Maximum size allowed by energy flux constraints

Discuss how polywell fusion works; share theoretical questions and answers.

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chrismb
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Post by chrismb »

rnebel wrote:If you are interested in pumps, the specifications for ITER can be found at:
http://www.iter.org/a/index_nav_4.htm
. If I am reading this correctly, the pumping power is about 60,000 liters/second. This is ~ 30 times more than the WB-7. It doesn't take a lot of power. Our system takes ~ 500 watts of power. ITER probably requires 10-20 kW.
WB-7 does not appear to have any relevance to a net-power-producing piece of kit, whereas JET and ITER do. I'm not sure of the purpose of raising such a comparison.

I don't have much interest in vacuum pumps, only that the demand on such pumps between, on the one hand, IEC devices (which rely on avoiding thermalisation) and on the other hand thermal magnetically confined plasmas (that positively rely on thermalisation to be the process of high energy collisions) results in these extremes of practicability.

Would you agree that a polywell needs 1E-9 torr operating pressure, and a >MW version would need >billion litre/s pumps? Or what else, if otherwise?

MSimon
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Post by MSimon »

chrismb wrote:
rnebel wrote:If you are interested in pumps, the specifications for ITER can be found at:
http://www.iter.org/a/index_nav_4.htm
. If I am reading this correctly, the pumping power is about 60,000 liters/second. This is ~ 30 times more than the WB-7. It doesn't take a lot of power. Our system takes ~ 500 watts of power. ITER probably requires 10-20 kW.
WB-7 does not appear to have any relevance to a net-power-producing piece of kit, whereas JET and ITER do. I'm not sure of the purpose of raising such a comparison.

I don't have much interest in vacuum pumps, only that the demand on such pumps between, on the one hand, IEC devices (which rely on avoiding thermalisation) and on the other hand thermal magnetically confined plasmas (that positively rely on thermalisation to be the process of high energy collisions) results in these extremes of practicability.

Would you agree that a polywell needs 1E-9 torr operating pressure, and a >MW version would need >billion litre/s pumps? Or what else, if otherwise?
Dr. B said the pressure outside the reaction area needed to be kept below 1E-6 torr. I chose 1E-7 torr as a reasonable number.

A 3E3 l/s pump is about 10 cm across. If pump volume goes up with the area of the intake (good BOE estimation) then a 1E8 l/s pump would be about 1,800 cm across - i.e. 18 meters. And of course if 1E-6 torr operation is possible then the pump dia is about 6 meters. i.e comparable to the size of the reactor vessel.

Whatever is done it is going to be a custom job. The first one is going to cost a lot.
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MSimon
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Post by MSimon »

What do you reckon the density of those much larger neutral boron molecules is that will be floating around??
Pumping capability of a turbopump goes up as the mass of the pumped particles goes up. Pumping B is not a problem. What I worry about is B condensing on the turbine blades. Now there is a real problem.
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MSimon
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Post by MSimon »

You're dead right there, I think. Fundamentally, tokamaks work on the principle of a theralised plasma, whereas IEC cannot function in this way. So thermal plasma fusion has the advantage of density - and it is a huge advantage!
Not exactly. In the reaction area the density of a Polywell is much higher than in a tok. The Polywell has a lower average density and a higher reaction volume density. The higher reaction volume density gives a much higher power density and thus the Polywell is smaller for equal fusion power.

The pumping problem is difficult. It is not intractable.
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MSimon
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Post by MSimon »

WB-7 does not appear to have any relevance to a net-power-producing piece of kit, whereas JET and ITER do. I'm not sure of the purpose of raising such a comparison.
Give me the ITER budget for one year and in 2 to 3 years I will have built your relevant device. And likely I will have a fair amount of cash left over. On the order of 80% of the cash left over in fact - unless I use some of that money to speed things along.

