Standard fusor geometry but with opposite polarity ??

[Rich Gorski]

It has occurred to me that fusion might (should) be possible if a fusor inner spherical grid were at a high positive potential and the chamber wall at ground. After reviewing the simulation work by Liam David, the results indicated that most of the fusion events happened by +D2 collision with neutral D2 along the ion's acceleration path. There were some beam to beam fusion events but the majority of fusion events were between accelerated +D2 ions and neutral D2 molecules. So in a positive inner grid fusor +D2 ions would be accelerated to the chamber wall and collisions with neutral D2 molecules should still take place…thus fusion. In fact, beam on target fusion events may be enhanced because of the huge area of the chamber wall compared to the BOT on the smaller inner grid. Fusion might be even more enhanced by and extra layer of titanium (grounded) and placed against the wall to absorb deuterium.

Anyone have thoughts on this or actually tried it?

Rich G.

[Richard Hull]

All it would take to try this idea is someone with a potent normal negative ground, positive "hot" supply to plug it into the fusor in place of their negative hot supply. All metering leads would need to be reversed, of course.

It would have to be a trusted fusioneer with good neutron counting capability able to hit 35kv at a minimum, I would think.

Richard Hull

[Rich Gorski]

Yes, the metering would have to be reversed. I would give it a try but my fusor is not the normal type having ion sources mounted on the wall of the chamber which are designed for negative accelerating potential. I would have to remove the ion sources in order to try this and change the acceleration rings to some more appropriate geometry. I do have a positive 40kV Spellman but its only good for 5mA. I'll have to give more thought about how much work is involved.

Rich G.

[Joe Gayo]

The breakdown characteristics will be quite different.

[Frank Sanns]

I have two Glassman 50kv supplies with opposite polarities. Here is one of the configurations that I ran way back.


viewtopic.php?p=55766#p55766


My conclusions were that running opposite polarity or running a high differential voltage to cut down on x-rays at 100kv differential was not the same. Running opposite polarity failed miserably with neutron numbers. HOWEVER, I did not run long enough to load my outer aluminum grid (far from ideal) but the number were so low, I did not bother. The 100 kv differential did not work either. Hollow metal spheres run the charges to the outside. Definitely a complicating factor.

[Rich Gorski]

Frank,

Thanks for steering me to your "pit fusor" experiment. Great idea trying to get to 100kV by using two smaller opposite polarity supplies and an inner and outer grid structure. I think Dennis was looking into this recently as well.

You mentioned that when the outer grid was positive w.r.t the chamber the neutron numbers were very low. Was this experiment also using the glass bowls? If so I suspect the bowls severely diminished the path of + ions going out to the chamber wall. Maybe that would explain the low neutron count. If it is true that most of the fusion events in a fusor are between accelerated +D2 ions and background neutrals and collision accelerated D2 neutrals with background D2 neutrals then my thought is that the direction and formation of D2 ions into a beam should have little effect on neutron count. So if the current level and pressure is the same then neutrons should be produced whether the +D2 ions are going toward the center or toward the chamber wall. The beam formation will be quite different between the two polarity cases since the masses of electrons and deuterons are 3600X different. So I would expect the plasma appearance to also be quite different.

If the effort is not too great and my +40kV supply still works I might give this idea a try.

Rich G.

[Dennis P Brown]

Yes, I have made some effort toward that concept but have been overwhelmed by so many critical tasks eating up all my time and energy the last few months - ugh!

Hope you can tackle the project before I (hopefully) get a chance - the key is proper instrumentation - current and voltage for both supplies. A neutron detector would also be useful for comparison.

I now need to fix my turbo controller(various jumpers and switches.) I did build the new 10 inch diameter secondary electrode assembly (metal plate with gasket & home made (aka likely leaks) HV feed-thru.) My 40 kV pos low current power supply now works again (had to reassemble it - another waste of time mini-project because I could ...) and my existing 30 kV neg high current supply is still fine. All now have current measurement gauges and HV gauges installed. My current baratron capacitance manometer vacuum gauge started lying to me big time but I can live w/o that gauge; its just for the foreline, anyway.

So, I was (VERY slowly) getting there. Of course, yet another new major home repair (do they stop?) is on my plate. So my latest plans for the lab are now out the window and my slow progress goes to a full stop; and indefinitely till I get this new repair done and of course, hold my breath hoping another does not crop up during or after that one - LOL

Retired appears to mean - more work then if I was actually being paid to work.

[Frank Sanns]

Rich,

Actually the insulating bowls came second. The initial experiment was without the bowls. I was trying to oscillations around the intermediate grid so the energy of the ions would not be lost on a single path. The idea was to try to get some recirculation around the intermediate grid.

I was not getting very good numbers with some of the configurations. It was then that I tried to insulate the two inner grids from the outermost grid near the shell of the fusor.

