Steps towards FF-1 Feasibility

[Joeviocoe]

Feasibility to become a net power producer fusing pB11 aneutronic fuel…. as outlined by Eric Lerner in the May 1st 2012 Agrion Webinar.

So as I understand it, to gain higher yield and to attain “feasibility” the following steps are being done over the course of the next year (2012):

1) The “teeth that chew the sheath” tungsten crown to regularize the filaments – 10-100x yield
2) Full power output of Capacitors and to ‘Imitate’ the heavier mixuture of pB11 by using Deuterium/Nitrogen.
3) Shorter Electrodes, slower run down, more fill gas.
4) New Raytheon switches for more Current from capacitors – 10x yield.
5) Switch to pB11 (incrementally higher percentage from the D/N mix) – 15x yield.
Goal: 30 kJ* gross fusion energy per shot proves feasibility of a positive net power output Generator using aneutronic fuel!
*A 5MW production reactor would have about 66 kJ gross fusion yield per shot*

Is this about right?

[zapkitty]

I haven’t gotten at that presentation yet but at least nothing you’ve listed is out of line with what has been discussed here, so… 🙂

Joeviocoe wrote:
4) New Raytheon switches for more Current from capacitors – 10x yield.

After all the switch history with LPPX I wonder what these are like… anyone have a link?

[asymmetric_implosion]

That’s an ambitious list.

The switch upgrade is a great idea. I hope these Raytheon switches are the ones developed for the next gen marx generators and LTDs. If they are, the switches are highly reliable and can hold off far more than 45 kV using only dry air. The data from the LTD tests at 200 kV, 1 Hz were very impressive. I know Raytheon recently purchased K-tech. K-tech was involved with the LTD work at Sandia for the 1 MA LTD modules. Moving up to the theoretical limit of the machine would be interesting.

The nitrogen/deuterium mixing should be interesting. N2 is an interesting gas. It will be an interesting study since most people shy away from heavy diatomic gases in a PF. I’m not a fan of oxygen in my PF. My limited experience with nitrogen was mixed. Some days it ran really well and other it was poor. There was no obvious rhyme or reason to the whims of the machine when we never broke vacuum.

I hope the yield number is wrong…66 kJ per shot with a 5 MW plant means 75 Hz operation…so 100 Hz operation after all is said and done. To my knowledge, one one group has operated a PF >100 kA near the 100 Hz level and it required substantial effort and the yield was well below the optimum with soft x-rays. There are substantial problems moving up in repetition rate. I’m fighting a few right now as we move one of our machines from 1 Hz to 10 Hz. It is not as straightforward as one might believe. A combination of heat, residual ionization, anode erosion and chemistry have hampered our efforts to demonstrate something near the 1 Hz neutron yield at 10 Hz. The anode erosion has been a killer. Our little machine at ~60 kA is eroding anode material at ~10 ug/shot. One might laugh at this value but the beam can be highly focused on a small part of the anode. I’ve bored holes over an inch deep into SS304 anodes. According to e-beam scaling predictions (Stygar 1982), a 1 MA PF will be far worse. If someone is going to say use a ceramic, don’t bother. Ceramics are the devil. The anode base must be metal.

The engineering issues have become far worse than the physics problems with encountered. Repetition rate introduces a set of new problems that a few shots a day will not encounter. Just a heads up in case anyone thinks it will get easier once Q>1 is demonstrated.

[Joeviocoe]

asymmetric_implosion wrote:
I hope the yield number is wrong…66 kJ per shot with a 5 MW plant means 75 Hz operatio

That was taken from their Sankey diagram as “gross fusion yield” and after reasonable losses are taken away, they will get 5 MW @ 200 Hz.

asymmetric_implosion wrote:
Ceramics are the devil

😛

[Joeviocoe]

Yes, engineering problems take much longer, require more people, and result in much more frustration. I am skeptical that 5 or 6 years would be enough to work out all the problems. But LPP is counting on a flood of money and personnel around the world to be working on those engineering concerns once feasibility is proven. When (if) this thing hits the news. A low cost, proliferation free, no harmful radiation, abundant, small, quiet, ‘holy grail’ of energy solutions…. governments will focus all efforts to get that anode erosion problem taken care of.

[zapkitty]

Joeviocoe wrote: … governments will focus all efforts to get that anode erosion problem taken care of.

