Demo Fusor Progress Update

Current images of fusor efforts, components, etc. Try to continuously update from your name, a current photo using edit function. Title post with your name once only. Change image and text as needed. See first posting for details.
Jim Enright
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Demo Fusor Progress Update

Post by Jim Enright »

Hello everyone, after much time away from our demo fusor efforts due to water damage in our house and my father's passing (which also resulted in us missing this year's HEAS meeting at Richard's house), my 16-year-old son and I have gotten back to our demo fusor project. You may recall that we built a demo fusor using a borosilicate vacuum chamber in the Summer of 2020, and had achieved plasma (just before the Plasma Club rule change about metering so we were removed from the Plasma Club), but wanted to advance our system. During our time away from the project, we began the process of collecting the necessary stainless steel components and elements for an upgraded demo fusor. Our goal with this post is to document our efforts as we progress.

Our system is a 2.75" conflat system using a tee. The tee is mounted to a 4.5" open-center flange to allow us to connect the negative lead to the feed-through. Our power system is a 15kV neon sign transformer controlled with a variac. The vacuum is handled by a 8 CFM 2-stage Ritchie Yellow Jacket vacuum pump. The inner grid is constructed of 1mm stainless steel wire. A big part of our goal was to get this demo fusor running so we can add the necessary metering system for when we upgrade to a almost-fully-functional demo fusor, with the eventual goal of adding a gas inlet.

We finished constructing this demo fusor Friday, November 26. After a couple of runs, we quickly realized that we did not wipe down the inner grid or feedthrough, which definitely impacted our ability to generate plasma. In addition, it seems likely that there are leaks. This week, we took the chamber apart and cleaned the inside with isopropyl wipes again and added a viton gasket to the viewport flange (all of the flanges are sealed with viton gaskets). However, we still have an arcing issue at the bottom of the grid. I'm starting to think that we should just use the feedthrough that we purchased rather than the hand-made one based on the Make Magazine plans, and move everything to the 6-way cross shown in the pictures.

In terms of our future equipment, we have the following items:
1. A 6-way cross that will accommodate the feed-through (to be submerged in oil), TC, vacuum, viewport, gas, and a blank flange cap
2. 30kV precipitator power supply
3. Welch 1405 vacuum pump for the roughing pump
4. Turbomolecular pump given to us by Steven Sesselmann and for which we are grateful!
5. A PEM cell to extract D2 from heavy water (living a mile from the ocean, I wish I could easily extract the D2 from the ocean water!)
6. Needle valve for the gas inlet
7. Borosilicate viewport
8. Lead shielding will be made from my old scuba diving weight belts melted down (my new BC has integrated weights!)
9. The vacuum pumps will be connected to the cross using a bellows hose
10. The system will be mounted on a converted cart that will have the "star" grounding method
11. The inner grid will be constructed of 1mm titanium

As of right now, 2 major obstacles that we need to address are having a 240V outlet installed in our garage, and having the power supply and TM pump wired for 240V. We have started tackling the metering issue with guidance from Mark Rowley and hope to have the metering system operating on a plasma-producing demo fusor. To accommodate the metering that we need to have in place, we are thinking about converting the system to the 6-way cross now, rather than get things perfected on the tee, only to have to start all over again.

We welcome feedback or insight about our current demo fusor, or our future plans. Thanks!
Attachments
IMG_4883.MOV
Video of our current stainless steel demo fusor - video taken 12/2/2021.
(19.02 MiB) Downloaded 203 times
Some of the equipment for future iterations of our demo fusor, end eventually a fully functioning fusor.
Some of the equipment for future iterations of our demo fusor, end eventually a fully functioning fusor.
Some of the equipment for our future iterations of our demo fusor, end eventually a fully functioning fusor.
Some of the equipment for our future iterations of our demo fusor, end eventually a fully functioning fusor.
The TM pump that Steven Sesselmann gave us!
The TM pump that Steven Sesselmann gave us!
Our Welch 1405 vacuum pump
Our Welch 1405 vacuum pump
The inner grid through the viewport
The inner grid through the viewport
The viewport
The viewport
Our stainless steel tee demo fusor setup.
Our stainless steel tee demo fusor setup.
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Dennis P Brown
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Re: Demo Fusor Progress Update

Post by Dennis P Brown »

First, so very sorry for your tragic lost.

A 'home made' electrode (see my post) can be problematic and unless one has the special supplies, and equipment, can be a bear to make leak tight - again, see my current post. Using a commercial unit is likely better. Besides, you have a rather nice electrode there.

Unless you have obvious oil contamination, I wouldn't bother to wipe my interior vacuum surfaces down with alcohol. My system components have been exposed to air for five years and it is now at 4.5 microns with just the fore pump (yes, I had leaks and fixed those but the out gassing issue isn't difficult to handle by pumping and maybe baking.)

