[jamesr]

In lieu of the google docs link working, can you email me the pdf directly. Cheers.

I wasn’t going to comment on the write-up until I’d read the full paper, but since asymmetric already mentioned it, I too am surprised a two/multi-fluid approach would capture the behaviour properly. The kinetic vs fluid debate rages on in most areas of plasma physics. My own research, for example, uses 3D two-fluid simulations for modelling turbulence driven oscillations in the steep edge density & temperature gradient region of tokamaks, where it wins out over gyrokinetics. It really depends on what assumptions you make to simplify it (I make a lot!!), and what higher moments you include in the energy, heat flux etc to close the set of equations.

The horrible radiation terms are definitely what makes the problem hard, and I guess are the main reason for going fluid rather than PIC.

I can sympathise with Warwick on the numerical difficulties of capturing the shocks properly, thankfully I don’t get those.

I too busy right not trying to write up my thesis, but I’d be interested to know the initial conditions for the simulation (if its not detailed fully in the paper) so it could be replicated in other codes, There is a new rad-hydro code being developed in my department using a new variant of an ALE (Arbitrary Lagrangian Eulerian) type method, which although aimed at laser-plasma interactions may one day be able to cope with DPF type conditions.

[jamesr]

The link to the pdf doesn’t seem to work for me.

[jamesr]

The way I see it is that you don’t consider the bremsstrahlung x-ray radiated as losses. There will be some other radiative losses that you can’t recover but if the onion works as well as is hoped a significant (>70%) of the x-ray energy in the 10-30keV range could be recovered.

The key issue for getting a reasonable fusion burn in the plasmoids is that the x-ray cooling is not so high as to cool the plasma faster than the fusion energy from the fast He-4 products can be redistributed in the plasma keeping it hot.

The initial tests with DD done so far have shown the radiative losses are not so high, such then the heating during the pinch can get the plasma hot enough for pB11 ignition (but at lower densities).

The next test is to repeat that temperature threshold with higher Z gases where traditionally the Z^2 dependence of the bremsstrahlung would mean the cooling will be much faster.

Todd Rider’s thesis http://dspace.mit.edu/handle/1721.1/11412 and subsequent work, showed that this bremsstrahlung issue effectively rules out all other fusion fuels except D+T, D+D, and D+He-3, and furthermore for nett gain has to be at or near thermal equilibrium. This is partly why I don’t believe any of the other innovative concepts such as polywells will work. However Rider did not take account of the effect of the quantization of electron cyclotron orbits in very strong magnetic fields http://en.wikipedia.org/wiki/Landau_quantization. This limits the transfer of energy from the fast ions to the electrons, and effectively keeps the electron temperature much lower than the ion temperature. Even so it is a tall order to reach the extreme fields needed to reduce the key collision parameter known as the Coulomb Logarithm from the standard value of 15-20 beyond even Rider’s most optimistic value of 5.

[jamesr]

annodomini2 wrote:
Air with a turbine is only practical up to about Mach 2.5 at which point the air temperature entering the engine is so high that it literally melts the engine.

You can use a pre-cooler such as the SABRE design from Reaction Engines in the UK http://www.reactionengines.co.uk/

They are aiming to be able to have one engine that can seamlessly accelerate from 0 through mach 5, then transition to using a small onboard oxygen tank to morph into a rocket for the last bit to orbit, then all the way back.

(incidentally they are based on the same site at Culham where the JET and MAST tokamaks are)

[jamesr]

This review article from a few years ago covers the history of the cluster (molecule-like) approach dating back to
Hafstad, L R and Teller, E (1938). The Alpha-Particle Model of the Nucleus. Phys. Rev. 54: 681.

http://www.scholarpedia.org/article/Clusters_in_nuclei

[jamesr]

The title of the article is a little misleading, I think. Whistlers (Right had polarised waves parallel, or slightly obliquely, to a magnetic field) are a standard part of MHD theory, and are known to travel faster than the local Alfven speed for short wavelengths
See http://farside.ph.utexas.edu/teaching/plasma/lectures/node51.html

The new thing here is NOT the speed of the wave, it is the mechanism that excites them, where the full kinetic description of what is going on in a shock front needs to be taken into account

[jamesr]

BSFusion wrote:

I should point out that, none of these 15 are obstacles to Bubble-confined Sonoluminescent-laser Fusion (BSF).

Good list – I agree these are all major issues for LIFE (Laser Inertial fusion Energy), but you have to remember that this is not the primary role of NIF.

From the NIF website (https://lasers.llnl.gov/programs/nic/):

NIC’s ICF experiments are designed to advance the National Nuclear Security Administration’s Stockpile Stewardship Program as well as basic high energy density science research in such fields as astrophysics, nuclear physics, radiation transport, materials dynamics and hydrodynamics (see Science at the Extremes). Other experiments will provide scientists with the necessary understanding of the physics underlying the use of ICF for safe, clean energy production (see Inertial Fusion Energy).

Fusion Energy is just under their ‘other experiments’.

Just to pick 2 points from your list (13 & 14) Laser technology has moved on enormously since NIF was designed – for example, new diode pumped lasers are much more efficient, resulting in less heat needed to be dissipated between shots. They are not quite there yet, but progress is good.

I’m sure someone could come up with an equally long list of points regarding your BSF concept. Have you submitted any papers to peer reviewed journal that cover it? I find the paper format easier to scrutinise than a patent application, since journals insist on being suitably succinct.

