[jamesr]

Although twisting a rubber band and seeing it twist and kink may help figuratively in picturing what is going on, it can be misleading to think that the behaviour of plasmas are that similar.

A rubber band has a fixed topology – it cannot split into separate strands or merge back together. One of the key aspects of plasma instabilities is precisely that ability to filament, form ‘magnetic islands’ and reconnect. The transfer of energy to the plasma from the magnetic field and vice versa is intimately linked to the reconnection rate & changing topology of the field.

Only through simple idealized simulations like these:
– two-stream instability
– Double tearing mode plus a shear instability.
– 3-D evolution of Kelvin-Helmholtz instability
or full device models like this:
– DIII-D tokamak simulation

What we need is for the plasma focus device simulations that Eric Lerner and others are working on to mature to the level of some of the codes the tokamak or inertial confinement fusion communities now have at their disposal. This is what is going to take lots of funding in the years ahead.

The 1D & 2D plasma focus codes around now may be sufficient to characterize the first few phases of a DPF pulse, and separate codes could start modeling the properties believed to exist in the small plasmoid. Currently no one program can model a DPF as a whole.

A fully 3D program to model plasma focus devices that can cope with the vastly different time and space scales involved (even if written as separate modules for each phase), would do wonders not only for the science but also the PR point of view. With convincing 3D graphics based on a sound underlying model it will be a lot easier to convince people, rather that the simple artists impressions we have at the moment.

[jamesr]

Although this site has close ties with LLP it should not be thought of as a fly on the was of a research lab.

For any quality scientific research, whether by a private company or academic institution, I believe it is right and proper for any substantive developments to be first published at a recognized conference or peer reviewed journal.

While it is interesting to debate and inform a wider community of the science and technology behind focus fusion through this society and its forums. In particular because there are contributors such as Eric himself to enlighten and correct comments made on aspects of the theory and design. We should not expect shot by shot updates of LLP’s ongoing research.

[jamesr]

Its not quite as simple as that. There may be many filaments, and each one could be comprised of lots of micro-filaments. Plasma is an unstable thing. Density & temperature gradients will tend to cause instabilities which will cause splits and reconnections of the filaments and turbulent behaviour.

[jamesr]

theanphibian wrote:
Am I correct in taking that the purple image is from imaging from a real experimental test?

I believe the image is taken from Bostick, Nardi et al 1976 paper:
RADIATION DAMAGE (BLISTERING) IN Al, Cu, Si BY EXPOSURE TO A PLASMA FOCUS DISCHARGE doi:10.1016/0022-3115(76)90350-0

The caption to the image in the paper is:

(c) Image converter photograph of current sheath (5 ns exposure by visible light) 20-30 ns before maximum axial compression,
as sheath collapses toward the “pinch” stage. The plasma vortex filaments which are visible on the current sheath provide the “raw material” out of which the plasma
nodule will be probably formed. Maximum voltage applied to the electrodes: 15 kV: local current within the nodule can be much larger than peak current on electrodes
because of current loops formation in the plasma. Plasma nodules are strong sources of bremsstralung X-rays and can be observed by pinhole camera photographs.
In one discharge the emission intensity from one nodule is usually higher than intensity of other nodules when a multiple-nodule structure is formed in the
plasma within the axial column as it is outlined in (a).

[jamesr]

Although it may be a little frustrating seeing other projects get this much investment; I take it as a positive sign that there is still money around whether from governments or private industry for this kind of research.

What you have to remember is the physics of fission and neutron transport is pretty well understood, unlike some aspects of plasma physics. Accelerator driven fission, in particular is something that an organisation like SCK-CEN has a lot of experience in, since that is how a lot of isotopes for medical uses are made. So they seem well placed to pursue this.

Once the key physics behind FF, like the suppression of bremsstrahlung, has hopefully been demonstrated to be a big enough effect to make breakeven possible. Then, after a year or so for another lab to verify the results, the proposals for serious funding can go full steam ahead.

