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 » Sun Feb 28, 2016 6:24 pm

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

Post by Dennis P Brown » Mon Feb 29, 2016 11:48 pm

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

Post by Dennis P Brown » Wed Mar 02, 2016 2:49 pm

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

Post by Dennis P Brown » Sun Mar 06, 2016 6:34 pm

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.
Attachments
MVC-001L.JPG
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MVC-007L.JPG

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Richard Hull
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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by Richard Hull » Mon Mar 07, 2016 4:43 am

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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

Post by Dennis P Brown » Sun Mar 13, 2016 5:53 pm

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

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

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

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

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

Post by Dennis P Brown » Fri Mar 18, 2016 1:29 pm

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

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

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

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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by John Futter » Fri Mar 18, 2016 5:55 pm

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

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

Post by Dennis P Brown » Sat Mar 19, 2016 6:39 pm

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

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

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

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

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

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

If that looks promising, then I will most likely up the motor speed by simply changing the pulley's on the motor/drive roller. That can get me up to 40 mph rather easily.
Last edited by Dennis P Brown on Sun Mar 20, 2016 5:29 pm, edited 1 time in total.

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Re: Linear deuterium Accelerator-Ion Gun Issue

Post by John Futter » Sun Mar 20, 2016 3:02 am

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