A Thought Experiment on Ideal Conditions

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
S Silvawalker
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Re: A Thought Experiment on Ideal Conditions

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Re: A Thought Experiment on Ideal Conditions

Post by John Futter »

Storm
I have taken time to look through your document
several things you need to improve on
1`./ vacuum your test rig has many leaks --this from the plasma pics you are at torr not millitorr. you need a good pirani gauge
2./ reusing electron optics means you have to use them at the design voltage and vacuum for crts around 2 x 10-8 torr and if a colour set of size 32" then about 36kV to run the optics
3./ I work in an ion beam lab and we go to a lot of trouble to remove electrons from our systems so that they do not neutralize any of our ions --we cannot steer or manipulate neutrals magnetically or electrostatically
4./ you need to get a copy of Simion to help with your design verification before you expend a great deal of time and money going down a dead end
S Silvawalker
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Re: A Thought Experiment on Ideal Conditions

Post by S Silvawalker »

Screenshot_20200803-152227_Gallery.jpg
Screenshot_20200803-152227_Gallery.jpg (80.95 KiB) Viewed 11816 times
I am using a very different setup to my one in 2018 and I now have a pressure in the 1 to 100 micron range. I modified the original circuitry of the sets to get the required voltages and filament currents. I have yet to run any simulations as I wanted to know I could fabricate my device before pushing the theory further since my university is unlikely to help and most of my work will be self funded.

Since I'm doing something I have found no evidence of anyone trying before even if i don't find what I'm looking for here this device will likely have more value as a pathfinder for my future builds.
S Silvawalker
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Re: A Thought Experiment on Ideal Conditions

Post by S Silvawalker »

Re ionization seems to be caused by beam collisions in an EBIT so I wonder if that would solve the problem of neutral atom formation when combined with the accelerating potential? I will try to make simulations but that will be later on
Patrick Lindecker
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Re: A Thought Experiment on Ideal Conditions

Post by Patrick Lindecker »

Hello,

Thanks for the interesting document. I looked at your main diagram and I hope that I undestood the principle.

It seems possible to create an electrons cloud in the A zone but at a price of an enormous electrons injection power.
Each electron is injected with a yield of 0.5 for a good ion gun (kinetic energy/electrical energy). The electron kinetic energy is completly lost by colliding the electrode 9 (kinetic energy -> mechanical and radiation energy). As you proposed a direct electrostatic conversion would be possible but it is complex and the yield (electrical energy/kinetic energy) is not equal to 1 (rather 0.6).

The confinement time of an electron in the cloud is extremely small, just the time to cross the A zone (several ns). The potential created in the A zone will be extremely low (mV or microV ?) except by using very powerful ion guns (but the final yield of this apparatus will be, at best, the same as the fusor one, about 1E-9). Note that the goal would be to have a potential of at least -35 kV.

In my opinion, the diagram misses only a way to confine electrons in the A zone during, let's say, 1 sec. In that case, the neutral pressure will have to be extremely low (<1 microPa) to avoid to lose electrons energy in collisions with neutrals.

Patrick Lindecker
S Silvawalker
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Re: A Thought Experiment on Ideal Conditions

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My idea is to not try and confine the electrons at all rather they never lose enough energy to recombine with the ions. Think of an electron beam ion trap but with 3 or 4 beams instead of 1. The key is that the electrons don't have to be lost and in a final system the losses can be minimized from the electron beams by slowing and recollecting the electrons after they pass the centre. It is based on the idea that in an idea world a particle accelerator with no collisions would only have to impart 1MeV to each ion to give the highest probability of fusion which could release more.

If any one point along the beam of electrons is treated as a point charge, equivalent to the number of electrons in that cross section of the beam, then the charges and masses of the infalling particles, assuming the electrons are fixed and solve for the required distance for the ions to gain 1 MeV. Assuming a beam current of 1 micro amp and only deuterons being accelerated the acceleration distAnce needed is 8 ish mm which fits my chamber. The remaining problem is finding a high enough accelerating voltage for the electrons such that they aren't scattered significantly by the infalling ions or other electron beams.
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Re: A Thought Experiment on Ideal Conditions

Post by Patrick Lindecker »

Thanks for the explanations.

>in a final system the losses can be minimized from the electron beams by slowing and recollecting the electrons after they pass the centre.
However, due to successive yields, you will recover perhaps 1/3 of the primary energy as a maximum. It seems difficult to do better.

