Linear deuterium Accelerator-Ion Gun Issue

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Dennis P Brown
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Dennis P Brown »

Quick update: Started to clean & polish the dome - easier than I thought but still slow. The section I polished (1/4 of a half section of the dome) is a major improvement compared to the original surface - the dome was outside for many years and had been used for many other purposes (like a drum ...amazingly, very few dents and no scratches so the dome is in rather good shape to say the least.) After some polishing I can see my reflection, darkly (lol) but most areas of corrosion run just too deep to be removed even by mild chemical etching/cleaning but really, irrelevant. While the area polished is unimpressive compared to commercial domes the fact that this dome was "free" makes this dome ideal (even if a good bit larger than I wanted. Static loses could be an issue unless in very dry air so may have to address that issue.)

The belt is ready to install but realized I need to cover the rubber rollers with metal tape; forgot about that so need to address that problem - the reason for this is that the static charge created by the rubber roller and belt fiction effects could seriously interfere with the polarity of the power supply spray (i.e. the belt/roller may not create a positive charge so this causes negative charge build up on that section of the belt thus canceling part of the charged delivered by the spray system.) Could test to see if that is an issue but once the belt is installed, removing it would require cutting so I just need to address this issue first.

I was amazed to find 2 amp 30 kV diodes for under $3 a piece. So, ordered a few. Unfortunately, they are coming via a ultra slow boat from China and who knows when they will arrive ...should have paid for fast delivery ...lol. So, with my 40 kV caps (0.01 mF) and 7.5 kV NST (the system will have very, very little load so both the voltage and current will be near max values, I'd think ...not that the belt will draw even 0.1 ma at best.) I intend to both filter the NST output with three of those caps and then double the voltage (and it too will have a few caps to filter out the ripple) before spraying onto the belt. This is one of the few times a simple full wave multiplier and a NST can easily handle the load - a Van de Graaff requires very little current sprayed onto the belt to work well. I believe sources indicate that a good belt can, at best, carry just 0.001 milliamps per 50 sq. inches of belt area per sec passing the spray system. Guess I will see.
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Dennis P Brown
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Finally received my 30 kV, 2 amp diodes yesterday so I guess I really must assemble my 25 kV, multi-milliamp positive voltage spray system this weekend. The system is based on a 60 ma, 15 kV NST, will have full wave diode rectification w/caps, and full wave voltage multiplier. The volt-multi will be under oil.

Also, got the metal tape so I really need to fix my Van de Graaff (VdG) rubber rollers and install the belt I made (10 cm width, over two meter total length); also, just do the work and finish polishing the VdG's dome.

Also, need to strengthen the motor support housing and improve its support base. Amazing how the details grow, and grow even with the VdG nearly fully constructed.

Still, the electro-static accelerator is 100% complete/tested so this is the only issue really holding me up from getting to the finish line; so time to start addressing this part of the puzzle ... .
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by DanielSandner »

Hello,
Your Dome looks quite good and I can't wait to see first results.
But i don't understand why most of you use van de Graaf generators to gain high voltage. As the top is like a capacitor the Voltage can be described with U = Q/C. The higher the beam current, plus Corona discharge and so on, the lower the Voltage. If you want to measure the voltage with a spark gab, this won't be reliable because the Voltage is much lower if you have a constant current.
I'm a member of a German high voltage forum and someone build this: http://web367.login-102.hoststar.ch/kaskade_180kv.htm
The Ouptput is around 2mA and 180kV, with this high current you can also power more stages.
Compared to vacuum parts it was also pretty cheap, you can also reduce the capacity of the capacitors because you don't need a high current.
Maybe someone wants to build something like that, but also good luck with your van de Graaf.
kind regards, Daniel Sandner
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Richard Hull
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Almost no one here at fusor.net uses a van de graff to generate high voltage! Virtually 100% of us use formal plug-in-the-wall high voltage supplies capable of hundreds of watts at full voltage. The ion-gun forum, for some strange reason has people building accelerators, (of which, Ion guns are part), are using VDGs, yes! Thus far, none have been successful in doing fusion. I worry that such linear accerators in past literature have used large VDGs for HV sources and this is more or less a "hangers-on" phenomena.

I can't explain the above propensity and have constantly noted there is no real acceleratory energy to be found in a VDG of amateur proportions. Still, everyone who desires to take a "whack at it" in their own particular manner should be allowed the thrill of the hunt and adventure into VDG land....and more power to 'em....literally!

Richard Hull
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Hello Richard, and thank you both for the comments; also, thank you Mr. Daniel Sanders for the link (very nice system! and glad to get someone from Germany to comment!)

