Linear deuterium Accelerator-Ion Gun Issue

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
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Dennis P Brown
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Linear deuterium Accelerator-Ion Gun Issue

Post by Dennis P Brown »

Update on gun issues:

I've decided to remove my original deuterium gun and re-install the unit as a 'removable system' - previously, the ceramic base of the gun was epoxied to the end of the accelerator tube. Previous pictures already shown this arrangement in the "Imags du Jour" section under the Linear electro-static deuteron accelerator.

As I posted a few days ago, I was fighting with a minor leak that varied a bit (often got to the mid 10^-6 torr in the accelerator tube but sometimes pump rate was very slow and sometimes couldn't get past the high 10^-6 torr range'. I believe this was caused by slow release of gas in the gun's feed tube.) The straight forward solution (or so I thought!) was that I needed to have a high vacuum purging line to the gun (I already have a low vacuum purge but a few microns is large compared to 0.001 micron.)

After adding the high vacuum purge line to the gun (and discovering this created a massive leak - locating that new leak was a pain and turned out (after two false test results!) that the "new" (read ebay low cost) KF-40 mm adapter flange I had to add to the turbo assembly to create the by-pass line was total and complete junk! So much for saying money.)

Aside: glade I did this - this forced me to remove the accelerator tube from the system and I discovered another serious problem - a significant piece of one end of the glass tube was broken due to stresses from the mounting system. This badly needs a redesign (currently doing that but a discussion of this topic is not relevant to this section.)

I realized this problem would have been trivial to solve if I had a method to isolate the gun assembly. So, I decided that I'd do both upgrades. That is, I'd install both a permanent high vacuum by-pass for the gun (ordered a (really, this time) new flange - leaned a painful lesson on cheap "used" stuff - read worthless) and will make the gun assembly removable (pictures when I do this.)

This later feature will enable me to test other gun types on the accelerator in the future (if the thing ever runs (lol); still, that might be some useful science) and do easier vacuum leak checks - by enabling me to isolate any given sub-system in my accelerator. Hopefully, a win-win.

The delay will be minor (a week or so) but since I am waiting for a large order of high voltage diodes (so I can complete a new voltage multiplier to replace the Van da Graff - hope this new power supply can exceed 300-350 KV; I'm tried of humidity issues and erratic behaviour of the VdG; the current will remain in the micro amp range), this delay will have no impact on the accelerator project's first light, anyway.

Currently, the accelerator tube is now off the system, and the gun has been removed (ugh, not fun cutting through that epoxy!) I am also taking the time to fix a few minor problems with the wiring and shielding system for the accelerator since I now have time on my hands this weekend ... . Also, it was nice to confirm that the anti-electron back streaming grid/ring assembly is perfectly aligned with the target and accelerator tube's center line really does agree with this grid assembly - since that apparatus is critical for preventing dangerous x-ray radiation from emanating from of the system I have a vested interest in ensuring that device is properly installed! Shielding is nice and essential for possible radiation hazards but better still, is a system that prevents the radiation from being created in the first place!
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Dennis P Brown
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Well, still waiting for parts I ordered to arrive - the new vacuum flange (KF-40 to 0.25 inch pipe Swagelok adapter) I'd think should be here by the weekend; the diodes - ugh! Who knows.

I machined on a lathe today my own KF-25 fitting out of aluminium to mate with a brass adapter (also KF-25) that I epoxied to the accelerator tube (also 25 mm diameter.) I epoxied the new deuteron gun assembly onto this aluminium KF-25 I had made. This deuteron ion gun (now attached to the accelerator tube, of course) has passed its first leak check and appears to be exhibiting normal out gassing - another day or so should prove that one way or another. In either event, vacuum testing got a whole lot easier now since I can finally isolate this last sub-assembly for the vacuum system and accelerator. Rather than being epoxied to the one end of the accelerator tube like before, the gun is part of a standard size KF-25 fitting. Since the accelerator tube also has a KF-25 adapter, with an O-ring, the system seals and breaks down easily - no epoxy to cut off (which would badly damage the gun requiring a rebuild (done that a few times, too, alrady.)

One nice feature of this work - that is, having the accelerator tube removed - the remaining vacuum system/target chamber/feed-lines and detectors with all their assorted connectors/tubing has passed leak testing with flying colors - in 24 hours the system out gassed just 220 microns and considering it had been open to atmospheric pressure three or four time over two days, that is rather good without any bake out.

Did get the wiring issues resolved and created some extra shielding in an area that I had overlooked. So, more progress but not the type I really want - that is, accelerator's first light!

With the new high-vac by-pass system (all assembled and installed except for the new flange), I feel that the system will be more robust to operation, and with the ability to swap out guns (at some point, I'll reassemble the one I removed to test it, as well), this feature could offer some interesting research on optimizing deuteron gun design ... at least, when I get first light ... .

