Fusor Running, No Neutron Detection

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Mark Rowley
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Re: Fusor Running, No Neutron Detection

Post by Mark Rowley » Wed Jan 29, 2020 3:27 am

Alan,
I think your detector is too far away from the grid.

For this type of arrangement, the detector tube distance should optimally be about 15-18cm / 7 inches from the grid. Especially since your initial neutron rate will be low until you become familiar with driving the system.

To be clear, the detector tube itself (moderator excluded) should be around 18cm from the grid. As it looks now, I don’t think you’re getting enough neuts into the moderator to be thermalized for guaranteed detection.

Mark Rowley.

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Re: Fusor Running, No Neutron Detection

Post by Mark Rowley » Wed Jan 29, 2020 3:50 am

Here’s a couple pics of my geometry for reference. The red cap on the screwdriver is equal with the location of the grid within the chamber. The brown cap in the paraffin moderator is the end of the detector tube. Distance between the two are 18cm/7”.

The front picture is just for orientation purposes of where the cross point is located.

A couple more thoughts.

The precip supplies generally don’t need a ballast resistor as they have a built in current limiter. You may be choking off your supply. Also, is the current monitoring circuit installed before or after the ballast resistor? Should be after, but I’d suggest removing it altogether.

Lastly, your detector has a ton of moderator. You may be absorbing your thermalized neutrons before they get a chance to get to the tube. But then again, possibly not. Depends on the diameter of your tube. I think 3.5-4” of moderator around the tube is what’s normally called for. I’m sure others here can weigh in on that better than me.

Hope this helps

Mark Rowley
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Re: Fusor Running, No Neutron Detection

Post by John Futter » Wed Jan 29, 2020 5:56 am

I would have thought 2" thick wax moderator all round would have been enough
Too much absorbs all ie thermalized to zero. I know our Cosmic neut He3 counters only use 6" thick moderators and the cosmics are much higher in energy than DD fusion

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Richard Hull
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Re: Fusor Running, No Neutron Detection

Post by Richard Hull » Wed Jan 29, 2020 10:38 am

Carl Willis put up diagrams related to moderator thickness years ago. I found a couple of images that I captured years ago. They are related to radiative capture in Silver, but you will note that simple high density polyethylene which is close to Paraffin wax peaks near 5cm or 2 inches of moderator any thicker and it degrades rapidly. I use a 3" water moderator surrounding the 3He tube. (centered in a 6" water cylinder.)
The second image relates to Paraffin specifically. Closer is, indeed, better with any moderator/detector neutron counting situation for new fusor operators.

The upshot is.....I had to say this.....

use moderation in moderation.

No apologies offered.

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Fusion is the energy of the future....and it always will be
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Re: Fusor Running, No Neutron Detection

Post by Alan Sailer » Wed Jan 29, 2020 3:18 pm

Mark,

The distance issue is valid. I'll look into changing this. I'm at work right now but I'd guess that my grid to He3 tube
distance is twice yours which would reduce the flux by a factor of four.

The voltage is being measured after the ballast. Your observation about the precipitator having current limit is true.
In my reading of the FAQs/threads I got over-sensitized by the insistence on a ballast. In retrospect the power supplies
being ballasted are probably heavy iron monsters. It's probably not an issue but I will think about removing it.

John,

Since the only neutrons I have been measuring are background maybe the 3" paraffin was enough.

Richard,

Thanks for the curves. From the bottom one my 3" (7.6cm) moderator would be "killing" close to 50% of my theoretical D-D
neutrons. Coupled with Mark's distance observations this may be the reason I'm not seeing anything. I work in microwave amplifier
engineering and 9bB of neutron "power" loss is a lot.

My goal will be to reduce both the grid/detector distance and the thickness of the moderator. Should give me a better chance.

Cheers.

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Re: Fusor Running, No Neutron Detection

Post by Alan Sailer » Sat Feb 01, 2020 11:37 pm

All,

Very discouraging results today. I spent a few days reducing the moderator thickness from 3 to 2 inches. I positioned the moderator/He3
tube much closer to the grid, 5 inches vs ~16 inches.

The run started OK. No neutrons at about 28kV, 30microns and ~3mA. Then, without any drama (current or voltage swings) the precipitator supply
just died.

I am a careful worker especially around high voltage. I have built and operated several high voltage supplies in the 10-28kV range.
So I have some experience with this stuff. These precipitator supplies are not very good supplies.

