This topic contains 6 replies, has 3 voices, and was last updated by  Maury Markowitz 1 month, 4 weeks ago.

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  • #1675

    TikiB
    Member

    Has anyone here heard of Robert Stienhaus’s Mini Mike concept?

    Its basically using a tiny ball of D-T as a catalyst for D-D fusion.

    The design goes back to basic princples and the first is how do we get gain from fusion? The most logical way of doing this is to look at the hydrogen bomb, the gain on a hydrogen bomb is huge. And if your looking at EROI (Energy return on investment) one particular fusion experiment has the highest of them all and thats Ivy Mike, the reason is because this experiment got most of its energy from D-D fusion the cheapest kind.

    So how do we make electricity from Ivy Mike? Well the simplest way is to just denotonate it in a large pool of water and drive turbines with the steam. However this way is the least efficient way and won’t get you electricity competitive with mains electricity. (It will generate net electricity though).

    So how do we make this cheaper?

    Three ways :
    Replace the fission primary with an electrical fusion driver and recycle the tritium
    Make the Design smaller
    Improve Energy recovery.

    All of these things ultimately lead you to the Mini Mike design Robert Steinhaus (LLNL) suggests.

    Okay so what are technical problems with a Mike-MIke Design?

    Heat
    An active heat recovery system that turns the heat into electrical energy.

    Pressure
    The blasts occur in a vaccum surronded by walls thick enough to withstand them.

    Ignition
    This is the biggest problem but the efficiency of the design means you could afford to use a significantly more powerful laser than the ones at NIF if you had to.

    Neutron bombardment
    The D-T blast chamber has a berylium shell

    #13649
    Breakable
    Breakable
    Keymaster

    I read someone mentioning that name on our Facebook group a while ago, but I was not able to find any good links that describe it. Thanks for the reasonable description, I would certainly be interested to read a little more about it.

    #13650
    Breakable
    Breakable
    Keymaster

    This is a decent description:
    http://www.quora.com/Will-we-see-applicable-nuclear-fusion-any-time-soon
    Unfortunately it does not explain the ignition part. Is it actually using fission bombs to do it?

    #13651

    TikiB
    Member

    This is the picture he uses to illiustrate it.

    Attached files

    #13652

    TikiB
    Member

    Well you could use any device powerful enough to ingite so laser, ion beam, or a fission primary. Steinhaus’s favoured method is a light ion beam.

    I think Stienhaus quoted the driver would have to deliver between 50-100mj per shot.

    #13653

    TikiB
    Member

    The major advantage is that it uses cheaper D-D fusion but at a much lower size then using magnetic confinement.

    #30570

    Maury Markowitz
    Participant

    I hope it’s ok to reply to old threads here.

    Stienhaus’s “concept” is pants. Come on, the guy can’t even figure out how to center one circle inside another in his presentation graphics, and we’re supposed to believe he has some idea how to build a working fusion machine?

    Let’s start with the obvious issue that all he’s done is drawn a diagram of a two-stage thermonuke. A thermonuke works by capturing the x-ray output of the primary in a radiation channel, which then compresses a cylindrical secondary to fusion conditions. This relies on geometry; the collapse of the cylinder results in the pressure/density in the center being very high due to the shock wave converging.

    Now let us consider Stienhaus’s diagram (posted above). In it, we have a D-T primary on the left, and a secondary on the right. Apparently, the primary is supposed to be ignited by a driver, and the energy of the resulting reaction is supposed to cause fusion in the secondary. Ok, so…

    1) how are we going to cause the symmetrical collapse of the primary with the secondary in the way? We can’t get symmetrical collapse under perfect conditions in NIF, and in this design, one entire side of the primary is shadowed and cannot be “hit”. Good luck with that.

    2) fusion burning in a D-T or D-D fuel occurs when the alphas deposit their energy back into the fuel. In order for this to occur you either need a very large volume, like ITER, or very high density, like NIF (NIF is 100x lead). You also need geometry on your side – the alphas are isotropic. The secondary in Stienhaus’s design is cylindrical meaning that the majority of the alphas will be lost from the fuel for purely geometric reasons. Its also only mechanically compressed, meaning the chance the alpha will be captured is very low even if it just happens to be going the right direction.

    3) what exactly is the mechanism that starts fusion in the secondary? The diagrams say something about a “shock detonation wave”… is he actually claiming that a shock wave is going to do this end-on in a mechanically compressed fuel mass?! He also seems to be proposing this is the mechanism that causes the continued burn down the cylinder. Is he not aware that the alphas and neutrons are moving orders of magnitude faster than a detonation wave and will thus carry away all the energy before it can heat the adjacent fuel mass?

    4) then there’s the problem that the diagram shows the primary “burning” at the size of the original sphere. After compression, it would be a sphere about the width of one of the lines around the secondary. That means it is separated from the secondary by a relatively large distance, about half the diameter of the secondary. Which means that whatever magical process he claims will start the fusion in the secondary is geometrically limited to the solid angle of the internal fuel plug, what, 10% of the energy released?

    5) anyone even passingly familiar with ICF will know that the primary problem with achieving ignition is Rayleigh–Taylor instabilities. These are created when you have fluid movement in areas with different densities. In the case of NIF, that’s the difference between the pusher shell, the fusion fuel, and the empty space in the center and outside. In this design, the secondary consists of a cylinder with fuel in the center and some sort of shell on the outside, surrounded by nothing. Better yet, it’s long and skinny. This is the sort of design you make when you want to demonstrate R-T effects (and Richtmyer–Meshkov). The density difference also means that the shock wave will not travel linearly down the secondary, it will be refracted into or away from the shell depending on the relative densities (this is the basis for shaped charges). There is exactly zero chance that the fuel mass will remain stable.

    6) and finally, think about this dynamically as the primary completes the fusion process (assuming it could, which it can’t). Under perfect theory this creates a spherically expanding mass of a bunch of different things – first you’d get some x-rays, then the relativistic neutrons, then alphas and other fusion products, and then a mix of ablator and other junk. Now zoom in on the end of the secondary when any one of these expanding shells reaches it… the first point to be hit is the center of the fuel, and then as the sphere continues to expand, a circular contact patch that expands across the end of the fuel. Do you see why that is? Ok, so basically *whatever* magical process is supposed to start the fusion in the secondary *isn’t symmetrical across the fuel* for *purely geometrical* reasons. Good luck with that too.

    Basically, there is no way this will work. To borrow a phrase from the SDI era, this proposal is “one view-graph deep”.

    • This reply was modified 1 month, 4 weeks ago by  Maury Markowitz. Reason: gr touchup
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