Kick the tires, light the fires...

If polywell fusion is developed, in what ways will the world change for better or worse? Discuss.

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Mumbles
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Kick the tires, light the fires...

Postby Mumbles » Fri Jan 18, 2008 2:17 am

I have an open question on the start-up procedure for an eventual Polywell. What sort of energies will be required to start the reaction (light the fire) ? Specifically in terms of thinking about transportation - ships, railroads, vehicles (tractor-trailers have been discussed here before - I am not sure I understand how feasible they might be...) or even aircraft/spacecraft - what start-up procedures, supporting facilities and/or energy supplies might be required?

Comparatively, an internal combustion engine with a relatively small battery can spin up the rotor - including some cylinders experiencing compression - introduce fuel and spark, get ignition, and start producing power. (And then an alternator is used to re-charge the start-up battery.)

An external compression engine (jet engine) has a much longer spool up time (RPMs order of magnitude nearer to 10,000 rather than 1,000 of an internal combustion engine), then fuel and ignition. Yes, fuel is usually introduced in the 10-15% max RPM range, but the spin up energy is not small. Larger engines often use external compressed air - sometimes bleed air from a smaller jet engine (auxilary power unit (APU)) - to spin up to starting speed. But the "power" (either electrical or compressed air) is supplied either by a small external attachment (compressed air hose or power cord) or piggybacked from on-board sources (battery, another engine, or an APU).

As I see it, Polywell needs to establish a vacuum, charge up the MaGrid, introduce sufficient electrons to establish the well, provide ionized fuel from high-voltage ion guns (or ionize the fuel at introduction), and get the fire lit. Since the best concept is for direct electrical power extraction rather than going through a thermal cycle, once the reaction is going, the device should power itself (if it works...).

So will a battery suffice? Or will we need to kick it off with a conventional generator? Or will we need to have a larger power supply to have a successful cold start? What do you all think?

Thanks
Be Safe
Mumbles

MSimon
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Postby MSimon » Fri Jan 18, 2008 3:27 am

I think a 1 to 2 MW diesel generator (DG) will be required if no grid power is available.

Start up from no vacuum might take as long as 3 or 4 days given cook out rqmts. However power rqmts for that will be on the order of a few 100s of KW with final reactor start up taking a few minutes or less at full DG power.

Of course that is just an estimate.

If the start up pulse is short enough a big flywheel hooked to the generator might do the trick, thus allowing for a lower power generator.
Engineering is the art of making what you want from what you can get at a profit.

Mumbles
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Out-gassing and Throttling down...?

Postby Mumbles » Fri Jan 18, 2008 7:54 pm

MSimon wrote:Start up from no vacuum might take as long as 3 or 4 days given cook out rqmts.

Are the cook out requirements to maintain sufficiently austere vacuum conditions? (Prevent out-gassing from materials inside the reaction space?)

Would a "seasoned" reaction chamber be expected to require a shorter preparation period for a second (or many later) start-up?

If it is purely a vacuum thing, is there a way to accelerate the preparation through ionization of neutrals in the interior (we would have significant control over many very powerful electromagnets...), or is it a decreasing exponential issue due to pumping to get to the correct vacuum level?

Finally, for shipboard or outer-space use, would having redundant Polywells enable a quick start from one to the other? (I am assuming the vacuum conditions in space - above some critical altitude - are sufficient to get to pre-start conditions... Let me know if that is not correct.)

Break, break... For a smaller reactor - railroad train or semi-trailer sized - is there an "idle" setting where the electrical output would near the power required, so we wouldn't have to figure out how to deal with all that excess power available? Fuel for this thing is cheap - get it going and keep it going. But too much power could create a dangerous situation. Can a Polywell be "throttled"? Thanks.

Be Safe
Mumbles

MSimon
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Re: Out-gassing and Throttling down...?

Postby MSimon » Fri Jan 18, 2008 8:10 pm

Mumbles wrote:
MSimon wrote:Start up from no vacuum might take as long as 3 or 4 days given cook out rqmts.

