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Point out news stories, on the net or in mainstream media, related to polywell fusion.

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ladajo
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Post by ladajo »

WB8 and 8.1 were/are never intended to be continuous run machines.
What ever gave you that idea?

Betruger
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Post by Betruger »

DeltaV wrote:
Skipjack wrote:I dont think that you need to refine the theory in order to refine the details of the actual device.
That would imply that the equations describing Polywell operation are exact, using only fundamental physical and mathematical constants and no "fudge factors", and that they can be implemented without any change in a computer simulation.
Exact enough, anyway.

choff
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Post by choff »

My understanding is that WB8 can be run for comparitively long periods at low power and progressively shorter periods as the applied power is raised.
CHoff

ladajo
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Post by ladajo »

Based on what?

choff
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Post by choff »

RNebels statement that WB8 would have a more dynamic range than WB7
CHoff

ladajo
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Post by ladajo »

He never stated or implied a long run machine. In fact he stated several times, and I believe even the contract chain stipulates a pulsed machine.

choff
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Post by choff »

Longer pulses.
CHoff

ladajo
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Post by ladajo »

Not so much.

To get the energy levels required/desired, lengthening the pulses would require much more depth in the power bank.

The machine is operating on the same time scales as previous builds. It has never been implied nor stated any other way.

Why do you persist in thinking this? What is your reference? Please cite it directly.

TallDave
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Post by TallDave »

Rick did imply that they at least wanted a steady-state machine.
That's why the proposed phase II machine will be a steady-state machine at a considerably larger size. It should resolve these issues.
viewtopic.php?p=4840&highlight=#4840

Now of course that was in Apr 2008. We later learned WB-8 was in fact pulsed (or at least it's being run that way).

We know they had time domain information as early as WB-7. I think they just have better diagnostics than Bussard was using for WB-6.

It's possible they are running longer pulses, which would make sense as a step toward a reactor because they'd be able to start looking at the PID loops that will keep things at beta = 1 instead of blowing through it in a pulse. OTOH, there's not a lot to suggest that, and Rick did say this (regarding WB-7):
By working with shorter discharges, we have also been able to reduce the size of capacitor bank. The first day I started working at LANL 30 years ago, Syllac (which was located right next to my office) blew up a capacitor. Syllac had three stories of capacitors. When this one went, it ignited the insulating oil and blew flames about 20 feet into the center of the experimental bay. The video was plenty cool, but I've had a healthy respect for capacitors ever since. You don't want to have them anywhere near the operators (and we don't).
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...

MSimon
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Post by MSimon »

I finally posted a report in the usual places.

http://powerandcontrol.blogspot.com/201 ... -2011.html
Engineering is the art of making what you want from what you can get at a profit.

ladajo
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Post by ladajo »

The contract specified a pulse machine as I recall. I will have to look at it again. But that said, yes they could run longer pulses, but to what point or goal? And at what cost and risk for the larger banks?
The purpose of WB8 is to test the scaling law. That does not mean they need longer pulses. Just a bigger machine with stronger coils. That is what they built and that is what they are operating. We can speculate, but the more reasonable thing is to stick to the facts we know.
In 2008 they were still debating the go for broke approach. Just build it and see. The WB7 results "nuanced" dictated another small machine to test scaling and get better data. But that said, it performed well enough to allow building in an option for 8.1 to the contract. If it had not performed well enough, they would not have added the 8.1 option. It would make no sense.

KitemanSA
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Post by KitemanSA »

So given what we think we know about WB8, what would limit the pulse duration? Almost certainly it is not the power for the magnets.

Ideas?

ladajo
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Post by ladajo »

What time scales are we talking?

D Tibbets
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Post by D Tibbets »

Pulsed, steady state... It depends on who you ask. Even the Sun is not truely steady state. It all depends on your frame of reference. Bussard considered 0.25 ms as effective steady state because the physics was occurring on the microsecond time scale.

