Polywell: We'll know in 7 months time?!

[MSimon]

It should. I wrote it.

...

Just what has got you so twisted?

The irony.

[EricF]

So far we've got 3 blips on a neutron counter for >25 years work

Those are just the WB-6 results. IEC devices (including other WB devices) have produced lots of useless neutrons, just like toks.

Tokamaks had a lot more positive results by then.

Tokamaks have no more plausible path to commercial technology than Polywell/IEC, despite tens of billions more in spending. If we had dumped $50B in Polywells over that time with no more progress than we have today then we could say they were doing about the same.

Isn't the choice of fuel used to provide the 'substrate' (for lack of a better word) for the fusion reaction the main determinant factor in neutron production, and not the method used to achieve fusion ignition temperatures (magenetic confinement vs interial ect ect)? IE pB11 vs D-D or D-T. I think you could hardly level a reasonable condemnation of all IEC devices because they have produced neutrons in the past using Deuterium based fuel.

[TallDave]

EricF,

Sort of. It's always been easier to get higher temps in IEC (it's just voltage) and better containment in MC while the reverse has always been more difficult (containment is harder in IEC, temp is harder in toks), and aneutronic fuels require much higher temps. Then there's the cyclotron probem, the Maxwellian distribution problem...

I don't know anyone who thinks tokamaks can burn p-B11 in any reasonable timeframe (someone correct me if I'm wrong here), while WB8.1 is slated to do so next year. Not sure where FRCs are on this; there are some papers but afaik the Tri-Alpha guys haven't released any p-B11 data.

[Robthebob]

...I don't know anyone who thinks tokamaks can burn p-B11 in any reasonable timeframe (someone correct me if I'm wrong here), while WB8.1 is slated to do so next year...

oh...

Dr. N seem to have always maintained that D-D is gonna be easy enough for polywell. We're going after the big one now?

[TallDave]

Yep, according the contract they're going to try p-B11.

3.2 Option for further development and testing (WB8.1).
3.2.1 Enhanced Ion Drive with PB11 (proton/boron 11): Based on the results of WB8 testing, and the availability
of government funds the contractor shall develop a WB machine (WB8.1) which incorporates the knowledge and
improvements gained in WB8. It is expected that higher ion drive capabilities will be added, and that a “PB11”
reaction will be demonstrated. The contractor shall investigate and validate the plasma scaling laws with respect to
B-field, voltage and reactor size. The contractor shall investigate the feasibility of a neutron-free fusion power
reaction using a polywell WB machine. It is anticipated that improvements in WB confinement, ion energy, and
fusion reactivity will be demonstrated in WB8.1. Improvements over the WB8 predictive, computational model are
expected, which should yield a better understanding of the WB fusion reaction thus allowing optimization of the
WB machine.
3.2.2 The contractor shall deliver a report detailing the results of the experimental testing of WB8.1. The report
shall provide sufficient information to guide programmatic and design decisions about further, refined design efforts
for similar devices. The report shall address the plasma dynamics of WB devices, and shall address the scaling laws
that apply to polywell fusion, and the feasibility of the PB11 reaction. The report shall address the conceptual
requirements for a polywell fusion reactor capable of generating approximately 100mW. (A0001)
3.2.3 Within 30 days of testing, the contractor shall update the predictive computer model of WB behavior created
under paragraph 3.1.4 using the PB11 reaction and shall deliver the model within 30 days of completion of initial
tests specified in paragraph 3.2.1.
3.2.4 The contractor shall refine the experimental database created under paragraph 3.1.4 including detailed 2D/3D
profile measurements of plasma density, ion energy and WB magnetic field structure to validate the scientific basis
for a Polywell fusion power reactor and to guide further research. The contractor shall coordinate with the
Government for a program review meeting at the contractor’s facilities to be held no later than 40 days after the
testing of the PB11 and shall demonstrate the database at this program review meeting.

They mean 100MW of course. No one would build a reactor that produced milliwatts.

[KitemanSA]

Yep, according the contract they're going to try p-B11.

3.2.2 The contractor shall deliver a report ... The report shall address the conceptual requirements for a polywell fusion reactor capable of generating approximately 100mW. (A0001)

They mean 100MW of course. No one would build a reactor that produced milliwatts.

That is not established. A plant that produced 100mW of continuous NET power would be a great step forward.

[Aero]

How long could one of these WB research machines run before melting, if it generated 100MW net, i.e. above and beyond drive power? They aren't making any arrangement to extract the energy, so all the power in and power generated just heats the reactor, doesn't it? Maybe it really is milliwatts.

[EricF]

How long could one of these WB research machines run before melting, if it generated 100MW net, i.e. above and beyond drive power? They aren't making any arrangement to extract the energy, so all the power in and power generated just heats the reactor, doesn't it? Maybe it really is milliwatts.

How destructive are high energy alpha particles? (I'm not being smart, I am genuinely curious)

[Aero]

That's kind of the question I was trying to ask. Alpha's are not penetrating particles, but they are hot, like 3 MeV each (p-B11). How many does it take to make 100 Megawatts? A lot, I guess. And how much input power will it take? Say Q = 1.2, then the machine would have about 500 MW to dissipate in structure. How long would the test run last? There are a bunch of other people who post here with a better handle on it than I have.

