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I What is the type of field is exerted by argon plasma?

  1. Feb 27, 2017 #1
    when argon gas is transformed to plasma by an electric current, what is the type of field (electric field or magnetic field) and will that field have any effect on electric machinery put in the plasma container like a hand drill or something? assuming we can have argon plasma with high pressure in a certain container?
     
  2. jcsd
  3. Feb 27, 2017 #2
    A solid object immersed in a plasma will become negatively charged, due to the formation of a Langmuir sheath.
    http://farside.ph.utexas.edu/teaching/plasma/Plasmahtml/node41.html
    This negative charge will accelerate argon ions into the surface of the object, causing some etching on the surface.

    If it's a weak plasma (low ionization fraction) at low temperature for a short time, then the damage might be negligible, or maybe just cosmetic. For a strong high temperature plasma, it will melt or sputter the materials it comes in contact with, and eventually destroy it.
     
  4. Mar 1, 2017 #3
    another situation, what if i attach an electrode(positive) to a drilling machine under ground and release argon gas from the surface (negative electrode) to give the argon gas the electric current it needs to transform to plasma, will that situation also destroy the machine?
     
  5. Mar 1, 2017 #4
    also another thing, is there a way to protect the solid object immersed in plasma? Insulators coating or anything?

    would really appreciate your help, thanks in advance
     
  6. Mar 1, 2017 #5
    You can cover your things with some sacrificial foil. How long that lasts depends on the parameters of the plasma. Magnetic fields can redirect the plasma so you could use magnets to protect certain parts of your equipment
     
  7. Mar 4, 2017 #6
    another issue i wish that you could help me with is that i need to calculate the amount of argon gas and the electric current so that when argon gas is transformed to plasma by electric current it exerts pressure X. How do i calculate the amount of gas needed and the amount of electric current needed to exert pressure X assuming it's in a certain container with volume of 10,000 litres. what is the formula itself?
     
  8. Mar 4, 2017 #7
    Well,
    PV = nkT
    where n is the density of particles in the plasma. If it's mostly neutral, then n would be the density of argon. I imagine your system is fairly low ionization fraction, so the pressure is probably close to the neutral pressure. But what do I know about your system
    'If ionization is significant, then the density would be the sum of the electron density, ion density (of each ionization stage), and neutral density. The electrons and ions and neutrals probably have different temperatures, so you would add them.
    ##P = P_{ion} + P_{electron} + P_{neutral}##
    where ##P_{ion} V = n_{ion} k T_{ion}##, etc...
    It's kind of difficult to get quantitatively accurate values for the temperatures and densities of each ionization state. You can try looking at the description of the MIST code
    R.A.Hulse, Nucl. Tech./Fus. 3, 259 (1983)
    It's for fusion-like temperatures, which I imagine is much hotter than what you are working with, but maybe it could help you understand the equations.
     
  9. Mar 5, 2017 #8
    thank you so much!!
     
  10. Mar 5, 2017 #9
    so now in that equation, i will assume n is the density of argon which is 1.449 kg/m3 and K is the boltzmann"s constant right?
    when i try to caluculate the equation, the pressure is incredibly low. it's because of the boltzmann's constant is 1.38065x10^-23. i don't get how this is the situation?
    could you please explain to me this situation. i'm trying to make the pressure be equal to 1000 psi for instance. does it have something to do with the electric current passing through. like should i convert kinetic energy of electric current to kelvin and write it as the temperature?
    i assume that argon plasma can exert pressure up to 1000 psi or even more, right?
     
  11. Mar 5, 2017 #10
    Density is the number density, not the mass density.
    I don't think it's possible to get a plasma at 1000 psi with your setup. Keep in mind that most hobbyist plasmas are done at low pressures, and the breakdown voltage increases exponentially with pressure.
     
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