recirculation - acceleration

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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recirculation - acceleration

Post by Richard Hull » Wed Jul 18, 2001 9:44 pm

The discussion of gas mixtures and such has some thinking of increasing the density of the core in the fusor by reflecting deuterons back into the core with argon gas atoms.

It must be remembered that we are electrostatically accelerating the deuterons. A deuteron decelerated and turned or reflected at the core would waste its energy in creating a fast argon neutral or a singley or multiple ionized argon ion. the deuteron could not now fall through the full gradient and be at nearly zero KE on arrival at the core.

The beauty of the fusor is that the recirculation is ideally completed over a full circuit (the gradient being more or less evenly distributed over the radius of the device.)

We are colliding pairs of high speed deuterons and not attempting to bombard a mass of core trapped deuterons. The former requires less energy per fusion per pair or, restated, the cross section for interaction increases with the former over the latter at any given voltage gradient applied to the device.

I will try and restate my fusor definitional verbage which was long ago posted on the songs BBS.....

The fusor is an inertially confined, electrostatically accelerated, deuteron collider where fusion occurs in velocity space, NOT by maxwellian heating of a plasma.

We are not bombarding a target. A straight tubed linear accelerator can do that much better, but with no benefit and higher voltage requirements.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

guest

Re: recirculation - acceleration

Post by guest » Fri Jul 20, 2001 6:34 pm

All I have to go by is the old material.
Frenckel 1-5
I guess I'll just have to build one and see.
Has 123 Bang gone by the way side also?
Is the hydrogen Thyratron just for amperage or high speed
switching?

Larry Leins
Ole Miss Grad Student

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Re: recirculation - acceleration

Post by Richard Hull » Mon Jul 23, 2001 1:59 pm

The hydrogen thyratron can handle huge currents (hundreds to thousands of amps). It also switches same in the sub-micro second time frame.

It is a super high current, fast switch.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

guest

Re: recirculation - acceleration

Post by guest » Wed Aug 01, 2001 5:40 am

Greetings,

Does the poissor it act as a true blackbody?

One would think not due to nuclear resonances;
this might suggest measurable realtime-diagnostic
to locate band-gaps where recirculation vs power levels
fall in a preferred nuclear-mode vs radiative mode.

Is there any published information available on the
light/power vs spectral characteristics of the poissor?

guest

Re: recirculation - acceleration

Post by guest » Wed Aug 01, 2001 4:34 pm

I differ in the sense you do have a target area - a shell
of incoming ions - thick at the center - thin else where.
the problem is the ions are still thermal in order.
One could add more order to the stream of ions so you have a
better chance of hitting something the first time around.
The one mode of operation of the original RF fusor may been that in dense ion cloud a empty space was cleaned out at low electric field strength giving ion bundles and accelerated when the field strength was highest. Could a fusor be adapted to this idea permiting a higher density operation at the cost of adding more grids.

guest

Re: recirculation - acceleration

Post by guest » Wed Aug 01, 2001 4:47 pm

I am unaware of any publications dealing with the visual aspects of the central poissor region. The Fartnsworth ITT team came to a genral consensus that the visual appearance gave no operating clues.

I do now that lasers have been used to determine density within the central region and spectrophotometers have been used to determine the velocities of the deuterons entering and leaving the area due to doppler broadening.

Richard Hull

guest

Re: recirculation - acceleration

Post by guest » Wed Aug 01, 2001 4:51 pm

This concept was Farnsworth original idea which saw a real life tube called the multipactor based on the idea of RF packing and nodal group accelerations.

Unfortunately, the idea was seen to not be viable at the time and after spending about 2 years on it, the thought was abandoned. This doesn't mean, of course, that someone couldn't pick up the mantle and try and make it work.

Richard Hull

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Re: recirculation - acceleration

Post by DaveC » Wed Aug 01, 2001 10:58 pm

What type of fusor are we discussing here? I would expect the ion gun type of fusor to have characteristics that differ significantly from the simpler spherical grid (or cage) electrode systems.

As long as the mean free path of the ions is much greater than chamber dimensions, multiple passes in and out of the cathode potential well will occur without further "real" ion currents being required. The system ion current simply oscillates between the potentials.

The actual irreducible loss ("grid loss" of a related, earlier question) is approximated by the projected area of the cathode and anode cages (2*pi*Dcage*dwire*nwires)as a ratio of the area of the potential shells they define (pi*Dcage^2).

A 1.25" diameter cathode cage of 3 rings of .020" dia wire (my design at the moment) has a ratio of (.2356 /4.9087) = 0.04799 or about 4.8% opacity. Thus I would expect about 4.8% loss or expressed another way.. the upper limit to circulating currents would be something like 20 times (~ 1/.048) the input current.

Thus the system looks somwhat like a lossy capacitor.

However, I can't at the moment think of a way to measure the circulation at any non-zero pressure. We can of course only guess at the mean free path of an accelerated ion, since its actual temperature and hence velocity enter into the MFP calculation and differ everwhere along its trajectory. Fun stuff.

An electron trajectory plotting program ( I have one) for relatively low vacuums, uses a Monte Carlo method to plot trajectories, and generally assumes the ions are static relative to the electron velocity. For electrons at kev energies and ions at room temps, this works great.
For gas ions at kev energies, the problem is not so "easy".


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Re: recirculation - acceleration

Post by Richard Hull » Thu Aug 02, 2001 1:45 pm

We were talking about fusors in general, but I got the impression we were discussing the simple fusor working at 5-10 microns. Here the mean free path is real short, maybe a chamber radius or so, and re-circulation is just about non-existant. Only gunned systems working at 10e-4 torr or lower or special systems with re-entrant schemes can reduce losses of the ion current to collisional neutralization.

A simple wire gridded, non-gunned system can, indeed, be operated to 10e-6 with carefully designed electron emitters which are a form of defacto gunning, albeit shotgunned systems.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: recirculation - acceleration

Post by DaveC » Thu Aug 02, 2001 9:37 pm

Thanks Richard for the additional clarification.

I have been thinking some more about the mean free path of ions. The way it is usually calculated involves the avg velocity of the gas molecule, its effective radius and number density. Since the avg velocity derives from the mean temperature, when we are dealing with accelerated (and also acclerating) ions, they are effectively at much higher temperatures, although not in equilbrium with the remainder of neutral gas molecules. Since the velocity increases as the square root of voltage for an ion, the mean free path should increase in the same manner. Thus for the keV ions, their mean free path should be much larger than the neutral gas molecules at nearly room temp.

Then, the more dense core (poissor?) of the fusor with decelerating ions adds more fun to the whole picture.

Dave Cooper

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