[MSimon]

How long could one of these WB research machines run before melting, if it generated 100MW net, i.e. above and beyond drive power? They aren't making any arrangement to extract the energy, so all the power in and power generated just heats the reactor, doesn't it? Maybe it really is milliwatts.

How destructive are high energy alpha particles? (I'm not being smart, I am genuinely curious)

If the magnetic fields are high enough they never touch the magnets.

The crossover point is about 1T for a 1 m bore. A 3T magnet for a 1 m bore should do. And is more or less off the shelf. Scale it up or down accordingly. 6 T for a 50 cm bore. 1.5 T for 2 meters.

[MSimon]

That's kind of the question I was trying to ask. Alpha's are not penetrating particles, but they are hot, like 3 MeV each (p-B11). How many does it take to make 100 Megawatts? A lot, I guess. And how much input power will it take? Say Q = 1.2, then the machine would have about 500 MW to dissipate in structure. How long would the test run last? There are a bunch of other people who post here with a better handle on it than I have.

(3 MeV/ particle) * (33.3 Amps) = 100 MWf.

Add in the usual factors for losses for a real number. My guess is roughly 100 Amps (300 MWf) to get 100 MWe. Improving as time goes on.

[chrismb]

How destructive are high energy alpha particles? (I'm not being smart, I am genuinely curious)

Eric,

I keep trying to tell people here and I've gone over this several times, but it seems to me that they wish to remain blissfully hopeful.

Alphas *are* radioactivity and even if 1% of [100MW] made it to the walls, that'd be 1 MW of incredibly damaging and eroding radiation. Alphas are much much worse, in 'volume-density' damage terms, than neutrons or gammas once they interact with something. Alpahs can't penetrate much matter because they dump their energy very quickly into the other material. So the front-most facing layers will soon become highly sputtered and eroded.

[EricF]

How destructive are high energy alpha particles? (I'm not being smart, I am genuinely curious)

Eric,

I keep trying to tell people here and I've gone over this several times, but it seems to me that they wish to remain blissfully hopeful.

Alphas *are* radioactivity and even if 1% of [100MW] made it to the walls, that'd be 1 MW of incredibly damaging and eroding radiation. Alphas are much much worse, in 'volume-density' damage terms, than neutrons or gammas once they interact with something. Alpahs can't penetrate much matter because they dump their energy very quickly into the other material. So the front-most facing layers will soon become highly sputtered and eroded.

So if there is nothing to slow down the alphas, they will hit something and start heating things up. I can see this being a problem in a prototype that doesnt harness the energy of those alphas, but by the time they start using the charged collection grid to allow the alphas to drive current, they will be low energy and non-damaging by the time they hit anything, at least thats what I assume.

If alpha particles are really that damaging, I am still curious why the military isn't pursuing 'Focus Fusion' for particle beam weapons alone (and power production as a fortunate side effect).

[chrismb]

If alpha particles are really that damaging, I am still curious why the military isn't pursuing 'Focus Fusion' for particle beam weapons alone (and power production as a fortunate side effect).

It is not that they have a *high energy*, per se, but that they have a very high specific energy. This is the nature of 'nuclear radiation' - that there is such a highly concentrated packet of energy that it doesn't just 'heat something up', it mutates it into a different substance! At the very least, it physically bashes the nucleii around so that they are no longer in the place where they were and so the substance just literally falls apart. This is what is referred to as 'DPA' - displacements per atom - and is a rating for how many times each atom can withstand being given a shove whilst part of the structure it is in.

For example, stainless steel in tokamak reactors is generally rated for 3 dpa. Now just think about it - if a fast neutron goes piling through 10" of SS it will potentially knock into any atom within that 10" as it can penetrate that far. If alphas only get a hundredth of an inch then it means the dpa rating for the alpha irradiation is going to be one thousand times more - but just at the surface - than in the 10" case for neutrons.

Raidation/fast alphas/neutrons are nothing whatsoever like 'a hot flame' that heats up a thermal blanket. You can't draw the same analogies.

[TallDave]

That is not established. A plant that produced 100mW of continuous NET power would be a great step forward.
...
How long could one of these WB research machines run before melting, if it generated 100MW net, i.e. above and beyond drive power? They aren't making any arrangement to extract the energy, so all the power in and power generated just heats the reactor, doesn't it? Maybe it really is milliwatts.

There are several problems with this interpretation:

1) They are calling it a "reactor" design, which connotes useful power. They make repeated reference to studying the suitabililty of Polywell as a reactor. It's very clear from context that by "reactor" they don't mean something that produces AA battery levels of power.

2) 100mW net power would be a very strange and arbitrarily precise requirement. It's like saying you want a vehicle to go 50.000001 mph. In a net power machine, 100mW isn't even a rounding error; you would have a hard time even measuring net output that small. One would expect the requirement to be simply "Q>1" or "net power" in such a case.

3) If they don't mean net power, 100mW makes even less sense. That's closer to what WB-6/7 produced than what we expect from WB-8. It makes no sense to ask for a design and feasibility study to produce WB-6 power levels after WB-8.

4) The plan all along, going back to Bussard's Tech Talk, was to build a 100MW Polywell reactor. It's been on EMCs web page from the beginning. It strains credulity to think we're on the path that was always envisioned, except for some reason we're delivering a design that produces 9 order of magnitude less power. After ~4 years of work.

It seems vastly more likely it is simply a typo. The technical writing in the award is a bit sketchy anyway.