[jamesr]

As far as I know you would always need neutron shielding. The small proportion of side reactions is still enough to be concerned about, while the device is operating. In nuclear safety the principle is of “As Low as Reasonably Achievable” (ALARA) or in the UK its known as “As Low as Reasonably Practicable” (ALARP). Basically means if there is something you can do to lower the dosage and risk you should do it. Any regulator would insist on it.

So the DPF device (outside the onion but inside as much else as possible) would be surrounded by a water blanket doped with boron-10, or alternatively plastic shielding tiles like Boratron. The hydrogen in the water/plastic slows down the neutrons to a low enough speed that they can be absorbed by the B-10. This absorption releases gamma rays, so outside the neutron shield you need a further small amount of lead or high density concrete gamma shield.

[jamesr]

I was trying to maintain a list of papers using the zotero plugin for firefox, but I’ve been pretty useless at keeping it up to date.

Anyone can view it at https://www.zotero.org/groups/focus_fusion/items/
just request to join the group and I can add you as an editor as well.

In the mean time here’s a dump from it in bibtex form and a pdf report zotero can generate

https://files.warwick.ac.uk/jamesrobinson/browse#FocusFusion
(I tried to attach them to the post but I get “The file could not be written to disk.” error)

[jamesr]

There was an interesting talk by Francisco Suzuki-Vidal from the MAGPIE group at the IOP conference last month about radiatively cooled plasma jets, and I was wondering how good their GORGON MHD code would be at modelling a DPF (the initial phases of snowplow, shock, rebound etc, not the plasmoid)

This is the paper that goes with it – http://pop.aip.org/resource/1/phpaen/v19/i2/p022708_s1

[jamesr]

The article seems heavy on PR trying to convince the reader of the important contributions the US programs at PPPL and MIT are making to fusion plasma research (presumably to bolster their requests for dwindling DOE funding) , but does little to explain how with this new ‘discovery’ we will be able to design better tokamaks.

In a quick skim read through the PRL paper http://prl.aps.org/abstract/PRL/v108/i16/e165004 they take a simple cylindrical model with a chain of small magnetic islands around it, and work out the power balance from the ohmic heating within the island, the external heating flowing around it and the radiation emitted via bremsstralung & line emission from impurities. They find the scaling is roughly in line with the Greenwald limit on plasma density, which is proportional to the total plasma current.

They go on to mention the relationship between neoclassical tearing modes briefly at the end,

Additionally, radiation driven islands should be exacerbated in plasmas with high noninductive current fractions, since only the Ohmic current participates in heating
the interior of the island. This may explain the common practice of using ‘‘preventative electron cyclotron resonant heating’’ to avoid the onset of neoclassical tearing modes.
In fact, this phenomenon may partially explain the difficulty in finding a reliable predictor for the onset of neoclassical tearing modes because the radiation driven terms
are not considered in neoclassical island threshold analysis

But they completely fail to mention turbulence, which as far as I’m aware, is the primary way heat leaks into and out of island structures, as small eddies in the plasma flow on the scale of a few times the ion larmor radius (few mm) cause small perturbations in the electric & magnetic fields and let ions & electrons on the outside to collide with those ‘trapped’ on the inside & vice-versa.

The paper does suggest an explanation for several long standing problems, such as how the density limit changes when switching from a deuterium plasma to a helium one, and should be testable with some of the advanced diagnostics being fitted to several tokamaks.

[jamesr]

inertial fusion peaks at about 1000x solid density. The peak focus of a DPF will (hopefully) be just under solid density, whereas tokamaks are ~10^-9 times solid density. So what each community calls dense is very different.

[jamesr]

Given that the bulk plasma in the device should not cool between each pulse below ~800C or so, you could just extend the helium gas cooling needed for the anode to the rest of the walls (making them out of something like tungsten), and run it through a brayton cycle turbine.

But as has been said before it would be much better to avoid having to use a thermal cycle and just extract even just 10-15% directly from the xrays to push over the Q=1 and dump the rest as waste heat.

asymmetric_implosion: The 500kV pinch voltage does not relate to the energy of the x-rays. The x-ray energy peak from bremsstrahlung is a function of electron temperature (http://en.wikipedia.org/wiki/File:Bremsstrahlung_power2.svg ). If the electrons are at ~150keV then the bremsstrahlung peak will be around a quarter of this – so around 30-40keV.

[jamesr]

asymmetric_implosion wrote: It seems like a daunting problem considering the plasma interacting with the first wall of the onion leading to eddy currents and other electrical noise that will screw up the collection of photo electrons.

I was assuming it was outside the vacuum chamber. OK the chamber wall itself will absorb most of the softer xrays, so a final one would want the minimum obstruction before it. However, for the harder (10-200keV) xrays, you could test the concept.

useful tables and graphs of X-ray absorption can be found at
http://www.nist.gov/pml/data/xraycoef/index.cfm

[jamesr]

zapkitty wrote:

Now, if someone would want to build and donate a test panel of “onion” structure to LPP then perhaps something could be done that way?

Seems the sensible way to go.

Similar to the way diagnostics and other equipment is added to tokamaks & other experiments. Get a collaboration with some university then some PhD student can build & test the device, with LPP specifying the physical constraints of size and where it could be mounted. Once built & tested in their home University they can bring it along and mount it and spend a few weeks gathering data (working around LPP’s main campaign)

Obviously the tricky bit is getting the funding/collaboration sponsor for it. Maybe good for one of these new crowd-sourced funding projects.

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