[jamesr]

I have been thinking that trigger system looks quite complicated. Can someone explain why there is a separate trigger on each capacitor? If they are all charged in parallel to the same voltage, can’t you just have one spark gap in the middle?

If you do need separate triggers why not use some of the techniques used in Marx generators. Such as all the gaps should be able to see each other, so the UV light from one spark can help trigger the others. Then the time difference between them is down to how close together they are. The other step that is apparently used, is to dope the electrodes with a radioactive isotope, to give a consistent breakdown point.

James

[jamesr]

Aeronaut wrote: Think we could do that in PWR fashion by pumping water through a beryllium anode and controlling the steam pressure with the cooling water pressure? I hear PWRs are making a comeback these days :shut:

There is no way a small beryllium electrode could withstand water pressurised to the 160bar or so needed to keep it liquid through the primary circuit, as they do in PWRs

As I understand it, the plan is to use helium gas as the primary coolant. What you then do as a secondary stage largely depends on how high a temperature you can let the helium outlet be. I am guessing no more than 480C. In which case a standard boiler & small forced cooling heat sink would be enough to dump 2MW. If you have several FF units together, the secondary circuits could be linked, and make it economical to put the steam through a turbine and recover 35% or so of the heat energy.

If the anode can cope with the helium temperature outlet being above 800C, then direct cycle options such as gas turbines become a possibility. But not probably worth it. High temperature gas turbines are being proposed and worked on for 4th Gen Fission reactors like the GT-MHR. However, even if you could operate at this temperature, I think the maximum pressure the anode can handle may be a limiting factor.

[jamesr]

Separating the isotopes of Boron is much easier than Uranium because the ratio of the mass differences is much larger.

Boron is used extensively in fission power plants as a neutron absorber – here B-10 +n -> Li-7 +He-4. Also there are well established industrial processes for purifying and enriching Boron for this purpose (where they want the B-10) so the ‘depleted’ B-11 is already there as a byproduct.

B-11 is also used in preference to B-10 in electronics, especially in high radiation environments like satellites. Where you want to avoid the B-10 +neutron reaction at best flipping bits or worse permanently damaging the semiconductor.

James

[jamesr]

The ‘surface’ as far as incoming radiation goes doesn’t have to be the solid planet surface. For Venus the surface for the Sun’s visible light is the layer of dense sulphuric acid clouds around 60km high where most of it is absorbed/reflected. The dense mid-level atmosphere is warm and so is the entity re-radiating in IR, blanketing the planet.

I wouldn’t be surprised if the total radiation coming from Venus is more than is coming from the Sun. The planet like ours (but less so) still has a hot core producing some heat through radioactivity but is overall cooling by radiating the heat into space. This is not anomalous.

The day/night side temperatures are not the same – see http://www.esa.int/esaMI/Venus_Express/SEM5A373R8F_0.html for more details.

[jamesr]

Brian H wrote:

In part, this says that any given CO2 molecule may or may not re-radiate energy it has gained from either thermal contact or IR influence. It may just bump a nearby molecule and lose its excess energy to some other gas. If it does re-radiate, it will be in some random direction, possibly back to space, possibly sideways, possibly down. This does not permit any kind of averaging computation.

Bingo. The more CO2, the more absorption. The more absorption, the more downward re-radiation. The more downward re-radiation, the less gets through to warm the stratosphere. Therefore the stratosphere cools, the surface warms. Exactly what we are seeing.
False. Only a small fraction of the absorbed radiation ends up going down; there is no conservation of “radiation”

The fraction of absorbed radiation being re-radiated down would be almost exactly a half, since the CO2 molecule will deexcite in a random direction. The half that is re-radiated upwards still has a chance of being absorbed again higher up. Of course one initially scattered down could also be re-scattered upwards. This kind of linear chance of interaction and being scattered out of a particular direction is the similar to say gamma rays being absorbed/scattered as they pass through sheets of metal. If you double the thickness (equiv to doubling the thinkness of the atmosphere) you half the amount getting through. Similarly if you double the density of atoms/molecules, and so increase the probability of an interaction, you half the amount getting through. The result is an exponential fall off of radiation of those particular energies corresponding to the CO2 absorbtion bands with height, with the constant in the exponent being proportional to the number density of CO2 molecules.

