extracting energy out off the plasma soup

[busuttil]

is there another way to get energy out off the plasma :question:

[Jolly Roger]

This is a good question, but one better asked in the Technology section than here in the Fundraising section. [Note: moved by admin]

[Brian H]

Jolly Roger wrote: This is a good question, but one better asked in the Technology section than here in the Fundraising section. [Note: moved by admin]

Doesn’t make sense to me. The plasma must be maintained at a high temp to be useful, and that’s where the energy from the electron beam goes. Why would you want to drain power/heat from the plasma? Defeats the whole purpose.

[jamesr]

Brian H wrote:

Doesn’t make sense to me. The plasma must be maintained at a high temp to be useful, and that’s where the energy from the electron beam goes. Why would you want to drain power/heat from the plasma? Defeats the whole purpose.

Surely you can’t maintain the plasma at a high temperature. OK you want it to get very hot at the focus, but at the end of a pulse the small proportion of gas that was heated to a plasma is going to carry on bouncing round the chamber and heat up everything else. You need to keep the electrodes cool enough to keep their surface vapour pressure down so they can survive for a reasonable length of time, and the copper or beryllium vapour doesn’t poison the reaction.

I would suspect though that the heat extracted from the cooling mechanisms needed on the whole device will be low level thermal waste and not useful for generating any power. It could heat a few buildings or greenhouses though.

James

[Brian H]

jamesr wrote:

Doesn’t make sense to me. The plasma must be maintained at a high temp to be useful, and that’s where the energy from the electron beam goes. Why would you want to drain power/heat from the plasma? Defeats the whole purpose.

Surely you can’t maintain the plasma at a high temperature. OK you want it to get very hot at the focus, but at the end of a pulse the small proportion of gas that was heated to a plasma is going to carry on bouncing round the chamber and heat up everything else. You need to keep the electrodes cool enough to keep their surface vapour pressure down so they can survive for a reasonable length of time, and the copper or beryllium vapour doesn’t poison the reaction.

I would suspect though that the heat extracted from the cooling mechanisms needed on the whole device will be low level thermal waste and not useful for generating any power. It could heat a few buildings or greenhouses though.

James
No, the whole plasma has to be kept quite hot; cooling the electrodes is a big engineering challenge, though.

But there will be waste heat from that, and maybe there’s a way to use it:

http://www.livescience.com/technology/070604_sound_electricity.html.

At any given temp, a particular resonance frequency is set up, which can be manipulated to extract power.

[Viking Coder]

A FF engine generates electricity through particle beam & x-ray recovery rather than heat extraction. This is why the construction cost is so dramatically lower.

A decelerator, as opposed to a particle accelerator, is put in the line of the tight pulsed beam of charged alpha particles (He nuclei) that is the result of the pB11 fusion. More electricity is generated by passing the x-rays through a shell of thin metallic foils, with the electrons captured on wires held at negative voltages.

https://focusfusion.org/index.php/site/article/35/#el
https://focusfusion.org/index.php/site/article/simulation_results/

An artists’ rendition of the FF engine is on the right side of the header on the LPP site.

[Brian H]

Viking Coder wrote: A FF engine generates electricity through particle beam & x-ray recovery rather than heat extraction. This is why the construction cost is so dramatically lower.

A decelerator, as opposed to a particle accelerator, is put in the line of the tight pulsed beam of charged alpha particles (He nuclei) that is the result of the pB11 fusion. More electricity is generated by passing the x-rays through a shell of thin metallic foils, with the electrons captured on wires held at negative voltages.

https://focusfusion.org/index.php/site/article/35/#el
https://focusfusion.org/index.php/site/article/simulation_results/

An artists’ rendition of the FF engine is on the right side of the header on the LPP site.

Yes, I’m quite aware of how FF power is generated, but the point of the thread is that there is lost heat, waste heat, that might be expoited. If efficient direct conversion of heat to electricity was possible, that might add to overall efficiency. Some have suggested Peltier thermoelectrics, and the sonic tech is a new approach to the same idea.

