Measurements of Ion Energy/Temperature

[Rezwan]

From the LPP April 2010 Technical Report 2.

Analysis of shots we did in March gives more convincing evidence of high ion energies, certainly more than 40 keV (440 million degrees) and probably above 65 keV in the best shot (715 million degrees). These are very encouraging results, as they are as good as or better than those obtained in Texas at peak currents that were nearly twice as high. This note is more technical that our others have been, but this is necessary to make clear how we arrive at our conclusions.

Read full report to discuss.

[Aeronaut]

Very good signs, indeed. It’s up on FB now.

[QuantumDot]

What are the requirements for the other fuels like helium 3, and how does the current density compare to that required net energy? because if its just a matter of increasing current then its just a matter of time until you guys can finally say that you net power. and that will have to be something like the moon landing in that everyone will want to remember the day.

[Aeronaut]

QuantumDot wrote: What are the requirements for the other fuels like helium 3, and how does the current density compare to that required net energy? because if its just a matter of increasing current then its just a matter of time until you guys can finally say that you net power. and that will have to be something like the moon landing in that everyone will want to remember the day.

He3 isn’t on this year’s hit list. Once we show repeatable pB-11 burns, unity with a nearly unlimited supply of fuel should be within striking distance this year.

[Tulse]

But theoretical unity should be easier to demonstrate with He3, or even deuterium, right? The FF device isn’t designed to extract useful energy out of these reactions, but it should be able to show theoretical over-unity with these fuels at much lower temperatures than pB11. From a funding/publicity perspective, is there any value in demonstrating over-unity with these fuels before going to pB11, or would those just be distractions?

[Aeronaut]

Tulse wrote: But theoretical unity should be easier to demonstrate with He3, or even deuterium, right? The FF device isn’t designed to extract useful energy out of these reactions, but it should be able to show theoretical over-unity with these fuels at much lower temperatures than pB11. From a funding/publicity perspective, is there any value in demonstrating over-unity with these fuels before going to pB11, or would those just be distractions?

Since we’re on Goal #6, which includes “heavier gasses”, helium3 may be included, but I doubt it due to all the potential for that rare and expensive fuel to confuse things.

Goal #7 is to demonstrate the pB-11 fusion that FF-1 was designed for, and Goal #8 results from tweaking it until the neutron tof detectors confirm that more energy came out than went in to start the fusion reaction. My guess is that LPP’s going to have some amount of over unity in the bag before announcing unity.

The drift tube’s Rogowski coils would be a nice addition to the diagnostics, but they aren’t absolutely required to demonstrate net theoretical energy.

[QuantumDot]

I understand your point but since there is a lot of helium 3 on the moon and supposedly on mars it would be one reason to go and it would encourage funding into DPF and other advanced fusion projects with advanced fuels.

[Aeronaut]

QuantumDot wrote: I understand your point but since there is a lot of helium 3 on the moon and supposedly on mars it would be one reason to go and it would encourage funding into DPF and other advanced fusion projects with advanced fuels.

First we have to power the ships. 😉

[Tulse]

I’d be curious to see some solid analysis of the economics of harvesting lunar He3 for use in terrestrial fusion plants. My guess is that the mining, He3 extraction, and transport costs would vastly outweigh any economic advantage of using He3 versus conventional D-T fusion reactions, much less pB11. I’d wager that, if we had such in-space industrial capabilities available, it would make far more sense to construct solar power satellites instead.

[QuantumDot]

Here is a file from MIT on the expected price of helium3 taken from the moon or from nuclear decay. but from what i say they both need a temperature of about 100keV so boron11 should be cheaper, but at an expected energy price of about 7 dollars a gallon for the equivalent energy its better then gas but not boron.

ocw.mit.edu/NR/rdonlyres/Nuclear…/22…2006/…/helium3_fusion.pdf

the file is too large for me to attach

[Augustine]

QuantumDot wrote: Here is a file from MIT on the expected price of helium3 taken from the moon or from nuclear decay. but from what i say they both need a temperature of about 100keV so boron11 should be cheaper, but at an expected energy price of about 7 dollars a gallon for the equivalent energy its better then gas but not boron.

ocw.mit.edu/NR/rdonlyres/Nuclear…/22…2006/…/helium3_fusion.pdf

the file is too large for me to attach

Neptune has helium 3 in abundance. I think that any fusion fuel that leads to a reactor with Q > 1 will win. If it is fusion then aneutronic that is nice but I think that human society can live with neutrons being produced.

