[jamesr]

MAST, the spherical tokamak at Culham is due to get a Super-X divertor in its upgrade which starts next year.

http://www.ccfe.ac.uk/videos.aspx?currVideo=5&currCateg=0

[jamesr]

The other aspect to D-T fusion fission hybrid designs is that you can take a fusion reactor (whether ICF or MCF) that would not be able to achieve nett gain on its own, to a system that with the extra heat of the actinide fission (plus decay heat of fission products) makes a whole system that can generate nett power. However unlike a standard fission reactor it is sub-critical without the fusion neutrons so there is no chance of runaway chain-reaction.

So it has all the benefits of the accelerator driven sub-critical reactor ( http://www.world-nuclear.org/info/inf35.html ), but swapping the problems of designing a stable, efficient, high current particle accelerator with the problems of laser or magnet design.

[jamesr]

The neutrons are still much lower energy than the 14MeV ones emitted by the D-T reaction.

The idea is hydrogen in the water thermalises the neutrons so that by the time they diffuse through to the B10 they are sufficiently low energy to be captured. The B10+n capture reaction then releases gammas which is what the final few cm of lead is for.

There is also the slight chance that some neutrons will be captured by the hydrogen forming deuterium.

[jamesr]

Thanks for the links. I haven’t read them all, but in R. Petr et al’s paper their ‘high power’ is 1.5kJ input yielding 0.08% of X-rays (ie 12J).

Using the figures from Eric’s 2007 Tech Talk (http://www.youtube.com/watch?v=O4w_dzSvVaM 36m30s in) he had:
Peak I 2.0MA
Gross input: 13.1kJ
X-Ray/Input: 81%
Beam/Input: 98%
(Beam+X-Ray)/Input: 1.79

so 0.81*13.1 = 10.6kJ ie. ~1000x as much X-ray energy as these lithography devices. One or two orders of magnitude more and maybe erosion resistant materials can cope with a reasonable lifetime, But we are talking about 3 orders of magnitude higher fluxes. The end of the anode has got to absorb only a tiny fraction of the X-rays passing through it if it is going to survive. Basically that means Beryllium is the only candidate that comes close.

[jamesr]

I agree, if Be can be avoided that would be great.

However, for a device hoping for good fusion yields you need to be very careful that no high-Z ions can be eroded off and pollute the hottest part of the plasma as they will cause rapid cooling. But more importantly the pinch X-ray flux will be orders of magnitude higher than any ‘low power’ studies done before, and we need to be able to recover the X-rays in the onion. Which means the anode must be as transparent to them as possible, to avoid shadowing a large portion of the collecting area.

Having said that I wasn’t aware Molybdenum had been studied before – do you know the source paper(s)?

[jamesr]

Interesting paper but for EDM they have a peak current of 6A at 90V. Not really in the same ballpark as 2MA at 45kV.

[jamesr]

I doubt any kind of coating would be better than just solid beryllium electrode. The interface between the bulk and the surface would always be a weakness. I suspect by alloying the beryllium with other metals you may be able to improve some properties (at the expense of others) in order to optimise the electrical, physical and x-ray absoption characteristics.

Such as a beryllium-copper alloy with ~60% Cu by weight (ie mix of delta-Be2Cu and beta-Be phase grains) with other minor (<<1%) components such as Indium or Manganese. Then fine tweak the grain structure between surface and bulk by heat treating, giving a smooth transition from bulk to surface.

[jamesr]

Sorry to just link to Feynman again, but this snippet springs to mind http://www.youtube.com/watch?v=b240PGCMwV0

[jamesr]

you should watch Feynman http://www.vega.org.uk/video/programme/47

you cannot understand electrons without appreciating QED.

[jamesr]

As with any scaling, whether empirical or theoretical, it will have physical bounds. The I^4.7 scaling is very good but other than the effects mentioned above governing factors like the inductance of the circuit and so the rise time. If the peak current is increased much more the pinch forces on the conductors will create stresses beyond that any material can withstand. Also the Ohmic heating of the thin skin in which the current flows becomes an issue, causing differential thermal expansion and further material stresses.

[jamesr]

I think the first layout with the logos at the bottom worked better.

One comment: Although it may seem to clutter it slightly I think we should include citations wherever possible on any promotional material to back-up any claims made (such as the corporate coffee spending in this case). For reports & press releases they can be detailed directly in a footnote. For more graphical flyers & posters etc maybe the easiest way is to include a QR code graphic linking to a URL of the fuller referenced report on the website.

[jamesr]

malaga2022 wrote: What is the percentage of laser that is scattered by the plasma?

Magnetically confined plasmas are at such a low density that the chance of a photon scattering is incredibly small.
Typically for a Thomson scattering laser system you’d get back 1 photon for every 10^14 – so if the laser pulse is 3GW around 30 micro Watts get back to the detector.
or in percentage terms 0.0000000000001%

I’m not sure what you mean by the rest of your comment??

This give a bit more background on the systems used at MAST, JET and what is proposed for ITER
http://www-fusion-magnetique.cea.fr/ppe/TrainingWeekCulham/OpticalDiagnostics-ScatteringDiagnostics-MarkKempenaars.ppt.

The Tri-alpha plasma will be a little bit denser than a tokamak, so they can get away with a slightly less powerful laser, but the fundamentals are the same.

[jamesr]

That should be GeV not Bev.

Here’s a couple of related links
http://www.cenbg.in2p3.fr/heberge/MSPWorkshop/IMG/pdf/Grondin_LPTA_0510.pdf
http://arxiv.org/pdf/1105.3400

[jamesr]

malaga2022 wrote:
How tri alpha measures plasma temperature?

Ion temperature is found via a spectrometer looking at the doppler broadening of line emission. You also get the flow towards/away from the detector via the blue/red-shift of the line. NB since the deuterium will be fully ionized except at the very cool edge, it is normal to look for the transitions of impurity ions like carbon C6+ -> C5+. The measurement will be the average along the line of sight.

Electron temperature is done via Thomson scattering, whereby a high power laser pulse is fired through the plasma, a few photons are scattered off the electrons back to a another spectrometer camera looking for the doppler broadening of the scattered laser light. Here normally the laser & detector are arranged so you get a profile of temperature across the plasma. http://en.wikipedia.org/wiki/Plasma_diagnostics#Thomson_scattering

[jamesr]

Nice graphs.

Although at the temperatures achievable in any practical device only cross-section below 500keV incident energy is important. In particular for p-B11 it is the small resonance spike at 148keV that helps boost the overall reaction rate in the 10-100keV temperature range.

If you take these cross-section vs incident energy curves and average over a Maxwellian velocity distribution you get the more meaningful reaction-rate vs temperature graph.

Here is one from Wesson’s Tokamaks book which shows pB11 in comparison to DT DD etc, but doesn’t show all the Lithium reactions

Attached files

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