Re: Nuclear heater for Expeditions

Dan Clemmensen (
Sun, 11 Jan 1998 14:40:22 -0500

Hara Ra wrote:
> Dan Clemmensen wrote:
> > > and the other is based on sonoluminescence (SL). SL is still a
> > > macroscopic process but I could imagine a SL reactor in the kilogram
> > > size range.
> > >
> > nanotech is not magic. As 'gene says, it may not even be feasible. My
> > guessitmate is that is feasible. The requirement for fusion is that
> > atoms must slam into each other fast enough. The requirement for
> > useful fusion is "engineering breakeven": The process must emit
> > more useful energy with no external input. In the particular
> > application we're discussing, the useful energy is low-intensity
> > heat, which is the easiest goal to reach.
> >
> You must recover enough high quality energy to operate your device. So
> far, all fusion devices need a lot of high quality energy.
Correct, but that's why we want to use nanotech. You need "a lot"
of high-quality energy because today's Fusion techologies are
large. With nanotech, we may we able to get tne required energy
density in a smaller space, meaning that we'll need less high-quality

> > It's not proven that SL is blackbody rediation and therefore
> > indicative of near-fusion conditions, and the phenomenon is
> > not well enough understood to find a useful set of conditions
> > whereby you can extract useful energy: currently, SL is observed
> > only at temperatured near the freezing point of water. Don't count
> > on SL for micro-fusion.
> >
> An announcement in Photonics Spectra (photonics trade magazine) stated
> that a supercomputer simulation of SL, with the right kind of driving pulses
> could reach fusion temperatures.
I personally believe that the weight of evidence favors high temperature
as the source of the SL glow, and that the phenomenon we see on the
lab bench, using equipment you can build at home, is in fact within
a factor ot 4 of the (temp x density) needed for D-T fusion. However,
The SBSL bubble must be maintained in the middle of a flask of water,
if the water temperature is much above freezing the phenomenon
disappears. So, even if you can get fusion in the bubble, how do you
propose to extract useful energy?

> > I envision an D-D fusion reactor based on a form of inertial-confinement
> > fusion, using a truly tiny holraum and starting in an environment with
> > very high static pressure. The environment is the center of a set of
> > diamondoid spheres, each of which contributes a megapascal or so of
> > pressure differential.
> Your geometry won't work. Each shell must be larger than the previous
> one. In the end your maximum strength is no larger than that of the bulk
> material.
The strength of the bulk material should suffice. The point of the
is to permit us to build a machine inside the resulting big diamond and
to build machinery throughout the whole structure to perform the power
generation and cleanup/repair functions.

> > The D-D reaction emits no primary neutrons.
> > The innermost sphere brings the interior static pressure up to the
> > highest level that remains consistent with diamondiod nanotech and
> > diamondoid compressive and tensile strength. The nanotech machinery
> > contained within the inner shell then delivers a transient implosive
> > pulse to the holraum (mechanically, or with lasers, or with explosives)
> > to cause fusion.

John Clark pointed out that I had made a mistake: D-D fusion also emits
neutrons. I should have checked references instead of relying on a
clearly faulty memory. I'm certain that I recall a higher-temp
fusion reaction: H-H perhaps?

> I rather suspect that nanotech becomes quite limited at high pressures.
> At extremely high pressures the forces of chemical bonds are of the same
> magnitude and you just can't build nanotech.

Not sure on this. At extreme pressure, various phase changes occur,
yielding crystals witb different properties. Why not build the innermost
portions of the device from these? I can think of several serious
objections, the most obvious being that a machine whose structures
are only stable at extreme pressure must operate in a liquid or a gas,
and nanotech is usually envisioned as working in a vacuum. In any event
I'm not sure where diamondoid becomes unusable on the temp/pressure
plane. Does someone have a reference? Remember: the diamondiod is
used to bring the static environmental pressure up, the actual
fusion pressure is generated dynamically as an increment on the
static pressure, so the diamondoid doesn't need to maintain
the full fusion pressure.

> > This geherates a lot of heat, raising the temperature
> > of th interior. The reactor uses the thermal gradient from inside to
> > outside to capture the energy neeeded to drive the next pulse.
> High pressure and temperature only reinforce my point.
> > Agreed. Given nano, you can get very efficient in every way. In
> > particular, forget the tent. Just reconfigure your body's resident
> > clothing nanos to provide an insulating skin of the type you describe.
> >
> Tents are nice, they provide privacy. Of course your clothing could
> reconfigure into a tent.
> BTW, I think a "mister fusion" is like backpacking a Winnebago...
> > Some elements capture neutrons very efficiently, but I want to
> > start with a reaction that doesn't emit neutrons at all.
> Ok. You have: Neutrons, skip those. Ok, energetic alphas - still capable
> of considerable nano mayhem. (and you gotta have alphas, ok?). Then
> there's betas, which have a range of inches, at least. OH, and I forgot
> the gammas, with a range of several feet even in rock.... Nice device
> you have here...
We may need to use lead or worse even heaview metals to shield the

> > It doesn't have to be efficient. It doesn't even have to
> > break even. It just has to be able to bust up these ugly big
> > radioactive isotopes that are not amenable to destruction by other
> > means.
> Using precious high quality energy here. I can see it now. 100 KW, of
> which we budget 10 KW to run the Mr Fusion, and 10 KW to run the accelerator,
> with 80 KW of waste heat!
I realize I'm doing major hand-waving here, but so are you. I haven't a
clue as to the amount of waste generated per KW of fusion energy, or of
how much of the waste will need accelerator treatment.

> > The problem is that for esthetic and political reasons we want this
> > tiny accelerator to be contained within the "mister fusion" housing.
> > What I'm banking on here is a major deux ex machina, even worse than
> > the inertial confinement system above: There are ways to use lasers
> > to pump energy into a particle beam with extreme efficiency, yielding
> > a very high change in Mev per meter of acelerator.
> Catch is the efficiency of making dose laser beams.

Even worse is the efficieny of the waste recapture system, which will
require continuous rebuilding of the entire structure by our busy little
> > I further assume that
> > an accelerator built via nanotech to atomic precision can achieve the
> > nearly the theoretical efficiency limit.
> Gotcha on this one! The nucleus is 10^5 times smaller than the atom. No
> way can you create this precision with nanotech.

Accelerators work today. Macro-scale machinery is capable of bashing
What I'm going for here is the ability to increase the efficieny of
macro-scale machinery by taking advantage of nanotech's atomic-scale
precision. There is no requirement for nuclear-scale precision. If
I could get nuclear-scale precision, I'd simply build a perfect
proton-proton fuser and dispense with the rest of this.
> > This should permit each nasty
> > heavy radioneucleotide atom to be bashed with extreme precision into
> > little pieces that are more tractable, all (I hope) in an accelerator
> > that's less than a meter long.
> And you expect all those random flying bashed pieces to be nice? hah!

No, I expect a large amount of messy garbage which will have to be
recycled thru the fast-nuetron deactivatin section, but the net
effect will be a reduction in heavy radioisotopes on each pass,
bringing the remaining load to effectively zero.