Still have to bore out one of the Van da Graff's collector plates (used to electrically 'seal' the deuteron gun globe) needs to be opened to pass the new KF-25 fitting on the end of the accelerator tube. Always, one step backwards to get two forward (lol.) Should be able to re-assemble the entire gun/HV power system/battery all back into the accelerator tube's globe this weekend and test all vacuum fittings to 10^-6 torr as well as reconfirm HV operation for the gun - maybe (though I hope not!) I'll get a chance to use the new leak detection idea the one member here suggested.


Update: the collector plate has been bored out to pass a KF-25 adapter ring. Will soon try the accelerator tube to high vacuum - the real leak test. If it passes, then onward.

I guess will continue to wait for the diodes and hope that project for the 360,000 volt power supply then really works - I'll test a few stages as I build them. The probe I have is good to 50,000 volts. After that, use a giga-ohm resistor and try to measure a few stages after that but seriously, not interested too much if a few stages do work; the issue of HV leakage without oil immersion makes such measurements futile, anyway.

Of course, if the humidity ever drops I will then try the VdG and see if the new gun really works and maybe see first light (or at least, develop some secondary x-ray radiation to measure (lol.))
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Gleedaniel Martin »

Hopefully, your order will arrived as soon as possible so that you can post some pictures about what you have done already.
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Yes I did get the supplies I needed (a year ago!) and reassembled the whole thing (with a new and improved ceramic accelerator tube.) Then I discovered that the VDG was a pain to get enough current out of (after very good advice here on checking it) so I did a rebuild on that monster; this also meant that I had to modify my accelerator tube to improve the field/voltage from it (it was drawing far too much current.) Then to my surprise I discovered that my turbo has a tiny piece of broken glass deep in it - I stopped all work so the turbo wouldn't be destroyed. I used a dead turbo I had on hand to dis-assemble and discovered that taking one apart is easy but trying to re-assemble one back is a bit of a reach for me! Need to machine a special tool to help dis-assemble the device before I attempt to get the glass out; next for my to-do list. So, after some critical life issues arose, I put this project on hold. Maybe I will start again but really, until I fix the turbo (isn't broken - thank goodness - but needs that glass removed) and I face up to my real problem: either up the current on the VDG by clever redesign or just buy a more powerful unit - I can't get this project running no matter but else I do. This project has been a royal pain - one issue after another but some of these problems would never have occurred if a more experienced person was doing it. I will say that after looking online over the years that a lot of the posts, articles and information out there on accelerators is either wrong or worse, misleading to the point of harmful. This site is the only place I feel one can get good info and even better advice.

By the way, have considered a lower voltage source (100 - 120 kV) using door knob caps but haven't figured out what diodes would work and how to solve the power supply for them - so I have a pile of 30 kV door knob caps collecting dust (lol) ... . Collecting dust is also what my accelerator/vacuum system is currently doing - what a waste.
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Richard Hull
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Richard Hull »

Amateur van degraff's, even moderately larger ones, are just not up to the task of operating a winning accelerator beyond a few microamps. Most such failures are due to leakage currents that are little appreciated by those who have limited experience with voltages at or over 100kv. I have noted this more or less forever.

An amateur van degraff that might be suitable would sport a 6 to 8 inch wide belt and have a 3 to 4 foot diameter sphere or oblate. The beauty of a van degraff is the voltage attainable with virtually zero electronics. They are definitely out for any fusor effort and are limited in very large sizes to linear accelerators where they tend to shine if big enough.

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Re: Linear deuterium Accelerator-Ion Gun Issue

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Finally picked up the 4-inch wide belt sander that was on sale that I need to get my accelerator project back on track. Will use the motor, its drive system, rollers and mounting parts of the sander to build my large (and hopefully) high current Van de Graaf.

As Richard pointed out, commercial VdG's just aren't up to the task of creating a current buildup required to drive an electro-static accelerator (Found this out.) Also, decided not to build a real high voltage system since it would be far too dangerous.

So, with a four inch wide belt (I will make from the material I have), the six inch diameter plexi-glass support tube (4 1/2 feet long), and high voltage spray system, and large dome I have on hand, I just needed a motor w/drive and roller system (which I now have) to get the project going. So, that project starts tonight. Should be fun and entertaining to build - guess I will learn a great deal on VdG's real issues; read a few papers by people who build them and frankly, surprised at how little these designs agree. Guess it is also more art than engineering.

