[jamesr]

Here’s an image of what I reckon it should look like (photo is actually of a lightbulb filament)

Attached files

[jamesr]

benf wrote: There’s a bend function that allows me to bend a coil into a semi circle. So I don’t need a formula after all. I can make a full circle by splicing. I wonder if there should be multiple stacked coils? Or is just one going to soak up all the energy of the beam?

I would think it was easiest as a formula. I’m not sure how your program expects it, but a Rogowski coil (or coiled coil) could be parameterised by the following

if R is the major radius, and r is the minor radius, and the coil is extending H per major turn in the z direction, and h per minor turn along the major coil.

The the position of its the major axis in Cartesian coordinates

X = R cos(theta)
Y = -R sin(theta)
Z = H*L
where theta = 2*pi*L*H

and defining the minor spiral as
x’ = r cos(phi)
y’ = r sin(phi)
z’ = 0
where phi = 2*pi*h*L

Then superimposing the two gives the final position as

x= X+ x’ cos(theta) +y’ cos(alpha)sin(theta)
y= Y – x’ sin(theta) + y’ cos(alpha)cos(theta)
z= Z + y’ sin(alpha) + z’ cos(alpha)

and alpha is a constant tilt angle

I haven’t checked this, but I think the form is roughly correct.

mmm… looking at it now maybe there is an easier way!

[jamesr]

Lerner wrote: Great! If we sent you some solidworks drawings and where the potential is, could you get us a plot of electric field strength?

I’m not sure it imports solidworks files directly, but I’m sure I can convert them to whatever it needs.

But, as I said I’m very much a beginner with Comsol so don’t trust any figures I get without checking them!

[jamesr]

We have a version 4.0a licence installed on our network (with CFD, ACDC and Chemical Reaction Engineering modules). It is used a bit by someone in one of the other research groups I think. It seems to run up OK on my machine. I tried to have a go with it a while ago (just going through the basic tutorials) but never got very far, but if you send me a basic model to get me started I can have a go.

[jamesr]

Alex Pollard wrote:

These findings should have significant implications for fusion research and the physics of magnetic reconnection.

Doesn’t magnetic reconnection stem from mistaken attempts to explain solar flares without acknowledging the electric currents that cause them?

http://www.thunderbolts.info/forum/phpBB3/viewtopic.php?f=12&t=22&start=0

Doesn’t inspire any confidence that Tri Alpha are on the right track.

Magnetic reconnection is key , as you say, to solar flares. But I wouldn’t say they are mistaken attempts. They have known for years simple resistive MHD models are insufficient to explain reconnection rates that fast, and that you at least need to consider the Hall term in Ohm’s law ie currents flowing across the field, and the differing resistivity parallel and perpendicular to the magnetic field.
There has been quite a bit of progress in recent years modeling for example Ellerman Bombs, and how they relate to flux emergence from the sun’s photosphere.

Here is one paper from 2002 on observations
http://iopscience.iop.org/0004-637X/575/1/506/pdf/0004-637X_575_1_506.pdf
And one from 2009 on the modeling
http://www-solar.mcs.st-and.ac.uk/~vasilis/12455.pdf

[jamesr]

Brian H wrote: You might like to get your hands on this new linear equation algorithm presentation: http://www.physorg.com/news/2010-10-barrier-important-class-linear.html

It looks like just about any SDD-based operation is about to become exponentially faster:

The algorithm, which applies to an important class of problems known as symmetric diagonally dominant (SDD) systems, is so efficient that it may soon be possible for a desktop workstation to solve systems with a billion variables in just a few seconds.

I wouldn’t be at all surrounded if this has major implications for the Plasmoid simulation requirements, too. And once the engineering phases start in earnest, it could multiply speed of progress significantly!

Interesting. I’ll have to read the paper in more detail, but I suspect it has limited use for plasma simulations which are highly non-linear by nature.

On a related note Comsol are running some seminars over here (UK) I assume they’ll be doing some similar ones in the US on their new plasma module.
http://www.uk.comsol.com/events/cps/12588/. From what I understand it won’t be able to cope with the complex nature of the plasmoid formation, but should be able to model the switch spark gap breakdown fairly easily.

