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Confinement of hot plasma in a solid dielectric container - Kapitza Nobel Lecture

  1. Jun 29, 2007 #1

    mheslep

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    Kapitza won his prize for low temp. physics but opted to give his Nobel lecture on nuclear fusion possibilities. I was interested in the plasma thin layer heat insulation effect he mentions, as I wasn't previously familiar though Kapitza says Langmuir first described the effect. Kapitza achieved a temperature gradient of > 1e6 degrees K over a couple mm at high pressure, indicating the heat flux was almost nil. The effect is apparently caused by by the higher mobility electrons penetrating deeper into the dielectric container wall than the heavy ions and thereby
    .
    My question then: can anyone comment on the limitations of the plasma insulation, and can some tough container, say quartz, be made that could confine a plasma under Lawson (density-time) fusion conditions?

    mheslep

    http://nobelprize.org/nobel_prizes/physics/laureates/1978/kapitsa-lecture.pdf
     
  2. jcsd
  3. Jul 6, 2007 #2

    mheslep

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    :confused: What a lonely post.
     
  4. Jul 6, 2007 #3

    berkeman

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    Thanks for the bump. I'd missed this before. Pretty interesting stuff!

    Remember that a lot of people in the US are on vacation this week, so hopefully you'll get some replies when they get back. If you don't get anything by about mid-week, bump it one more time.

    What a neat plasma/solid effect!
     
  5. Jul 6, 2007 #4

    berkeman

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    BTW, that Nobel lecture is from 1978. Do you have any more recent links on the subject?
     
  6. Jul 6, 2007 #5

    mheslep

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  7. Jul 14, 2007 #6

    Astronuc

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    I doubt it since the hot plasma would etch any material, and Al, Si and O atoms will enter the plasma, which greatly increases the radiation losses.

    With respect to heat transport, the plasma density (~1014 particles/cc) is very low, so that even if the temperature is in the millions of degrees, the energy transfer by conduction is low since the particle density is very low. Remember that solids have atomic densities on the order of 1022 particles/cc - which is 8 orders of magnitude above plasma density.

    IBM has done a lot of work in plasma etching. Many years ago, I attended a lecture by one of IBM's lead scientists in the area of plasma etching with high energy Ar plasmas. I think the answers to one's question will be found within the literature, but finding the specific answer may require considerable time and effort.

    It comes down to finding the appropriate collision rate of the plasma atoms on the solid surface, and then determining the rate at which the solid's atoms are ejected/recoiled from the surface. Someone skilled in the technology/physics could probably apply some basic equations to the problem and give a quick answer.

    Confinement of plasmas is inherently limited by the enormous pressures involve, and for a given pressure limit, one has to balance the particle density, n, with the temperature, T. The relationship is P = nkT where k is Boltzmann's constant. For a fixed P, n must be inversely proportional to T. It's that simple.

    One way to get around the pressure constraints of magnetic confinment is to use particle beams or currents, but then one has to deal with beam optics and collision processes.
     
  8. Jul 14, 2007 #7

    mheslep

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    The point was the plasma contact is reduced because of the sheath caused by the higher mobility electrons embedding in the surface w/out ions which sets up an E gradient preventing more electrons from entering.

    Yes lets forget about confinement. Up beams. The collisions problem has a promising solution - add a resonating RF on top of the electrostatic gradient:
    "Experimental Observation of a Periodically Oscillating Plasma Sphere in a Gridded Inertial Electrostatic Confinement Device" Park, Nebel, Stange, Murali. PRL 2005
    The idea is all the ions collapse together ('phase locked') into the center. The center focus density limit for such a device would be very high, and at the outer edge of the potential well T is very low.
     
    Last edited: Jul 14, 2007
  9. Jul 15, 2007 #8

    Astronuc

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    See Section 24G of Dolan's Book.

    Chapter 24: Materials Problems
    http://www.fusionnow.org/Chapter24.pdf

    There is a section on sputtering, and it's not so much the hot plasma ions (with energies in the keV range), but the fusion products in the MeV range.

    I'm not sure about that. Is this the plasma sheath?

    One would have to look at the mean path length for nuclei (about same as an atom), and compare that to the sheath.
     
  10. Jul 15, 2007 #9

    ZapperZ

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    There is one very important issue that has been overlooked here. Dielectric are notorious in producing a multipactor situation. This is where you have a cascading situation where a primary electron produces more than 1 secondary electron, resulting in a cascading effect. This can have a devastating effect - it has been known to cause RF windows to break down.

    Zz.
     
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