Things I have noticed,

1) No bleeder resistors on the input capacitor. This helped me kill supply number one. Electronics 101 ignored.
2) One supply had two different MOSFETs in the half bridge. This screams that they are doing whatever they can to ship these things.
Bridges are supposed to be balanced.
3) The mounting holes for each of the three supplies I have are all different. Quality control? No.
4) Potentimeters are mounted any way the assembler puts them in. Two supplies CW one CCW. Poor quality control.
5) High quality Bourne 10 turn wire-wound resistors kill low quality precipitators.

I cannot ignore the fact that several people on this forum have built successful fusors using precipitator supplies. From the evidence I have
seen they may just be lucky, getting a good unit through terrible quality control.

My past experiences with Chinese high voltage equipment matches what I see in these supplies. Years ago I went to a company that specialized
in high voltage pulse capacitors. I ended up paying for two units, both of which internally arced as they slowly destroyed themselves. The Maxwell
units I did use lived through thousands of discharge cycles. This is only one of several experiences with high voltage and Chinese corner cutting.

When I was working an home built palsma tubes/globes I got the see what was happening in the plasma art community. Several of the artists were
having serious issues with the power supplies they were buying form Information Unlimited. The common denominator were the output transformers,
Chinese flybacks. I was worried about this problem when I started using the precipitator supplies and have never operated them without putting
them in x-ray transformer oil.

This leaves me in a difficult position. I hate giving up on a project. But it just isn't any fun at this point. I have spent most of my efforts on
a fusor trying to fix or work with the precipitator. To move forward I'd have to spend a lot of money building a real HV power supply.

I'm closing my diatribe by mentioning the obvious, you get what you pay for. The precipitator supplies are ridiculously cheap for a high voltage supply.
My contention is that they cut way too many corners.

Cheers.

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Re: Fusor Running, No Neutron Detection

Post by Richard Hull » Sun Feb 02, 2020 8:15 am

I cannot pontificate on what I have no real experience with, but much of what you speak of is probably the case.

First, these so-called supplies,were made as precipitators and not power supplies per se. This leads to the idea of electrostatic action as opposed to real current flow in any form of arc condition or any form of current delivery at voltage that is anything short of a flawless fixed small current. Glow mode operation can be hectic and kick back spikes and other trash into the chi-com supplies that were designed for simple establishment of an invariant electrostatic field under static conditions perhaps at microamp current flows when functioning between fixed plates in air. (the original design criterion)

They are being rather misused over there designed function in fighting to just achieve smooth gas load with the highly spike laden start up barrier being a storm tossed gulf over which it must sail before the gas load more or less settles down.

The term power supply without a specific moniker like "Precipitator" are typically expected to supply any voltage at any current over their entire range within specification. Good supply design will have protection circuitry that will shutdown the supply safely when any significant spike outside of design current or voltage delivery is seen, (Spellman,etc.)

The wonderful world of solid state, long ago abandoned heavy, high power, custom wound, low frequency line transformers of very high voltage output that would sustain tremendous over load currents. These, if expected to deliver smooth filtered DC power, demanded large capacitance, high voltage storage capacitors needed to smooth to near perfection a 30-50kv smooth DC delivery under load. The older supplies could withstand horrid abuse. This including arcing and exceeding pulse spikes in the 10X power delivery range showing up as nothing more than a temporary dip in voltage without so much as straining to do it!

Admittedly, no one on earth can, today, will accept a DC supply that is delivering anything other than smooth DC to a smooth well calculated stable load current. It is actually easy to make a modern "rough and tumble" HV DC solid state supply that will handled nasty load spikes 10X the power output rating of the supply with 2 full second long, dead short, shut down protection, paying no attention at all to 1/2 second dead short spikes. No problem at all, really, but...Who wants them and how many of these solid state "try and kill me" supplies would you sell in a year??

Most such supplies are one off, custom built units costing $$,$$$ in under 3kw delivery and $$$,$$$ 100kv 40KW delivery.

Now to the self built amateur supply

Sadly, for the amateur, the no kill supplies will tend to be line frequency units with smaller, low impulse delivery storage capacitors where high to full ripple delivery at under 1kw is highly acceptable and perfect for fusor operation. The ultimate in simplicity would be a totally non filtered, full wave rectified DC supply with 120hz of natural ripple. Only the transformer and diodes would rule the destruction limit of the supply with zero backup filtering and ,thus, zero deadly impulse storage in circuit! A working neutron producing fusor will gain little from a smooth ripple free supply.