If the VdG device works (current levels) I will build a cheap enclosure around my accelerator to provide a dry environment for both the VdG and accelerator to operate within (picked up a free de-humidifier that I will use to keep that area dry.) This deuteron accelerator project - really all the secondary systems - has grown into a world class pain and makes me wonder how anyone ever did manage to build one of these beasts ...certainly, many who think they did, didn't and I see why some who start never post any images of a successfully operating accelerator. Hope not to end up in that situation after all the work to date ...but that is how home science, and limited budgets work, I guess.
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Well, machined a collar (out of Teflon) to hold the upper bearing/roller for the main Van de Graaff's vertical plexi-glass column (turns out that is 6.5 inch in diameter.) The collar needs a bit more work - need to enlarge the hole for better belt clearance a bit and then add leveling screws - and that part should be done; This collar will also allow the upper bearing tension to be adjusted as well as leveled by way of these screws. I will add two horizontal set screws to lock the collar/column together tightly once it is level/belt tight.

Disassembled the store bought belt grinder. Looks easy to obtain all the parts/assemblies I want - the motor, pulley system and roller/bearing are a very nice unit and should be easy to adapt to my VdG. The motor/pully/bearing system is already on the original mount and that assembly is very nice. The whole belt grinder costs less (under $65 w/tax) than individual parts if I had tried to buy them on line and even then, there would have been no nice mount for the assembly.

Tomorrow I will try and make a few minor plexiglass parts to get rid of some metal parts used to hold the motor/roller assembly to the original belt bed (that was all metal and has been removed.) These are simple cut and drill clearance hole steps. Not hard at all. Then I need to install the upper roller to my new collar - not fully resolved on how I want to do that.

I found a really nice plexiglass box that will hold the motor/drive/roller assembly and the high voltage polarity spray system for my VdG charging belt. This box should allow the plexi-glass column to be mounted on top of it - might need to reinforce it, however.

Looks like I now have close to 70% of the new VdG assembly done and all other parts are on hand except the new dome - got lucky on finding useful pre-made parts that work nicely.

Someone has recently offered to give me a very large dome (already in two halves) for free - just need to cap over one end (each half has an access hole.) Guess the acid test will be affixing the dome & corona rings. Then finding/fixing/mitigating all major corona leakages/current loss issues using a few tricks I have tried/read of before. Still, have a good bit of experience with those issues on my commercial unit and discovered that installing HV sprays isn't as easy as it looks. They really, really like to short everywhere! And arcing through the belt to the ground post is rather hard on the belt (lol.) So, this is always a fun part of the assembly. Still, have too much experience working with that issue and getting shocked as well (lol.)

These last steps and testing is where both engineering and art will meet, I guess.

For a change, this has been fun - even the machine (lathe/mill) work has gone smoothly. This project is strangely starting to come together nicely and that worries me. So, either I am overlooking something or this just will not work - its been far too easy ... . Never works that way in real life for me (lol!)
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Picture of various components for my the new ultra-large Van de Graaff (VdG) that is being constructed. The first picture is the motor assembly only - this has a motor, drive belt w/pullys and roller (w/internal bearings), the second picture is the powered roller in its Plexiglass box. The next two pictures are the upper roller/bearing on its special mount (that has five major degree's of freedom for leveling, yaw, tilt, rotation and even three for just the roller by itself (its own tilt,and two degrees of planar translation!)

Notice that the pic of the upper roller/mount and has numerous adjustment controls. Learned this from dealing with a commercial unit and modifying it - discovered that getting a belt to run smoothly with limited degree's of freedom for the mount is not easy so decided to incorporate enough controls to head off issues (I hope!) The last pic is of the unit parts together - far from finished but getting there. Hope the dome (yet to see it) isn't a project in of itself; still, I have my original plan that should work if that one causes problems.

So, to get some neutrons, I started a deuteron accelerator project which became a rather involved project with perfecting the accelerator tube, vacuum system, gas feed for the dome (isolated from the VdG potential), HV gun system and gas supply system and vacuum gauges and ...and ... well, the list goes on; the support systems are far more complex than I had ever thought. Now I am building a semi-lab grade VdG - the belt will be 10 cm across and the length about a meter! This isn't a home project so much as a build up of a semi-professional grade laboratory (lol) and is almost on a par with getting an advanced degree ... lol. And what I want the neutrons for is yet another project ...well, at leas the fusor is done and ready for testing but that is yet another project (lol.)

I intend to build a motor mounting plate that will allow this plate to support two axis of horizontal motion (x-y) of 1-2 cm and vertical adjustment Z-axis (10 cm.) This should allow me to both get the lower roller unit nicely aligned with the upper roller and adjust belt tension in an easy manner - important considerations in any home-made VdG. Having extra room in the box for the high voltage polarity spray system will be a be plus or in this case really - plus; as in positive since this will accelerate deuterons!

