Magnetic bottle in a magnetic bottle

Discuss how polywell fusion works; share theoretical questions and answers.

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jartsa56
Posts: 4
Joined: Fri Aug 07, 2015 7:08 am

Magnetic bottle in a magnetic bottle

Postby jartsa56 » Sun Aug 09, 2015 4:32 am

Here's a plasma containment desing I invented a minute ago:

1: A negatively charged magnetic bottle.
This device contains ions perfectly. Leaks electrons. (here "contains" means "keeps inside some radius")

2: A large positively charged magnetic bottle.
This device keeps electrons inside some radius.

3: We put the device number one inside the device number two.

Is there some reason some particles would still leak out?


EDIT: How do we charge the bottles? We put a spherical metal net around a bottle, then we connect the net to a negative or positive voltage. According to Gauss's law there's no electric field inside the sphere.

EDIT2: An improvement: Let's change the magnetic bottles to magnetic mirror machines, and let's scrap the metal nets and charge the coils of the magnetic mirror machines.
Last edited by jartsa56 on Mon Aug 10, 2015 12:20 am, edited 1 time in total.

D Tibbets
Posts: 2775
Joined: Thu Jun 26, 2008 6:52 am

Re: Magnetic bottle in a magnetic bottle

Postby D Tibbets » Sun Aug 09, 2015 4:45 pm

You are essentially describing the Polywell with a centrally (small radius) located virtual cathode (-) and a larger (greater radii) anode (+). The virtual cathode is shielded in the since that there is no physical structure/ surface for ions to hit. The anode is magnetically shielded. Simplistically this solves the problems. Actual performance is far from this simplistic ideal situation though. Neither electrostatic or magnetic confinement or shielding is 100 % efficient. Up scattering, thermalization issues play a role; ExB diffusion through a magnetic field plays a role; MHD or edge instabilities plays a role in many systems though perhaps not in a Polywell; cusp losses- holes in the magnetic field plays a role in the Polywell, not so in a tokamak; radiation like Bremsstruhlung increases losses/ cooling of the plasma; pollution- contaminates play a role, thus the need for diverters ,or scrape off layers (?) in some design.

The Polywell with the positively charged magrid (magnetically shielded anode) ideally fits the bill, but losses are still to great. A Polywell with a grounded magrid but high voltage electron guns may perform similarly with trade offs that may or may not have a net advantage. Things like electron recirculation, ion annealing , and other interventions/ properties need to be invoked before breakeven can be approached. Other issues like the difficulty of injecting electrons into a good electron containment volume, ignition issues in some machines, waste heat management, etc.' etc. needs to be addressed.

In The polywell the ions are contained electrostatically, the electrons are contained magnetically (Recirculation is an additional contribution to electron magnetic confinement- it is an electrostatic confinement contribution, so electron confinement in the Polywell primarily magnetic with an electrostatic confinement supercharger). This has advantages and may lead to a solution. As for two physical grids/ electrodes, one outside the other and both magnetically shielded to prevent impacts but not actually contain either species would seem to fit the bill. I have recently struggled with this recently. In principle, with dominate Gauss Law conditions, it would seem to work. But recall that Gauss Law only applies absolutely in a closed conductive sphere or other shape- it does not have to be a sphere. But, it does have to be completely closed. Any holes starts to break down Gauss Law, the contribution may be trivial or major depending on various considerations.
Also, a plasma, unless it is absolutely mono energetic- no thermalization at all, will continuously lose particles from electrostatic confinement as they are up scattered to energies above the potential well depth. This process alone may be sufficient to prevent breakeven, unless you can control it at least partially. Thermalization may be slowed or impeded, but it cannot be stopped. If you want ignition, them thermalization is essential.

Electrostatic confinement cannot be perfect in a collisional plasma- necessary if you wish any fusion to occur. Magnetic confinement or shielding also cannot be perfect. The compromises and partial solutions have to add up to good enough. This is difficult as the partial solutions for one thing often are harmful in other ways.

Dan Tibbets
To error is human... and I'm very human.

jartsa56
Posts: 4
Joined: Fri Aug 07, 2015 7:08 am

Re: Magnetic bottle in a magnetic bottle

Postby jartsa56 » Mon Aug 10, 2015 12:59 am

I have made some improvements. See edit2 in post #1.

After those improvements the device seems to be a modified fusor, modified so that the inner grid is a coil, and a current runs through the coil.

I disagree with anyone who says these are polywells. Because there's not a single virtual electrode anywhere, just metal electrodes.

D Tibbets
Posts: 2775
Joined: Thu Jun 26, 2008 6:52 am

Re: Magnetic bottle in a magnetic bottle

Postby D Tibbets » Mon Aug 10, 2015 4:18 am

Look up the Elmore Tuck and Watson modification of the Fusor. This the starting point for the Polywell.

Dan Tibbets
To error is human... and I'm very human.

D Tibbets
Posts: 2775
Joined: Thu Jun 26, 2008 6:52 am

Re: Magnetic bottle in a magnetic bottle

Postby D Tibbets » Mon Aug 10, 2015 4:40 am

I am not sure what you mean with edit #2. Scrape the coils/ grids. Do you mean magnetically shield them? Do you mean adding electrostatic charges to the mirror machine? Both have been done I think. Efforts to block magnetic losses through cusps by using cusp plugging with electric fields. This has been tried with various electrode arrangements, including efforts by EMC2. None have worked. Anything that you do to improve electrostatic confinement of one species will tend to worsen electrostatic confinement of the other. This is why the Polywell does not attempt to do this (with some qualifiers) The electrons are contained magnetically, they would disperse extremely quickly without the magnetic confinement. The ions are confined electrostatically as a secondary effect from the magnetic confinement of the electrons in excess. This separation of the confinement approaches is a key of the Polywell that allows for confining both species adequately- at least that is the goal.

Magnetic containment or shielding of ions is much more difficult that for electrons, mostly due to ExB issues. Basically you cannot magnetically shield a grid against ions reaching it unless you use large and powerful magnets like in a Tokamak. You can do this with electrons. This is why having a virtual cathode embedded in the cloud of ions is important. There is no physical surface for the ions to reach through leaky magnetic fields. There is only a space charge due to the excess electrons. Note that electrons also penetrate through the always leaky magnetic fields but at a much slower and hopefully tolerable rate.

Dan Tibbets
To error is human... and I'm very human.


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