UW IEC 2009 Spatial and Energy profiling off D-D Reactions in an IEC

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
Post Reply
FogerRox
Posts: 10
Joined: Sat May 05, 2007 4:55 pm
Real name:
Contact:

UW IEC 2009 Spatial and Energy profiling off D-D Reactions in an IEC

Post by FogerRox »

I hope this isnt a dupe, and in a good location, and is relevant, I noticed this report by David Donovan from the 2009 IEC conference @ UW.

http://fti.neep.wisc.edu/static/TALKS/1 ... viddon.ppt

Original Thorson results indicated less than 10% of D-D Fusion events occurring within Cathode radius.

Initial TOF results indicated that at least 50% of the D-D fusion reactions occur within the Cathode Radius
Dan Tibbets
Posts: 578
Joined: Thu Apr 17, 2008 1:29 am
Real name:

Re: UW IEC 2009 Spatial and Energy profiling off D-D Reactions in an IEC

Post by Dan Tibbets »

This information has been debated before. In a gas discharge fusor (no ion guns) the neutrals outnumber ions by a large proportion (CB has given a ~ 60:1 ratio). Even if the ions are converging towards the center, they will most often collide (and be scattered) with neutrals which have a random distribution within the vessel. While two centrally colliding ions may have a higher closing velocity, some of the neutrals are probably not too far behind due to the thermalizing collisions. So any fusors with a lot of neutrals will have difficulty achieving tight focusing of ions towards the center. I assume that is why ion gun based fusors such as Hirsch's was so much more efficient.

[EDIT] Also, note that in the next to last slide, it seems that they are claiming that 50% of the fusions occur within (or on?) the cathode instead of the earlier 10% results. Silly me, that is what the original poster stated.

One way of looking at the numbers is that 10% (or 50%) of the total fusions occur within the grid (core). Another way to look at it is that despite the contaminating neutrals the fusion rate in the core is perhaps 100-500 X per unit area. Rember that the core only consists of eg: 10 cc, while the entire vessel volume might be 1000 cc (or scalling up to their sizes still gives the ~ same ratios).

Dan Tibbets
FogerRox
Posts: 10
Joined: Sat May 05, 2007 4:55 pm
Real name:
Contact:

Re: UW IEC 2009 Spatial and Energy profiling off D-D Reactions in an IEC

Post by FogerRox »

THis might be it, TA Thorson wrote a 1998 paper, I think its on his tests, though its not available to my computer I may have found it elsewhere.
It might be all things equal that this recent test is the best in class effort. Slide 23 of the PPT shows clearly some reactions at the grid, but more well inside the grid.
FogerRox
Posts: 10
Joined: Sat May 05, 2007 4:55 pm
Real name:
Contact:

Re: UW IEC 2009 Spatial and Energy profiling off D-D Reactions in an IEC

Post by FogerRox »

Thorsons 1998 abstract

http://www.iop.org/EJ/abstract/0029-5515/38/4/302

Abstract. The deuterium-deuterium (D-D) fusion reaction rate in a spherically convergent ion focus is observed to significantly exceed the rate predicted by a collisionless flow model. However, a careful consideration of ion-neutral collisions and the trapped neutral density in the cathode account for the extra reactivity without invoking anomalous ion trapping in the converged core region. This conclusion is supported by proton collimation measurements, which indicate that the bulk of the observed reactivity originates outside the core region. In addition, a classical flow model, where charge exchange collisional effects on the ion and fast neutral distributions are included, provides fusion rate estimates that are quantitatively consistent with the observed D-D fusion neutron production rate.

While Donovon seemed to measure both protons and tritons?

Did Thorson use ion guns ?, I think Donovon did use 6 ion guns on the UW machine, Egle wrote it up here:
http://fti.neep.wisc.edu/static/TALKS/1 ... ianegl.pdf
User avatar
Doug Coulter
Posts: 1312
Joined: Sun May 27, 2007 3:18 pm
Real name: Doug Coulter
Location: Floyd, VA, USA
Contact:

Re: UW IEC 2009 Spatial and Energy profiling off D-D Reactions in an IEC

Post by Doug Coulter »

I find this timely and relevant myself, it's an area I've been wanting more data on, and it's not exactly real easy to get in a home lab, even a pretty nice one.

My suspicion is that where the neutrons come from is going to be a large function of other parameters indeed. I have run mine with and without an ion gun, and in both static and pulsed modes with one.

I get very different results depending on all this. At pressures were I can run without an ion gun (eg higher ones) the thing seems to become its own best ionizer, and I would surely dispute the idea that it is mostly neutrals in there at that point, because I see a time constant in current that differs with how much extra volume there is in the tank, as in a big tank with the fusor on a sidearm taking longer than a small tank with no wasted volume for the same current buildup effect to occur.

In other words, this data doesn't control for all the obvious effects -- not that it isn't useful stuff.

Running at low pressures in pulse mode, evidently free running and triggered by ion buildup from the gun, I see a much lower voltage threshold for good fusion output, perhaps because there's no space charge and few neutrals inside the grid to slow incoming ions? Don't know yet, that's conjecture. But it would seem that in that mode, there are a lot more head on, full energy collisions to account for the results, however that is actually happening.

I run cylinder grids here. I get a star with rays at high current non-pulsed mode (which makes fewer neutrons per second than pulsed mode, and with FAR lower Q for static mode). The rays come out from the center of the length of the grid, not near the ends. So I'd be really interested in finding out where the neutrons are coming out of that -- same place as the rays, or everywhere else seem like things worth finding out about, for example. Would longer grids show more than one ray center? Don't know yet. Are rays merely losses of neutrals, eg exhaust? Don't know. And so on. There's a heck of a lot that falls into the dunno category still. So this kind of data is always welcome here.
Why guess when you can know? Measure!
Frank Sanns
Site Admin
Posts: 2119
Joined: Fri Jun 14, 2002 2:26 pm
Real name: Frank Sanns

Re: UW IEC 2009 Spatial and Energy profiling off D-D Reactions in an IEC

Post by Frank Sanns »

Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
Post Reply

Return to “Fusor and/or General Fusion Theory (& FAQs)”