OK to accelerate ions with electrons, via Coulomb collisions between ions and electrons. Of course, you know that energy transfer coefficient between a light particle (electron) and a heavy particle (D+) is low (a mean value of 2*me /mD+, so about 0.00054), with a big scattering angle for the electron an a very small one for the D+ ion.

However why not... Good testing.

Patrick Lindecker
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Re: A Thought Experiment on Ideal Conditions

Post by John Futter »

Storm your new plasma pic still is about the 100's of microns
do not forget that mean free path at 1 micron is only 5cm and an electron hitting an air molecule is immediately going to disappear at some weird angle with out doing very much to the air molecule as pointed out by Patrick
As pointed out before Simion ( or Comsol multiphysics) does also allow electron trajectories and intereactions your University will /should have this program (ours do).
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Dennis P Brown
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Re: A Thought Experiment on Ideal Conditions

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Don't get discouraged - all new ideas run into problems and people here are trying to both help you understand issues with your ideas/approach and trying to help you correct possible short commings in your system. But new ideas that push at extremel parameters often require both good setups and more theoretical understanding.

To get realistic free paths for ions and electrons, both a very high quality vacuum system and a diffusion pumps w/cold trap or a turbo is absoultely required (generally, 10^-6 torr is a good bench mark.) There is no way around that issue. You simply can't accelerate electrons to high energy without a very good/high vacuum.

To accelerate electrons to 1 MeV requires that voltage! As pointed out, very little of that electron energy will be coupled to ions due to the mass difference and low propablity for a direct strike - you can't change physics. So to get a significant current at 1 MeV even for just the average fusor, would require a significant output of a power plant. That is an easy calculation and you really need to look at that - remember, current is everything when it comes to fusors and even then all you get is their trivial fusion rate.
S Silvawalker
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Re: A Thought Experiment on Ideal Conditions

Post by S Silvawalker »

The necessary energy for the electrons in the beams and therefore the needed accelerating potential is still an unknown. The 1MeV stated was the approximate per ion energy to maximize their cross section for fusion in the case of deuterium and tritium and did not refer to the electrons. The image is from a run using some old oil I'm doing a series of oil changes and pump tests to get the pressure down. I will be back at my university after January so until then I only have so much time and space to work with and within so I am only going to be using a mechanical pump, which is rated to reach 0.75 microns although it is quite old. There won't be much scientific rigor to these tests but if I get any neutron detection then i will be confident it moving to the next build.
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Dennis P Brown
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Re: A Thought Experiment on Ideal Conditions

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Using deuterium ions instead of electrons makes the effort even more difficult in energy costs for MeV level ion energies. One would never use electron collisions to accelerate deuterium to such high energies. MeV level deuterium ions are generally achieved by using large accelerating electric fields - like a Van de Graaff. And the x-ray flux from any electrons in such a field would be highly dangerous.

As for your pump, if mechanical, getting down to 5 to 15 microns is possible (sorry, highly unlikely any mechanical pump can do 0.75 microns - if you can reach 5 microns you have an excellent pump.) The issue is often leaks in the system, rather than the pump. To test that, connect a vacuum gauge that can read microns to the pump inlet and measure the pump alone. That tends to give a better idea on if the pump is the issue or leaks.
S Silvawalker
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Re: A Thought Experiment on Ideal Conditions

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It isn't the electron- ion collisions that are the primary acceleration source that is the accelerating potential between the electron beams and the housing. Ions will be attracted towards the beams and repelled by the positively charged housing and CRT anodes. I saw experiments with pressures around 13 microns getting neutrons so 5 to 15 is reasonable. I don't expect the pump to reach its stated pressure I had to do a double take when I saw what it said it could do as well. I predict that so long as the pressure is low enough for the electron beams to be fired, this setup should be more forgiving towards pressure when compared to a regular fusor.

In an electron beam ion trap the ions are confined radially by their attraction to the electron beam through the centre and along the length of the beam by the positively charged drift tubes. These devices are operating at far higher charge densities within the beams when compared to mine but can also confine heavy elements such as uranium ions so lighter ion confinement should also be possible.
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Dennis P Brown
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Re: A Thought Experiment on Ideal Conditions

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Yes - 5 to 15 microns (and higher for smaller fusors) is absolutely the ideal range. However, you have indicated you are aiming for long lived ions; and this is only possible at much higher vacuums. Ditto for electrons and them forming a trap. At 5 to 10 microns, most electrons will be scattering off other ions or electrons. To form any type of ion trap, the very high vacuum must be achieved. Ditto for 'drift tubes'. Just calculate free paths lengths for given pressures or just look them up.