The total effect is small compared to the infuence of water vapour, but CO2’s absorption bands are at different wavelengths – that happen to lie around the black-body emmision from the earth.

How specifically significant the anthropogenic CO2 contribution to greenhouse warming is, I would happily debate on, but the effect itself I think is sound.

[jamesr]

I second Keith. That thesis is so flawed & quality of argument and writing so poor I’m surprised any institution like Technische Universität Braunschweig would pass it.

I just had a quick skim though, but it seems to be rambling on about whatever came to mind at the time. I love the bit where they try and go through Maxwell’s equations and so talk about magnetohydrodynamic turbulence, but completely fail to make any kind of point. I think they were trying to say something like because fluid equations are non-linear, and so can’t be analytically solved, we can’t hope to find out any useful information from modeling.

I would have expected in all the stuff about radiation to have a graph of the CO2 and water absorption spectra like this: http://upload.wikimedia.org/wikipedia/commons/7/7c/Atmospheric_Transmission.png, but no – not even a mention

[jamesr]

I posted a reply to the site as follows:

The Focus Fusion process is designed to work with hydrogen and Boron-11, not neutrons. The protons (ionized hydrogren) and boron fuse, then decay into 3 heliums. NB the early experiments will be done just with deuterium to verify the plasma conditions.

The device is designed to be pulsed at several hundred Hz. So although a small amount of energy is released per pulse, a focus fusion device running at ~300Hz could produce a few MW of nett power output. If the experiments verify the theoretical models.

Conventionally nuclear reactions involving light nuclei are termed fusion and those over the mass of iron are fission. This is due to the shape of the binding energy per nucleon curve http://en.wikipedia.org/wiki/Binding_energy#Nuclear_binding_energy
Most nuclear reactions involve combining two nuclei (or a nucleus and a neutron or proton) followed by the breakup due to the amount of energy available due to the mass difference between the compound nucleus and the final end products.

The beauty of the focus fusion approach is that there are no appreciable neutrons or radioactive products produced. Also since the products are all charged the energy can be recovered much more directly to electricity than conventional fission power stations, and proposed tokamak fusion designs which rely on heating water to drive steam turbines.

[jamesr]

Weren’t you talking about trying out some of the solspace addons a while ago that enable ratings etc. This way the good posts get tagged up or down etc and earn the poster ranking points.

[jamesr]

Here’s a few quick comments on the first few sections, I’ll have a look through the rest later.

Aneutronic Advantages – Don’t have cold fusion statement first. I think you get a kind of guilt by association, we do not want FF to be associated in peoples minds with this so even a statement saying it is NOT this creates an association. Don’t be so black&white;with the No neutrons – we need to be honest about the small percentage of low energy neutrons.

A comparison of typical Conventional and aneutronic fusion fuels – mention other aneutronic reactions and that pB11 is just the most favourable of these.

Dense Plasma Focus (DPF) Advantage – Mention why pB11 will not work in conventional tokamak design (they can never get hot enough). Fusion with higher charged ions such as Boron will only work in a device that can create the huge magnetic fields needed to suppress the cooling by radiation mechanism. Also mention efficiency due to direct conversion to electricity rather than the thermal cycle.

I think there should be some mention of other plasma focus research around the world. Although LLP may be the only company working on it as a power source there are many groups using and researching plasma focus devices for other uses. They are not something new – we can bring together and discuss relevant advances from other groups.

[jamesr]

belbear42 wrote:

That is the worry I have as well. According to Eric’s simulation results in the Technical Paper 1 the maximum reasonably achievable ratio of (Xray + Beam) / Input is 1.57.

There seems to be a little error in this paper:
On the bottom of page 5, it says “Fuel: B10H1” Shouldn’t that be B11H1?

I think it means the B_10H_14 decaborane – which when sublimed into the moderate vacuum will begin to dissociate and the hydrogens get knocked off. The partially ionized plasma will then completely break up the molecules when the discharge goes through it.

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