Actually, as has been mentioned before when this question has been raised, per LPP the electron beam is not expected to make it out of the plasmoid in an all-up p11B configuration.

It will exist, as it is paired with the ion beam just as in a normal DPF, but it is expected to expend its energy heating the plasmoid and increasing the fusion rate.

While the anode is going to have a lot to deal with, it is thought that the concentrated damage from beam strikes is not going to be the deal it is with current DPF units.

[break]

Joeviocoe wrote: governments will focus all efforts to get that anode erosion problem taken care of.

But even goverments can’t do magic. Exspecially goverments can’t do magic!

[Lerner]

To be more exact, we expect that with higher plasmoid density, msot of the energy of the electron beam willbe absorbed before the elctrosn leave the plasmoid. Andoe erosion is still a major concern as the anode must be kept cool. Cooling is one of the three main engineering challenges.

[break]

And the other two are…?

[Joeviocoe]

break wrote: And the other two are…?

1) Several MW of waste heat

2) Very high efficiency of Ion Beam energy conversion. Roughly 80%

3) Energy extraction from X-rays using the photoelectric effect. The science is WELL known, but I don’t think engineers ever had reason to build such a thing. X-rays are usually produced from other power sources because X-rays are desirable. This, I believe, would be the first device that is the other way around. LPP wants greater than 80% efficiency with this as well.

http://www.youtube.com/watch?v=FSYOIayQ7bI

@ 4:02

[Joeviocoe]

Lerner wrote: To be more exact, we expect that with higher plasmoid density, msot of the energy of the electron beam willbe absorbed before the elctrosn leave the plasmoid. Andoe erosion is still a major concern as the anode must be kept cool. Cooling is one of the three main engineering challenges.

What are the physical principles that allow the electron beam to be absorbed so well? Is it by shear density that prevents the electrons from leaving the plasmoid? Or is it because the + charge of Boron is 5 times greater than the Deuterium and thus 25 times (squaring law) greater at braking those electrons and converting their energy to bremsstrahlung?

[asymmetric_implosion]

Pinch/plasmoid break up is being neglected. The e-beam can escape the pinch during breakup of the plasmoid. The damage can be substantial and it might be even worse if the electrons are high energy. You can superheat a larger volume of metal and erode more mass. It might be possible to reduce the beam current but eliminating it will be a problem. I believe the e-beam confinement by the LPP model is due to extremely large magnetic fields in a toroidal geometry. This works well until the plasmoid falls apart. Then you have hot electrons running around everywhere.

200 Hz operation is problematic for many reasons. We are finding that operating above 5 Hz is not intuitive as it was up to 5 Hz. We are thermally managing a Mo anode to control the temperature, but temperature control alone is not enough. The e-beam erosion can do two things: release gases trapped in the metal like hydrogen, oxygen and other common gases, erode the anode material into a vapor that cannot plate out before the next shot. High Z vapor like tungsten or Molybdenum seems to help the neutron yield as was reported for high Z inert gas/deuterium mixes. The current thinking on our experiment is at high repetition rate the vapor density is beyond the optimum mixing ratio which depresses the fusion yield. LPP might be able to push beyond 5 Hz if the e-beam is suppressed but plasma erosion will eventually supply enough material corrupt the gas and spoil the fusion gain. Flowing the gas a modest rates is not enough to maintain a clean environment. Even the lithography folks operating at 80 Hz had some problems with this. The solution they found was to increase the anode size above the optimum and operate with reduced yield. If I understand LPP’s operating regime, it relies on small anode diameters and high pressure. Increasing the anode size for a fixed current requires operating at lower pressure. The problem is somewhat constrained due to the PF physics.

Relying on governments to get this working is a joke. Resources are key and private resources would be better suited to drive this forward. I don’t know if a global collaboration will come to pass if successful, but the problems are materials limited. All fusion concepts have materials problems and they are not addressed because most fusion folks have a plasma background rather than a materials background. I agree that more can be done but materials are going to be a limiting factor in any fusion device. I’ve done a small materials survey and no material I’ve run across can withstand the e-beam and/or plasma erosion without sacrificing grams of material for the 1E7 shot operation at 100 Hz and 60 kA.

[break]

Joeviocoe wrote:

And the other two are…?

