Deuterium Accelerator and Electro-Static Power Supply

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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Deuterium Accelerator and Electro-Static Power Supply

Post by Dennis P Brown » Wed Oct 11, 2017 11:48 am

Well, as mentioned in the previous post that was restarted (thanks - I think - for reminding me of this type of project!), I have started looking at my old electro-static deuterium accelerator again (Third pic.) The unit is complete but needs an electric field to accelerate and guide the deuterium ions. The extra large Van da Graaff I built I have never bothered to test since at the time, I happened to obtain a fusor grade transformer that could do fusion (alas, a unit I will have to return in the near future ...sigh. Just so grateful they lent it to me!)

Well, here is a pic of the new voltage multiplier (First, second, forth & fifth pics.) The long vertical "rod" (see fifth pic) is two high voltage resistors - one 5G-ohm and a single 1 M-ohm. The first two pics show more details of the stack - since the two cap types have different thicknesses I had to use spacers to help keep the units fairly inline - not the easiest solution but works. This entire system will be under oil (still finishing that new tank.) The resistor stack will serve two purposes: 1) as a bleed resistor to discharge the system when I turn off power 2) As a voltage divider so I can measure the actual voltage (if it does go over 100 kV.) That vertical stack will also have a plastic pipe cover as well as be in oil.

In an air test using a NST (7.5 kV, a few ma at best) driver I did get the output of the VM to read 50 kV (direct measure using my HV probe with a built in meter.) The variac was at 50% and since this was in air I hope when in oil it will do closer to 120kV (my red line for accelerator use.)

A few notes: I use two sets of door knob caps because these things, even surplus, are not cheap - I got a deal on each set so I use both types; each is rated for the same voltage - 20 kV; just an issue of different capacitance values. The diodes can handle 30 kV except for the first one - that is one of my chinese made 20 kV 2 amp models. I was short since I never thought I would have to have this many stages to get + 120 kV. The oil I use is synthetic motor oil - does a great job and is cheap. Removing and allowing the original stack to drip for two hours made the stack fairly dry and no issue to handle. Oil immersion isn't the hassle I thought it might be. Besides adding two more multiplier units (4 caps) I changed out the hardware from plastic to metal - decided the plastic was more trouble than I got from reduced corona issues.

The accelerator design is simple: my turbo and vacuum pump system can reach the low 10^-6 torr; the large SS globe contains a battery operated ionization unit (25 kV) to convert the deuterium gas into ions. A small deuterium tank (see image) feeds a needle valve and allows a very small amount of deuterium gas to bleed into the high voltage needle to be ionized and accelerated. I have electro-static lens along the tube length (in hind-site, way too long a tube and only two lens should have been made - live and learn.) The end target will be either a duetrated plastic or a Ti foil with deuterium. The target is water cooled. That target is electrically isolated so I can read the beam current directly. Also, the target has a reverse field coil near it to stop electron back flow (nasty source of x-rays from the unit.) I do have shielding but it isn't in place.

The VM will be used to provide a +120 kV charge on the globe (like charges repeal.) With the correct deuterium flow, this will produce a deuteron stream hitting the target. This can produce a decent neutron flux (like a fusor including 4pi Steradians directional flux) with a deuterated target or I can activate some types of materials - like boron ... . Assuming all works as planned. This project, compared to a fusor, was a significantly more difficult build - providing the high voltage using a VDG is NEVER worth ones time. Hopefully, I can get the VM to work at the full voltage; take note: VM's do not easily get to these high voltages - these are projects, too (my first attempt using slightly smaller caps never worked for reasons I think were driver/Freq. related but again, these are never simple projects despite what one reads by posters - lol; learning curves can be steep.)

