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Can you make plasma with UV Rays?

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  1. Jul 16, 2013 #1
    If the sun is producing plasma on a large scale on a regular basis, isn't it then true on a smaller scale that we could use the UV Rays of the sun to produce plasma by smashing two magnified rays and liquid hydrogen together in a high speed chamber? The result would be hot plasma that could be blended with another gas to produce energy as in fusion or to use in propulsion of space craft!
     

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  3. Jul 16, 2013 #2
    The sun isn't producing plasma, it IS (mostly) plasma.

    I don't really understand your project, but I'm sure if that could exist, it would exist ;)
     
  4. Jul 16, 2013 #3
    Right it is mostly plasma, but the UV Rays are not! Correct?
    If you put take the sun rays as you do when you use a magnifying glass to burn something, then pass it through some reflecting mirror's and focus the light on the center of a magnifying disc; would it not make the stream of light stronger?
     
  5. Jul 16, 2013 #4

    mfb

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    The surface of the sun has a temperature of ~6000K. With a clever setup, you can (in theory) heat something to the same temperature with sunlight, but not more.

    Fusion needs something like 100 million K to be useful here on earth. There is a factor of 10000 missing.

    The core of the sun has a temperature of "just" 15 million K, but its fusion power density is too low for a practical application here on earth.
     
  6. Jul 16, 2013 #5

    Drakkith

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    Yes, you can focus the UV rays down, but you are limited by the sheer size of the optics needed. It simply isn't possible to build lenses and mirrors large enough. Plus I think you may be limited by some aspects of how optics works. For example, a magnifying glass doesn't focus ALL the light from the sun down to a single spot. It actually forms a very small image of the Sun on the ground. Larger lenses that have a longer focal length actually form a bigger image than a magnifying glass does, so you are limited to how much light you can actually focus onto an area, which is far far too little to do what you are suggesting.
     
  7. Jul 21, 2013 #6
    You can boil water with one magnifying glass! You can boil water faster with multiple magnifying glasses. These magnifying glasses are small handheld. If you were to use small optical magnifying glasses (one on top of the other) would it not do exactly the same thing when using multiples to boil water.
     
  8. Jul 21, 2013 #7
    Well you may think that this is like in audio were you put the signal through every next amplifier and get it stronger because the amplifier is getting power to do that.
    Optical lenses don't put and they can't put any additional power into what they magnify.The only power you got is the one coming from "the sky" at that moment and the lens is just collecting it in a small place but it's not amplifying it in any way.
    Putting a dozen of them on top one another would make no difference for the total power that entered the first one.

    The thing that a magnifying glass does is it collects light that would normally land on a much bigger surface and collect it to shine on a much smaller one which results in that smaller area getting much more Em radiation (light) but the difference is that only the intensity has changed not the wavelength of light and as we know the strength of light is measured by it's wavelength , to get more power you need to have a higher frequency , magnifying glass doesn't do that.

    As for fusion I would suggest electrostatic or electric fields , high frequency radio waves for heating a conductive plasma etc, those are the closest of conditions we can make here on earth to what the sun makes to have that process going on.
    You really need a dramatic pressure and a pretty high temperature or if you don't have the pressure then you need an absurdly high temperature to get things going because the electrostatic repulsion of the ions are a pain in the a** :D
    Now do some google search and who knows maybe you will come up with an idea.
     
  9. Jul 21, 2013 #8

    mfb

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    That is not right, wavelength and intensity are different quantities.
    The most powerful lasers reach intensities above 1026 W/m^2 (1023 times the intensity of sunlight on a bright day), and they operate in the same wavelength range as sunlight.
    It is unrelated to the issues of magnifying glasses, however.
     
  10. Jul 22, 2013 #9
    Well I know that I just didn't make myself that clear perhaps , as with power and wavelength I was thinking that with a higher frequency light (smaller wavelength) you get more power per photon hence more power in overall assuming that the intensity stays the same.

    Just more intensity would mean more photons per same area.Now that is what the magnifying glass does.
     
  11. Jul 22, 2013 #10
    I'm embarrassed to admit this, but I don't quite see why this is correct (but I'm not disputing it). If you have a large collection area, and can focus it to an arbitrarily small point, you should be able to achieve any energy-density you want - so why can't you use sunlight to raise the temperature in a small area to a temperature much higher than the surface of the sun?
     
