Lawaranceville E-Newsletter

[rcain]

...Re Focus Fusion -- Lerner's good at fundraising. I don't believe electrode erosion is going to allow sufficient pulses to get anything like a reactor going.

if they get 'anything' like a net reactor going i think any erosion problems will be solved (or at least mitigated) pretty darn rapidly. its 'just an engineering problem' after all, and that has long been the claimed space of Polywell, at least by Bussard.

hell, if they had to replace the whole electrode assembly after each shot, i'd say we were on pretty assured territory, so long as Q>1 and they have some 'domonstrated' means of converting all those x-rays, etc, back into drive current.

theres an interesting background treatment to electrode erosion here - http://etd.lib.ttu.edu/theses/available ... 287171.pdf - notice it deals with 'moving arc' discharges, just as Lerners machine already utilises. the problem is thus already reduced significantly.

there are also advances in materials science which i'm sure could step to the rescue - graphene perhaps, carbon nanotubes, boron doped diamond even (fuel cycle?), oxide coatings or high-temp-high-hardness sintered materials? already in active use.

theres also reverse pulsing the electrodes, vapour redeposition, conventional cooling - all sorts of angles of attack.

i cant see it as a show stopper.

[Skipjack]

I agree, if this thing does work, a lot of people will suddenly look into it and will work on improvements. Look how far the diesel engine has come since its conception!

[Brian H]

... locked-room mystery... power failure in close orbit around Jupiter... the storm shelter will protect you from the Jovian radiation belts... but how do you get out long enough to make repairs and leave orbit?

Teleoperated Robots...

Screw that. I'm in Jovian orbit for the view on my 22nd honeymoon. The septuple-redundant AI systems are taking care of all that crap.


Re Focus Fusion -- Lerner's good at fundraising. I don't believe electrode erosion is going to allow sufficient pulses to get anything like a reactor going.

Uh, with all doo-doo repect, Lerner wandered in the funding wilderness for almost a decade before getting shoestring backing to proceed with. The total spent and raised to date since late 2008 is well shy of $2 million, including the one-time expense of lot purchase and construction of the experimental cell thereon. He and the small (2) group of physicists, and some associated (volunteer) computer modellers have been hands-on daily in setting up and running the experiments, and crunching the results since then.

Your opinion sounds very ill-informed, TD.

http://focusfusion.org/index.php/site/a ... ion_right/

[zapkitty]

side note: the electrodes for the operational reactors are to be beryllium in order to cut down on x-ray heating.

Apparently all alternative materials and coatings suitable for extending electrode life also absorb x-rays and heat up. Not good for an operational reactor that gets its net power from x-rays.

Indeed, their current test rig is to have its copper electrodes replaced with beryllium units when they "go for the gold" with b11...

Whatever the electrode lifetimes may turn out to be they are to be replaced and scavenged for their material when they wear out.

Yes, their forum members have already worked out that current beryllium supplies and production will suffice for the conversion to a fusion economy.. they're not that different from here...

(of course quite a few are already here)

(... they're already here?... we expected them to come in metal ships...)

[Skipjack]

Hmm, if you can cool the electrodes somehow, you could use the heat for heating buildings. I guess the salvageable heat would be to little for a steam cycle though.

[zapkitty]

Hmm, if you can cool the electrodes somehow, you could use the heat for heating buildings. I guess the salvageable heat would be to little for a steam cycle though.

Using an aneutronic fuel, yeah. The x-rays would provide a few megawatts thermal instead of 5 megawatts electrical. A carbon-fueled power plant boiler would just laugh at the thermal output of a DPF.

That's why aneutronic DPFs need the x-rays to pass through the electrodes and be converted to electricity in the foil layers around the reactor. The plan is that the alpha and beta beams from the plasmoid should be just enough to prime the system for the next pulse... which leaves the x-rays to provide the net energy profit.

If the x-rays are trapped as heat in the electrodes then the net energy profit goes bye-bye and you have an oversized water heater on your hands.

[KitemanSA]

That's why aneutronic DPFs need the x-rays to pass through the electrodes and be converted to electricity in the foil layers around the reactor.

Has this conversion method been demonstrated yet? I mean, this should be very easy to demonstrate.

[zapkitty]

That's why aneutronic DPFs need the x-rays to pass through the electrodes and be converted to electricity in the foil layers around the reactor.

Has this conversion method been demonstrated yet? I mean, this should be very easy to demonstrate.

?

The photoelectric effect of x-rays is well documented... so there's nothing wrong with the basic concept.

We'll find out whether they can make it work for this application on the scale they want.

p.s. if the gamma output of a polywell turns out to be as bad as some of you fear the PW could use the same principle to turn the gamma flux into usable electric power... although you wouldn't get for much and the "onion shell" would do terrible things to spacecraft mass margins

[TallDave]

rcain,

No, it's a physics problem, unless you consider unobtainium an engineering problem. If we say Bussard's physics assumptions were questionable, then Lerner's are wildly optimistic. It's nice they can get one or two pulses out, but you need millions and millions of pulses to get economic net power from this, even if you can get Q>1. It's a really really nasty first wall problem. It's a bit like claiming you have an economic car design that under exceedingly optimistic assumptions involves replacing the engine every 1,000 miles.

Brian,

I said he was good at fundraising. I did not say it was an idea that should attract a lot of funding. It's pretty amazing he got what he did.

Lerner was kicked off of Wikipedia, which says... something. Could FF work? I wouldn't completely rule it out. It's certainly somewhere ahead of BLP.

