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?

[Rich Gorski]

Alexey,

Adding Titanium to the wall to absorb D2 and increase neutron production was my thought too. I might give it a try since I'm already set up to test this. The complication is that the added grounded Titanium will change the three dimensional electric field so I would have to redo the entire experiment. That's not a problem except for the fact that I'm running out of heavy water and a new supply is $150.

Rich G.

[Richard Hull]

Way back, I thought about heavy electroplating my spherical fusor interior walls with palladium. But the thought went away due to expense and sheer idleness on my part. There are advantages to the spherical chamber. Relatively even distribution of electrostatic fields.

Richard Hull

[Alexey Khrushchev]

Perhaps a simple solution would be to vacuum infuse titanium onto the chamber walls. For this purpose, it is enough to replace the central anode with a titanium wire and create a potential difference of 5-10kV at a current of about 50 mA in a hydrogen medium.

Heavy water is quite expensive. My wife gave me 50ml of D2O for my birthday at a cost of $50.

[Dennis P Brown]

If you want to coat the chamber with Ti, then use an argon trace gas (somewhere in the range of 50 microns to 250 microns using that voltage/current.) Using hydrogen is a bad idea - it is far too reactive and will prevent high purity Ti from coating the chamber walls.

[Alexey Khrushchev]

On the other hand, if we use deuterium instead of argon, the walls of the chamber will be covered with Ti#D, which is what we need).

[Dennis P Brown]

I do not think chemically bonded deuterium in the walls is anywhere near as efficient in supporting fusion as unbonded deuterium. Think about it - deuterium chemically bonded to titanium is not ionized so is not striped of its electron. The electron orbital between the titanium and deuterium - a very powerful covalent bond - will not easily permit other deuterium's (even ionized ones) to closely approch the bonded deuterium's nucleus. One reason deuterium gas (D2) doesn't undergo fusion naturally (lucky for us.)

What you want is ionized deuterium loosely 'bonded' via Van de Waals forces to 'hang around' the surface of titanium. So the deuterium is still not really bonded (have 'orbital' electrons); that is, the deuterium has no electron cloud around it. Then other free and ionized deuterium in the fusor plasma will collide and interact/fuse with those similarly ionized but loosely 'bonded' deuterium nuclei being held in place by the titanium on the walls.

So I would suggest pure titanium coating the walls - this provides vastly more such potential bonding sites compared to Ti--D complex.

[Richard Hull]

Titanium deuteride in the walls of a fusor is constantly bombarded by super high energy electrons. These dislodge the deuterium and ionize it right at the wall where it is repelled and accelerate toward the grid in the center!

Exactly the ideal situation. Likewise fast and slow D neutrals if not re-ionized in velocity space are doomed to hit the walls creating more titanium deuteride. Remember, wall loading of D is recorded to a limited degree in SS. Imagine a wall of palladium or titanium!! The loading occurs interstitially to a depth of only a few microns. Know well from cold fusion work and noted by us as well. The chemical bond in the deuteride is relatively weak and an impact by a 10-50kv electron will easily break the bond freeing a deuteron.

Richard Hull

[Dennis P Brown]

I certainly agree with what you said, Richard. I also think a pure titanium wall film would provide a better surface for those reactions and achieve all you mentioned but at a higher rate. Loading the pure metal Ti with deuterium by simple deuterium gas (during fill before striking a plasma) would provide more available deuterium for collisions (after coating using argon, admit D2 gas afterwards to load the walls.) Not sure the difference is worth all that effort but would be an interesting experiment for someone interested in the net difference.

[Alexey Khrushchev]

I'm not sure the efficiency of deuterium uptake by pure titanium would be as effective as preloading during sputtering in a deuterium atmosphere. For example, pulsed neutron sources use targets made of titanium that has been loaded with tritium under special conditions.

Loading titanium with deuterium is the only way to increase the local deuterium concentration without increasing the pressure. The more deuterons we collide, the more neutrons we get).

The binding energy of deuterium-titanium is ridiculously small compared to the energy of the deuteron falling on the target. The chemical binding energy is only a few eV. Therefore, ionization will occur instantaneously. However, this is rather a negative process, since there is a Coulomb repulsion between the falling deuterons and those knocked out of the target, which will slightly reduce the efficiency of the interaction.

[Richard Hull]

True deuterons are produced only at the shell or in velocity space within the fusor. As such, all deuterons will never impact the shell. (Repelled)
Only slow and fast deuterium neutral gas atoms will hit the wall or shell as they are not repelled electrostatically. These can form the deuterides in the wall. One needs to consider and keep in mind that the number of deuterons are a tiny fraction of the neutral deuterium gas atoms in the fusor at any given instant during operation. The number of deuterons at full fusion energy at any instant are miniscule!
All of the above have been discussed and put in FAQs many times in these forums under the moniker of "how the fusor does fusion."


When one considers the number of deuterium gas atoms at operating pressure in a fusor....deuterons in the fusor are a tiny fraction of the deuterium gas and full energy deuterons are virtually non-extant. Slow and fast neutral deuterium atoms make up most of the deuterium gas in the fusor. For every neutral deuterium atom, there is a high speed electron eager to get to the shell or wall, but they are also possible of re-ionizing neutrals on their way there. Electrons cause the shell to heat along with the slow and fast deuterium gas atoms.

The fusor operates at a 10e8 or 10e9 net energy loss to fusion energy produced. (typical 300-500watts input... 1microwatt of fusion out.)

Richard Hull

[Rich Gorski]

Interesting discussion.

One problem incorporating titanium in the vacuum chamber is the fact that titanium like aluminum and magnesium will quickly develop an oxide layer TiO2 (Titanium dioxide) when exposed to air. This is a several nanometer layer of essentially ceramic that will develop within a day and greatly hinder the ability of titanium to absorb hydrogen. So somehow the titanium has to be cleaned of the TiO2 before introduction of deuterium gas for absorption and will have to be done every time the chamber is brought up to air. There are several ways to clean the TiO2 from the surface (chemical, mechanical) but maybe the best would be an ion etching before the introduction of the D2.

My thought right now is to just purchase a thin sheet of titanium and place it appropriately inside the chamber and try some things out.

Rich G.

[Paul_Schatzkin]

.

I just tuned into this thread when it appeared at the top of the Active Topics:

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.

And that, I dare say, is a strong argument FOR what I'm calling "The Waterstar Project"

Got an interesting idea? We've got a machine... here's a budget, let's see where it goes....

--PS