Plan on a somewhat smoothed 120hz ripple linear system that once pulling 5 or 20ma under a smooth running fusor gas load to be almost flawlessly smooth DC in delivery using a small storage capacitor in circuit. Design to let it buckle to fully unfiltered 120hz DC when taking a punch on the chin during start up and operator errors. Once stable glow and fusion is achieved the capacitor will smooth it out a good bit without having to store 100's of joules of back up energy.

A very old dental x-ray unit would be the ideal starting point and just might be a negative HV system as is, needing only a suitable variac to be fusor ready. You will need to obtain the supply, purchase only a variac and truss for "below".

The only other path is to buy and modify an extant solid state system, or use a monster audio amp feeding a custom wound high voltage, high frequency transformer with very fast HV rectifiers and associated filtering capacitors.

The ideal, simple, 20-60kv fusor supply is and will most likely remain a bridge too far for many among this site's hopefuls in doing fusion. Such a supply is often the show stopper for many of the less adroit or less electrical and electronically capable. Only the inveterate, lucky scroungers will not need the foregoing knowledge, winning the occasional super great find as they root about doing their thing.

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.

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Re: Fusor Running, No Neutron Detection

Post by Mark Rowley » Sun Feb 02, 2020 8:29 pm

Alan,
I sincerely hope you don’t abandon ship this late in the game. Your input numbers fully indicate a very high probability of easily detectable neutron production.

As I have said, the power supply acquisition issue has been the ruthless assassin to many aspiring Fusioneers. Folks who have easily acquired the mega expensive Spellman systems or the unobtanium 1950’s HV transformers don’t quite understand the difficulty of finding suitable power systems. The only analogy that comes to mind is it’s equivalency with searching for the Lost Dutchman’s Mine. Regardless of ones astute scrounging abilities, finding the 100lb behemoth supply is darn near impossible and the expense of doing so is pricy as well. The hard cold fact is that aspiring Fusioneers are cash strapped. We have to make due with cheap Chinese power supplies. For only a fraction of the expense used to build a supply from scratch, effort could go into hardening and cleaning up the issues found in a precipitator supply. There’s no viable argument against this.

Alan, I started this venture in early 2002. The cost factor involved in getting a fusion capable power supply was a clear and present danger to the financial state of my then fledgling family. As a result I was happy with my demo bell jar system for years. I experimented with different grid designs and honed my welding, electronic, vacuum, and HV skills in the meantime. I don’t see why you’d want to end the pursuit when there is so much more to do and learn. Failure within a hobby should not initiate anger or reduce its fun factor. Hobbies are all about learning and devising new ideas and methods.

Back on the precipitators. Rather than foster or hold a negative mindset about the precip supplies, it’s better to look at the possibilities they could and do provide.

As a group, we need to get away from telling or implying to folks “unless you get this impossible to obtain item, you will be forever banished to the Plasma Club”. Instead we should promote lesser expensive alternatives and help folks remedy their shortcomings.

Too much negativity.

Alan, I hope you stick around and continue with your goal.

Mark Rowley

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Re: Fusor Running, No Neutron Detection

Post by Richard Hull » Sun Feb 02, 2020 10:42 pm

I have been loath to make a rather obvious suggestion for the precipiteers. While dipping the HV components in oil has worked to a degree, one might look to the weak points in the design and beef it up in any number of ways which I leave to their capabilities and imaginations. The supplies are obviously designed for one thing and are, here, used for another completely different and often extremely taxing and highly divergent enterprise. (nuclear reactor power in a tricky gas, glow mode environment). Complaining about failures should put one in motion and has, indeed done so for many here. Fixes and protective measures have worked for many. That is just swell!

As an electronics engineer and having worked actively in high voltage scientific work intently since the early 80's, I have developed a sense for what is weak and worthless, what is barely acceptable, and what is strong and desirable in the world of high voltage.

