[jamesr]

The other main fusion journals to follow are:

Plasma Physics and Controlled Fusion (PPCF) http://iopscience.iop.org/0741-3335
Physics of Plasmas (POP) http://scitation.aip.org/content/aip/journal/pop
and to a certain extent the more general
Physics Review Letters (PRL) http://journals.aps.org/prl/

James

[jamesr]

ikanreed wrote: PB11 by 2015? Sounds ambitious.

That’s what I thought. The plan outline looks OK up to September, but I suspect issues will arise handling Beryllium.

Also, I’m not sure how the peak temperature will suffer as target density is increased, ie. if a 100-fold increase in density is achieved it would not equate to a 100-fold increase in yield.

[jamesr]

Its not even “more energy than was absorbed” really, as they’re just counting the proportion absorbed in the compressed core of the pellet not the large fraction absorbed in the ablative outer layers (or by the hohlraum).

As far as I’m aware the big achievement is that the experimental yield is only a few percent away from the simulations – something that has dogged them for years. If the simulations now match that indicates they mostly understand the processes involved.

[jamesr]

I just sent an email to add my name.

James

[jamesr]

vansig wrote: ok, so i still dont have the actual figure for % yield for carbon-11, but if it were 0.1%, then the amount in a reactor when you shut it down will equal the equilibrium value reached during continuous operation; as above, we have 7.18 x 10^18 reactions per second; hypothetically * 0.001 = 7.18 x 10^15 carbon-11 atoms created per second. (x 20.334 minutes = 8.76 x 10^18 atoms created during one half-life period).
at equilibrium, decay rate equals creation rate, so there would be twice this, or 1.752 x 10^19 atoms in the reactor, when you shut it down, or 320 micrograms.

make adjustments for actual yield

To put it in context another way: If you were standing 1m from a naked source of those 1.7×10^19 atoms of C-11 with no shielding for a few hours (ie long enough for pretty much all of it to decay) then the dose you’d get would definitely be lethal.

Working as follows:

Most C-11 decays via positron emission – with a range of energies averaging a few hundred keV. the positron will then annihilate producing two ~511keV gammas back to back.
If we discount the positrons themselves (since they won’t get very far) and just have the dose due to the gammas

gamma energy = 1.022MeV = 1.022e6*1.6022e-19 = 1.64e-13 J
1.752 x 10^19 atoms * 1.64e-13 J/decay =2.87e6 J total

fraction of surface area of sphere of a person at 1m ~ 8%

8%* 2.87e6 J = 2.30e5 J

energy distributed over ~75kg => 2.3e5/75 ~ 3000 J/kg

So you’d get very roughly 3000Gy dose!!!

Of course you’d actually get nothing like that much in reality since most of the decay energy would end up being absorbed close to the source and converted to heat, but still you get the idea that it’s a really good idea not to go in and service the device for at least 8 hours after turning it off.

After 8 hours (or ~24 half lives) the activity will have dropped to 0.5^24 =6e-8 times lower, so your dose working for a day after waiting the first 8 hours would be around 3000*6e-8 = 0.2mGy which is liveable, but still too high to meet the ALARP principle

If you wait an extra few hours, so 12 total (36 half lives) then the remaining potential dose drops to roughly 3000*1.4e-11 or around 40nGy – much more acceptable.

The question is: Is C-11 the longest lived of the by-products? The design of the device, down to the last nut & bolt will need to be considered when working out the actual dose limits. For example, some 1st & 2nd Gen fission reactors had a little cobalt in the structural steel alloys – this with its ~5yr half life now makes up a major part of the decommissioning burden.

[jamesr]

Kind of unrelated – but it really bugs me when organisations quote figures like 500,000 deaths from cancer each year without qualifying it or putting it in any sort of context.

So if we say the USA has roughly 300million people and they live and average of 80 years (just ballpark figures). Then the annual replacement rate is 300m/80 = 3.75m. So the figure of 500,000 would mean only ~13% of people die from cancer. Since everyone has to die from something then all that means is those dying from cancer are not dying from anything else. Wanting to reduce the death rate from cancer implies we want to grow the population. Only if we ensure a simultaneously reduced birth rate does it lead to just living longer.

In actual fact the birth/death +immigration/emigration rates are not equal, with the total deaths in the US lower at only ~2m per year. The full breakdown from the CDC for 2010 is

Heart disease: 597,689
Cancer: 574,743
Chronic lower respiratory diseases: 138,080
Stroke (cerebrovascular diseases): 129,476
Accidents (unintentional injuries): 120,859
Alzheimer’s disease: 83,494
Diabetes: 69,071
Nephritis, nephrotic syndrome, and nephrosis: 50,476
Influenza and Pneumonia: 50,097
Intentional self-harm (suicide): 38,364

http://www.cdc.gov/nchs/fastats/lcod.htm

[jamesr]

The other thing I’d suggest is a good pair of closed back headphones for the operator to wear. So they are listening to what the mic(s) are actually picking up – not the ambient sound in the room. It then becomes obvious is a fridge motor, AC unit, plane overhead etc is adding unnecessary background noise. Also watch the audio level meters (most cameras have an option to show them as an overlay).

