Maximum size allowed by energy flux constraints

MSimon · Post by **MSimon** » Thu Apr 09, 2009 11:18 pm

chris,

It will cost you time (waiting for others) or money (to shorten the time).

If you have neither, well then....

MSimon · Post by **MSimon** » Thu Apr 09, 2009 11:20 pm

Torulf2 wrote:Watt is the need foe pumping with the D+D reaction?

Mass flow is how you maintain a given pressure with vacuum pumps.

Torulf2 · Post by **Torulf2** » Thu Apr 09, 2009 11:28 pm

Is this the show stoper?

MSimon · Post by **MSimon** » Thu Apr 09, 2009 11:41 pm

Torulf2 wrote:Is this the show stoper?

I don't think so. In fact Dr. Bussard was such a careful engineer I'm sure he figured it was a solvable problem. Or as many prefer: just engineering.

TallDave · Post by **TallDave** » Fri Apr 10, 2009 2:26 am

(When I say 'cool divertors', these babies are sucking up 20MW/m^2 which is the upper limit of materials, so it is not clear to me that such large tokamaks are viable anyway, in material terms.)

Whoa! 20 MW/m^2? Give us that on the Magrid and our first-wall issues don't become a problem till ~2GW, iirc.

But once again I am too lazy to dig up MSimon's post and do the math to be sure. My Oracle DBA exam is calling.

Possibly related: modelling vacuum pump flows for ITER. They actually use 5 different sets of equations.

http://www.iter.org/IAEA2006/ITERP2-12.pdf

Oh, and I assume Rick's 500W comment was for a reactor, not for WB-7. It's a much smaller volume than ITER, in fact it's much closer to the WB-7 volume.

Joseph Chikva · Post by **Joseph Chikva** » Sat Jun 16, 2012 5:50 am

I see there only the answer on your comparison of Polywell with klystron:

rnebel wrote:for Polywells which should operate in the quasi-neutral limit where Debye lengths are smaller than the device size.

So. comparison of Polywell with any vacuum tube for which Debye lengths are bigger than the device size, would not be legit.

And "no data" means "no evidence of existance".
And during my life I have seen number of fusion p[ower plant designes based on different concepts. For example toroidal theta pinch. This is an answer on 1.5m 100MW reactor for DD fuel and 2m for pB11 and then speculations on TOKAMAK, friggates and aircraft carriers. Only direct energy convertor for 100MW pB reactor would have dimensions larger than the biggest carrier in the world.

hanelyp · Post by **hanelyp** » Sun Jun 17, 2012 1:22 am

Still trying to apply a direct conversion design intended for a thermal plasma, when the polywell running p-B11 is expected to selectively emits fusion products within a narrow enough energy range for a reverse Van de Graaff accelerator to work?

MSimon · Post by **MSimon** » Sun Jun 17, 2012 12:32 pm

hanelyp wrote:Still trying to apply a direct conversion design intended for a thermal plasma, when the polywell running p-B11 is expected to selectively emits fusion products within a narrow enough energy range for a reverse Van de Graaff accelerator to work?

My rough estimate is that direct conversion will run about 50% efficient due to the range of energies in the alphas. Possibly efficiencies might go to 70%.

The big plus is that a steam plant is much more expensive and takes 2 to 3 years to manufacture. Direct conversion can be manufactured in about 6 months - once it goes into series production.

mvanwink5 · Post by **mvanwink5** » Sun Jun 17, 2012 4:52 pm

What about steam generator replacement on an existing fossil plant?
Best regards

kcdodd · Post by **kcdodd** » Sun Jun 17, 2012 5:55 pm

what about supercritical CO2 Brayton cycle. Running at much higher temperature.

MSimon · Post by **MSimon** » Sun Jun 17, 2012 8:58 pm

I didn't do any calculations for those types of plants. It seemed too obvious.

As far as I know no one else had even done the preliminary work (what I did) for direct conversion. There is some literature out there on the subject but it is sparse and mostly theoretical. I applied some engineering to the question.

The big cost for direct conversion is the down converter from about 2 MV DC to a more tractable 100 KV AC. I look forward to the day when we have 2 MV DC lines criss crossing the nation. That would make very long distance interties (>2,000 miles) a reality. I looked at that question (2 MV - conversion and transmission) too.

It is all in the archives here. If you can find it.

DeltaV · Post by **DeltaV** » Mon Jun 18, 2012 5:14 pm

MSimon wrote:My rough estimate is that direct conversion will run about 50% efficient due to the range of energies in the alphas. Possibly efficiencies might go to 70%.

Maybe the "Venetian blind" concept can be rethunk to come up with an energy-independent, or at least energy-quantized, direct-conversion scheme. Properly shaped concentric collectors, aligned with coil axes (assuming the alpha spray stays somewhat conical), electrostatic and/or magnetic "guidance" for different alpha energies.

Somewhat analogous to frequency-independent spiral/helical antennas, but I don't think spiral collectors would work here due to the different potentials (maybe with a geometry-dependent resistivity?).

MSimon · Post by **MSimon** » Mon Jun 18, 2012 5:30 pm

DeltaV wrote:
MSimon wrote:My rough estimate is that direct conversion will run about 50% efficient due to the range of energies in the alphas. Possibly efficiencies might go to 70%.
Maybe the "Venetian blind" concept can be rethunk to come up with an energy-independent, or at least energy-quantized, direct-conversion scheme. Properly shaped concentric collectors, aligned with coil axes (assuming the alpha spray stays somewhat conical), electrostatic and/or magnetic "guidance" for different alpha energies.

Somewhat analogous to frequency-independent spiral/helical antennas, but I don't think spiral collectors would work here due to the different potentials (maybe with a geometry-dependent resistivity?).

Good ideas. I didn't go any deeper than I did because I was unsure if it would be worth more than a week's effort. i.e. will Polywell work.

KitemanSA · Post by **KitemanSA** » Mon Jun 18, 2012 11:37 pm

The whole point of the "venetian blind" style converter IS to sort the ions by energy. Otherwise it would just be a flat wall to run into. Each level of energy will travel futher up the potential and when turned will run into it's own slat.

MSimon · Post by **MSimon** » Tue Jun 19, 2012 12:50 am

KitemanSA wrote:The whole point of the "venetian blind" style converter IS to sort the ions by energy. Otherwise it would just be a flat wall to run into. Each level of energy will travel futher up the potential and when turned will run into it's own slat.

Obviously there is a trade off between the number of slats and efficiency.

And you need to know the distribution to decide what the trade offs would be. I just explored the concept because I had no data.