As to the relevance of ITER vs WB-7 for pumping power - I think the point is that pumping is not going to consume a lot of watts. And most of the energy will be going to replace losses in the pumps not into compressing the gas.
Engineering is the art of making what you want from what you can get at a profit.

chrismb
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Post by chrismb »

MSimon wrote: Dr. B said the pressure outside the reaction area needed to be kept below 1E-6 torr.
mean free path = 600m
MSimon wrote: I chose 1E-7 torr as a reasonable number.
mean free path = 6000m

Are these distances really long enough to ensure fusion, rather than collision/thermal loss, of a fast ion? I've posted my calculations otherwise, feel free to show the errors.... I'm not suggesting there aren't any, but you know me, I like to see the argument as numbers rather than the hand waving.

chrismb
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Post by chrismb »

MSimon wrote: I think the point is that pumping is not going to consume a lot of watts. And most of the energy will be going to replace losses in the pumps not into compressing the gas.
no disagreement there, the low vacuum is surely going to account for next to no pumping losses, but the driving power required for the billion litre/s pumps is going to be enormous. I am not sure anyone even knows how to make turbo pumps of that rate, there are some fundamental physical issues there, I think.
MSimon wrote:
What do you reckon the density of those much larger neutral boron molecules is that will be floating around??
Pumping capability of a turbopump goes up as the mass of the pumped particles goes up. Pumping B is not a problem. What I worry about is B condensing on the turbine blades. Now there is a real problem.
not at all convincing. turbomolecular pumps are not *mass* pumps, they simply biff any odd molecules that have made it in through the vanes so that they stay that side of the vanes. There is no 'mass compression' or any other such bulk notions at those vacuums. Just based on particle numbers and, thus, volumetric for some defined pressure.
MSimon wrote:
You're dead right there, I think. Fundamentally, tokamaks work on the principle of a theralised plasma, whereas IEC cannot function in this way. So thermal plasma fusion has the advantage of density - and it is a huge advantage!
Not exactly. In the reaction area the density of a Polywell is much higher than in a tok. The Polywell has a lower average density and a higher reaction volume density. The higher reaction volume density gives a much higher power density and thus the Polywell is smaller for equal fusion power.

The pumping problem is difficult. It is not intractable.
*exactly* and *intractable*, I would suggest. "In the reaction area the density of a Polywell is much higher than in a tok." - always with the present tense. Show me....... allow me to witness a polywell reaction volume....many of the earlier tokamak and pinch project showed, albeit unstable, instrumented and monitored reaction volumes with much less money than Polywell has enjoyed. So I'm keen to see it. Wake me up when it happens.......the unsubstantiated speculations on how polywell *does* work are making me feel sleepy again...

icarus
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Post by icarus »

chrismb: your mean free path numbers mean nothing except to tell you that the ideal gas pressure/density relations you are using are next to useless ... if it says 600m and you in a 6m vessel you're in the wrong ballpark ... i.e. the game's not on today, regardless of what seat number it says on your ticket.

The pressure/density numbers you are using for your billions of litres per second fantasy will be nothing like that across the pump (if it is atmospheric at one side of the pump pressure will be rising rapidly before it even enters the pumping mechanism. It requires much more detailed calculations to make the widely sweeping statements that you are indulging in.

In any case, I think you have gone well off the topic of maximum size based on energy flux considerations, perhaps you'd like to start another pump sizing theory/design topic and run through the numbers there somewhere? I'll be vaguely interested to know how wrong you were.

MSimon
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Post by MSimon »

chrismb wrote:
MSimon wrote: Dr. B said the pressure outside the reaction area needed to be kept below 1E-6 torr.
mean free path = 600m
MSimon wrote: I chose 1E-7 torr as a reasonable number.
mean free path = 6000m

Are these distances really long enough to ensure fusion, rather than collision/thermal loss, of a fast ion? I've posted my calculations otherwise, feel free to show the errors.... I'm not suggesting there aren't any, but you know me, I like to see the argument as numbers rather than the hand waving.
Doesn't it all depend on density ratios and whether there is annealing of the thermalized particles?

Now density ratios I could give you. Rick says in the reaction space a 10T Polywell will have roughly 60,000 times the reaction rate of ITER (IIRC).