WB6 was limited by two things, the heating of the copper magnets- which seems to have limited run times to a few seconds. The primary limit though was the nature of the power supply and the gas puffers. The gas puffers were poorly controlled and the flood of gas into and subsequently out of the magrid before it could be ionized and trapped lead to arcing within less than a millisecond. Areas where WB7 may have improved on with the advantage of a little more money and hindsight, was a better gas puffer. This may have allowed run times of milliseconds or more (speculation).
In WB6 they did not have a power supply that could supply high voltage (~12,000 Volts) at high current. I think their supply may have been capable of ~ 2 amps. Because of this they used capacitor banks charged up from this power supply. When arcing started the current flow from the capacitors increased from ~ 45 amps (when the potential well was formed, maintained and neutron production progressed ie: when the Wiffleball existed and Beta =~1) and then amps increased up to several thousand amps with arcing. If arcing could have been delayed/ prevented., the run time could have been stretched to perhaps dozens of milliseconds (the capacitor bank had plenty of reserve as evidenced by the high arcing current).

Wb7.1 if equipped with ion guns of sufficient power might have run significantly longer than a few milliseconds, even with power supply limits and magnetic heating similar to WB6.

WB8, other than probably better instrumentation, would benefit from the larger size. This allows for more complete puffer gas ionization before it can transit and escape the magrid. This would delay arcing. Perhaps to several milliseconds (?) Bussard felt that a machine of ~ 3 meters would work so well with a gas puffer that the buildup of external gas could be controlled and arcing thus prevented.

WB8 with a rated magnetic capacity of up to ~ 8,000 Gauss allows for greater B field scaling testing, but run times would depend on the time to arcing conditions as mentioned above, and not the heating of the magnets, especially as there is more mass to absorb the heat in addition tho the less resistance of copper cooled to liquid nitrogen temperatures

Personally I would consider steady state conditions would be reached with ~ 20 ms. This is ~ the ion lifetime till fusion in WB6 type machines (I read this somewhere). This would result in high fuel burn up and resolve thermalization issues on the largest important time scale. I'm not sure what the average ion lifetime till fusion would be in larger machines. Presumably it would be less as the density goes up with increasing B field. The thermalization times would also presumably shorten, again due to increased density, and longer flight paths before opportunities for edge annealing. Issues of MFP, machine radius, voltage, voltage dependant fusion crossection / Coulomb scattering crossection, etc. all feed into the equation. Presumably this understanding was improved with WB7 and WB7.1, and is being greatly expanded with WB8.

I forget, but I believe one of the possible WB8 derivatives would possibly be a "steady state" machine. I don't know if this definition implies a run time of a few 100 milliseconds, or hours.

PS: One definition of steady state would be that instead of a progressive change to a peak, then a decline, a steady state is reached when there is a plateau phase that persists significantly longer than the up slope and down slope phases, thus Busard's claim that WB6 was steady state from the perspective of the electrons. Steady state need not imply continous operation.

Dan Tibbets
To error is human... and I'm very human.

mvanwink5
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Post by mvanwink5 »

In a couple of months more testing (presumably), WB-8 results are being targeted to justify launching a $200 e6 5 year project. I am not sure I would be satisfied with basing my decision on a 1 millisecond pulse test. I know in Dr. Park's interview with Alan Boyle that the expectation would be to go for a full size machine next and not an intermediate machine, but a continuous run, first, would go a long way in my non physicist mind to providing assurance that there would not be some microscopic issue lurking in the millisecond testing.

Maybe I am just being dense here. I can see scaling and containment proved with a pulse machine, but if money can't be ponied up for power supplies on a small machine, I can't see these same people suddenly springing for continuous full size at 25 times the ticket price. On the other hand, maybe they have the square jaw for it.

I remember, however, the corporate lawyers and environmental regulators in a cigar smoked room saying the engineers will figure it out.
Counting the days to commercial fusion. It is not that long now.

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