Helium-3 Fusor Thread

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Michael Bretti
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Re: Helium-3 Fusor Thread

Post by Michael Bretti » Fri Mar 23, 2018 1:45 am

Jackson,

Some very important things to note about these extra high voltages. Once you start getting up into the +100KV range, things get much, much more challenging to deal with. Working with a fusor at 50kv or lower is very different from 100kv, and don't assume that once you have worked with one level the other level will be the same. At these voltages, electricity can act quite bizarrely and counter-intuitively. Surface tracking for one becomes a major issue. High voltage at these levels will no longer necessarily take the shortest path between two points, and can track very long distances along a surface. Another major issue is corona losses. At these voltages, you will have significant corona discharge spraying from any metal surface that is not smooth or has a very large, even diameter. Any sharp edges drastically increases field enhancement effects, making these voltages even more difficult to deal with. Also, depending on the amount of corona losses you have, your load will suffer from fluctuations and instabilities. Large corona losses will also load down your power supply.

The injector of our facility's electron linac is biased anywhere from -125kv to -150kv. The whole gun and all of the controls, monitoring, pulsing, and drivers also float at this voltage on an isolated deck on top of a large isolation transformer. The entire deck, along with the injector has to be contained in a specially designed corona shield, which has very large diameter corners and smooth surfaces. The whole thing sits inside a large metal shack with several dehumidifiers and a temperature control unit to control ambient temperature and humidity. Even at the long distances, between the corona shield and overall enclosure, depending on the humidity, it can still arc occasionally. Especially on very humid days, in our second test injector, we can observe very large corona losses and instabilities at the higher end over 125kv. Also, current at these levels have a major impact, especially on corona losses, surface tracking, and arcing. We run our injector at probably less than a mA normally, but with humidity it can draw several mA from the supply. Turning up the current even just a couple of mA can introduce very large corona losses, and with it, system instabilities and arcing. Running a power supply for this type of fusor not only at +100kv voltages, but currents in the tens of mA range is incredibly difficult, and dangerous to control.

From the x-ray standpoint, our entire test bunker has several layers of almost 2 feet thick of special iron-weighted concrete blocks, stacked to prevent direct line-of-sight between seams of adjacent bricks to minimize radiation leakage (the actual linac injector, not the test stand, is inside a massively shielded room with many feet of shielding, but this is mainly for the neutron shielding.) Everything is controlled remotely from outside of the controller. It is not a small setup, and is much more complex than running a typical fusor on a workbench. At these voltage levels, you will be looking at a similar setup for the fusor.

If your insulator is only rated for 25kv, you may get away with running it at 50kv, as you have without issue. Over 100kv, this will not be the case. At these voltages, if the insulator is not long enough, the arc can very easily track along the surface (the reason why these insulators have wavy structures is to increase the surface distance between two points to reduce surface tracking possibility as opposed to a straight insulator.) At voltages and current you will be looking at, it is also very difficult to insulate, and can punch through even seemingly thick insulation with ease, especially if there are any gaps or defects. Even applying insulation yourself over a connector or between two points requires very special step gradations with various insulators and thicknesses to deal with and manage field potential distributions and gradients. The arc can snake in between cracks, seams, and joints. Something known as the "triple junction effect" also becomes an issue, where localized geometric field enhancement occurs when insulators of two different permittivities (such as air and ceramic) meet at an electrode, which can initiate discharges that can propagate along a surface. Add high currents to this and it becomes a very formidable challenge.

You also have to consider your vacuum system at this point too - all of the points above are only for the outside of the system, we haven't even gotten to issues actually in the system. Pressure and breakdown voltage are related - look up the Paschen curve. Under certain conditions, an arc can travel extremely far at even very low voltages. You also have to consider all inside surfaces that they are flawlessly smooth, especially your grid - any tiny sharp edge not perfectly ground down and smooth will cause immediate issues. You also have to deal with the effects of water vapor and surface contamination in your system - to run a fusor like this at these levels, proper conditioning is an absolute must. It takes us many, many hours of conditioning at high voltages before we can even turn on our electron beam - if it is not conditioned well enough at ultra-high vacuum levels, it will arc over internally when the beam is on.

For your idea on lining the inside with ceramic, this may not actually prevent arcing as you expect. Charged particles bombarding insulator surfaces in vacuum systems will build up a charge on the insulator, and can easily cause it to arc and flash over. This is very observable in systems such as high power RF windows as well as insulating structures in beam systems. RF windows actually have to be coated with a special metal layer to prevent charge buildup and secondary field emissions which in turn cause breakdown across the ceramic. In fact, one of the major issues for DC accelerators with a stacked ring-insulator topology, is that the beam cannot be allowed to "see" the insulators. If it does, charge will build up, causing arc over. Therefore, special shaped rings are placed internally to guard over the insulators to prevent charge from directly depositing on them. It's also a phenomenon in sputtering systems: one of the reasons why you cannot sputter insulators with DC is that charge will build up on the insulator surface from ion bombardment from the plasma. RF is needed to prevent this and sputter these materials correctly. Just adding ceramic insulators will not necessarily prevent arcing in your system, and depends how and where they are set up. If all of the walls are lined, it may also cause issues with actually running the fusor itself, and could lead to unforeseen instabilities.