Using a high frequency driver for a VM is, of course, the best method. My 60 Hz (really half wave) is an easy build but a poor way to get HV - door knobs are ideal for very high frequency driver circuits so (maybe not so much my one large diode), I really should have bit the bullet and constructed one; water under the gate now. Keep these issues in mind if anyone decides this is a worth while project to pursue - it isn't just get the high vacuum and the rest is easy (but that is another story.)
Attachments
MVC-004L.JPG
Detail of VM stacks (Caps & Diodes)
MVC-005L.JPG
Detail of base/resistor connection
MVC-003L.JPG
Electro-Static Deuterium Accelerator (Big Ion Gun)
MVC-001L.JPG
Voltage-Multiplier - Door Knob Caps with diodes; each unit stack can handle up to 20 kV
MVC-002L.JPG
VM-Side View showing resistor stack - top resistor not connected to stack

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Dennis P Brown
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Re: Deuterium Accelerator and Electro-Static Power Supply

Post by Dennis P Brown » Wed Oct 25, 2017 4:08 pm

Some rather good news on my quest for a Giga-ohm high voltage resistor: turns out I have five special high voltage resistors (rubber encased, over five inches long) that are about 330 Mega-ohms each (a sixth one (colored red) is about half a giga-ohm.)

Using these, I should have no issues adjusting the current output from my positive 150 kV voltage-multiplier/NST system. I had these put away and had forgotten about them - came across them today when I was checking for any old resistor's I might have on hand that were still in "long-term" storage (being a pack rat has advantages- lol); they were designed for electro-static service on accelerators. At the time, I figured I'd buy them and someday, maybe, use them on my small accelerator.

Looks like they are well suited for my HVM; I tested three in series connected to the VM output and they matched a one giga-ohm resistor in voltage response (15 uA when the variac/VM yielded 15 kV; this voltage was determined by my HV probe.) Hence, my determination of their resistance.

Well, maybe this project will move ahead; and possibly, even this weekend, time permitting, I may install and test the accelerator's ability to hold an electro-static charge and determine the max current the VM will supply for three of these in series. Of course, can remove or add resistors as needed to get the desired current on the accelerator's sphere.

Aside: a VM is not an electro-static supply. Not trying to confuse anyone but this title refers to my original attempt to create one and afterward, I decided to move on to a VM or HVM (High Voltage Multiplier.) The HVM/NST system will charge a sphere and that electric field will be used to "accelerate" deuterons in a manner identical to the initial concept.

MVC-007L.JPG
A rubber enclosed 330 Mega-ohm resistor (Pen for comparison)

I soldered three together and added end connectors:
MVC-008L.JPG
A One Giga-ohm chain Resistor
I will install these and make a test ... .
Last edited by Dennis P Brown on Thu Oct 26, 2017 6:02 pm, edited 1 time in total.

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Re: Deuterium Accelerator and Electro-Static Power Supply

Post by Dennis P Brown » Thu Oct 26, 2017 5:57 pm

Well, still wondering if the high voltage multiplier will handle the inevitable voltage loss via the accelerator's sphere; that will be a test that creates issues of believable proof for maintaining the voltage - that is, the voltage needs to be remain sufficient even if I hold enough current (I know the current will hold but very likely, the voltage will collapse for the reasons Richard cited. Numbers do not lie.) I guess I can install a 5G-ohm resistor to the sphere and attempt, via a voltage divider (i.e. my HV probe) a direct measurement on the sphere's voltage but that may or may not be valid - an arc test is a good indicator but again, an unknown but certainly a rough indicator if it works ... . Finally, a field build up by the sphere will offer some idea but is hardly proof.

Richard is likely correct that my caps simply can't handle the huge corona loss by the sphere resulting in a far too severe a drop off in the HVM output voltage but I intend to test this out - will be fun.

The good news for me, in any case, is that if the HVM can't directly charge my accelerator's sphere, it can certainly be used to charge my Van de Graaff's belt with a well over 50 kV or so positive charge (at the base of the VdG's belt); that should help that device overcome its possible issues (not sure the VdG even has issues but of late, how could it not?)

Again, reverting back to old projects but they do need to be tested for closure, I guess. The VdG is huge - the sphere is 2.6 ft in diameter and supporting column is about 3.7 ft - the belt is about 5 inches wide and the entire unit stands just over 5 ft tall.)