Building any VdG is all about the belt - the rollers, by the way, are "domed" so this will aid the belt remaining centered as long as all other adjustments are accurate.
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VdGMotor.jpg
VdGinBox&motor.jpg
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Motor, drive and roller w/bearings assembly
Motor, drive and roller w/bearings assembly
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Update on the Van de Graaff (VdG) 'project' for my "Ion Gun" (aka deuteron accelerator): built the new motor/lower roller base adjustment mount - a real monster. But it does allows vertical adjustment of 20 cm(!) and 3 cm in planar "y" and 2 cm in "x" for the motor/roller assembly. Also, machined a large upper support collar for the column tube to attach to the lower housing. This whole secondary project was far more complex than it needed to be but I used parts/junk I had on hand rather than build a simpler system from scratch, which in hindsight, might not have been the best move ... but I did learn a good bit on how to glue plexiglass panels together without creating a huge mess. Will provide pictures in a few days of progress to date.

Hope to get the dome soon. Also, once the main VdG system is finished, will cut and mfg the belt. Then I just need to install corona rings (esp. one for the dome/column interface), add the polarity high voltage spray system and finally install the upper ion collector system for the dome. Then this "minor" secondary project - my VdG monster - will be ready for testing and hopefully, will not disappoint (nor provide a dangerous level of current but not too concerned about ever having that issue with something I constructed.)
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Quick update: obtained the upper sphere dome (had the lower dome) - will need a lot of polishing ...ugh. Also, made a longer belt (still 4 inches wide.) I will post some pics of how I made the belt soon. Have started the high voltage multiplier (Cochcroft-Walton, aka Vitter multiplier.) This Van de Graaff is now nearing completion. This project is growing in size, complexity and in shear magnitude of effort in a manner that is simply out-of-hand. So, guess I have to decide soon exactly how far I will go if further issues arise otherwise, I will be no different then other fusion programs (lol.)

Still, I am reposting a few pics of the deuterium accelerator for those that haven't seen it. The first picture is, of course, the VdG dome; the second is the rest of the VdG (with the lower section of the full dome.) The third pic is inside my small secondary dome that is attached to the accelerator. This smaller dome houses the deuterium gas tank, leak valve, 12 volt DC to 3000 volt AC output power supply, voltage multiple (25 kV positive out put), 12 volt battery support, and all wiring/tubing. The end of the accelerator is inside this sphere as well.) The final two pics are of the accelerator without its secondary sphere (nor the sphere's contents) and high vacuum support system & gauges, all controllers, a dry air flush system, and deuterium supply station.

I should mention that the last picture shows that the accelerator ends in the main vacuum connection housing. This has a window for seeing (and focusing) the beam. A side "bellows" system allows a glass slide to be inserted or removed from the beam even under high vacuum. Also, another port allows me to measure the beam current by, again, inserting a small plate using a bellows system.) I am rather pleased by these two systems on how easy they were to make, how well they work, and how import this is if one really wants the device to work as a scientific tool.

The target mount (will hold a deuterated plastic target) is water cooled affair. If the VdG does produce 20 or more micro amps, the target would quickly be destroyed if it wasn't cooled so I designed this in at the start.

Haven't figured out how I will handle the vertical size difference between the main Van de Graaff sphere and the small secondary sphere of the accelerator. May have to rethink that part of the project ... hopefully, the two spheres will be close enough to make contact without issues of raising the main accelerator system. Also, I think that I will remove most of the wood table top under the accelerator: wood is a very good electrical conductor at these VdG voltages. If the VdG does produces enough current, I may fore go the environmental chamber (for now) that I planed on constructing around the accelerator.

By the way, all shielding has been removed but is easy to re-install. The shielding is good for 0.75 MeV x-rays so no way this isn't enough. The shielding is non-conductive so it shouldn't effect the VdG's electric field nor performance. Hope I am not still overlooking anything ...sure I will find I am. But on radiation, I think I have it covered (I have a number of those pen type radiation badges and they are calibrated. will wear one and have others located around the room to prove the shield system is working.

One last important point: This accelerator is for a fusor like system so it does apply to this forum (mostly.) That system, not unlike the ITER project, has yet to be built. But I do have the key parts ( a 50 kV 0.1 microfrad cap, 30 kV 20 ma power supply and a small palladium foil.) Just have to add this to my accelerator vacuum housing (end section) once (if) the VdG works as planned ...then once I design and prove the new neutron detector, I can try doing some real science. Slowly getting there ... .
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Re: Linear deuterium Accelerator-Ion Gun Issue

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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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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Dennis P Brown »

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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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Richard Hull »

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

Post by Richard Hull »

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

Post by Dennis P Brown »

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

Post by Dennis P Brown »

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

Post by Dennis P Brown »

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

Post by Dennis P Brown »

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

Post by Dennis P Brown »

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

Post by Dennis P Brown »

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

Post by Dennis P Brown »

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.

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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