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

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Well, not much is currently being posted in this section so I will give a short update on progress (or lack there of); the diodes arrived and I have all required HV caps. So could add three more stages to the voltage multiplier (VM) if I desired. Also, have the flyback transformer (allege 30 kV, 60 ma capable - right; give that claim a big laugh) but I still need the 20 volt 60 Hz to 50 KHz converter I ordered. That should get here this week. Will be interesting to see if that works as stated; the unit is just too inexpensive to believe but have been surprised before.

Once I have that converter (I have a big low voltage transformer that can deliver 20-30 volts at 30 amps +, so the converter will have its required power; not that the device needs more than an amp or two), I can then use my existing voltage multiplier system (four stage) to get in the range of 180- 240 kV (very unlikely to get near that high end value but anything over 120 kV would be overkill, anyway so, just hoping.) Since I do not want to increase the voltage multiplier stages due to the extra work (especially the mounting issues requiring oil to work properly) - besides, if the flyback works even close to the mid values, further stages would be a waste of time and just lower the current resulting a less powerful accelerator, anyway.) So, best to wait for the freq. converter so I can test the system (and avoid useless project building.)

If that does not work, then I will add two extra stages to the multiplier and see what voltage the NST will achieve.

Also, even if the flyback/VM system does work I will still test the flyback at some point (no voltage multiplier attached) to see if it can get in the mid to high 20 kV range and output at least 20 -35 ma (seriously doubt the 40 - 60 ma is even possible. The flyback just looks far, far to flimsy to operate anywhere near that level no matter what the company claims.) However, if it does get mid-20 kV and over 20/25 ma then for under $100 it would be a worthwhile experiment; better still, supply my fusor with a higher wattage power supply (current supply is a 28 kV, 15 ma unit - barely acceptable.)

The rubberized cloth company didn't send the proper piece so need to redo that order; so the Van de Graaff project continues to wait.
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Dennis P Brown »

Quick update.

Had issues with my low voltage, high current DC power supply. Had to gut it and isolate the transformer; then install a diode bridge.

Will have to now use a Varic to control the voltage but at least that power supply does appears to be working again (complex systems do tend to fail as they get old... .)

Hope to test my high voltage flyback transformer this weekend using this power supply with my my new high frequency converter. Be interesting to see what voltage I can get and possibly, measure the current.

If time permits, I guess I will test one of my high voltage diodes to see if it can handle a full 15 kV without failure. If so, maybe test my voltage multiplier to see if the diodes can handle the very high frequency ... be surprised if they do.

Should be a fun, but hopefully not too exciting weekend (as in blown diodes!)
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Wow - a first for me; the high frequency converter had its caps (2) blow up in my face. Guess the DC polarity matters (it is not marked so I assumed it didn't matter - wrong.) That hurt (the debris hit hard even those caps were small)- even at twenty volts the power supply can delivery 4 amps but its ripple cap (for the diode bridge I put in) is 6000 mfd and stores a lot of power. Guess I need a new on (another two weeks to wait.) Really should be marked if it matters but cheap is cheap for a reason, I guess.

The up side is my new power supply works (too) well. It can deliver 20, 40 or 60 volts DC of either polarity. Since it was junk, got it for a few bucks (new, likely over $1000) but I just gutted the electronics (too complex to bother with); installed a new bridge and wired some outputs myself.
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Dennis P Brown »

Guess I will add a few images for fun. First photo is of the destroyed Freq. converter - one of the two removed blown caps is shown on it side. I think the device needs a proper ground and lack of one allowed the voltage to exceed the rated value of 30 v DC; the power in my ripple cap was just too great so once the voltage margin was exceeded, boom. The last pic is of the PS with both the freq. converter and flyback installed. Hope to get to this point again and actually get it to work properly. Amateurs often learn the hard way and lucky this didn't endup with an injury - respect caps even at low voltage!
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Destroyed Freq. Converter
Destroyed Freq. Converter
Original Micro-electronics
Original Micro-electronics
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Power Supply Panel (stripped)
Current PS (no flyback/Freq. Converter)
Current PS (no flyback/Freq. Converter)
Future 30 kV Power Supply
Future 30 kV Power Supply
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Dennis P Brown
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Learning from mistakes is slow! Also, doing the reverse engineering to figure out what went wrong and researching the issues discovered takes a lot of time for the electronic illiterate ... . So, as I discovered the hard way, turns out that grounding one side of the transformer and not the diode bridge results in floating the potential of the diode bridge and having the device using the bridge see an "effective" double voltage that a meter does not "see" - end result: burned out ZVS by exploding all caps; also, didn't realize my voltmeter was both low (for reading DC by 25%!) and only reading RMS on the AC side (a new meter does not have either issue.) Result - again, blew up the caps on a new ZVS system.