This overly large VdG was built before I obtained the fusor grade x-former and created a neutron source via that method. This VdG unit remains untested since its operation, at the time, was not required. It runs fine (motor/belt/pulley all work well togther) but getting it to charge was not done at the time (since its belt system does not create fictional charging (all metal rollers) this necessitates that an external voltage spray be used and is its only real source of charging for the VdG's belt.) That external supply has never been hooked up (the corona spray/pick-up arrays are installed in the VdG.) To date, this device has only been eye candy.

If my direct charging of the accelerator fails via the HVM, then I will use that HVM (adjusted to max voltage supportable (what ever that is)) to charge the belt and see what happens relative to charge build up on the large sphere. That isn't a test I will attempt lightly - if it does work, that sphere can carry an overly large current that might not be something one wants to get hit by.)


This is, of course, a real electro-static generator (or is meant to be one. Except for the sphere, all other components for this VdG were obtained from materials bought at local stores.)
VandeGraaff.JPG


Aside: the motor/lower bearing/frame are all from a cheap mini-table sander; as is the upper bearing/support!
Below is a link to other images of the VdG and its internal components:

viewtopic.php?f=12&t=9384&hilit=Van+de+ ... =20#p70504

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Finn Hammer
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Re: Deuterium Accelerator and Electro-Static Power Supply

Post by Finn Hammer » Thu Oct 26, 2017 7:40 pm

Dennis P Brown wrote:
Thu Oct 26, 2017 5:57 pm

The good news for me, in any case, is that if the HVM can't directly charge my accelerator's sphere, it can certainly be used to charge my Van de Graaff's belt with a well over 50 kV or so positive charge (at the base of the VdG's belt);

SNIP

If my direct charging of the accelerator fails via the HVM, then I will use that HVM (adjusted to max voltage supportable (what ever that is)) to charge the belt and see what happens relative to charge build up on the large sphere.
Dennis,

With regard to the function of a VDG, you are drawing some erroneous conclusions.
The charge delivered to the top terminal via the belt is directly determined by the area of belt entering the terminal per time unit. And the charge density on the belt. The charge density is the real limiting factor, because there is nothing you can do to increase it, if you try to, the charge just slips off the edges of the belt.
I can assure you, that you need a very weak supply at the bottom of the belt, only enough to create a corona discharge in the tip of the needles that form the comb.
I have used a simple oscillator driving a TV flyback transformer for this purpose, and with a 120Mohm series resistor to limit current so that the corona does not progress to form an arc.
You need to observe the comb under total darkness, let your eyes adjust over 2 minutes, and then you can clearly see the corona, it is _that_ weak, but it is enough to deliver the charge to the belt, if the distance to the belt is around 5-10mm.
Under these dark conditions, you will also see how the belt is lit up by a layer of corona, yes, the charge lights up on the belt when the charge density is at it's maximum.
Do this, you will be enlightened and you will thank me.
You can arrange an extra set of combs in the top terminal, to induce the same amount of corona on the belt on the down run, and this doubles the current.
A very bright professor down in Brazil, Antonio Carlos M. de Queiroz, who knows everything worth knowing about electrostatic machines, has made a small program to calculate the current you can expect from a VDG, you can download it here:
http://www.coe.ufrj.br/~acmq/programs/elcal.zip

You do not want to use a voltage higher than 10kV at the base of your VDG.

There are also very good online calculators which will reliably predict the output of any Cockcroft-Walton-generator, which is what you are building, There is a nice one here at Blazelabs:
http://blazelabs.com/cw-brm-java.asp

Hope this helps,

Cheers, Finn Hammer

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Dennis P Brown
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Re: Deuterium Accelerator and Electro-Static Power Supply

Post by Dennis P Brown » Thu Oct 26, 2017 7:52 pm

I REALLY do appreciate any comments, insights or details (and so will others) on both Van de Graaff operation, techniques and do's/don't and what should be done. Misconceptions like mine do harm and are far too often propagated in articles on the subject. So, any corrections are highly and gratefully appreciated!

Thank you again and I will post results as they become available.

