[jamesr]

AaronB wrote: Here’s a general idea that might inspire some thoughts. The atmosphere has a jet stream, as do the oceans, and plasma filaments are little jet streams. They pretty much appear anywhere there is a big potential difference and a path of least resistance through a viscous material. For example, I propose that there are jet streams going through the magma under the earth’s crust, and that could drive continental drift. Where else might they pop up?

Jet streams are different in nature to ocean currents and flow along plasma filaments. As far as plasma phenomena go, “zonal flows” in tokamaks are the closest analogy. In the atmosphere of earth (or other planets such as Jupiter or Saturn) they come about by the Hadley cell flow up from the equator then flowing north (or south in southern hemisphere) to the tropics where they cool and fall. This combines with a second cell & third cell from the tropics to the pole – see http://en.wikipedia.org/wiki/File:Jetcrosssection.jpg. These north-south eddies interact with the Earth’s rotation to create flows perpendicular to the main eddy rotation. At low altitude they are the trade winds, at high altitude the jet streams.

In tokamaks the turbulent flow outwards from the core (& perpendicular to the magnetic field) creates motion in the third, poloidal, direction perpendicular to both the B-field and the pressure gradient know as zonal flows, which can help in forming barriers to the flow of heat out of the tokamak.

The main point it jet stream type flows are perpendicular to the forcing potential (temperature gradient from equator to pole in this case), not down the potential as normal flows are.

[jamesr]

As with most things – I think the devil is in the detail. Molten salt reactors would be great but even with the latest Gen IV designs there are still a number of serious engineering challenges to overcome.

From the 2002 original gen IV roadmap http://nuclear.energy.gov/genIV/documents/gen_iv_roadmap.pdf

The MSR has a number of technical viability issues that need to be resolved. The highest priority issues include molten salt chemistry, solubility of actinides and lanthanides in the fuel, compatibility of irradiated molten salt fuel with structural materials and graphite, and metal clustering in heat exchangers. Specific areas of this viability research phase include:

• Solubility of minor actinides and lanthanides in molten fluoride salt fuel for actinide management with high actinide concentrations
• Lifetime behavior of the molten salt fuel chemistry, and fuel processing during operation and eventual disposal in a final waste form
• Materials compatibility with both fresh and irradiated molten salt fuel for higher temperature applications
• Metal clustering (noble metals plate-out on of the heat exchanger primary wall)
• Salt processing, separation, and reprocessing technology development, including a simplification of the flowsheet.

I have yet to see if any of these issues has been solved.

[jamesr]

[merged post – admin]
The BBC has a news article today about progress in laser spark plug technology:
http://www.bbc.co.uk/news/science-environment-13160950

I know people have been working on this for a while such as this from a few years ago.

I wonder if this kind of ceramic laser technology could be used to trigger high power spark gap switches at the precision required.

[jamesr]

The nature of the decay of the excited C-12 into the 3 alphas I thought would have nothing to do with the beam formation or xray output. The assumption I thought was that the alphas with thermalise with the plasma (keeping it hot or heating it up a little in the process). The exact timing of the C-12 first breaking into an exited Be-8 and one alpha, and whether the Be-8 has time to de-excite at all before it breaks into the other two alphas is the topic of the paper. The two steps could happen so close together that they could be regarded a single 3-body decay, in which the energy can be spilt in a number of ways, or a two 2-body reactions in which conservation of momentum restricts the distribution of energy to the classically assumed values.

[jamesr]

Of course you’d be eating a nice Brazil nut & banana desert at the same time.

[jamesr]

Given that it is on the outside of the cathodes and the ends are still slightly proud would mean it shouldn’t get in the way of the foot point of the current filament as they rise up the last bit of the cathode.

If it were purely for structural support, I wonder what difference it would make if it was made of an insulating material rather than metal?

[jamesr]

At the moment the balance of the game seems to be heavily biased towards biofuels and solar. There is no way even with maxing out the research of getting fusion much sooner. By the time any of the advanced techs come into play it is already too late to avoid financial collapse in around 2070. You can delay the collapse by 5 or 10 years and make it a little less painful, but it always happens. Most of the time you have to resort to geoengineering (ie pumping sulphates into the upper atmosphere) to stop the warming reaching 3 degrees by 2100.

Digging a little deeper you can see all the stats of how much energy of each type every region is using. Together with the demographics of the population, GDP by sector etc. All of the figures look pretty sensible to me. You just have to come to the scary conclusion that the world is in for some very difficult decisions over the next few decades.