[jamesr]

Brian H wrote:
P.S. BTW, James, your PM mailbox is in need of housecleaning. It’s chock-full and you no longer show up on member searches as an eligible recipient! And an attempt to PM you directly from the link here was rejected. :ohh:

Access thru the link in the page header.

I have nothing in my PM box?? very strange – anyway I’ve sent you my direct email details.

[jamesr]

Carrera has got most features you could ever need, but as with any 3D package there are so many controls & different ways of doing things that they take years to master. You’re doing pretty good so far. I agree a certain amount of artistic license is needed when trying to make something visually appealing. Particularly things like your choice to have less cathodes as it makes the whole thing less cluttered and easier to see whats going on.

However, like Brian said I think if you can get a little closer to the shape of the anode in the photos of the real FF-1 it will be easier for people to relate them.

I found this clip http://www.youtube.com/watch?v=oYH-ZVNGXVE of someones demonstration of using objects as a light source in Carrera – it would be so cool if you can do this with the plasma.

One last comment.. the sheath part of the plasma seems to go back down a bit at the end, rather than carrying on and fading out. Essentially the sheath needs look as if it is collapsing into, and becoming, the filaments. Then when the filaments reach the focus you want a bright flash before the beam shoots out.

[jamesr]

What 3D package are you using? I have been meaning to learn Blender (http://www.blender.org/) for ages. It can do really good glowing plasma effects (with some effort). I think the reason your one still looks a bit odd is the copper is too shiny, the mirror-like reflections in it should be much more diffuse. If you can’t go the whole way of having the plasma itself as the light source, then it should just be lit by a global ambient light rather than the one casting shadows.

[jamesr]

Brian H wrote:
Perhaps you could inform me about something I’m disputing about on another site. When the steam condenses, does it thereby heat up its container/shared atmosphere (if any) in direct transfer of latent heat energy?

Steam condensing is just like sweat evaporating in reverse. So whereas evaporation extracts heat from its surroundings (like your skin) to overcome the latent of vaporisation. Condensation will return exactly the same amount. So water vapour condensing on a cold window or bathroom mirror will warm it up slightly.

[jamesr]

JimmyT wrote:
We are talking airplane design here. Right?

Neutron shielding is always going to be bulky (from the moderator/absorber part) and heavy (from the gamma shield), especially for the high energy neutrons from D+D or D+T. That’s the beauty of p+B11, the few neutrons you do get from side reactions are much lower energy. So you only need a relatively thin layer of borated polyethylene to slow & absorb them. After this you still need some heavy metal shielding to capture the gamma-rays produced in the neutron absorption reactions. The gamma shield will also partly double as a neutron reflector, as described above.

I’m sure if the DPF was in the tail or out on the wings it would be viable to put them in an airplane. The radiation levels would be down to below what pilots are getting from cosmic rays anyway. (cargo planes at least – passengers may take a little more convincing)

[jamesr]

JimmyT wrote:

I have been reading about mobile and deploy-able Focus Fusion Reactors and have a couple of ideas to offer.

For some of the applications (aircraft) weight and size are a big issue, most of the weight and size are concentrated in to three areas: Shielding, Capacitors and Cooling.

Idea #1:
Most of the size and weight is in the neutron moderator (is that the right word? I mean the material that slows down the neutrons, usually water). I realized that the neutrons could be trapped inside a container filled with water and Boron10, by using a neutron reflector wrapped around the water container (http://en.wiki.org/wiki/Neutron_reflector) something like the attached pic1. The neutrons would bounce around until they where slowed down enough to be captured by Boron10. Would this work? Would the increased radiation levels cause problems? Would the extra neutrons interfere with the main reaction?

