Talk-Polywell.org

mad_derek · Joined: 08 Jan 2008 Posts: 46 Location: UK (mostly)

OK, like many others I suspect, I'm getting bored with AGW, no news, no ideas etc.

I was looking at the possibility of formation of a potential well at the (approximate) centre of a polywell. I came up with a bunch of integral equations which looked quite horrific ... and then I thought, wait aminute, isn't that what we used to use analogue computers for?

Given the advances in analogue electronics generally, since the late 60s early 70s, wouldn't an analogue model help quite a lot with progressing (or otherwise) the theory of the Polywell?
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DeltaV · Joined: 12 Oct 2009 Posts: 574

2D electrostatic problems (e.g., electron microscope lenses) used to be simulated by various analog means in the good old days. An e-lens was in one case simulated by a rubber sheet stretched upward by posts representing the potentials, and electrons paths were then simulated by projecting onto a horizontal plane the paths of ball bearings as they rolled down the potential slopes. Fluid flow from sources to sinks was also used for some other electrostatics problems.

There was a recent science news article somewhere about lasers being used to force circular or spherical bubbles into squarish shapes (transiently) that had me also thinking about analog computing, but I'm not able to locate it now.

For Polywell, the combined electric and magnetic fields in 3D are probably not suitable for mechanical analog computing, but I'd be happy to be proven wrong. As far as electronic analog computers, they'd have to be able to simulate the "full bounce-averaged Fokker-Planck equations" IIRC from earlier posts on this forum.

There is a building-block approach to analog electronics that's very interesting and might have some application to this problem:
D. Grundy and J. Raczkowicz, "Structured Analogue Electronics", Electronics World & Wireless World, 97, pp. 965–969, November 1991
http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?isnumber=4992&arnumber=193543&count=15&index=12
shorter is sweeter

chrismb · Joined: 13 Dec 2008 Posts: 1544

That's the point of an experiment. It is an analogue compter of itself that replicates every detail!

Plasma physics has always been this way. I would like to know of any plasma experiment that has done what it was, a priori, predicted to do.

Show me an accurate simulation of a 1-D gas discharge in a cylinder..... even that simple arrangement defeats MHD and kinetic theory, so how is any theory gonna hit Polywell's arrangement?

DeltaV · Joined: 12 Oct 2009 Posts: 574

Solo · Joined: 29 Jun 2007 Posts: 223 Location: TN, USA

Check out what they are doing at U. of Washington - Seattle: a DOE project to make a predictive computer experiment system for exploring innovative confinement concepts. Pretty sweet, huh?

http://www.aa.washington.edu/research/PSI/
http://www.aa.washington.edu/research/PSI/research.html

"The PSI-Center's primary objective is to develop predictive capability for "Concept Exploration"-level experiments, so that one can design and model new experiments in fusion science and in other areas of plasma science, but without actual construction."

rcain · Joined: 14 Apr 2008 Posts: 392

wow! nice find. wonder why i've not come across it before.
lots of collaboration happening there.
perhaps good people to ask about resolving any Polywell confinement debates.

MSimon · Posted: Fri Feb 05, 2010 11:54 pm Post subject:

I'm with chris.

The difficulty is that plasma is chaotic. Small deviations (in both the simulations and reality) lead to unexpected effects. This leads to divergence between models and reality.

Nick Krall was discussing a Polywell simulation (in a private e-mail) and said you need a a very low density of gas and an electron imbalance of a "gazillion to one" to get the electric fields to work in a Polywell. That means that the you need a a simulator with enough significant digits to represent the system to a factor of a billion gazillion to be able to run a large number iterations. That says 128 bit or 256 bit numbers plus an exponent.

Once you can cross confirm simulations with reality you may be able to simplify the code. Until then it is just shots in the dark.
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mad_derek · Joined: 08 Jan 2008 Posts: 46 Location: UK (mostly)

DeltaV · Joined: 12 Oct 2009 Posts: 574

My hope for analog simulation of Polywell would be for qualitative, not quantitative, results. The SAE method maps everything into logarithms and has a very wide dynamic range however, IIRC, due to the inherent characteristics of semiconductor junctions, and might give better numerical performance than traditional analog computers. Can't find it on the web though; it's been too many years since I read the 1991 EW&WW article to recall details.

Analog computer for beam control:
"Programmable VLSI Extended Analog Computer for Cyclotron Beam Control"

http://www.cs.indiana.edu/pub/techreports/TR441.pdf

MSimon · Posted: Sat Feb 06, 2010 2:02 am Post subject:

DeltaV · Joined: 12 Oct 2009 Posts: 574

Noise is not always a bad thing. Which does not mean it wouldn't be bad for a Polywell simulation.

MSimon · Posted: Sat Feb 06, 2010 2:30 am Post subject:

DeltaV · Joined: 12 Oct 2009 Posts: 574

Stochastic resonance practical application

MSimon