Are the cook out requirements to maintain sufficiently austere vacuum conditions? (Prevent out-gassing from materials inside the reaction space?)


Yes.

Would a "seasoned" reaction chamber be expected to require a shorter preparation period for a second (or many later) start-up?


Maybe.

If it is purely a vacuum thing, is there a way to accelerate the preparation through ionization of neutrals in the interior (we would have significant control over many very powerful electromagnets...), or is it a decreasing exponential issue due to pumping to get to the correct vacuum level?


Maybe. Yes.

Finally, for shipboard or outer-space use, would having redundant Polywells enable a quick start from one to the other? (I am assuming the vacuum conditions in space - above some critical altitude - are sufficient to get to pre-start conditions... Let me know if that is not correct.)


Multiple reactors on ships is a definite rqmt. Along with a backup DG.

Fission Nukes shut down for over an hour or so require about 36 hours to restart due to Xenon 137 poisoning. So a 3 day restart regime is not too far out of operational experience.


Break, break... For a smaller reactor - railroad train or semi-trailer sized - is there an "idle" setting where the electrical output would near the power required, so we wouldn't have to figure out how to deal with all that excess power available? Fuel for this thing is cheap - get it going and keep it going. But too much power could create a dangerous situation. Can a Polywell be "throttled"? Thanks.


Throttling should be possible. We won't know for sure until we build some high power operating units. D-D should definitely throttle. pB11 may be tougher due to B11 condensing on the grids.

Be Safe
Mumbles


You too. But not too safe. What is life without risk?
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tonybarry
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Postby tonybarry » Fri Jan 18, 2008 11:48 pm

Startup for a polywell seems to involve a few things ...
** the vacuum
** the LHe for the superconductors
** the coolant for the MaGrid
** the polywell initiations sequence
- establish a mag field
- establish the electric fields
- pump in some electrons, add a few ions to almost balance,
- keep the vacuum going as stray He condenses on the outer collection grid
- add more of each till the wiffleball establishes itself

My knowledge in these areas is limited.

To establish the LHe environment will be a challenge as the coils will need to be filled with liquid rather than gaseous helium. The gas will need to be purged from the system and a cooling flow established. This might take a considerable time - I understand that LHe is a quirky stuff and flows in weird ways.

The coolant for the MaGrid (Simon has suggested a LN jacket, then a water jacket) must keep flowing during startup - so the LN and the water don't ice up from the LHe cooling.

The mag field may be a challenge to create - Simon suggested the superconductors need to be partially heated above their Tc to get a current "going" in the ring. I assume this is done routinely in MRI scanners so there are ways ...

The electric fields are colossal - the outer collection grid runs at 2 MV and will sustain a serious current (tens of amps) when the generator is at full power. If the polywell is in fact a pulsed device as some people are suggesting from sims (Dr Mike and perhaps Indrek) then the outer collection grid will have a serious AC component to this already considerable DC charge. The feedthroughs to the MaGrid and the coolant may well end up as ceramics (I can't think of what else will work here), and they will take some time to thermally stabilise.

The MaGrid also has a fair voltage on it - some 50kV, AC at perhaps 250MHz - according to Dr. Mike. That's no mean feat, when you consider it runs within the outer collection grid. I do not know if this will take any time to establish, or if it just comes up as the polywell comes on-line.

All in all, I would not be surprised at a three day startup sequence. I think the thermal stresses might also mean the polywell might take tens of hours from first light (break even power) to full power net positive, recharge the batteries and run the city operation.

Regards,
Tony Barry

Mikos
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Postby Mikos » Fri Feb 01, 2008 12:36 am

For Polywell start up and operation, I think that Superconducting Magnetic Energy Storage (SMES) battery would be great option. You already would have cooling system for Polywell reactor, SMES have really great round-trip efficiency (greater than 95%), power is available almost instantaneously and very high power output can be provided for a brief period of time.

Jeff Peachman
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Postby Jeff Peachman » Wed Jun 18, 2008 4:11 am

I know this is an old thread, but I've been curious about startup of a polywell after failure on something such as a spacecraft for awhile.