Back when Rutherford first fired particles at materials and witnessed scattering, we learned what a small part of any materials volume is occupied by it’s nucleus. Only a small fraction of the particles were deflected. Most simply went straight through the targets as though it were not even there. Yet this is precisely the way that neutron reflectors work. Some materials have bigger nuclei or have them more densely packed (Beryllium) making them more effective. But even then, only a small portion of the incident particles are reflected. These materials are only called neutron reflectors compared with the even poorer reflective ability of other materials. But don’t think of them as a mirror. Any more than you would think of highly polished chicken wire as a light mirror. It does reflect some back doesn’t it?

I find your analogy is a little misleading. Neutrons are uncharged – so their chance of being scattered is even smaller than the charged alphas Rutherford’s assistants observed coming back off gold. But mainly – it is not a surface effect – since the chances of collision are so low the neutrons travel deep into the material before scattering. The reflection comes from many scatters deep in the material turning the neutron by different angles (most small). After a while some neutrons have the chance of being turned by a large enough angle to make there way back to the surface they entered from.

The mean free path (ie average distance between collisions) of a fast neutron in steel for example is around 6cm

So think many millions of layers of very fine chicken wire and you’re a little closer.

[jamesr]

I thought the axial phase of the plasma was like a snowplow pushing all the gas in front of its bow-shock and ionising it – so increasing the density of the sheath as it sweeps down.

If the cathode was one piece then there is nowhere for gas to fill in behind the sheath, creating a low pressure area behind it. This back-pressure would slow down the sheath and reduce the energy of the focus.

As for the filamentation -it will always happen when you have a current flowing through a plasma. These filaments will also always go kink-unstable at some point (its in the nature of plasmas). But in order to get consistent firing of the DPF you want the instabilities to be seeded at the same point every pulse.

going back to #1 – neutron reflectors have to be made of heavy elements and are never perfect (think firing ping pong balls at an array of skittles). They just bounce around off the atoms in the reflector quickly loosing sense of their original direction, some then find their way back to a surface and come out again.
Lighter neutron moderators can be made of stuff like polythene or paraffin wax, as these have much higher hydrogen to overall density ratios than water. But only for neutron fluxes that are low enough that you don’t have to worry about the heat deposited in them.

[jamesr]

I know what you mean about all the different choices for axes. I think the most sensible bet it to keep them as temperature in Kelvin, and density in m^-3 – ie. SI units. Combining the energy confinement time into the density axis (Lawson parameter) means highlighting any areas is specific to a particular reaction ie D-T.

For a fancier animated version you could include the confinement time as a third axis – so make it a 3D cube you are flying through.

Also alongside each axis you could have other reference points such as the density of water.

Style-wise I was looking recently at some of the xkcd posters such as http://xkcd.com/681/ or http://xkcd.com/482/ where the large scales of the universe are explained with ease (and a little humor) Maybe we could get him on-board to do a fusion poster and post it on xkcd – that would generate some publicity!

If you want to see how a magnet bends a plasma, watch this: http://www.youtube.com/watch?v=3grPo81fBrA The mugs were available from thinkgeek.com but I can’t see them on their site right now

[jamesr]

Steven Sesselmann wrote: That sounds like an almost impossible task…, I assume this method can only work with pulsed fusion. If the fusion was a steady state reaction it would not be that simple, unless you could measure the neutron energy in a scintillator.

Steven

I forgot to mention they use two neutron detectors at difference distances. So each one gives a peak shaped according to the fusion reaction rate lasting the 50ns or so lifetime of the highly compressed plasmoid. As I understand, it is by taking the difference in spread of this pulse shape as it stretches out between the near and far detector that you recover the velocity distribution. You also have the profile in the x-ray flash (the light obviously travels at a fixed speed), but this is more related to the electron temperature than the ion temperature

There may in future be the possibility of using neutrons from different reactions. So you have the main 2.45MeV neutrons from the D+D ->He-3 + n. But from the tritium produced in the other branch of the D-D reactions, these can undergo D + T -> He-4 +n, where the neutron has 14.1MeV.

NB. There are other reactions that produce neutrons but most of these result in 3 bodies so the energy can be split in any amount rather than giving a fixed neutron energy as you get in 2 body reactions (due to the conservation of momentum).

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