You are both correct - most Van de Graaffs are a joke in current supply (and why only voltage is generally advertised) and not the best way to go if one wants current! That is why I am building a monster VdG - to get the required current of 20 - 30 micro-amps at 200 - 400 kV. Since, any powerful voltage multiplier - whether a standard Vitter, or a Marx unit - are far easier to build than a VdG, to say the least(!) my issues are two-fold relative to that route:

First, I can build a monster VdG without too many issues -either cost or parts. That is, I have the massive dome (given to me for free), I routinely make VdG belts (rather easy and have two now ready for my new VdG), the motor/roller system was very small in cost and taken from a belt sander(!), and I had both the plexi-glass tube and the high voltage spray system parts so this whole unit will cost less than $100. Also, I have access to a machine shop and it is easy for me to make the required and rather unique parts any useful VdG often needs to enable the belt to run without issues.

The second part of this long explanation is more serious - frankly, I am afraid of any powerful (read high surge current) 30 kV+ power supply (much less those over 100 kV) since these are always lethal, behave in strange manners (arcs can jump further and towards things one would never guess) and I would need to work around that monster while it was charged! Not my idea of a home project! (lol.)

So, I decided to try a primitive high voltage and safe current device - ie: an over-sized VdG, for now. I do not need more than a few 10's of micro-amps to get 10^8/9 protons resulting in a narrow beam of 10^7 neutrons or so. Also, I can easily measure the VdG's current output and if it is too high, it is trivial to de-rate the VdG so it will remain safe to work around even if I have to over built the thing (seriously doubt that will ever be an issue (lol.))

In summation, I do not believe anyone should use a VdG for a proton (deuterium) electro-static accelerator to do fusion; however, I have a rather strange end goal to test a fusion system that requires a high flux-narrow beam of neutrons and this will meet that requirement; also, I have a secondary experiment as well relative to testing neutron detectors and again, this accelerator is ideal for that type of experiment (also, that is a safe flux to work with!) So, the trouble for me is worth it (also, I have spend less than $700 on the entire accelerator project, including all vacuum parts, to date.) This does not include the fun of building this stuff nor using this forum!
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Jeroen Vriesman »

How could this produce a "narrow beam of neutrons" ?

The neutron energy is much higher than the initial deuteron energy, so with beam on target you still have neutrons going in every direction? Or am I missing something?

If you do need more current, you might try to build a Felici generator.
http://lyonel.baum.pagesperso-orange.fr/felici.html
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Indeed, in D-D fusion, there is no beaming. The general assumption and published data proves this out. In D-D fusion the neutrons are emitted isotropically provided the energy used to accomplish this is well below the resultant fusion neutron energies. That said, once isotropically emitted, there are many environmental issues around the fusion event that can cause detection, at range, to appear anisotropic..... (scattering, absorption, etc.)

Neutron beams are classically produced from intense neutron sources being forced to herd those few chance directional neutrons through a tunnel of shielding. The most intense used to be from a fission reactor's core through a hole in the containment.

Today there are a number ways to produce neutron beams in big science efforts that do not involve a fission reactor.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Good to know - just assumed (without thinking) that momentum would be conserved but both of you are absolutely correct. I missed the nuclear reaction energy aspect/reaction of this whole process (lol.) Duh, as one will say after hitting one's head with the palm of their hand. Still, the Van de Graaf is built so, not ready (or willing) to change the high voltage field, yet. Will see how the VdG performs ...or doesn't ... .
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Finally got back to the Van de Graaff (VdG) after other issues have taken me from the project. Finished the dome - had to remove a center "collar" that separated the two domes (and was used to hold each hemisphere to the other.) This collar just created an extra "seam" that would increase corona discharge without really adding much current "storage" area so I decided to remove it. Required machining new clamps to hold the two domes together but that wasn't very difficult. Also, finished the polishing and removing dents.

Another issue - started work on a cover for the top of the dome. The upper dome (like the lower one) has an 7.75 inch access hole in the top. Cut some Al plates to fit inside and remove the "hole" so the top of the dome is closed. The design I have started will allow easy removal/access of this cover so the inside of the dome can be quickly accessed. Handy to have that ability. Amazing how many details need to be addressed for a single VdG which is a side project but as I learned on the little commercial unit I had and modified, without all these extra's, any VdG unit is a problem to operate and not likely to run well.

Decided to fix a problem with the motor mount in the VdG so as to make belt tensioning easier but was more work than I thought (lol - always is ... .) Need to install the metal tape on the lower roller - not sure I need to worry about the upper roller relative to that need.