Tried the calculator - if my input numbers are correct (they are close), then I should get (roughly) 200 kV and 37 micro-amps. These are the numbers I do require - so, if this device can operate close to this, then the accelerator should work. Again, will have to test. I will absolutely follow your procedure for the voltage adjustment for the lower "comb". That is an excellent methodology!

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Re: Deuterium Accelerator and Electro-Static Power Supply

Post by Dennis P Brown » Sat Oct 28, 2017 6:30 pm

Following Finn's excellent advice, I assembled a 7.5 kV power supply to use with a variac to function as a high voltage corona spray for my Van de Graaff belt.

I had a 7.5 kV NST (no CFI; 60 ma) on hand, as well as numerous small HV diodes (20 kV, 30 ma) and a cap along with some 50 M-ohm resistors I bought. I built a bridge rectifier along with the HV cap (40 kV, 0.02 uF) to filter the output and this in turn, then runs through three 50 M-ohm resistors in series (so 150 mega-ohm.) All this is mounted on top of the NST using ceramic stand-offs and is enclosed for convenience and prevention of getting a not fun shock - I can often find a way ... why I am hyper careful with my fusor supply and have it shielded and doubly and independently grounded.)

A quick test showed the system reached a 7.5 kV (max) positive output (the negative side of the bridge is grounded.)

I will closely follow Finn's method tonight and adjust the lower corona spray needle array (for the belt.) I will also install a micro-amp meter to the dome and out put this meter to ground - this will let me see what the VdG can put out (via the belt) and keep the dome from charging while I do all of this (not interested in getting zapped if this all works according to plan.)


I have already tested the operation of the VdG motor/belt system and it works well.


MVC-012L.JPG
Corona High Voltage Supply with Van de Graaff

MVC-009L.JPG
Corona Supply

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Finn Hammer
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Re: Deuterium Accelerator and Electro-Static Power Supply

Post by Finn Hammer » Sat Oct 28, 2017 9:19 pm

Dennis,
Sounds good.
With 150Mohm in series, you will be good. I hope you will get a dark night, where you can see the corona on the tips of the comb. I wonder how the silver paint on your belt is going to influence the operation, but am very interested in hearing about your observation of the corona on the belt in darkness.
Although it glows as bright as phosphorescence in the sea, where the water around the boat can light up a meter out, and the dolphins appear to swim in a sea of light, it is too dim to photograph, even with a very sensitive camera, the eyes are a wonderfully sensitive transducer, and I really hope you get to see it.

Good luck,

Cheer, Finn Hammer

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Re: Deuterium Accelerator and Electro-Static Power Supply

Post by Dennis P Brown » Sat Oct 28, 2017 9:29 pm

Thanks for the help; I may need to replace the belt - what material do you use?

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Finn Hammer
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Re: Deuterium Accelerator and Electro-Static Power Supply

Post by Finn Hammer » Sat Oct 28, 2017 9:44 pm

I will have to look it up, It is a transport belt used in the food industry, you know, to get the cookies and bisquits from the oven to the packing machine.

The company that produces it is called Habasit and the product number is F-2EQWT.
Not sure they are in business anymore. But any thin polyurethane white belt from the food industry, without antistatic measures, will be fine.

You might like to read this thread about the first VDG i built:
http://4hv.org/e107_plugins/forum/forum ... hp?26708.0

Cheers, Finn Hammer

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Dennis P Brown
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Re: Deuterium Accelerator and Electro-Static Power Supply

Post by Dennis P Brown » Sun Oct 29, 2017 10:54 am

That is your first VdG! That is interesting because that is the design that I first looked at to get answers on how to "how to build a Van de Graaff"! LOL. That is an extremely sophisticated device, and the most technically advance VdG that I have seen.

As for observing the corona, no luck - I even set up a single needle to the power supply to enhance the effect and that didn't work, either - I confirmed that the supply reached 7 kV and was working current wise (I could get a small arc from the supply.)

I will do a search for that type of belt material today. I will also do more work on the power supply and try to determine why the corona (lack there of) is such an issue; are your power supplies high frequency, maybe? Operating 60 Hz might be the issue. I might have a higher frequency unit somewhere.

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