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Alpha particle confinement question

  1. Aug 28, 2013 #1
    A theoretical question , imagine we have a theoretical spherical confinement (don't tell me it;s not possible as I know that already :) )
    Now we would set that spherical confinement to a high positive potential , inside it we would have a ionized gas , now the electrons would tend to distribute themselves uniformly to the confinement as close as they can get (assuming a isolation between the confinement and gas)
    Now those electrons would form a kind of potential well , now if fusion would be to take place inside where the ions are at center would these electrons sticking close to the positive confinement would catch the alpha particles emitted from the ion collisions at the center ?
    Or are alphas able to go through such electrons well due to them being more energetic? But anyway how far could they go if the outside confinement is positive and alphas themselves have two protons so they would be more likely repelled and stuck back to the electrons?
    Ok can anyone elaborate a little on what would happen at such a situation?
  2. jcsd
  3. Aug 28, 2013 #2


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    It is pointless to ask what current physics would predict for things that are impossible with current physics.

    Electrons cannot catch moving ions - the ions are heavier by at least a factor of 2000. Ions can catch electrons, but they won't slow down significantly. The probability of that process depends on the density, speed and other parameters.

    You might be interested in the Polywell concept.
  4. Aug 28, 2013 #3
    yes mfb thanks I already am familiar with polywell concept , I know they use magnetic field to trap electrons , the whiffle ball concept etc , I was just asking this for a better understand of some physics for myself , the spherical electrostatic confinement structure was just a way to explain what I mean I was actually more concentrated on the alpha particle interaction process.

    Ok I see electrons are really lightweight and so their effect on high velocity ions is small but if those electrons are located close to a wall (whatever actually for the sake of an argument)
    which is at a very high positive voltage and has a strong E field then they would be repelled , so I was wondering how do the electron cloud contributes to such a scenario if at all?
  5. Sep 2, 2013 #4
    Ok as I reread what I wrote I understand that I wasn't clear on what I thought , so I will rephrase the question.

    If we have say two plates separated at a distance x and the one plate is at a high positive potential the other at negative , now we have a ionized gas between those plates the electrons have struck to the + plate the ions to the - one.
    Now precisely between those two plates we put an alpha particle to which side it will be more likely to attract , to the negative which already has attracted all the ions or to the positive due to the fact that there are a lot of electrons with their negative charges?
    this experiment is assuming the plates are isolated so that the electrons and ions cannot run into them directly but get as close to them as possible.
  6. Sep 2, 2013 #5


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    The alpha particles would be attracted to wherever has the lower electrical potential. The idea of the polywell is that the electrons create a region of low electrical potential in the center (so it acts like a virtual cathode)
  7. Sep 3, 2013 #6
    Yes I see that , so in my case the lower potential would actually be at a plate which is directly attached to say a batteries negative terminal rather than the electrons held in place on the high + plate right?
  8. Sep 3, 2013 #7


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    Well, if the plates are holding onto all the charges, I'd say that their charge hasn't been completely neutralized by the ions and electrons. But that's just a guess on my part.
  9. Sep 3, 2013 #8
    Hmm okay , but the question still remains , two plates , one positive one negative , both insulated the positive having a cloud of electrons around it and the negative a one of ions , but hence the alpha particle is basically two positive charges (protons) it should be attracted to the negative side, but since we already have ions at the negative side I guess the alpha particle would experience some repulsion while trying to get to the negative plate?

    But then again it would feel some attraction from the negative electrons on the positive side but once coming closer would again feel repulsion due to the positive plate attracting the negative electrons.
    And electrons having so much smaller mass than ions would be insufficient to fully attract the alpha if a solely negative plate would be present at the other side ?

    This is kinda frustrating so at the "end of the day" how do you think to which side the alpha would go in the scenario mentioned above?

    Oh and by the way even though neutrons have no charge while being part of the alpha particle how do their added mass contributes to the alpha movement in such electric field and charge situations?
  10. Sep 3, 2013 #9


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    I think that as long as the charge from the negative plate isn't fully screened by the ions then the alpha particle should be attracted to it.

    What does mass have to do with this?

    Personally I think it would go to the negative plate.

    They just add to the mass and make it take longer to accelerate.
  11. Sep 3, 2013 #10
    about the mass , i was saying about that because of the alpha being so much heavier and when accelerated due to the electric field present that would contribute to how strongly it would crash through the ions on the negative side to get to the negative plate would it?
  12. Sep 3, 2013 #11


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    It's hard to understand you. Try to use proper grammar and punctuation.

    I think you have some errors in your physics. The acceleration energy of the ions is the charge of the ion times the potential difference between the source and target. The mass will affect the speed, but not the energy.

    You seem to be suggesting that the potential will go up and then go down as you move toward the cathode. I think it will probably just be monotonically decreasing. Are you trying to build a Fusor? Or a Polywell? Or something different?
  13. Sep 3, 2013 #12


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    I don't see how this is even related to the original question.
  14. Sep 4, 2013 #13
    i'm not trying to build a polywell nor a fusor , well I'm working on something different let's just say but at this point I am not building anything. just have some ideas and I'm learning with them so I have some questions time after time.
    My biggest problem is that I imagine physics and understand the theory but it's hard for me to do the math behind many of the problems.
    But math is more needed when you have a ready theoretical model in your head that you need to calculate will it actually work and how good if at all.

    I'm sorry about the grammar it's just that my thoughts run faster than I can write them down so sometimes they make a messy sentence and later on while rereading I cannot understand it myself.

    The thing why I asked about the neutron added mass was that just as @
    Khashishi said that the acceleration is the charge and the potential difference which equals the field strength but when that charge is under acceleration it ca either be a simple ion (1 proton) or an alpha like (2 protons) so the charge is twice as strong + the neutrons which hold up to that particular charge add up the mass so it means that the field has to accelerate a heavier object now is that right? And when a heavier object is accelerated to the same speed as a lighter one upon impact the heavier one will have more momentum right?
  15. Sep 4, 2013 #14


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    An alpha particle experiences twice the force of a single proton, but it has 4 times the mass, so it doesn't reach the same speed.
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