Still deciding on the caps to use for the positive high voltage spray - reluctant to install my rather big ones that can carry a lethal charge (but adding resistors to auto-discharge would make that safe but still, stuff fails and I don't want to add more dangerous issues to the system.) Also, can't make up my mind on how best to enclose that system.

Finally, mostly settled on the design for the change transfer systems for the voltage spray (base of the VdG) and pickup's in the dome. Looks like a return system, connected by a large series of resistors, is often used in bigger domes so I put one together - just need to install it in the dome. This will help "return" charge down the belt helping to further "charge" the upper dome positive.
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Some good news on my accelerator project/fusor/ion gun - my Van de Graaf has passed its first (minor) milestone.

After realizing the motor mount needed another (!) degree of freedom (horizontal rotation - 5 - 10 degrees.) I made this change and also a few others: added another support rod to the motor mount (now a set of four); installed more flush allen bolt heads in the dome assembly and performed any extra counter sinking where needed; also, provided a lock for the upper roller stand (it can be rotated for adjustments but then must be locked in place).

After lengthen the belt I installed it and adjusted the tension using my vertical control of the motor/roller system.

I then ran the motor and the belt performed well but, of course, wasn't running true. So I made some minor adjustments but having all the small extra adjustment degree's of freedom (motor, rollers, column, and others) enabled me to quickly get the belt to run very smoothly and remain centered on both the lower and upper rollers.

I will next tackle the upper system of high voltage collector electrodes - a positive pick up array two inches below the top roller as it enters the dome and another two inches below the roller as the belt exits the dome. An expert in the field recommends this arrangement. I will also have a resistor loaded system that connects the dome to the inside of the belt on its exit so that reverse current flow can stabilize any downward current polarity issues (this allows better current loading of the belt/dome or so I have read.)

The project is moving along nicely after a long wait dealing with a host of related but slow to solve issues. If the upper electrodes work well I may attempt the lower array of electrodes for the high voltage spray system. But that may or may not be possible since I have a list of projects also waiting for tomorrow (lol.)
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Installed the two multi-pin (twenty acupuncture needles per array) collectors in the top dome. I think I will also add a third collector at the peak of the belt/roller as insurance. Of course, keep making adjustments to the assembly since the belt is so close to the edges of the vertical tube (the belt is 10 cm and the tube, where the belt edges enter have just two or three millimeters clearance (ugh.)) Homemade does have its problems since one builds with what one has, rather than the better - that is $$$ - materials.
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Quick update: finished the lower emitter electrode array and its support system and made a third upper collector electrode for the dome. Will need to install them; also, I will need to further mod the vertical belt tube system to make better belt/roller alignment; and finally, assemble the high voltage multiplier/polarity power supply. Slowly the very large Van de Graaf is nearing completion.
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Re: Linear deuterium Accelerator-Ion Gun Issue

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The Van de Graaff is done - assembled the last parts and made all adjustments worth doing - runs well; just need to build the high voltage supply for the emitter in order to charge the belt (positive.) Still deciding on the basic design of the voltage multiplier but have all the electrical components. The issue is deciding on the diodes (either 2 amp 30 kV or 0.3 amp 25 kV), which, in turn, will determine the caps I end up using.

Guess I will go with at least a four stage voltage multiplier since that shouldn't cause current issues with moderate caps - want the unit to reach or be in the 30 kV range at least.

Might build a series of HV supplies and just test issues (current/voltage) but in either case, that is the last sub-project before I test the VdG for real - if this doesn't work, I have to admit that VdG's just aren't ever going to cut it - this VdG unit has a 21 inch diameter dome, stands 5 feet 2 inches tall and has a 4 inch belt that is over seven feet long. So it had better produce over 20 microamps above 150 kV; otherwise ... . Well, guess I'll cross that bridge if I come to it.

Will provide some detail pics soon.
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Here are some pics of the completed Van de Graaff (VdG). I built the first stage of the full phase voltage multiplier and it worked well - converted the 7.5 kV NST (which is rated 15 kV but is centered taped) and raised it to the full 15 kV positive (full wave.)

The first pic is obviously the VdG; stands 5 ft 2 inch.

The second pic is the emitter electrode array (with the high voltage wire.) This has twenty + pins inbeded in a copper foil within a plexi-glass box.

The final three photo's are different views of the upper collector electrode array. Note the various controls to adjust the belt - these are very fine adjustments and they work very well. A close up of the collector array shows the details of the collector needles. There are two more collector arrays but they are located further down near the base where the belt enters the dome. These are not easy to image.

Until I install the high voltage spray, will not be-able to test the unit. That part of the project is nearing completion. I am building the other three stages now - the first stage used large caps (0.01 mfd, 40 kV and 1 amp 25 kV diodes.) The remaining stages use smaller 20 kV, 4700 pF caps and 0.25 amp diodes.
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Richard Hull »

Very nice machine work and clever use of materials inside the dome. All the best.