Again, a fusor, or any high voltage system, is very different at tens of kv vs. over 100kv, and there are many things to consider, both inside and outside the system. It will become a much more serious engineering effort and require a lot more planning, research, and money. It is do-able, but you are entering the realm outside of what can be done on a desk at home.

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Richard Hull
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Re: Helium-3 Fusor Thread

Post by Richard Hull » Fri Mar 23, 2018 4:19 pm

As I noted, 3He-D fusion is more or less impossible in amateur hands for far more reasons than enumerated here. Money is the big stopper of big dreams. The thoughts and ideas cost nothing. The verve to see it through would require someone with the time and energy to spare....Very, very rare.

The less machining, high voltage and materials skills one possesses, means more and more big money would have to be poured into the effort. The general meaning here is that you would have to bring to bear expensive outside talent, billed by the hour.

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.

Michael Bretti
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Re: Helium-3 Fusor Thread

Post by Michael Bretti » Fri Mar 23, 2018 5:18 pm

As Richard Hull said, thoughts and ideas cost nothing. Continue to explore and research! Even if there is something you may not actually be able to build or run yourself, you will gain invaluable knowledge nonetheless, which could help you in other pursuits. There are so many fields and applications that have overlapping fundamental principles that you could very well use to solve other problems in areas that you can tackle. D-He3 fusion is not impossible, but from a technical and financial standpoint it is beyond what most amateurs and home experimenters have access to themselves, and requires much more planning than a standard fusor. It starts entering the realm of better equipped and funded research labs. But you can still glean a lot of valuable information still studying these systems, and having the drive and motivation to further explore and push forward on these ideas and pursuits is an admirable trait and will drive you towards a bright future.

Collect papers on anything and everything even remotely related to these topics, immerse yourself in the field, and build up a library of knowledge and reference material. Over the years I have collected and read over a thousand technical, academic, and industry papers on everything I can find on high voltage, plasma, pulsed power, etc, and have been building up a large amount of supplemental resources - binders, notebooks, and textbooks full of data and reference material. Even though most of the technology is not stuff I can build myself (mainly from a financial standpoint), it has been beyond valuable in my own pursuits in engineering. Especially now that you have started these pursuits so early, you have a very large head start, especially if these are fields you want to continue exploring as a career/hobby.

Since you already have a verified, working neutron producing fusor, why not work on further optimizing your output and experimenting with your system? You have run the fusor to produce neutrons, but have you done more to push your system? Have you hit the meganeutron mark? What about 2 million n/s? What about 5? Have you tried different grid topologies? Ion beam injection? Pulsed operation? Activation? What about an automated pumpdown and control system with a full user interface and data logging? There are still a ton of things to explore now, and having a working system is the very beginning of the pursuit! That is where the real fun begins!

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Frank Sanns
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Re: Helium-3 Fusor Thread

Post by Frank Sanns » Sat Mar 24, 2018 10:35 pm

Early on there was much discussion about Helium-3 and Phil Fostini actually did some fusion runs. He has several posts on it. Here is one in the Images Section.


viewtopic.php?f=18&t=7695


Also, as previously stated. U of Wisc Madison has some papers on using it as a fuel. Graphs and neutron output vs voltage and pressure are out there. They were also the subject of discussion on here back around 2005-7. Maybe.

Michael Bretti
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Re: Helium-3 Fusor Thread

Post by Michael Bretti » Sun Mar 25, 2018 2:13 am

While it is very cool to see different color poissors in a fusor (the blue glow of an argon one would be awesome to see), the issue is mainly running proper voltage and currents for the reaction to occur and verifying He3-D fusion, with proper safety measures. The pictures in the referenced post from Phil Fostini do not show anything more than a fusor running on different gases. Reading the archived posts, I do not see any data verifying the reaction, unless I am missing it. Anyone can inject any gas into a fusor, including He3. However, just running a fusor with He3 in it does not show He3-D fusion, nor does more than produce different color plasmas. Since the reaction produces no neutrons itself, the fact that neutrons are measured only shows D-D fusion occurring. In order to verify He3-D, more advanced activation or detection is required.

The paper from University of Madison-Wisconsin verifies this reaction with activation of Mo-94 to Tc-94m. This requires very high voltage at reasonable currents, and enough proton flux for activation. Someone could get away with it at lower inputs, but the time required for activation will go up considerably. It is do-able, but such power supplies, shielding, and activation is considerably greater of a challenge than most people have access to on the average hobbyist budget (not to mention the cost of He3 to begin with.) AlI things considered, for someone who has experience at these voltage levels and shielded systems I don't believe this would be difficult to run or be an insurmountable technical feat, it mainly comes down to cost - power supply, gas, shielding, supporting infrastructure, and a means of verifying the reaction, the easiest of which would probably be activation.

Michael Bretti
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Re: Helium-3 Fusor Thread

Post by Michael Bretti » Sun Mar 25, 2018 3:15 am

Here are a couple of more papers I have on the subject regarding He3 beam-injected fusor systems:


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