The part I don't know at all depends upon this: what value of G can we expect polywells to achieve? Is it dependent upon the radius or is there a fundamental upper limit on G?

If G is high enough, then you could image a staged process: starting a very large polywell using a smaller one. The advantage of a large polywell, assuming the scaling laws are right, seems to be a better power/weight ratio than 2 separate reactors with the same combined net output. But having two polywells increases reliability. So, if your on your spacecraft and your primary reactor breaks, you can shut down the engines and fix the polywell, then use your secondary (small one) to start it back up.

If both fail, then your DG will need a lot less fuel to start up the small one than the large one. And, you don't incur the same weight penalty of having 2 equally sized polywells.

But how big of a size difference can be achieved between the reactors? Could one finish this 3 or 4 day startup process for a really huge 10 meter reactor using a secondary only 5 m in size? (If not 10, how big maybe?)
- Jeff Peachman

drmike
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Postby drmike » Wed Jun 18, 2008 1:44 pm

If you have a gain of 100, then you only need 1/100th the size, and what you are describing makes sense. If you only have a gain of 5, then you might be better off with a different kind of power for back up (like radioactive decay heat with 10,000 years half life).

We'll see when we get real system up and running!

MSimon
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Postby MSimon » Wed Jun 18, 2008 7:54 pm

From strictly theoretical considerations of cross sections in a balanced fuel pB11 reactor you can get an energy gain of about 22X (resonance peak) or about 8X (broad peak) depending on the reaction density you desire. The gain being lower at the higher density.

Some people think that a factor of 5X to 10X more is possible.

So to answer your question: an informed judgment is not possible at this time.
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tombo
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Postby tombo » Wed Jun 18, 2008 11:03 pm

A fission plant I toured once had several (3?) diesel-electric railroad locomotives parked on site for their emergency backup power.
Those are a few thousand horsepower ~= a few megawatts each.
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TallDave
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Postby TallDave » Wed Jun 25, 2008 3:16 am

Yah, my guess is on a carrier (the only mobile app I can see making sense) you would have a fission reactor to start your fusion reactor. It takes a LOT of juice to get the thing going.

Of course, a lot depends on whether p-B11 fusion is possible.

MSimon
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Postby MSimon » Wed Jun 25, 2008 3:46 am

On my ship each reactor (we had two) had a 1 MW DG (roughly 2,000 HP) set for emergency cooling and reactor re-start after a scram (other reactor offline).

==

If max power for start up only requires a 10 second 10 MW burst then 120 seconds or so of a DG charging a flywheel would be enough for start up. A 4:1 variation in flywheel speed would extract around 95% of the available energy. Under normal conditions the pulse power device would be kept charged up by the running reactors. Or utility power when dockside.

A roughly 200 HP (100 KW) gasoline powered generator could give you a start up shot every 20 minutes. A 20 HP (10 KW) generator could give you a start up shot every 3 1/2 hours. A 1.5 KW gen set about once a day.

Such an impulse generator might have some other uses as well. :-)

This doesn't seem like a big problem to me.
Engineering is the art of making what you want from what you can get at a profit.

David_Jay
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Postby David_Jay » Wed Jun 25, 2008 4:25 pm

I am facinated by flywheel storage systems. I first started to think about them in the late '70s. I wanted to build a braking system for my car, storing the energy in a flywheel instead of dissipating it as heat!

These guys have a nice 2MW off the shelf solution:

http://www.activepower.com/fileadmin/do ... SDC_ds.pdf
not tall, not raving (yet...)

David_Jay
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Postby David_Jay » Wed Jun 25, 2008 4:29 pm

These guys look even better - vacuum chamber with magnetic levitation bearings - 20 year maintenance free.

http://www.pentadyne.com/site/our-produ ... ology.html
not tall, not raving (yet...)

drmike
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Postby drmike » Wed Jun 25, 2008 8:32 pm

Cool! I can't imagine having a business like that, but I'm glad somebody knows how to!


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