The ions in a fusor are traveling at fairly high velocities so even if one has a 'negative' charged region (i.e. as a polywell was supposed to do) the amount of ions then being 'trapped' would extremely small. Plus ions that are trapped, can only fuse via tunneling and that is very difficult for slow ions. So trapping deuterium ions would more likely lower fusion rates. The ion speed does assist in getting the ions close enough that tunneling can be enhanced.

Last, when you say that the ions are accelerated by the potential between the case and an electron beam - sorry but no. First, at 5 mircons you won't have any defined electron beam (again, see free path.) The charge created by the electrons striking deuterium molecules cause a small region near the gun to be filled with positive ions so the net field in that area will be essentially neutral. That is why fusors use very powerful transformers to create the electric field to accelerate ions and not electron beams.
S Silvawalker
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Re: A Thought Experiment on Ideal Conditions

Post by S Silvawalker »

Firstly, I agree for future builds I will definitely need a higher vacuum pump such as a turbo or diffusion one. However, for testing with ions only traversing the diameter a few hundred times each the ions are long lived enough.

Secondly, the electron beam will be well defined as the electrons travel unscattered enough in a CRT television, at 300 microns far more than I am working at, to form a sharp image at, in the case if the televisions I used, over 25cm away from the accelerator. I had seen the negative region I predicted was not far in front of the anode so for this build the region where the beams cross is only 1 cm in front of the accelerating anodes and the square the beams trace is only 2cm to a side. This minimizes the distance needed for the electrons to travel.


Unfortunately my deuterium is taking longer than expected to arrive and I am still chasing leaks so I still have to work from theory for a bit longer.
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Re: A Thought Experiment on Ideal Conditions

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All CRTs are pumped to at least 10e-6 torr usually deeper, if possible. 10e-6 torr is .001 microns! We never use micron terms, however for deep vacuums that are in CRTs. 300 microns are terrible junk glow discharge ranges. 300 microns = .3 torr. CRTs are at .000001 torr.

Richard Hull
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Fusion is the energy of the future....and it always will be
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S Silvawalker
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Re: A Thought Experiment on Ideal Conditions

Post by S Silvawalker »

My apologies I completely misread the pressure of the tubes I was using, the mean free path with the pressure I hae is too short. My chamber can definitely work for the pressure but there is no way I'm going to be able to get there with this pump. I need to find an oil diffusion pump in the next 2 weeks which is a more difficult challenge than the actual experiment but I will find a way.
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Dennis P Brown
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Re: A Thought Experiment on Ideal Conditions

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Now that you are starting to understand the issues facing your experiment, I would caution you about high vacuum work: it is a very difficult techonolgy to master without proper equipment. Certainly a good vacuum system is required - hence you need to select connector types - either kf connectors (ok down to 10^-6 torr) or conflat (copper gaskets; essential for better than 10^-6 torr).) Building a quality vacuum system is essential for both achieving a leak tight system and one that can be more easily leak tested - which for high vacuum is an essential skill. This means finding good deals on e-bay or paying big $$$ on new.

A diffusion pump (DP) without a cold trap means you will be restricted to 10^-5 torr range - period; also, a dirty system. If you need 10^-6 torr or better, then a cold trap is essential (as well as a super clean and leak proof system.) Further, the vast majority of DP's available require water cooling; so that means plumbing of water lines. Air cool exist but are hard to find and need special adapters (usually must be custom made - this is true for many water cooled DP's, too. So that is a consideration in selecting units.) For these reasons (and others), most people use turbo's for high vacuum work.

Again, glad you are both experimenting and following your ideas. Good luck and do ask about specifics on DP's before buying one so you get both the right DP for your needs and a proper price. If you are going low cost, learning to use a lathe/drill press/mill are essential skills (and for undergrad physics students this use to be part of our suggested lab training - so maybe your future school will allow you access.)
S Silvawalker
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Re: A Thought Experiment on Ideal Conditions

Post by S Silvawalker »

I am using all KF 50 pieces and have the system baked for 2 hours at 200°C, should be good for the diffusion pump setup. I have experience working with precise metal fabrication, I learned making art pieces and turbojet when I was younger and have a full shop to work with. I'm employed, with no tuition, and in my second year in aerospace engineering, so I have all the resources I need to pursue this the only resource I don't have at the moment is time. My deuterium gets here on the 19th so I'm moving heaven and earth to get a working diffusion pump and test the electrical before then. I am aiming for 10^-6 torr with this new setup but the next one, likely next year, will need to use a custom housing and cathode ray tube setup with as few openings as possible. This summer I'm rushed but this is definitely a long term project.
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