There was also another post that looked at where the ionization was occurring. Here are some links.

viewtopic.php?p=55858#p55858


viewtopic.php?t=2507


viewtopic.php?t=7844


Some of my pictures are either missing or in another forum as Richard was placing them in the appropriate forums and not all in the Images Section.

[Patrick Lindecker]

Hello Rich,

I calculated in this paper (§2.5) (http://f6cte.free.fr/Comparison_of_the_ ... ources.pdf)the performance of a D2+ beam injected in a D2 gas. Perhaps it can help.

Patrick Lindecker

[Rich Gorski]

Happy to report that positive polarity center grid does produce neutrons.

This test compares the neutron yield for negative versus positive polarity applied to grid. It is generally thought that most fusion events in the typical fusor are due to high energy D2 ion collisions with neutrals and accelerated neutrals (due to collision) with other neutrals. The bright star mode feature in the center of the negative grid might appear to be a point where beam on beam collisions are taking place. However beam on beam collision are probably a small percentage of total fusion events. If this is the case then should the direction in which D2 ions are accelerated matter? In the standard negative grid mode ions are accelerated toward the negative grid at the center of the chamber while in the positive grid case ions would be accelerated toward the wall of the chamber.

This test uses the standard spherical grid consisting of dual 1.5” diameter loops in a ISO160 chamber with four ISO63 cross arms (see first photo below). The test was run at -/+25kV with a D2 pressure around 1mTorr. Neutrons were detected with a 15 inch B10 tube running at 743 volts. The positive polarity supply is a Spellman 40kV unit with 5mA maximum current capability. The negative supply is much larger 75kV, 100mA Spellman. For this test the D2 pressure in the system was adjusted to achieve 5mA current while at 25kV in both the positive and negative modes. The results in terms of neutron production rate and additional comments and photos are shown below. The NPR was taken over a 1 minute period.

Observations and comments:
a) The neutron production rate for the negative mode was 93 CPM ( at P = 0.9mTorr) while under the positive mode (P = 0.3mTorr) the NPR dropped to 5 CPM. However when placed in positive mode at P = 0.9mTorr, the current level due to gas ionization increased beyond the capability (5mA) of the positive PSU. Therefore the pressure had to be reduced by three times to 0.3 mTorr in order to achieve 5mA current. This will cause a drop in neutron production simply due to less molecules available. Assuming a linear relationship of NPR to pressure we could conclude that the 5 CPM should be normalized to 3*5 or 15 CPM. That would produce a pos to neg NPR ratio of 15/93 or 16%. In other words the NPR in negative mode was 6.25 times the NPR in positive mode.

b) The next question to ask is why did the pressure have to be adjusted to achieve the same PSU current? The electrode geometry didn’t change, the electric field reversed direction but the strength was the same (25kV both cases). So, why does positive polarity produced a greater level of D2 ionization?

c) There was an obvious difference in the where the power (0.005A * 25000V = 125 Watts) was being dissipated between the two polarities. In the positive case the grid became yellow hot as you can see in the third photo below. However when in the negative mode the grid did not appear glowing hot at all (second photo). This must be due to the difference in mass/volume of the electrode receiving the electron flow. In the positive case the tiny grid dissipated the 125 watts of power and turned yellow hot while in the negative case the electrode was the much larger and more massive chamber wall that was dissipating the 125 watts of power. In the positive mode the grid became hot enough to actually melt a small portion of one of the loop (this is visible in the positive photo).

d) Comparing the two photos of plasma at 25kV the negative polarity mode showed a much brighter plasma than the positive mode. However this could be an artifact because of the bright yellow illumination from the hot grid in positive polarity making the glow of the plasma less visible to the camera.

e) In the negative polarity mode the dual wire spherical grid produced both vertical and horizontal beamlets with the vertical beamlets being much brighter than the horizontal ones. I assume the difference in brightness is due to the larger diameter ISO160 vertical cross arms compared to the horizontal ISO63 arms. In the positive grid mode the horizontal beamlets are just visible in the photo but the horizontal ones are not visible.

Conclusion:
The main purpose of this test was to note the difference in neutron emission between negative and positive polarity on the grid while keeping PSU current and voltage level constant. A difference of about 6X was observed between negative and positive central grid polarity.

Rich G.


SETUP

NEGATIVE GRID

POSITIVE GRID

[Richard Hull]

Interesting results in your report. Nice to know the standard negative grid, positive grounded shell or chamber is the best performer.
As many know, I am one of the few here who work in a spherical system. Crosses are the norm now. They have a special electrostatic
asymmetry due to the arm weld seams appearing as 4 to 6 more intense field regions.

Again, good experiment and report.

Richard Hull

[Dennis P Brown]

Outstanding work - the fusor knowledge base improves via experimental data. Someone builds it and tests it.

[Alexey Khrushchev]

Thanks for the interesting experiment!
Do you think that if we cover the walls of the chamber with titanium sheets it can lead to increased neutron yield in the mode with negatively charged chamber wall?