting a sandwich shell construct with different properties is... well i think you can never build a generator that neatly keeps the cold(er) plasma cold(er) and the hot(ter) plasmas hot(ter). You would probably need such plasma generators poking through the inner cold shell and interacting with the hot shell (to maintain and keep in place) while also having generators poke through the hot and cold shell to maintain the outer cold shell.
I will dedicate a bit to the actual use of cold plasma, because they're not investing thousands of dollars on useless stuff. One use is for aircraft. i've seen ideas for plasma-shielded aircraft where the plasma essentially lubricates the craft and vastly reduces the air friction. I've seen ideas where the plasma reflects radar and so creates stealth without the complex design or black paint (although, it would probably be an additional in stead of replacing measure). It could shield satellites from radar too. It could act as a heat shield for spacecraft re-entering the atmosphere. Time and again the same problems are run into: it costs a ton of power and the equipment is heavy.
Rail cannons/Coil guns/auto cannons , proton beams, neutron beams, infrared lasers, x ray lasers, gamma ray lasers, nuclear fission/fusion devices, EMP, and radiation bombs?
Particle beams are more difficult. Below a certain energy the shield will work. Any kind of serious beam (a beam generator 100m+ or cyclic generator) will puncture through. Proton beams have scatter problems (making them less long-ranged than lasers but more long-ranged than kinetic weapons), neutron beams are godaweful hard to make.
A laser is simple. If the frequency of the weapon is higher than the shield it'll go through. Otherwise, part gets deflected and part gets absorbed.
Fission/Fusion depends. Both have a strong spray of X-rays so if the shield is X-ray proof it'll work.
EMP depends on the wavelength and so on the shield. However, EMP protection should be fairly easy.
Radiation bombs? like how? because in space, a nuke will mostly emit radiation.
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