Friday, September 14, 2007

Maxwell Don't Live Here

There have been numerous people asking how it is possible that the Polywell anneals the particle energies so that plasma does not Maxwellianize (thermalize). That is the situation where through particle collisions particle energies are no longer bunched but get spread out in a thermal distribution. It turns out MIT has the answer.
Experimental fusion production and energy efficiency in IEC devices to date has been hindered by confinement limitations. Analysis of the major loss mechanisms suggests that the low pressure beam-beam interaction regime holds the most promise for improved efficiency operation. Numerical simulation of multiple grid schemes shows greatly increased confinement times over contemporary single grid designs by electrostatic focusing of the ion beams. An analytical model of this focusing is presented.

With the increased confinement, beams self-organize from a uniform condition into bunches that oscillate at the bounce frequency. The bunches from neighboring beams are then observed to synchronize with each other. Analysis of the anisotropic collisional dynamics responsible for the synchronization is presented. The importance of focusing and density on the beam dynamics are examined. Further, this synchronization appears to modify the particle distribution so as to maintain the non-maxwellian, beam-like energy profile within a bunch. The ability of synchronization to modify and counter-act the thermalization process is examined analytically at the 2-body interaction level and as a conglomeration of particles via numerical simulation.
Self bunching at a resonant frequency is a klystron type phenomenon.

It looks like Dr. Bussard got the re-normalization of energy correct but got the mechanism wrong. It may not be an edge phenomenon at all but a beam phenomenon.

Here is a nice animated picture of an electron simulation showing the bunching. Click on the icon to get it to play.

Here is more from MIT on plasma behavior in an IEC device.
Also, a curious synchronizing collective behavior is observed in simulation. Particles injected uniformly in 3 separate beam paths ‘clump’ and form pulses. As the simulation progresses, these pulses are observed to synchronize between the beam channels. The steady-state behavior under constant injection is then observed to be a global pulse with the majority of the confined ion arrived near the center of the device at the same time.
Update: 27 Sept 007 0851z

Here are a couple of good papers on the experiments:

Experimental Procedures - Dietrich [pdf]

Theory Derived From Experiment - McGuire [pdf]

13 comments:

Cormac-Ballz said...

They're using electrostatic fields in their models and their reactors, is it directly equivalent? I mean the magnets actively recycle the electrons between the core and the outside in the polywell which is different to the case with grids right?

To be honest I'm barely grasping what they're suggesting with the new models... I guess I'm just wondering could someone clarify what they're getting at? I did read all the links btw ;)

M. Simon said...

There are a lot of things going on at once.

It is very hard to get at first. It took me six months to get it. It should take less time with the resources on the sidebar.

==

In terms of the oscillations - I believe it is an interaction between incoming and outgoing beams.

It causes bunching similar to what you find in a klystron. (for a different reason).

The bunching re-normalizes the particle energies. Very important in this device.

M. Simon said...

BTW keep asking questions until you feel you understand.

It will help me develop better explanations.

Cormac-Ballz said...

Right now that the internet has informed me what a klystron is, I'm starting to get ya.

Initially I was thinking maybe it was slight variations in the density of the incoming beams interacting with each other to create oscillations (like the quantum fluctuations just after the big bang are thought to have resulted in galaxies) . But you say that the outgoing beams interact with the incoming ones... I'm having a problem with that since the animated model shows the beams clumping before outgoing electrons are shot out from the core (are they what you mean by "outgoing beams"?).

Either that or the animated model is not showing everything which might be confusing me.

M. Simon said...

OK, the most definitive statement I can make at this time is that the beam clumps.

Since this is not the normal behavior of a vacuum tube the MIT guys think it is part of the interaction of the incoming and outgoing beams.

There may be another explanation. It is the best we have so far.

We know that particles in the system have a natural frequency based on their travels through the system. Perhaps this natural frequency causes everything to self organize.

Cormac-Ballz said...

m. simon said:
"We know that particles in the system have a natural frequency based on their travels through the system. Perhaps this natural frequency causes everything to self organize."

Interesting, I love this cutting edge stuff :D Wish I could download the paper. Any good papers you know of in this area outside of Bussard's work?

M. Simon said...

cormac,

Why are you having trouble loading the MIT papers?

They are freely available.

You might want to look at the Nebel, Park POPS stuff which is based on these interactions IMO.

M. Simon said...

cormac,

If the papers are not too large I could e-mail them to you.

Send me an e-mail.

Cormac-Ballz said...

Whoah, thanks for the links man. Um, like what site do you get them from? do you have to register to a site or something. All i can get are abstracts to that paper that you linked to in the article (I got the last 2 links to those papers fine, thanks very much).

M. Simon said...

Cormac,

My secret is I'm "retired".

So I spend my days scouring the net. I use Google Alerts to notify me of topics of interest.

I found those papers by doing a search on the names given in the main MIT fusion site.

For the time being I see my job as educational. So I look for stuff to help get others up to speed in less time than it took me.

If Polywewll (or some other IEC device) takes off we are going to need cadre who can hit the ground running. It is my job (self appointed) to get that cadre ready.

Cormac-Ballz said...

Well that absolutely intrigues me because I want to get into the field and am at a loss as to where to start. I'm a Physics & Astronomy graduate and i've been pondering this for a while now (well Bussard's video hit the internet anyway).

By the way if IEC doesn't take off then at least we can say we're all mad scientists right? :)

M. Simon said...

Where to start:

Read all the papers on the sidebar. Several times.

Then pick a part of the design you want to do (I'm focusing on controls and power supplies) and start writing. I can post your stuff or you can start a blogspot blog easily enough.

Then invite people over (a post to NSA Spaceflight, the IEC Fusion yahoo group, and talk.polywell should get the ball rolling.

If you are good people will notice.

There are people watching those places with the expectation of bringing people on board when the time is right.

Expect withering criticism. Engineering is not nearly as genteel as academics.

Cormac-Ballz said...

Uch engineering, I forgot most of the physics had already been covered :)

Well thanks man, you've given me much food for thought! And lots of papers to read... this may take some time :)