To Focus or Not to Focus, That is the Question

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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Frank Sanns
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To Focus or Not to Focus, That is the Question

Post by Frank Sanns »

With the proliferation of cube fusors, some questions come to mind. The biggest one that I have are related to the marks etched into the end caps of these BOT devices.

It is obvious that the marks are from impingement of beams hitting the end caps. Not only are they clearly present, but they can "walk" around to different areas near the center of the end caps. It is not unusual for beams to walk around in any of our fusors so this is nothing new.

The question then is about the high neutron numbers with BOT devices. Do this devices perform better when they focus to a small area of the end caps compared to arriving in a more diffuse form.

Assuming all deuterons are arriving at the same kinetic energy to the end caps. There are exactly the same number of them so the beam current is the same for a focused spot or a diffuse area.

If it is a simple BOT, then it should not matter if the beam is focused or not. It should only be dependent upon the energy and the number of deuterons. But is it or is it also dependent upon beam density?

If it is due to beam density then what is the mechanism for enhanced fusion rates? Is it localized heating ejecting deuterium back into the beam increasing its cross section? Is it a localized enhanced fusion environment? Does this happen if the end target ends are rotated so a fresh cool area is always under the beam when there is no great heat build up? Or does it make no difference if the beam is concentrated or not?

Just some pondermnets as I work on the next iteration of my parabolic grid BOT setup. Built it with mesh to start to see the beam behaviors. Now time to make one designed for high output and not just plasma study.
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
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Jim Kovalchick
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Re: To Focus or Not to Focus, That is the Question

Post by Jim Kovalchick »

I wonder if there aren't some time and therefore fluence based conditions at play. We believe that D loading of walls helps. The faster you load a spot the better. So, for a given current and chamber pressure two spots are better that 6. You get to a beneficial loading faster. Of course you also get to wall temperature that's not so good too unless you cool or have a big thick target wall heat sink. The other factor is geometry. For a given chamber shape, the grid geometry may need to match in order to avoid diffuse and wasted beams.
Jon Rosenstiel
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Re: To Focus or Not to Focus, That is the Question

Post by Jon Rosenstiel »

Frank,
Good luck with your BOT project, I’m looking forward to reading your reports.

I’ve attached a couple images of the endcap patterns you mention.

Images 1 and 2: Uncoated endcaps and torus shaped aluminum cathode. NPR was not as good as that of my spherical fusor.
Images 3 and 4: Titanium coated endcaps and stainless-steel cathode. NPR nearly three times that of my spherical fusor.
Image 5: Six-inch fusor shell.

You mentioned that it’s not unusual for the beams to walk around, but that’s something I’ve not seen. (Other than that time the grid came loose)

Jon Rosenstiel
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Frank Sanns
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Re: To Focus or Not to Focus, That is the Question

Post by Frank Sanns »

Perhaps walk around may have implied a random walk over the entire surface. What I meant was a the focus is not just a single point in time. The plasma moves around somewhat during fusion. This is an interesting phenomenon that can put a beam at a view port or can cause irregular patterns from burn in over time. Your marks at the end of the flanges appear to be diametrically opposed patterns of some diagonal movement. At least one would assume that since the focus is a spherical end cylinder. The focus should be a spot or at least a diffused spot and not a line. Why lines at both ends if there was not some time dependent movement of the spot especially in your first photo?
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
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Richard Hull
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Re: To Focus or Not to Focus, That is the Question

Post by Richard Hull »

My original sphere fusor III had 13 beams minimum, (see my little avatar), with the original well done geodesic type grid. With the assumption all are BOT and wall loading opportunities and that the forward neutron emission due to same is present preferentially at these points, the bulk of the net current applied at any voltage is divided by 13 to some varying degree. Further, for the sake of argument and due to research done and reported by U of W that the fusion in velocity space is where the bulk of the fusion takes place, (due to any number of factors), and at the inner grid, minimal, we see that to some extent we might assume a certain limited amount of isotropic emission due to velocity space fusion and some more intense point fusion due to BOT at beam points. (iso + BOT)

Now there is no real detector that can measure 2pi emission. Thus it becomes a matter of detector/moderator position about the fusor. I posit that is why I never detected more than about 300K TIER from fusor III and at the same moment why I got that high a count!!

Explanation on fusor III

With so many beams, any moderator would certainly intercept about 3 of those 13 BOT points at 1/13 focused BOT + ISO each or 3/13th of BOT + ISO.
With my current (since 2005, simple "Rosenstiel" 6 beam grid) I might intercept no more than 2 BOT points + ISO. Thus the superior performance of fusor IV. 2/6 = 1/3 + ISO much better than 3/13 + ISO. Thus, for a given moderator size, which is the true detector volume, fusor III did not fare as well as fusor III. Still, due to sheer volume, any sphere will do very well in true ISO emission in velocity space compared to smaller volume devices.

Those new fangled cubes!

The cube takes its current to two BOT beams and 1/2 of the total focused current in beam energy is readily seen at each of two beam points. Jon Rosenstiel has reported intense emission at the two end of his cube and still some notably reduced neutron emission "off axis". Add to this the ability to place optimized absorptive loadable target material, (Titanium), at the focused beam points, recording better numbers in the BOT+ISO cube.

Now much of the really huge numbers reported are due to higher pressures and voltages and currents. So some of this is apples and oranges. Make of this, what you will. But I posit focused BOT on suitable absorptive targets of limited size tend to out perform the sphere. Again, so much of the recorded numbers is also highly related to moderator size.

for activation purposes, this smears a bit, but again, activation is just another fusion counter and the larger the moderator, regardless of beaming, the more ISO will come into the mix.

Finally, the moderator volume and intercepting face and detector volume within plays a huge role in reported numbers from any fusor or fusion neutron emitting source. Again, apples and oranges.

This is why the idea of a standard of detection and performance efficiency in an activation moderator placed at a standard distance is about the only true indicator in our work. Proposed but left hanging with no further discussion.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: To Focus or Not to Focus, That is the Question

Post by Matt_Gibson »

For whatever it’s worth:

I’ve tried using these cylindrical cathodes in my 4 way cross for a few weeks and found that they didn’t perform as well as my 3 ring spherical cathode. (1/3 the neutron count).

I would see the focused beam from the cylindrical cathode causing a hot spot (bright Orange) on the chamber wall during operation. With the 3 ring spherical cathode, no hot spots.

So from my view, focused may work in a cube fusor, but not a cylindrical cross.

-Matt
Jon Rosenstiel
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Re: To Focus or Not to Focus, That is the Question

Post by Jon Rosenstiel »

Frank,

I’ve always assumed that the elongated spots are related to the cathode’s feedthrough connection screwing with the cube’s electrostatic field.

In my thinking the walk around phenomenon is related to fusor size, grid/shell symmetry, and power per beam. Many beams mean low power/beam which in turn means these beams are easily distracted by even the tiniest amount of internal asymmetry. Just my 0.02 cents.

Jon Rosenstiel
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Richard Hull
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Re: To Focus or Not to Focus, That is the Question

Post by Richard Hull »

Jon is correct, I think. I had beams walk about in demo fusors where low currents are the rule in a sphere. Much of it was due to minor eccentricities. They never walked all around but more or less flicks to their various focus points based on grid geometry. Once the current increased the dancing, on and off beam ballet ceased and all grid openings had beams. I have not seen this since I got my sea legs on fusors in 1998 as I have had the power needed to light all beams to their fixed focus points.

The lozenge look is related to the beam's shape out of the geodesic grid structure. A picture of sorts of the exit window. In short, the impact points are images related to their origin.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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