1. Determine minimum requirement for the supply.....multiply power out by 3X minimum! In high voltage supplies this always tend to center around the current demand at voltage.
a. What voltage will be the maximum genuinely needed to accomplish the desired goal.....be realistic, assuming you fully grasp how far you need or plan to go in the nuclear effort.
b. What current will be the minimum demanded to genuinely get the job done. Multiply by 3X....Why?... If you need to ask, you really have never done any work in stressed environments.
c. Consider what kind of insulation and volume the finished item must be to work 100% of the time under 3X current conditions
2. Start at the front end. Is the goal to be totally electronic?... electrical? or a mixture of both?
3. What is available off the shelf doing all you want right now? Really cast about on this one and never grasp at straws. This will be your turning point. Be smart
4. Can off the shelf stuff that is barely to not really acceptable be modified to serve?
a. What holds the off the shelf item back?
b. Is there any possibility of modifying the off the shelf to work?.... Especially, if the supply is cheap and almost "there". Do I have the skill set to make the attempt?
c. Since it looks weak, identify the weak points. If just one or two weak areas are seen, can they be strengthened to serve?
d. Note and identify the strong points and plan all work around them.
5. If economically viable, off the shelf, gear will not work or can't be found within a budget, you must custom build from scratch to within your capabilities and knowledge of high voltage electronics and high tension circuit wiring and insulation background.
6. Failing #s 4 and 5. Put on your scrounging shoes...... No scrounging shoes? Assume only now that you are S.O.L and find something easy like stamp collecting to occupy your time.

If I had the chi-com supply.......

Correct me If I am wrong

I note and assume the flybacks are used in series?? or parallel?? I have heard no one claim failures within these critical components producing negative, internally rectified, voltage. These seem to be a more or less strong point in the system, though not tested to my satisfaction yet.

The electronics is intrinsically crap or a very failure prone edifice for those using the system for horrid nuclear purposes rather than their intended smooth functioning design purpose.

Does any of this suggest a complete redesign or at least a super beefing up of the electronics, perhaps at the driving end of the electronics?

These supplies might be fixable to do real work.......or not......

I leave all of this to the student as an exercise. I got mine, now you figure out and get yours. Struggle, adapt, create or leave the field. It is all about packing the gear needed to succeed. I can and will do only so much. I loath spoon feeding the lazy regardless of their hopes, dreams and desires. Time to put on the big boys pants and, or, scrounging shoes. If this paragraph hacks anyone off....that's tuffski stuffski. If it makes you mad enough to get out there and "do", then it has all served me, you and perhaps others in future, well.

This tough guy, drill instructor mentality worked for me in college. I and my classmates where confronted with a professor in two major, difficult classes who considered everyone in his classes indolent dolts made of worthless cloth. He taught well and gave no quarter, demeaning those giving wrong answers when they were the product of poor thought processes. He made you so mad that you pushed to impress him. In exchange for better work in future, you were never rewarded or acknowledged with an atta-boy. Good work was expected as a minimum. You received the grade you earned. The reward was more than a grade, but an instilled willingness, not to impress, but to succeed against what are perceived to be tough odds.

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.

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Re: Fusor Running, No Neutron Detection

Post by Alan Sailer » Sun Feb 02, 2020 10:56 pm

Mark,

I really value your input and once again do understand that others have made a successful neutron production attempt using the precipitator supply.
They are a GREAT bargain compared to other options. I also understand that you want to have a "fusion for the masses" approach to the hobby.
Which I agree with. Everyone should not have to repeat the heroic efforts of past pioneers.

But every story has two sides. I gather that others have had issues with the precipitator supplies. True?

I now have three dead units. In a lifetime of working with electronics this is a first.* I can either blame the supplies or myself. Rather selfishly I blame
the supplies. I, unfortunately, am another data point. Data points that support a hypothesis are just as valid as those that don't.

The other issue is neutron detection. Before I "magically" killed supply number three I was in the sweet spot for neutron production 28kV, 30microns 3 mA.
If my tube was any closer to the grid it would be inside the vacuum chamber. Nothing, nada, nil, no neutrons. Which makes the most likely problem the detector.

More parts, more money more time.

As far as giving up it's a very good option. I have money to throw at the problem and some talents with construction and problem solving. I do hate giving up.
But the issue is motivation. Honestly at this point when I think about working on my fusor I am filled with dread not anticipation. It is NO fun anymore. I hate
breaking stuff. I hate breaking stuff for no apparent reason even more.

I am taking time off to let the issue settle into a stable state.

Thanks again for all your help.

Cheers.

* Normally when I destroy a circuit I learn something from that. With these supplies all I have destroyed three and learned (almost) nothing.

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