So, I am again rebuilding the DC 0 - 60 volt (pos)/high current system using these lessons learned - also, the unit will now have a built in voltmeter so I can read applied voltage in real time; further, I decided to install an internal Variac to better allow the system to be controlled accurately and free up the larger variac for other experiments (the non-exploding cap type.)

Most older hands here will be amused by this method of electronics development, no doubt.

Once the new ZVS arrives will try again and hope to avoid exploding caps. If I get this ZVS driver system to work I hope to then try using this to get the well over 100 kV with a voltage multiplier ladder I already have successfully constructed (the 30 - 45 kHz 20-40 volt AC output system will power a flyback for the 30 kV AC I need). Takes 15 days to receive a new ZVS - so, now on my third one already but believe I have discovered/fixed all issues ... . Learning electronics by building devices and experimenting isn't fast - it is effective if one ignores the rather dangerous exploding caps!

On the Van de Graaff front I have obtained the silver epoxy I require - guess I will try and create a belt that has narrow metal strips (horizontal) on its outer face along its entire length to better charge the upper sphere. Hope this approach results in a better total charge.
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Dennis P Brown »

Well, the power supply works well; 5-8 amps max and 0 - 20 or 0-40, or 0-60 volts DC (can be pos or neg.) Can't believe how much trouble building this was but I did learn a good bit about transformers and diode bridges and issues both about grounding and filtering - as Richard says, build it.

I have been studying ZVS (zero voltage switches) oscillators and if my new one causes problems again (shouldn't since I have a stable and accurate power supply now) I will build my own; turns out I have 90% of the key components it is just a matter of creating a proper circuit board. Making a high current 30-50 kHz low voltage supply using an existing 60 Hz supply is rather easy or so it is claimed (lol.)
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Finish the 0-60 volt DC power supply; realized the issue with the ZVS - it had no marking for the ground and pos inputs which ended up damaging the unit since I didn't know this used polarized caps! So after tracing the circuit determined the correct polarity and realized this was the real issue. Replaced the destroyed cap with a far larger/higher voltage one and replaced a bad resistor. The device works well now.

My flyback is too large for the power supply - 6 amps just isn't enough and the unit tops out at 28 volts creating an extremely low 5 kV from the flyback. Guess I need a better supply - guess I might as well just use my monster 60 - 120 amp, 50 volt transformer (a very big - read heavy - unit. Uses, of course, 220 v)

Glad I am getting some experience with real circuits and able to do some elementary repairs. Also, guess I will hookup my oscilloscope and look at the output frequency later this week.

Below are images of the ZVS freq. converter and a high voltage probe measuring through a HV diode connected to the flyback. Below that image, the entire system.

I installed a variac in the supply so I could free up my large variac. Also, I used a scrap panel meter for the voltage readout; to get it operating I just had to determine the correct resistors to add to get the meter linear over the range. The system works very well (but is, unfortunately, still underrated!)

In any case, this rather long effort resulted in me building from scrap/non-working junk a rather nice variable output pos/neg DC power supply; some interesting theory on ZVS converters and even the chance to repair one. All this just to begin building a alternate 100+ kV supply ...still, learned a good bit (far, far more to go) but has been a rewarding experience through a bit aggravating one ... .
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Hate to preempt the really great post here but just need to update on my accelerator.

I have made a new belt for my Van de Graaff (VdG) - after removing the metal tape on the rollers (caused the belt to short out from getting metal on the inside surface; that was a surprise. Guess the people who recommend that never tried it) - I made a new belt (same plastic material) but have rectangular squares of conductive silver epoxy every 2.5 cm (each about 1 cm "high" and 8 cm wide) along the entire belt (outside only! Otherwise, the same shorting issue would quickly occur!) In this way I have a "metal" link belt without the need to create a chain system (very difficult.) The belt is 10 cm wide so with a 7 kV spray, I hope this belt can charge the dome rapidly enough to create enough current to power the linear accelerator.

