Viewing 13 posts - 1 through 13 (of 13 total)
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  • #1664
    Tim_Petrik
    Participant

    I recently stumbled upon Focus Fusion and found it to be fascinating and was surprised by the simplicity and beauty of the involved machinery and physical principals.

    After reading Dr. Lerner’s latest publication, I have come to understand that the plateauing of the fusion yield is believed to be caused by impurities introduced by vaporization of cathode material. That got me thinking and here are my 10 cents:

    What if the cathodes were made out of ionized gas? Ionization could be realized by shining laser light into the reactor at appropriate times. The possible benefits would include: (1) No vaporizing cathode material; (2) Greatly reduced x-ray absorption by cathode; (3) High level of control over the conductivity of the gas-electrodes by varying the laser intensity; (4) Possibly some pre-ionization of other gas volumes in the reactor through mixing.

    I’m curious to read what the community thinks!

    Greetings,

    Tim

    #13596
    Francisl
    Participant

    There has been some discussion about pre-ionization. That will depend on how the experiments go with the new tungsten electrodes. Look at the January 27 report. You may also be interested in the News and Archives.

    #13597
    Tim_Petrik
    Participant

    Francisl, thank you for the links. I’d like to point out that I’m not suggesting pre-ionizing all of the gas in the reactor. Rather, I suggest shining laser light into the reactor to primarily ionize the reactor volume that is currently occupied by the cathodes. In other words, take out the 8 electrodes, install 8 quartz windows in the same place were the electrodes used to join the head plate and ionize the gas column where the electrodes used to be. When the caps fire, electrical resistance will be the smallest along the ionized gas columns, so the ionized gas columns will become your new electrodes with the benefits listed in my previous posting.

    #13599
    Ivy Matt
    Participant

    Wouldn’t this idea suffer from the same difficulty as the problem of designing a real-life lightsaber? That is to say, how do you give the electrodes a tip, or end-point?

    #13600
    Lerner
    Participant

    We always like new ideas–keep them coming. But the electrodes do have to be solid in a Mather-style DPF. If you eliminate the anode, the currents in the center will pinch together as soon as the current starts flowing, so you would need a much larger radius insulator to slow that down. If you put the insulator at the edge of the vacuum chamber, you get a Fillipov-style DPF. You don’t really need any pre-ionization, but you have less flexibility of design and you need a lot more energy for the same current.

    #13601
    Tim_Petrik
    Participant

    Ivy, I don’t think the gas cathodes have to end at the same plane as the center-anode. The current should stop flowing axially away from the back wall once the center electrode (solid) ends.

    Dr. Lerner, thank you for your encouragement! I don’t know enough about the differences between Mather/Fillipov-style DPFs to comment on the necessity of solid electrodes. But I’d like to point out that I only want to replace the outer electrodes with gas electrodes and keep the design of the center electrode and insulator unchanged. If the resulting design doesn’t fit with Mather/Fillipov-style DPFs, maybe a new name can be found 😉

    #13602
    BSFusion2
    Participant

    Ivy Matt wrote: Wouldn’t this idea suffer from the same difficulty as the problem of designing a real-life lightsaber? That is to say, how do you give the electrodes a tip, or end-point?

    Could he use intersecting laser beams to shorten the path of least resistance?

    #13621
    BSFusion2
    Participant

    Michio Kaku shows how to build a plasma lightsaber in this youtube video:

    #13634
    bcreighton7
    Participant

    Tim_Petrik wrote: Ivy, I don’t think the gas cathodes have to end at the same plane as the center-anode. The current should stop flowing axially away from the back wall once the center electrode (solid) ends.

    Dr. Lerner, thank you for your encouragement! I don’t know enough about the differences between Mather/Fillipov-style DPFs to comment on the necessity of solid electrodes. But I’d like to point out that I only want to replace the outer electrodes with gas electrodes and keep the design of the center electrode and insulator unchanged. If the resulting design doesn’t fit with Mather/Fillipov-style DPFs, maybe a new name can be found 😉

    That actually sounds like an elegant solution to a lot of the cathode problems the reactor would run in to such as avoiding degradation of a solid cathode, but presents some new engineering challenges, and may require more energy than its worth.

    I have a potential idea that seems it should use a lot less power, and should have less heat concerns – how about making the cathodes and maybe the anode of carbon nanotubes? It is a highly conductive and strong material, should be relatively cheap, and is structurally light enough to allow x-rays to pass through, although CNT has a somewhat high attenuation rate. My guess is the xrays may cause too much degradation of a CNT anode, but some long-term tests appear promising. Nevertheless, the relatively high x-ray attenuation of CNT makes it a less than ideal choice for an anode in this reactor. The cathodes might be able to be designed in a way to lessen the loss of X-rays. In a vacuum CNT is estimated to have a higher melting point than beryllium. I know next to nothing about the physics of such an application, but thought I might bring it up.

    #13635
    JimmyT
    Participant

    Is it possible that when the axial coil is used the dimple in the end of the cathode might not be necessary? Elimination of that dimple sure would simplify cathode cooling.

    #13636
    bcreighton7
    Participant

    Well, I should have known that LPPF would have known about such a material – after all it has been around for over a decade. Don’t I feel stupid…
    Apparently, Lerner is considering CNT as a coating for the electrodes.
    http://lawrencevilleplasmaphysics.com/carbon-nanotubes-may-protect-electrodes/
    I assume its absorption of X-rays has been deemed too great to use CNT as a monolithic cathode, but it seems the properties of CNT would allow for a smaller cathode…

    #13804
    Francisl
    Participant

    If a glow discharge works well for starting the shot, would a glow discharge around all of the electrodes reduce the intense reactions along the whole length of the electrodes?

    #13808
    Francisl
    Participant

    Here is possible method to produce an effect similar to glow discharge along the full length of the cathode arms. Indirectly heated cathodes could be placed along the full length and on both sides of each of the cathode arms. These heated elements would create a thermionic electron emission that would ionize the nearby gas similar to a glow discharge. The heating elements would only have to be operated a short time before each shot. A side effect is that the heater elements could also heat the chamber to a specified temperature so that there is more uniformity in shot to shot performance.

    This approach could be tested in a college physics lab. Place a Jacob’s ladder spark gap in a bell jar with the same pressure and fuel as used in a dpf. Put indirectly heated cathodes along the sides of the spark electrodes. Observe the operation of the spark discharge with and without the use of the cathodes.

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