As to annealing (i.e. maintaining the ions monoenergetic) the truth of that and the numbers await further experiments. Or the release of data from the current experiments.

And then you have the reports from simulations and some fusor experiments of collective behavior which I suspect may be klystron like. So the annealing may not be thermal in nature at all. It may be due to a phenomenon like klystron bunching. Which it may be possible to advance with the proper tuned circuits.

You want numbers (wouldn't we all) and all I can give you are hints. I do know the questions I want to ask and I'm comfortable with that. The soul of a good researcher is to be comfortable with ignorance (while trying to shine a light in the darkness). Not everyone is comfortable with ignorance and chaos.
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MSimon
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Post by MSimon »

not at all convincing. turbomolecular pumps are not *mass* pumps, they simply biff any odd molecules that have made it in through the vanes so that they stay that side of the vanes. There is no 'mass compression' or any other such bulk notions at those vacuums. Just based on particle numbers and, thus, volumetric for some defined pressure.
Uh. I'm not sure I agree. At least if you take the specifications of real turbo pumps into account. They work better with high molecular weight gases. And they can be tuned for a particular gas. i.e. the design of a pump that will work well with Hydrogen is different than one designed to pump atmosphere.

A look at this document (page 5) might provide some useful points of reference:

http://www.adixen.com/adixen_avt/downlo ... prod20.pdf

Here is a pump optimized for light gases (see page 2):

http://www.adixen.com/adixen_avt/downlo ... rod108.pdf
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MSimon
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Post by MSimon »

chris,

Since all this speculation (the heart of real research btw) makes you sleepy may I suggest you go to sleep for a couple of years and come back when it is possible to answer the questions.
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MSimon
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Post by MSimon »

Show me....... allow me to witness a polywell reaction volume....
Show me the money. I have a few experiments I'd like to do to answer your questions.
Engineering is the art of making what you want from what you can get at a profit.

icarus
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Post by icarus »

Can we all agree on this fundamental number for a working reactor?

Magnetic field 10T at the coils, therefore average field strength at wiffleball surface approx. 5T. (using Art's about a half guesstimate)

From here, using beta=1 we can get electron plasma pressure at wiffleball surface approx.

P_wb = (B**2)/(2*mu_o)

P_wb = 10 MPa

Everyone agreed?

Torulf2
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Post by Torulf2 »

Watt is the need foe pumping with the D+D reaction?

chrismb
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Post by chrismb »

icarus wrote:chrismb: your mean free path numbers mean nothing except to tell you that the ideal gas pressure/density relations you are using are next to useless ... if it says 600m and you in a 6m vessel you're in the wrong ballpark ... i.e. the game's not on today, regardless of what seat number it says on your ticket.
The particles reciprocate (!?!!), how else can the ions travel the 200,000m that they need to travel to find another with which to fuse? Or d'you think they all fuse on the first pass??
icarus wrote: The pressure/density numbers you are using for your billions of litres per second fantasy
yep, fantasy, that's my take on it
icarus wrote: will be nothing like that across the pump (if it is atmospheric at one side of the pump pressure will be rising rapidly before it even enters the pumping mechanism. It requires much more detailed calculations to make the widely sweeping statements that you are indulging in.
I agree, a detailed calcultion is needed, and it should show an even higher flow rate will be required (as I have simply taken the very best case of the displacement of output particles at the target vacuum pressure, when in fact they'd need to be extracted by a vacuum stream even lower than the target background pressure).
icarus wrote: In any case, I think you have gone well off the topic of maximum size based on energy flux considerations, perhaps you'd like to start another pump sizing theory/design topic and run through the numbers there somewhere?
energy flux=ion flux=amount of substance that needs to be extracted

max size - limited by pumping considerations of substance that needs to be extracted.

I think it is dead-on topic.
icarus wrote: I'll be vaguely interested to know how wrong you were.
me too. I'm always keen to learn, and face up to/loose to worthy verbal sparring partners with better mental arithmetic and bigger calculators (- so long as it doesn't cost me money)!

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