Still, pointless to test the unit until I build the room de-humidifier - otherwise, I know the system will short to air most the charge on the dome and prove nothing.

Still, not really counting on this design to work but it will prove the basic idea of the "if" of using a VdG and partly show IF such a thing is remotely reasonable. This is a big unit with a big belt so if it can't work, highly unlikely smaller units - especially commercial ones - will function for this purpose. I am not saying these things aren't good for creating extremely low current high voltage; just that an accelerator column creates too large a current draw for their practical use for this specific application.

IF (and only if) this new design works, will I post both pics and details on construction of the belt.

Backup plan one to this, is installing a neoprene belt on the VdG (no metal) with the rubber rollers - this is considered an ideal belt for creating a positive charge. Again, not convinced.

Backup plan two is to finish the tested and proven voltage multiplier and add the last two stages to get the 120 kV or so; appears to offer a good bit of current. That (see previous posts and images) existing unit is also a rather large monster and needs to be under oil for the last stages to have a chance to develop full voltage. As such, I am holding off on that device final build until the VdG fails.

Really like the previously posted neutron accelerator unit posted here - the VM design they use is a good way to go and most likely, I will end up following that path; I am using a NST since I have big caps and diodes. I did try a ZVS system but it isn't very good (not due to the diodes.) So, will continue with the NST system since it has been very good creating the 50+ kV to date.
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Cautionary tale:

Well, more progress but not bothering to do too much too fast - really, summer is a humid time of year. Recharged the de-humidifier (used propane) and it works great (very easy to do.) The room went from 61% to 32% but that is its bottom - guess long term drying would be required to get below that threshold.

Still, 32%, I feel, is just too humid to even consider running a Van de Graaff much less perform a "make or break" test on this new and very large unit. Need a fair test before I decide what to do.

So, next step is to seal the VdG and use a drying agent within it. Considered SF6 but just not worth the effort. Might create a small enclosure for the entire system (vacuum, ion gun, VdG) so the de-humidifier only drys that smaller space. Combing both is silly so may steal on one this week to be done next weekend.

Bottom line - while building a very large VdG is easy and rather cheap (under $200 for everything) just getting any VdG to operate is tedious and even then, no guarantee that it will work (current wise.) Still, traveled this far so I am determined to finish this project (the VdG) one way or another. Just herding cats isn't a lot of fun ... .
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Richard Hull »

A good friend, Bill Richards, an old member of TCBOR here, Now passed away, solved his VDG problems in a unique manner.

He bought a junk hair blower from a local trift store. $1.00 He made a duct/plenum to supply blower air to the column containing the belt. He attachted the dryer to a variac and let it heat the air just enough to be rather dry and warm. Now, this will not assist with moisture in the air around the top load. He would always wipe his oblate terminal with a 90 proof alcohol wet cloth to rid it of dust and lint, (major bleed points). It improved his output by 50% in humid summer conditions and made it spectacular in winter.

Running his VDG always demanded a 5 minute cleaning and de-humidifying prep and another 5 minutes of run before it stabilized.

I own the largest VDG that American Science and Surplus ever made (old Morris and Lee), but haven't run it in years.

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

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Thank you Richard! These are all great ideas (I can't believe I didn't think of the hair dryer!!!)

Very glad you mentioned this and how this was used.

I will definitely use a hot air dryer and with the room de-humidifier this should give me a good chance to get the air dry enough; I will keep a humidity meter in the unit to both confirm and monitor the air quality.

I use the alcohol trick and it does a good job.

Aside: Jeannette (a senior now at MIT!) is done the reading (research papers) for the project she was hired as a summer intern at the Max Planck Institute and starts today working on a 3 Tesla superconducting magnet for her research job at the Wendalstein 7-X Stellarator. Hope she remembers to remove all metal items before turning the unit on!
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Re: Linear deuterium Accelerator-Ion Gun Issue

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A bit of updating: the main Van da Graaff box/column/dome are all nearly sealed - a good bit of rebuild. Far slower than I thought!

Once done I will dry the room, add desiccant in the VdG and close the VdG box. I will then wait for the weekend so I can try to see if all my work was worth the trouble. I hope the new belt design with metal conductors will load the dome from my charging system (A NST and voltage multiplier system to make positive 14 kV for the spray system.) Will keep the hair dyer idea ready for further drying if necessary.