[Viking Coder]

An FF engine does not generate any significant amount of heat. The pulsed magnetic field constricts pinpoints of gas into plasmoids & those pinpoints is where the fusion occurs. The tokamak/ITER is the method that requires a sustained high temperature plasma.
https://focusfusion.org/index.php/site/article/heat/

The plasmoids have a top radius of 0.0018 cm.
https://focusfusion.org/index.php/site/article/re_analysis_of_texas_data/

Decaborane density is 950 kg/m^3.
http://www.webelements.com/compounds/boron/decaborane_14.html

plasmoid volume: 2.4 x 10^-8 cm^3
decaborane in plasmoid: 2.3 x 10^-8 g

I cannot find the heat capacity of decaborane in a freely available source, so I’ll use an absurdly high estimate of 100 J/g-K. Boron has a heat capacity of ~2 J/g-K at 600° K.
http://www.efunda.com/materials/elements/HC_Table.cfm?Element_ID=B

Based on that assumption, heating the decaborane in the plasmoid to 1 billion K imparts 2000 J (rounded down) of heat energy into it.
heat capacity calculator: http://www.ausetute.com.au/heatcapa.html

At a 1 KHz pulse rate that is 2 x 10^6 J/s or 50 kWh/day. Over the same time period, the engine generates 120,000 kWh of electricity.

The heat generated is less than 0.05% of the electricity recovered from the particle beam & x-rays.

The amount of heat produced can raise the temperature of 1 liter of water 30 K per minute.

[jamesr]

Not sure about some of your figures there.

Decaborane density is 950 kg/m^3.
http://www.webelements.com/compounds/boron/decaborane_14.html

You quote here the density of solid decaborane – this has nothing to do with the the density of the plasmoid or the average gas density in the chamber.

From http://arxiv.org/ftp/arxiv/papers/0710/0710.3149.pdf
Total input energy in this example is 14.6 kJ, x-ray yield is 9.5 kJ and beam yield is 13.4
kJ, so total output energy exceeds input energy by a ratio of 1.57. Preliminary estimates
indicate that energy conversion of both the x-rays and the ion beam can reach 80% with proper
design, so that net energy production with close to 50% thermodynamic efficiency should be
possible, if other losses in the entire system can be reduced to levels small in comparison.

If total energy output ratio is 1.57 and you can extract 80% of that for electricity then the remainder will ultimately end up as heat in the system somewhere. Whether that’s in the device itself or the surrounding shielding.

If electricity output of a device is 5MW then there will be 5/0.8=1.25MW of losses – ie. heat to dispose of. Even if the conversion efficiency got up to 90% then there is still 10% not being converted which has to end up somewhere. I don’t reckon anyones wildest dreams would think the heat would only be 0.05%

A key challenge as I see it is that unlike in tokamaks where the plasma is kept away from the walls of the chamber, in a plasma focus the plasma will be touching the walls – heating them up and cooling itself down.

In response to Brian:

No, the whole plasma has to be kept quite hot

I guess its a question of how hot. I thought the overall plasma would cool between pulses to of the order of 10,000K and recombine partially. But the electrodes need to be kept under ~1000K.

James

[Lerner]

Actually, preliminary calculations indicate the background plasma, the plasma in the whole vacuum chamber, will cool to something like 2,000 to 3,000 C between pulses. It just has to be hot enough to the boron will not precipitate out, which is a very complicated question of chemistry and dynamics. The electrodes propbaly have to be kept below 800 C to prevent rapid erosion.

[belbear42]

Brian H wrote:

A FF engine generates electricity through particle beam & x-ray recovery rather than heat extraction. This is why the construction cost is so dramatically lower.