Q > 1 and preferable Q > 3 (to give the engineers room to be lazy and to save money) is all that really matters. If you can demonstrate Q > 1 and provide the theoretical foundation then you have done something nobody else has done and the whole world will notice.

[Tulse]

I’ve done some back-of-the-envelope calculations from:

http://www.asi.org/adb/02/09/he3-intro.html

I get that to meet the energy requirements of the US for a year, one would have to strip mine 200 square kilometres of moon surface to a depth of three metres, digging up and processing using energy intensive processes about two billion tons of regolith to get the 25 tons of He3 needed (He3 is 13 parts per billion in the regolith). All of this will have to be done using heavy duty industrial mining equipment sent into space and landed safely on the moon, and the resulting material will need to be lifted off the moon surface and landed safely on earth.

For reference, strip-mined coal costs about $25/ton, which has to be close to how much it costs to simply move that much material. So if we were simply mining He3 on earth, it would cost approximately $50 billion just to move an amount equivalent to the regolith needed. This ignores the processing requirements, which are massive (since, unlike coal, all that regolith has to be heated to 600 C and the boiled off He3 captured), and ignores that we have to get equipment to move two billion tons of regolith onto the moon, and get the He3 back.

I cannot imagine any reasonable near-term technological advances that would make such a proposition anywhere near an affordable solution. Certainly it would be far cheaper to build solar power satellites, or thorium-based reactors, or vastly expand solar/wind/tidal/wave/geothermal generation.

Or successfully build pB11 fusion generators.

[QuantumDot]

In an article published in 2004[8], S. Son and N.J. Fisch identified a possible iginition regime for p-11B and D-3He, in which ρ > 105 g/cm, Ti =~ 200 keV and Te =~ 30 keV; for p-11B, the optimized fuel concentration overcoming the Bremsstrahlung losses would be nB/np = 0.3[9].

Hydrogen-boron fusion requires ion energies or temperatures almost ten times higher than those for D-T fusion. For given densities, the reaction rate for hydrogen boron achieves its peak rate at around 600 keV (6.6 billion degrees C) while D-T has a peak at around 66 keV (730 million degrees C). In addition, the peak reaction rate of p-11B is only one third that for D-T.

http://z-fusion.net/spip/spip.php?article61

So depending on the density it look like they could already do D-T fusion, but for p-11B you want about triple the average Ti temperature.

[Brian H]

There are a couple of FF tricks here that change the numbers. First, the brehmstrahlung is minimized by tweaking the ion/electron energy levels so they fall in a “gap” where ions can’t accelerate the electrons and generate X-rays. Second, temperature is measured in electron volts, and tiny-ness is FF’s friend; it’s not like raising the temp of a containment chamber; the relevant energy levels are attained within a microscopic plasmoid, which self-contains with EM fields.

As of the date of this writing, results for generating the temps and compressions needed are coming in even better than theory predicted.

[jamesr]

Brian H wrote: Second, temperature is measured in electron volts, and tiny-ness is FF’s friend

I’m not quite sure how you think the units you measure something in suddenly changes the physics of what going on, but I get your general point.

On a separate topic, one thing I came across today in a talk about astrophysical plasmas, was that in magnetic reconnection (ie where a a twisted or opposing field changes topology), the release of magnetic energy to the particles causes them to be accelerated to supra-thermal speeds. This mechanism of heating ions & electrons as the plasmoid forms could play a crucial role in the dynamics. In that you cannot consider the plasma in the plasmoid as it forms to have a specific temperature, as such, because the dynamic have forced it well out of a Maxwellian thermal distribution. The density and collisionality of the plasma probably means it will thermalise again within a very short time, so it may be insignificant, but then again this seed population of fast ions could propote more fusion, or on the other hand a population of fast electrons created by this process could promote extra bremsstrahlung & have a negative effect.

It seems the more I learn about plasma physics the less you can predict by simple analysis. The only way to really tell is to do a non-linear simulation to test the hypothesis, and even then it only tells you about the particular instabilities/modes that can be accounted for in whatever simplified model you are using.

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