I hope the VdG system (inside) gets below 10%. I already know that the room can easily reach 30% using the air drying system I put together. Will need this all to work for a valid test.

Again, not counting on this part of the project but would be nice to have a success with such a major rebuild.
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Well, the Van de Graaff sealing work is done; had to reduce the width of the new belt. Pictures to show the new belt - the "silver" rectangles are really silver (conductive epoxy: 2-3 ohms across each.) Humidity just isn't low enough in the room - from 70% to 40% just ins't gonna do it. So, will wait. Also, sealed the upper dome, too. When the room is dry enough, will add desiccant to the inside of the VdG (including the dome section.) Installed a humidity meter inside the VdG as well as one outside.

The idea is that the metal surface will accumulate a significant amount of charge from my high voltage "spray" system and transport this to the dome. In this manner I will get a greater charging rate than from simple fictional belt/slippage accumulation. That is the theory, at least. Works on professorial systems but this is very home built - 56" tall and the belt is about 4 inches wide. The dome is about 25 inches across so I am hoping this will create enough current for my needs - that is, if I can get a dry room!
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Re: Linear deuterium Accelerator-Ion Gun Issue

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A quick update on the status of my deuterium accelerator project: the room humidity, even with my a de-humidifier running all day, is well above 40%; so definitely, this project is on hold until cooler days of autumn (?). However, I did, as posted, build the very powerful high voltage positive 10 kV supply for the lower 'spray bar' that will be used to charge the belt (as can be seen in the photo previously posted the belt has 'silver metal' rectangles to carry extra charge up to the dome) for the Van de Graaff. Can't think of anything else to do for this project but wait for lower humidity conditions.

As such my postings in the "Fusor Power" section I have taken my partly finished fusor out of mothballs and will try to get that into operation now that I have a power supply that can handle the required power/voltage. Unlikely this will provide enough neutrons for my experiment but who knows? Worth trying and is kinda fun.
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Well, decided to change the "ion gun" assembly yet again on the gun; this requires de-mounting the accelerator and striping it down, "breaking the end seal (never fun)" and then I will do two things; first, add a high vacuum port/valve system so the small deuterium gas tank needs not be removed; this has the added advantage that I can refill the tank anytime without significantly disturbing the system. (Aside. My deuterium tank is stored inside my high voltage hemisphere. In this manner, I don't have gas lines leading to this hemisphere which significantly reduces current lose from the Van de Graaff.)

Second, get rid of the whole existing "ion gun" assembly that is based on ceramic and metal; rather, convert it to all metal. Using metal will improve the seal (decrease possible high vac leakage) and get rid of a highly delicate part that tends to fail if I disturb it in any significant manner. Machining a new part is trivial and I really hate that I didn't do that three builds ago ...learning, even after many years is always an on going experience with high vacuum.

Really might as well do these things since I still have a few months before humidity drops enough that I can run the new Van de Graaff.
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Re: Linear deuterium Accelerator-Ion Gun Issue

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Well, this job was easier then I thought since the 'delicate' section had not failed in any manner (vacuum wise.) So I really got rough with it by removing piping (which stress's the assembly when the couplings are undone) and installing an auxiliary vacuum fitting attachment coupling and redid all the pumping (leak valve assembly) so it is almost all SS now (more fittings but only one teflon tube now;) the Deuterium tank can be filled without removal, if desired. More to the point, all the volume of the gun assembly (piping, valve, and even the D2 mini-tank when open) can be evacuated independent of the main accelerator tube. This will help prevent residue gas contamination of the D2 supply for fills and make pump down of the entire accelerator system much faster. The gun's only connection to the main accelerator tube is thru a long, very fine needle (about 150 microns) which makes pumping through that orifice very slow after back filling the system for any maintenance.

In tests, the whole accelerator assembly with the D2 tank open, bottomed out at 1.1 x 10^-6 torr so apparently everything is still leak tight. The new gas line assembly for the gun is how supported by posts (all mounted in a SS hemisphere that will be charged by (hopefully) my new VdG) to reduce any stress on the weakest section; and hopefully, avoid any vacuum failure at the gun/D2 feed line/pipe coupling. While this, as noted, wasn't essential it makes sense to improve a possible trouble source while I have time to use waiting for the weather to change to low humidity.
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