I thing a little modding of the config files is in order to see if I can get fusion to kick in by around 2060 and see if it avoids the financial collapse, and subsequent famines.

[jamesr]

I was wondering about the collar as well. Other than the structural support which I too assumed was the primary function, it would short the ends of the cathodes together. Forcing equality in the electric potential of them all against any slight differences that build up due to feedback from the plasma interactions.
It would also allow the perpendicular components of the magnetic field around it to induce a current going round the collar.

These two interactions are just two ways of saying the same thing really since it is the current which will equalize the potential, but on different timescales, so you could have small current oscillations interacting at the frequencies of the order of the alfven, and magnetoacoustic waves in the surrounding plasma.

[jamesr]

In the couple of games I’ve played so far the population got upto around 8.5billion but then famines caused by drought started killing people off by 2070 so by 2100 it had dropped back to 7.5billion.

I tried as hard as I could to help, but the population kept falling. On the plus side the economic collapse that went along with it meant emissions fell sufficiently to only have a 2.5C temperature rise by the end of the century, rather than the 3.5C it was heading to.

[jamesr]

Tulse wrote:
That’s probably true for building an actual nuke, but dirty bombs are very easy to make, and if you’re not worried about eventually dying from radiation poisoning, the handling techniques don’t even need to be very fancy. A very small group of relatively non-technical people could slap one together from the appropriate materials (which are basically a van full of fertilizer and fuel oil surrounded by some spent rods), much more easily than such a group could build a reactor to breed the radioactive material.

Spent fuel is SO radioactive that it cannot be transported without heavy specialized shielding. Even if a terrorist got into a facility housing spent fuel, or hijacked a train/boat transporting it they would not be able take it out storage, or if it is already packaged up to open the container and get more than 100m without keeling over dead. At this level of exposure you die withing minutes not days/weeks, so even if you’re prepared to die you can’t get as far as making a bomb out of it.

So short of strapping enough explosive to blow a whole reinforced transport container into order to disperse the contents, high level waste is not that much risk for dirty bombs.

The main risk for dirty bombs as I see it is raw uranium, unused fuel, and radioisotopes prepared for medical uses. ie. stuff that is safe to handle as long as it isn’t ingested or inhaled, and is transported all over the place without much security.

[jamesr]

My take on proliferation has always been that if any organisation (state, terrorist group etc) has the resources to handle spent nuclear fuel and reprocess it into a bomb, or even just handle it and package the waste into a dirty bomb, without killing themselves in the process. Probably has the resources to build a reactor buried in a mountain and do it themselves from scratch without having to steal it.

[jamesr]

Reports on the EPR and AP1000 can be found at http://www.hse.gov.uk/newreactors/reports.htm These are part step 3 of the generic design assessment (GDA)

The final part (step 4) is almost complete. This article puts the EPR slightly ahead http://www.neimagazine.com/story.asp?sc=2059059

Hopefully since these plans are so far down the road, the events in Japan will not stall proceedings too much.

[jamesr]

The proposed new build in the UK by EDF and Horizon (aka EON/RWE) will have no government subsidy, and will have all the eventual decommissioning costs paid for upfront by putting aside money from each kWh into a separate fund. Any yet they are still the most cost effective large scale sources of power.

Both the EPR and AP1000 PWR designs have passive cooling systems and so need no power after shutdown, and have much stronger containment structures. and human proof safety systems – ie if a terrorist, or even a knowledgeable disgruntled worker, took an axe to the plant and started hacking away at things it would still be safe.

We need new fission plants now, and for at least 50years. It would be great if Focus Fusion works, but in the mean time we need to stick to technology that works. Regular tokamak or inertial fusion is at least that far away that a new generation of fission plants can have a full (ie long enough to payback capital investment) life.

[jamesr]

The first few years of ITER operation will be with just plain old H, not even D. As they want to avoid even the small amount of tritium made in D+D reactions contaminating everything and making it impossible for people to go in and maintain things. As soon as they start using even deuterium everything will have to be done remotely by robots

[jamesr]

mjv1121 wrote: “There is no ‘field-line reconnection’ that can transfer energy to the particles, nor release energy in any other way.” – Hannes Alfven 1976

…I have found an excellent page: http://sites.google.com/site/cosmologyquest/what-we-do-know/magnetic-reconnection

I beg to differ. That page is woefully out of date and misleading. Much work has been done in this area in the past few years and although not complete, our understanding of magnetic reconnection and assosiated energy release has moved on a lot since most of the papers cited on that website.