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Re: Linear deuterium Accelerator-Ion Gun Issue

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Thank you Richard! Hope it works as good as it looks - still, invested only $120 in the unit (not including the voltage multiplier.) Mostly time/effort has been its real cost.

I am partly through constructing the second stage of the voltage multiplier; this is a rather involved project now because I am building it to 1) Be capable of handling three more stages; 2) Be placed under oil to handle the corona issues; and finally, 3) handle large surge currents while having a fast response.

The reason for this significant overbuild of the voltage multiplier (really, two stages - a max of 30 kV is all that is needed - more stages for a VdG would be pointless) is in anticipation of failure of the Van de Graaf current wise (this unit without a multiplier easily reaches over 200 kV); and hence, have a ready 100 kV + voltage multiplier as a backup plan to replace the VdG. Since I have used small diodes/caps in the past with multipliers and obtained terrible results, I decided to build this one with the largest, fast diodes/caps I could reasonably buy without overly committing money (again, a cutoff of under $100 was set.)

I will provide pics of the unit later when it is finished and tested. This single stage, when added to my existing stage, will not require oil since it will only reach 25 kV to 28 kV. After that, oil will be essential if I don't want my current bleeding into the air or hitting me if I get careless (lol.) Since my final load will be in the tens of micro-ampere's I would think a five stage system with big caps/fast diodes could handle that ... I hope. Been wrong before ... .
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Re: Linear deuterium Accelerator-Ion Gun Issue

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The current output on this Van de Graaf is lacking (current: 3-5 um amps; the voltage was, however, not bad being able to support 20 - 23 cm arc's and was positive) and I will start looking at fixes. A higher voltage spray system for the emitter did not help at all (from 15 kV to 28 kV.) I have some ideas to check but this result is very discouraging considering the units size and careful following of design from a paper by an "expert" - a person who builds these devices routinely and even made a very large VdG for the Boston Science Museum.

As such, I will limit my redesign/fixes accordingly since pay-off is limited unless some significant improvements occur with a few of the more easy changes I envision. Otherwise, with little money invested in this unit, I may follow previous advice and look solely at very high voltage power supplies. Certainly, I will begin upping the voltage multiplier I have with more stages; however, I have little belief it can reach or exceed 100 kV even with the large NST I use. While that system is rather inexpensive, as well, I really think that route will yield insignificant voltage - the electric field needs to be significant to properly accelerate the deuterons along the rather long einzil system I have.

If all else fails, the VdG might barely work if I shorten my accelerator and modify the support structure. These are not fun changes but would significantly reduce current draw. Shielding concerns me (since that too may be a limiting issue but needs to remain in place. Not a simple issue to move that further away.)
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by John Futter »

Dennis
From what I understand from electrostatic engineering the current output from VDG's and Pelletrons is directly proportional to belt width and belt speed
Pelletrons are limited in the width department so parallel chains are used. The optimum belt speed for both is 40MPH (70km/hr).
This belt speed is the trade off point between belt leakage and dielectric absorption timeconstant
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Thank you for the response; certainly, few sites really address belt speed. I am certainly under that speed! May look into upping that.

Did notice that my newly made belt has an aluminum film starting to develop on its inner surface! That is really, really bad. This, I now realize, is due to the roller being designed to center the belt by having a raised central region thus causing this region to move faster than the outer area edges leading to belt slippage (as all Van de Graaff's have to do if their rollers are not flat) and causing wear between the belt/roller surface resulting in my belt becoming conductive (and hence utterly useless!) Using real aluminum tape (as I did) so the rollers do not create their own charge effect and interfere with my power supply/emitter system turns out to an issue. So, I have now removed the aluminum tape from both rollers and removed the belt. Later (after making a new one) I will test the existing "rubber" like rollers and see if they produce a positive "net" current on the dome. If they do, I'll leave them. If not, either I machine my own or buy metal rollers to replace these (not too likely to find ones that fit).

This rather rotten development proves (like I have discovered for a lot of sites on a lot of issues - amazing how much incorrect information has been put out there on just proton guns/accelerators!) that no one who makes VdG's and writes about them has really tried this fix (which so many of them suggest) for non-metal rollers. Had they, they would have noticed this effect immediately and warned people not to go this route! It is getting very old discovering that experts often give untested advice that is counter productive. Pays to only write what one has tested themselves ... .

My belt is history (now) so I will have to make another - may look further into alternate materials than vinyl to see if a better belt could be made since I have to do this. Anyone with experience with belts and would like to comment, please do!