A decelerator, as opposed to a particle accelerator, is put in the line of the tight pulsed beam of charged alpha particles (He nuclei) that is the result of the pB11 fusion. More electricity is generated by passing the x-rays through a shell of thin metallic foils, with the electrons captured on wires held at negative voltages.

https://focusfusion.org/index.php/site/article/35/#el
https://focusfusion.org/index.php/site/article/simulation_results/

An artists’ rendition of the FF engine is on the right side of the header on the LPP site.

Yes, I’m quite aware of how FF power is generated, but the point of the thread is that there is lost heat, waste heat, that might be expoited. If efficient direct conversion of heat to electricity was possible, that might add to overall efficiency. Some have suggested Peltier thermoelectrics, and the sonic tech is a new approach to the same idea.

Actually, the very concept of a FF power plant allows many direct uses of “waste heat” that are beyond the possibility of a large fossil fuel, fission or tokamak fusion plant. Given its small size and high safety, the FF power plant can be placed very near the power consumers. And practically everyone who needs electricity also needs heat.

For instance, a large hospital can have its own fusion power plant that generates half as much thermal power as electricity (assuming a 66% overall efficiency). This heat is then used for heating the buildings, laundry, sanitary hot water, sterilizing equipment etc… The same can be true for a community, a factory or a ship. In many cases the waste heat will not even be sufficient for the thermal demand and additional electric heating may be necessary.

Much depends on the “grade” of generated waste heat. Temperatures above 100�C can generate steam, (and thus drive turbines) which is considered “high grade”, while below boiling point it’s rather “low grade” heat that still can be useful for household use.
A FF power plant will generate both: high-grade heat from the reactor itself (vessel wall, electrode cooling, residual beam energy) while waste heat from the various electrical components (switches, capacitor banks, inverters, transformers..) will be very low-grade. In present-day power equipment this kind of heat is not used at all, rather vented through air-cooling.

[belbear42]

Lerner wrote: Actually, preliminary calculations indicate the background plasma, the plasma in the whole vacuum chamber, will cool to something like 2,000 to 3,000 C between pulses. It just has to be hot enough to the boron will not precipitate out, which is a very complicated question of chemistry and dynamics. The electrodes propbaly have to be kept below 800 C to prevent rapid erosion.

That looks pretty hot in there. Cooling the vessel wall seems very obvious but how are you gonna protect those flimsy thin X-ray capturing sheets of metal from melting in that kind of environment? Running coolant tubes through them seems to defeat their very purpose.
And what kind of temperature will the X-ray transparent inner electrode get, which does not only gets the heat burden from the plasma sheets but also has to receive the emitted high-energy electron beam?

Maybe one can build that electrode with coolant channels through it, like Rocketdyne does with those rocket engine combustion chambers and exhaust nozzles.

Chris

[Lerner]

The anode, the inner electrode will absolutely have to have helium coolant tubes running through it and will be the toughest engineering problem. The x-ray converter will be further away. Preliminary calculations indicate that the coolant tubes would not have to be so closely spaced as to cut back on the efficiency, but there are some challenges here too.

[jamesr]

Lerner wrote: The anode, the inner electrode will absolutely have to have helium coolant tubes running through it

If the coolant is helium – I’m assuming then it enters as liquid helium at cyrogenic temperatures. With such a massive temperature gradient through the anode this I would think would have implications for the conductivity. The combination of lower conducivity at the hot surface and the relatively higher conducivity in the cool core of the anode, goes against the normal ‘skin effect’ of the effectively high frequency pulse of current flowing mostly near the surface.

Has any modeling been done to incorporate the temperature differentials on the electrical behaviour of the anode.

I have been playing around with a trial version of Comsol http://www.comsol.com recently and it would seem ideal for this type of modelling.

James

[Lerner]

No, we were considering helium gas at high pressure. If you have modeling capabilities, this is very important. We have had two grad students looking at this, but they have had trouble finding the right tools. Could you please contact me directly about this at elerner@igc.org?

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