Alternative Reactor Design

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Niels Geerits
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Re: Alternative Reactor Design

Post by Niels Geerits » Sat Dec 01, 2018 4:17 pm

John, I deleted the quote. Assuming the information is stored as ascii that saved around 1.4kB (50n$). So I guess it is more about personal preferences, but since I don't pay I will abide by the hosts rules. Ironically discussing noise generates noise. I think these three posts distract more from the original topic than quotes do.

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Richard Hull
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Re: Alternative Reactor Design

Post by Richard Hull » Sat Dec 01, 2018 5:59 pm

For me, it has nothing to do with bytes consumed, but the assumption by the poster that no one has read any of the preceding parts of the thread.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Justin Fozzard
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Re: Alternative Reactor Design

Post by Justin Fozzard » Sun Dec 02, 2018 10:12 pm

Glasstone and Lovberg (Controlled Thermonuclear Reactions, 1960, p.67) discuss colliding beams as a possible approach to fusion and give some interesting figures that will put the idea into perspective.
They suggest colliding two 50keV deuteron beams with a (realistically achievable) current density of 100A/sq.cm, about 6x10^20 deuterons per sq.cm per second.
The mean velocity at 50keV is 2x10^8 cm/sec.
For the D-D reactions at 100keV (the relative collision energy of the beams), the power density would be about 10^-4 W/cu.cm and 2x10^-2 W/cu,cm for the D-T reaction. This would increase to 7x10^-4 W/cu.cm for 500keV beams but be less for D-T reactions due to the decrease in cross section.

Note that the beam power would be around 10MW for an output of a few hundred microwatts of fusion power at best.
As you can see, colliding beams are not really a realistic proposition for a fusion reactor, but might make an interesting demonstration device.

Patrick Lindecker
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Re: Alternative Reactor Design

Post by Patrick Lindecker » Sun Dec 02, 2018 11:42 pm

Hello Justin and all,

Interesting information. However, I suppose that the beams were not confined. Without confinement, as you know the beams expand due to space charge and collisions.Here a snapshot of beams confined in a trap and of course not confined outside the trap. It can be seen (I hope) that ions expand and so the density rapidly decreases (the number of fusions/s being proportional the density^2).

Image

Patrick

Note about quoting:
I don't know why it is not recommended to quote (in fact the inverse is recommended...). Sometimes without quote, the post is difficult (let's say impossible) to understand because it misses the exact context, and it is frustating. I'm new in this forum but I see that it is a forum of technicians, so used to be very precise in their work, and precision is the key because nobody can guess what you have in the head.
However enormous quotes (as sometimes it is seen in forums) are without interest because it does not help to distinguish the exact context, and reversely they are boring.
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Justin Fozzard
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Re: Alternative Reactor Design

Post by Justin Fozzard » Mon Dec 03, 2018 10:15 am

Hello Patrick,
Have you looked at the mean free path of the colliding beams?
Richard Hull has posted a very useful FAQ on the topic:
viewtopic.php?t=3557

You will find that even if you have some method of "compressing" the beams and re-circulating them, the chances of collision are pretty meager.

The Brillouin limit will affect any magnetically confined single component beam. See section C of this paper:
http://positrons.ucsd.edu/papers/NNP10.pdf

Another useful paper concerning electrons in magnetic fields is here:
http://sites.apam.columbia.edu/CNT/publ ... ylimit.pdf
(You can substitute the ion charge and mass in the equations to get an idea of the confinement limits for cylindrical deuterium beams)

A good general discussion of magnetic electrostatic plasma confinement can be found here:
http://www.askmar.com/Fusion_files/Magn ... nement.pdf

Finally, I would recommend reading Todd Rider's PhD thesis and subsequent papers for a good overview of the problems we face trying to fuse non-equilibrium plasmas at anything other than minuscule power output levels. (As Richard has pointed out many times before.)

Justin Fozzard

Patrick Lindecker
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Re: Alternative Reactor Design

Post by Patrick Lindecker » Mon Dec 03, 2018 9:20 pm

Hello Justin,

Thanks for the interesting links. I'm going to have a look on them.

Note: in my simulation only electrostatic confinement applied (magnetic confinement at reasonanable field value (i.e. B<1T) is not efficient at all).

>Todd Rider's PhD thesis
I read part of the two papers that he wrote. Very interesting.

Patrick

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