I have considered adding horizontal strips of conductive silver (submicron sized particles into the plastic - will not be solid strips but a conductive paste) on the belt (creating narrow strips separated by insulating belt regions of similar width) to create a more useful charge collecting belt. I am doubtful the work is worth the effort/cost, however. This design would create a belt similar to the metal/ceramic ones used on professional machines and if my VdG works (using a simple belt) I just might do this experiment in the near future.

Will make the new belt next week and test the VdG without the emitter energized and measure the dome's polarity; if positive, I'll measure the current and then test with the emitter to see the net results (if I get higher current.)

If that looks promising, then I will most likely up the motor speed by simply changing the pulley's on the motor/drive roller. That can get me up to 40 mph rather easily.
Last edited by Dennis P Brown on Sun Mar 20, 2016 1:29 pm, edited 1 time in total.
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by John Futter »

Dennis I admire your tenacity
Our Accelerator at work has not had a new belt since 2002 and it runs at 40MPH for 8 hours a day for around 200 days a year that is 896,000 miles or 1,568,000 kms the belt has traveled so far. As far as I know it is made from rubberised canvas and other fillers and is about 3 feet wide and pulley to pulley is around 10 feet.
I will find out the spray voltage and current for you (not to hand at the moment) but very similar to this beast
M&MS_2010_415.pdf
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Dennis P Brown »

John, thank you very much for the advice and especially the paper. I will read it. I am determined to test ideas/approach (as long as I needed put significant money into the idea) and check results. Discovering that a lot of people out there make mistakes and post without proper testing (ugh!) Still, fun to test ideas but I do desire to make progress at some point!
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Dennis P Brown »

Located an inexpensive source of "rubberized" fabric. That is JoAnn Fabrics ( http://www.joann.com/rubber-sheeting-wh ... l#start=10 ) Hope this works but is very inexpensive so worth a try. Cotton backed and white so I assume it wouldn't be conductive (unlike many "black" rubbers since these often contain carbon - or so I have read.)
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by John Futter »

Dennis
I have just looked at our accel.
belt charge 5kV 128uA
Corona stabiliser is @ approx 60uA for 1.9MeV
Column current is approx 70uA

which is close to 130uA total load which equates with the 128uA of belt charge PS the belt also produces charge with out the spray

target current after being through slits and collimators = 22pA
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Dennis P Brown »

Thank you John; that really helps me get a handle on issues like no other source has to date. Knowing the current (both applied and achieved) is critical in understanding what is reasonable and what isn't for a Van de Graaff. For me to get over 5 or even close to 10 uamps would be significant considering the value your far larger system achieves (and I bet it is under sulfur hexafluoride (wow, was this first post a funny mistake!)) I can do that for mine (internally only) but the work isn't something I wish to currently perform considering what I still need to do.)

Your post of a real system's actual values tells me a lot about previously published results that simply speculated on their tiny Van de Graaff current. Knowing a viable emitter voltage/current feed also clears up a great deal of confusion for me considering the very few articles that mention this subject at all.
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Dennis P Brown »

Ordered the rubberized cloth (white; hopefully, non-conducting) for my new belt.

I have a second NST so I will construct a 7.5 kV, full phase and filtered positive supply for my emitter. This should be more than sufficient considering your's.

To play it safe, I am also constructing a 60 ma (max. claim), 30 kV AC flyback transformer system (30-40 kHz) as a possible HV supply for my alternate method to achieve the very HV needed for the accelerator. This will supply my existing voltage multiplier and should achieve the 120 - 180 kV the hard way, maybe. The diodes I have may not support this higher frequency, however. In which case, the 30 kV system still has value.

That is, if the multiplier does fail to achieve the HV due to diode's not handling the high freq, and the flyback system does work (provides the first stage 25 - 30 kV with a current in the 15 - 45 ma range), it can then supply my existing fusor (I do have deuterium gas. Had a registered company # (for SBIR's) when that was still easy to do so took advantage of that.) So constructing this heavy duty flyback system will be worth the effort (again, total cost for this system will be under $100 so in the event of failure, limit my loss. I am able to keep the cost low because: 1) I already have a 15 - 30 volt, 60 Hz, 30 amp power supply for the 2) new, very inexpensive, converter (used to up the 60 Hz frequency to the required 15 - 70 kHz the flyback requires) and 3) the flyback was rather inexpensive.

Finally, as a back up to the back up plan (lol), I did order more of the inexpensive 20 kV diodes just to be ready to try adding more stages to the existing multiplier system; however, that is very iffy with a 60 ma NST (which will not deliver 60 ma under any real load.)
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