It’s not worth paying over the odds for ‘prosumer’ lapel mics, anything ending in an unbalanced 3.5mm mini-jack is limited in quality. Only if your recording device has balanced XLR inputs can the quality of a better mic (&preamp;) be noticed. A cheap $20 mic will be easily good enough for recording a piece to camera in a closed room with little background noise if used properly.

So if you’ve got a $200 budget spend $150 of it on the headphones and only $50 on the mic!

Even the best kit will give appalling sound quality if you don’t set it up properly, and most common mistakes can be picked up just by listening while you’re recording.

[jamesr]

Passed my viva today! So am now Dr Robinson ! yay! (with the expected few minor corrections).

Although my research has been on a particular aspect of tokamak related fusion it has always been the big picture of the goal of achieving fusion by whatever means that has inspired me. I Just want to take this opportunity to thank the contributors to this forum over the years to keep me thinking about the issues not just from the scientific perspective, but also the societal implications of fusion in the wider world.

[jamesr]

Oh and of course I found a place to mention pB11 fusion and dense plasma focus’ in the introduction, citing Eric’s 2011 paper.

[jamesr]

Welcome!

Feel free to ask away. As you probably realise some people here are more closely involved with LPP, and can answer specific questions. Others, like me, have just been following things from a distance, and try to chip in on the general physics.

[jamesr]

Thanks for that – I think I realised it was wrong a while ago but never got round to correcting it. They are both printed my the same publisher and use the same layout which is what confused me I guess. Both are good books although expensive so you need a well stocked library have them available.

[jamesr]

Henning wrote: Electrons fly off in the other direction than alpha particles, because of the magnetic field (right-hand rule).

It’s not the magnetic field directly. As far as I understand it, it is when the concentrated magnetic field created by the pinch collapses, the rapid change in magnetic field creates an electric field by Faraday’s law dB/dt=-curl(E).

The symmetry of the highly curved magnetic field creates the electric field such that it is directed along the axis of the DPF, accelerating the ions in a cone of around 6degrees away from the anode and the electrons in the opposite direction. However, the electrons have much lower inertia and as they start to be accelerated scatter off ions transferring some of their energy to them, before starting to accelerate down the E-field again. So rather than being able to build up into a coherent beam, a large fraction of the electrons don’t make it out of the plasmoid. Some do make it out and are accelerated enough to blast a little pit in the anode.

After the collapse of the field the plasma will of course react to re-establish quasi-neutrality where any imbalance has built up, but this is on a longer timescale.

It is also worth reiterating the formation of the beam of ions is nothing to do with the fusion or alpha particle directions. Ion beams are created in all DPF’s that manage to form a strong pinch, even with un-reactive gasses. Any fusion alphas (or other charged products in the case of other reactions), which although initially moving much faster than the rest of the ions in the plasma are still confined by the magnetic field of the plasmoid. It will take them roughly 20 collisions to dump most of that kinetic energy and thermalise with the rest of the plasma (heating it in the process) but this occurs on the pico-second timescale rather than the tens of nanosecond lifetime of the plasmoid.

[jamesr]

Not unexpected, but when you compare a project like NIF to say the recent successes of the LHC at CERN or landing the Curiosity rover on Mars, it puts into perspective how hard controlled fusion is. And hopefully make any breakthrough by them, ITER or LPP all the more rewarding in future.

[jamesr]

Just watching the video http://www.youtube.com/watch?v=Mg3KU8pkoEc. I see the shock issues are still there to some degree. Do you not have any shock viscosity term? I thought this would be essential, unless you go to a more involved (but much better physically) Godunov type scheme with an iterative Riemann solver.

It would also be interesting to see in addition to the density & temperature(s) evolution, the pressure, magnetic pressure and total pressure evolution (and plasma beta), as there are stages where across the shock it switches from high temperature/low density to low temp/higher density suggesting the shock in pressure is much weaker. This is also, I seem to remember, why a lot of codes use density and ion/electron pressure as their fundamental variables or even density and total energy, rather than density & temperatures.

[jamesr]

benf wrote: The link to the PDF is fixed now, sorry for the hang up.

Thanks Ben.

Warwick/Eric/John,

I realise the paper is still work-in-progress, and the model as a whole seems a pretty solid 1D scheme. But one thing struck me, you seem to be assuming the ions are singly charged, so the quasi-neutrality condition is simply n = n_e = n_i, and subsequently the current is J_z=qn(v_e – v_i). Would it not be easier to set the ion species charge as q=Ze, so
n=n_e = Zn_i and J_z=en(v_e – Zv_i). The step up from a deuterium plasma to one with a higher Z_effective is then carried through in all the equations.

You can say these simulations are for deuterium so Z=1, but having it explicitly in the equations always seems clearer to me.

[em]NB: read underscores as Latex style subscripts[/em]

I look forward to seeing the full results when finalised

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