1) Several MW of waste heat

2) Very high efficiency of Ion Beam energy conversion. Roughly 80%

3) Energy extraction from X-rays using the photoelectric effect. The science is WELL known, but I don’t think engineers ever had reason to build such a thing. X-rays are usually produced from other power sources because X-rays are desirable. This, I believe, would be the first device that is the other way around. LPP wants greater than 80% efficiency with this as well.

http://www.youtube.com/watch?v=FSYOIayQ7bI

@ 4:02

Thanks 😉

[break]

asymmetric_implosion wrote: Pinch/plasmoid break up is being neglected. The e-beam can escape the pinch during breakup of the plasmoid. The damage can be substantial and it might be even worse if the electrons are high energy. You can superheat a larger volume of metal and erode more mass. It might be possible to reduce the beam current but eliminating it will be a problem. I believe the e-beam confinement by the LPP model is due to extremely large magnetic fields in a toroidal geometry. This works well until the plasmoid falls apart. Then you have hot electrons running around everywhere.

200 Hz operation is problematic for many reasons. We are finding that operating above 5 Hz is not intuitive as it was up to 5 Hz. We are thermally managing a Mo anode to control the temperature, but temperature control alone is not enough. The e-beam erosion can do two things: release gases trapped in the metal like hydrogen, oxygen and other common gases, erode the anode material into a vapor that cannot plate out before the next shot. High Z vapor like tungsten or Molybdenum seems to help the neutron yield as was reported for high Z inert gas/deuterium mixes. The current thinking on our experiment is at high repetition rate the vapor density is beyond the optimum mixing ratio which depresses the fusion yield. LPP might be able to push beyond 5 Hz if the e-beam is suppressed but plasma erosion will eventually supply enough material corrupt the gas and spoil the fusion gain. Flowing the gas a modest rates is not enough to maintain a clean environment. Even the lithography folks operating at 80 Hz had some problems with this. The solution they found was to increase the anode size above the optimum and operate with reduced yield. If I understand LPP’s operating regime, it relies on small anode diameters and high pressure. Increasing the anode size for a fixed current requires operating at lower pressure. The problem is somewhat constrained due to the PF physics.

Relying on governments to get this working is a joke. Resources are key and private resources would be better suited to drive this forward. I don’t know if a global collaboration will come to pass if successful, but the problems are materials limited. All fusion concepts have materials problems and they are not addressed because most fusion folks have a plasma background rather than a materials background. I agree that more can be done but materials are going to be a limiting factor in any fusion device. I’ve done a small materials survey and no material I’ve run across can withstand the e-beam and/or plasma erosion without sacrificing grams of material for the 1E7 shot operation at 100 Hz and 60 kA.

So electrode erosion is a show stopper…

The question is: how long can one electrode be used? How many shots? 200 Hz -> 120 * 10⁶ shots per week. So one electrode needs to last at last 120 Million shots!

[asymmetric_implosion]

Anode erosion does not have to be a show stopper. As with any system, go in knowing it could be a problem and design for it. In my case, I didn’t consider e-beam a significant problem as my low rep-rate sources (~0.1 Hz) didn’t have any problems. Operating at 1 Hz all day for 10+ days showed a problem. We pulled an anode after 250,000 shots and found a deep bore hole in the anode that nearly broke out of our vacuum vessel. We thought refractory materials or ceramics would solve the problem. Ceramics were a miserable as they erode into gases and other things that made matters worse. We tried alumina and boron nitride. Refractory metals did a bit better but they were not the knight in shining armor we needed. The real goal should be to spread the e-beam out far from the pinch region (inches if not feet) and let the e-beam impact a specifically designed beam dump that will handle the e-beam. Our experiment does not allow us to do this so we have taken other steps that will work in the short term. Our next move is to implement a more reliable solution like magnetic deflection onto a beam dump. This should give us anode lifetimes that are on the order of our switch lifetime (~1E7 shots). For the purpose of illustration, our current solution is good for 50K to 100K shots. We need 100X increase in materials lifetime to make our source viable.

The LPP source could do better with plasmoid confinement of the e-beam but a switch that operates at 200 Hz for >1E8 shots and high voltage, high current is currently unavailable and again for materials reasons might not be possible. The solid state option is difficult to imagine working well at the 2-3 MA level with 50-100 kV on the bank. It is not impossible but you only get one case to screw up. Solid state will last forever (>1E9 shots if not 1E10 shots) if it is treated right but one bad step and it is done. It is my opinion that the switches will determine the tolerable lifetime for the other components.

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