[rcain]

rcain,

No, it's a physics problem, unless you consider unobtainium an engineering problem. If we say Bussard's physics assumptions were questionable, then Lerner's are wildly optimistic. It's nice they can get one or two pulses out, but you need millions and millions of pulses to get economic net power from this, even if you can get Q>1. It's a really really nasty first wall problem. It's a bit like claiming you have an economic car design that under exceedingly optimistic assumptions involves replacing the engine every 1,000 miles....

we will have to agree to disagree then. since the physics is known, i maintain it should be classified as an engineering problem - whether it can be solved readily with known matrerials remains a question, granted.

your example of a car engine that needs replacing every 1000 miles is also specious; i would point out that spark plugs do indeed need replacing every 10,000 miles or so, and we live with that fact just fine.

there are some estimates of erosion on the focus fusion site here - http://focusfusion.org/index.php/site/a ... estimates/ - to which Brain H posts an extrapolated estimate of approx 1oz of copper every 5-6 secs of operation. i havent checked his estimate, but suspect its not far off.

i think we all agree erosion is a problem, but unsurmountable? i am optimistic that methods and materials will be found that bring erosion down to tolerable levels. diamond is my favourite candidate.

time will tell, we will see.

[TallDave]

Well, the physics are (mostly) known, but they seem to say electrode erosion with existing materials would keep this from being economic. I would call that a physics problem myself, ymmv.

Thanks for the link. I'm not clear at what power they're talking about -- i.e. how much net power is expected at 300Hz at the size he's talking about?

In an ICE, spark plugs get fouled (you don't really need them anyway; diesel works on compression); you're not significantly eroding the cylinder walls with every combustion. If you were, the concept would be far too expensive for us to be driving them around all the time. That's why it's hard to see how DPF can work economically, even with optimistic assumptions. I don't know much erosion is enough to prevent a DPF electrode from functioning but I suspect it isn't a lot more than than a piston cylinder can take before losing too much compression.

The first wall problem in a car can be solved with steel. It's a lot tougher at fusion energies.

[rcain]

Well, the physics are (mostly) known, but they seem to say electrode erosion with existing materials would keep this from being economic. I would call that a physics problem myself, ymmv.

Thanks for the link. I'm not clear at what power they're talking about -- i.e. how much net power is expected at 300Hz at the size he's talking about?

In an ICE, spark plugs get fouled (you don't really need them anyway; diesel works on compression); you're not significantly eroding the cylinder walls with every combustion. If you were, the concept would be far too expensive for us to be driving them around all the time. That's why it's hard to see how DPF can work economically, even with optimistic assumptions. I don't know much erosion is enough to prevent a DPF electrode from functioning but I suspect it isn't a lot more than than a piston cylinder can take before losing too much compression.

The first wall problem in a car can be solved with steel. It's a lot tougher at fusion energies.

TallDave - i think your arguments here are getting pretty desparate. even to the point of stating the obvious (which btw isnt necessary).

this whole ICE analogy - wasnt it used not so long ago on this very forum to show how if we had believed the early detractors of the ICE, back in the day, no one would have bothered to go further and 'solve the problems'; they did, and as a result we have working ICE's (or is that stating the obvious too much?). and cylinder erosion in ICE's 'is' a problem - solved in this case with lubricants - again stating the obvious.

first wall problems exist for all fusion devices, Polywell also. DPF is no better or worse in that regard.

as to how this factor might affect the economics of the DPF approach, the experimental results of - Brzosko 2007 ( http://www.physicsessays.com/doc/s2007/ ... nds-bk.pdf ) - and others conclude that 'electrode erosion (in itself) is NOT a limiting factor'.

a bigger bone of contention economically may be (if i read the literature correctly), the quite low over-unity Q that can be expected from such devices, best case.

[TallDave]

Yes, but DPF's first wall problem is much worse than other concepts because the first wall is so much closer.

Yes, we have ICEs now, but notice they generally aren't powered by high explosive. Cylinder erosion from combustion is negligible; the oil's primary purpose is lubrication to reduce frictive wear between cylinder and wall. If you had to replace big blocks of expensive machined steel on a regular basis the ICE would be a lot more expensive. So even if they get past Q>1, which is a big challenge, I find it hard to believe the fusion solution that ends up being economically doable, if such ever exists, will be DPF.

"Not limiting factor" isn't the same as "can be done economically for millions of pulses."

[MSimon]

Yes, but DPF's first wall problem is much worse than other concepts because the first wall is so much closer.

It is not just the distance. It is also the pumping of megajoules of electrical current into the electrodes intentionally.

[Aeronaut]

Actually, a lawnmower ICE is a good layman's model for the axial phase, since a high voltage spark (albeit high current as well) ionizes the fill gas, and the output power is pulsed rather than continuous, as the PW aspires to be.

http://focusfusion.org/index.php/site/a ... estimates/ states "This turns out to be about 18 microns per pinch." referring to experimental copper electrodes which I gather were chosen not just for cost, but to assist in energy accounting.

Like any self-respecting reactor, it will make heat, and lots of it. In fact, until somebody engineers the methods and tooling to economically build X-ray converters, it's early markets are almost guaranteed to be providing process heat for furnaces, ovens, low pressure steam, and pre-heating other mass to reduce or eliminate the economic uncertainties of fossil fuel prices.

In that light, the biggest engineering challenge I see is the design life of the power caps, unless 2 or FF cores can be daisy chained in such a way as to make them work like a resonant tank circuit comprised of 2 or more inductances and extremely fast, high powered switches to correct the phase challenges.

This may not be as formidable close up, as a primed FF also has a capacitive property to some extent, and they are cheap enough to group redundantly for this or critical load applications.

The Be anode is to be actively cooled with high pressure He. As the output temperature is expected to be less than 800 degrees F, it won't drive turbines, but can make their steam cost less by preheating the feed water.

One last note is that a machine cycle is only around 1,020 nS every 300th of a second.