Here are just a few from a quick search:
A. Lazarian, G. Kowal, E. Vishniac, E. de Gouveia Dal Pino, Fast magnetic reconnection and energetic particle acceleration, Planetary and Space Science, In Press, Corrected Proof, Available online 22 July 2010, ISSN 0032-0633, DOI: 10.1016/j.pss.2010.07.020.
(http://www.sciencedirect.com/science/article/B6V6T-50KRYSG-2/2/ffd72a4b4edea898faa7379860361f3b)
Abstract:
Our numerical simulations show that the reconnection of magnetic field becomes fast in the presence of weak turbulence in the way consistent with the Lazarian and Vishniac (1999) model of fast reconnection. We trace particles within our numerical simulations and show that the particles can be efficiently accelerated via the first order Fermi acceleration. We discuss the acceleration arising from reconnection as a possible origin of the anomalous cosmic rays measured by Voyagers.

D.I. Pontin, Three-dimensional magnetic reconnection regimes: A review, Advances in Space Research, In Press, Accepted Manuscript, Available online 8 January 2011, ISSN 0273-1177, DOI: 10.1016/j.asr.2010.12.022.
(http://www.sciencedirect.com/science/article/B6V3S-51WV08G-2/2/325d6bef0a412cf8b82c51c436272364)
Abstract:
The magnetic field in many astrophysical plasmas – such as the Solar corona and Earth’s magnetosphere – has been shown to have a highly complex, three-dimensional structure. Recent advances in theory and computational simulations have shown that reconnection in these fields also has a three-dimensional nature, in contrast to the widely used two-dimensional (or 2.5-dimensional) models. Here we discuss the underlying theory of three-dimensional magnetic reconnection. We also review a selection of new models that illustrate the current state of the art, as well as highlighting the complexity of energy release processes mediated by reconnection in complicated three-dimensional magnetic fields.
Keywords: magnetic fields; magnetic reconnection; magnetohydrodynamics

M. Barta, J. Buchner, M. Karlicky, Multi-scale MHD approach to the current sheet filamentation in solar coronal reconnection, Advances in Space Research, Volume 45, Issue 1, 4 January 2010, Pages 10-17, ISSN 0273-1177, DOI: 10.1016/j.asr.2009.07.025.
(http://www.sciencedirect.com/science/article/B6V3S-4WXC26D-2/2/f28974a02cc3636b72bfc0ccef3f6562)
Abstract:
Magnetic field reconnection – considered now as a key process in the commonly accepted standard scenario of solar flares – spans over many mutually coupled scales from the global flare dimensions ([approximate]10 Mm) down to the scale, where non-ideal kinetic plasma effects takes place ([approximate]10 m). Direct numerical simulation covering all the scales is, therefore, impossible. Nevertheless, the filamentary nature of the current sheet fragmentation together with rescalability of ideal-MHD equations – which governs the processes before reaching the scales of non-ideal plasma response – allow to describe the large- and intermediate-scale dynamics of reconnection flow with highly reduced request for number of grid points. Since the smaller-scale (and faster) dynamics sets-in only in regions of enhanced current sheet filamentation, we focus just on these areas, which occupy only a small fraction of the total volume. Generally, as the fragmentation continues, it forms a cascade of filamentation until kinetic non-ideal processes come to play. Information relevant for description of the smaller-scale physics occupies only a small fraction of grid-cells describing the large-scale dynamics. Thus, one can subsequently zoom-in onto the regions of continuing current filamentation. The current-sheet fragmentation cascade anticipated by Shibata and Tanuma [Shibata, K., Tanuma, S. Plasmoid-induced-reconnection and fractal reconnection. Earth, Planets, and Space 53, 473-482, 2001], creates multiple dissipative regions in a single current sheet, which can play a key role for DC-field particle acceleration in a flare reconnection. The main goal of the paper is to numerically investigate the relevance of cascading reconnection for solar flares. The numerical algorithm implemented for that purpose and first results are presented in this research note. Proposed algorithm – though motivated by the self-similar nature of MHD equations – belongs in fact to the class of block-structured Adaptive Mesh Refinement codes.
Keywords: Solar flares; Magnetic reconnection; Numerical MHD

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