  12. Jul 22, 2013 #11
    the thing is this is not the same concept as with hydraulics and compression where you can take a small piston and making alot of movements force a large mass , this is different this is like the photoelectric effect , you can focus all the light emitted by the sun into a small space all that would happen is that that place would get really hot in a very small amount of time.
    Every photon has a wavelength and if that wavelength was say "x" at the sun then when it is here on earth it can't go higher that that "x" you cant have higher energy than the one you were to begin with.

    It's like an oven or a fire place you can use some oak which delivers say 1000 degrees c , now you can heat some large metal plate to that temperature slower or a small metal pen very quickly but just because you heat a small metal pen doesn't mean that the pen will suddenly be heated to 2000 c does it ?

    It's like with lasers used for cutting metal , it's not that the wavelength their emitting is somewhat stronger than the same emitted from another source , it's just that the one comming from the laser is extremely precisely focused and all those small packets of light called photons have the same energy but they just get to hit a very small area , so we say the intensity is high and that's why it gets to cut through metal.
    Pu that same wavelength but in a much bigger area and youll get nothing the photon energy is the same just spread out over a larger area.

    No need to be embarrassed we all get something wrong from time to time.
     
    Last edited: Jul 22, 2013
  13. Jul 22, 2013 #12

    mfb

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    That is not possible. Even if we neglect the diffraction limit - to get an arbitrarily small focus in that way, you need light coming from a single direction. But if you just collect light from a very tiny angle, the intensity goes down as well - the sun is not a single point.

    More formal, this is a result of Liouville's theorem and the second law of thermodynamics (which are equivalent in that context).
     
  14. Jul 22, 2013 #13

    jbriggs444

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    The thing is you can't focus it to a point. You can focus it to an image of the sun. The second law of thermodynamics says that the temperature on that image can't be higher than the temperature of the surface of the sun.

    You can try to "cheat" by making your optics bigger. But if you make the optics bigger by increasing the focal length, the image gets larger. So you can't win that way. And if you make them bigger by enclosing more area, you can't do any better than enclosing a complete sphere surrounding the sun so there's a limit that way as well.
     
  15. Jul 24, 2013 #14
    Hey plasma1,

    Just a quick thoughts about that plasma project. Firstly, I think that the plasma is not created by UV light, the UV is created due to the chemical reactions on the sun - nuclear fusion. Correct me if I'm wrong ; )

    Secondly, scientists are already working on creating the fusion here on earth by using high pulse power CO2 lasers. I think there is one project of petawatt pulse laser in Geneva(maybe). Why CO2 and not UV? It is easy to obtain high power density with it and the magnifying glasses as you suggested won't create AMPLIFICATION to the signal of whatever times you want. You need a gain medium to amplify a signal, but here if you think you could replace the magnifying glasses with laser cavities there is a huge problem of handling noise in such a system. Just like in audio amplifiers, there is an additional noise in every gain step only here, the light can reflect and back scatter which would make it all very messy and unusable. There are well developed excimer UV lasers but I am sure that the power you'd need is not sufficient for this. Besides, the optics that you'd need for selecting UV light from the whole bunch of wavelength spectrum with low loss etc is just... not paying off.
     
  16. May 13, 2015 #15
    The idea is to focus rays into a cavity which singles out each ray. Then a device collects that ray of light and magnifies it to such an extent (super hot) and then ignites a liquid fuel, thereby creating propulsion in space...not on earth!
     
  17. May 13, 2015 #16

    Drakkith

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    You are aware that a ray of light is not a real entity, and that you cannot amplify the light after you collect it without using an on-board power source (which takes fuel to run)?
     
  18. May 13, 2015 #17
    Consider that the fuel to run all these is produced on board?
     
  19. May 13, 2015 #18

    Drakkith

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    You can't produce the fuel on board without another source of fuel/energy.
     
  20. May 13, 2015 #19
    Producing fuel in space is relatively easy depending on the type of energy you are producing
     
  21. May 13, 2015 #20

    Drakkith

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    Please support your claim with appropriate references.
     
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