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Linear deuterium Accelerator-Ion Gun Issue

Posted: Sat Apr 26, 2014 9:30 pm
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!

Re: Linear deuterium Accelerator-Ion Gun Issue

Posted: Mon Apr 28, 2014 11:44 pm
by Dennis P Brown
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.))

Re: Linear deuterium Accelerator-Ion Gun Issue

Posted: Mon Mar 23, 2015 8:05 am
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.

Re: Linear deuterium Accelerator-Ion Gun Issue

Posted: Mon Apr 06, 2015 6:23 pm
by Dennis P Brown
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.

Re: Linear deuterium Accelerator-Ion Gun Issue

Posted: Mon Apr 06, 2015 7:35 pm
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.

Richard Hull

Re: Linear deuterium Accelerator-Ion Gun Issue

Posted: Thu Dec 17, 2015 12:45 pm
by Dennis P Brown
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.

Re: Linear deuterium Accelerator-Ion Gun Issue

Posted: Thu Dec 17, 2015 10:55 pm
by Dennis P Brown
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!)

Re: Linear deuterium Accelerator-Ion Gun Issue

Posted: Sat Dec 19, 2015 3:47 pm
by Dennis P Brown
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.

Re: Linear deuterium Accelerator-Ion Gun Issue

Posted: Wed Dec 23, 2015 12:45 pm
by Dennis P Brown
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.)

Re: Linear deuterium Accelerator-Ion Gun Issue

Posted: Thu Jan 07, 2016 2:18 pm
by Dennis P Brown
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 ... .