I used (till recently) a water cooled diffusion pump (DP) with great success and like it more than my turbo. Mating it to a chamber can also be problematic unless one is handy with a lathe (I am.)

Your fore pump (the belt driven one) is an excellent unit but be certain the interior is clean and in good shape.

Your other pump is likely the real issue that is causing you problems with arcing. It likely isn't providing a sufficient vacuum. Have you check it with a vacuum gauge (just the pump?)

Your cross is very small - I used one recently and it lead to disaster - luckily only my ballast resister. But I've definitely moved back to a large chamber.

Getting voltage and amp measurements requires proper electrical knowledge and do read the related FAQ's and follow carefully.

I would avoid melting lead - the vapors are toxic and frankly, lead sheet is rather cheap (esp. compared to one's health.) I will be using slate for the primary shield on my system - cheap, safe and available at the Home Depot. I have some lead sheet (painted and mounted in a wood frame) but prefer slate for its convivence, safety, non-conductive, and ease of disposal.

You have a lot of great parts and I look forward to you getting the demo together, getting back into the plasma club, and finally, doing real fusion.

Keep up the good work and best of luck.
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Richard Hull
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Re: Demo Fusor Progress Update

Post by Richard Hull »

If that is a 5 CFM yellow jacket pump and it looks new, It is one of the best direct drives in the refrigeration biz. I own one, used, and it will hit 10 microns at the head every time. A good pump. keep all vacuum lines as large in diameter and as short as possible.

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
Jim Enright
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Re: Demo Fusor Progress Update

Post by Jim Enright »

Dennis, thank you for the condolences. My dad was a Vietnam vet who was exposed to asbestos in the boiler room of a ship, and that is what ultimately caused his death. At least he is not suffering.

Dennis and Richard, thank you both for the feedback! Richard, the Yellow Jacket pump is an 8 CFM 2-stage pump SuperEvac model 93480. It is a bit on the older side, but I got it for a reasonable price and took a chance. You may recall that it did work well to create plasma with our borosilicate chamber Summer 2020. The Welch 1405 I picked up locally for $100 and couldn't pass it up based on the price. We have not run it yet other than when we purchased it. We will empty the oil and add new oil to get it operational.

For our Ritchie pump, we have not yet tested it. We didn't have our borosilicate demo fusor hooked up for any measurements but we definitely had a nice plasma glow. Unfortunately, the lack of metering got us removed from the Plasma Club, but we want to eventually get a fully functioning fusor so we wanted the metering anyway. But it did seem that the Ritchie pump was operating stronger at that time. We will test it this weekend with a digital gauge, and maybe even test the TC gauge on the chamber, although I do not know with certainty that the TC gauge works.

I do think we will just go directly to the 6-way cross and start setting the demo fusor components on that. Until we have the 240V line run through our garage, we will not be able to use the diffusion pump (I mis-spoke in my previous post when I mentioned a TM pump) or the power supply, both of which also need to be wired for 240V. The cross is based on Mark Rowley's fusor which used a 4-way cross and a tee. The diffusion pump is going to be connected to the chamber with a bellows hose and KF25 flanges. The roughing pump we use (probably the Welch) will be connected to the diffusion pump with steel-reinforced tubing.

For the voltage metering, we went back and forth about what to do. We considered a high voltage probe but finally decided on a hard wired gauging system based on the diagram below, and using a 50uA analog gauge. (Pardon the crudity of the drawing, I drew it out on my whiteboard at the school where I work.) The resistors will be under oil. For right now, we will connect it to the NST until we get the precipitator power supply wired. Hopefully this will at least help us see that the metering is working on the demo fusor. For amperage, we are intending to measure with a multimeter.

Again, I welcome any insight from the experts!
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Liam David
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Re: Demo Fusor Progress Update

Post by Liam David »

Watch out: your voltage measurement resistors are far too small. The current at 30kV is I = V/R = 30 kV / 1 M = 30mA. Way above your 50 uA meter. Also, the power dissipation would be P = I^2R = (30mA)^2 * 1M = 900W. Your resistors would be toast, as well as your precipitator supply. If you want to use your 50 uA meter then you need at least 1G resistance.

Also, I don't see it among your components, but you should put a valve between the chamber and diff pump to avoid wasting lots of deuterium in the future.

Keep up the good work.
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Re: Demo Fusor Progress Update

Post by Jim Enright »

Liam, thanks for the info! I'm still grappling with the voltage metering since that part is new to me. What I'm trying to do is create a voltage divider so that the 50uA gauge reads voltages per 1,000. I thought that two 500k resistors would divide my voltage so that if 20,000 V were being input, the gauge would point to 20. Is there something different you would do? Again, I'm new to this, so your feedback is much appreciated!

I forgot about a valve between the chamber and pump, but we will add that afterwards. The drawing started off more as a way of diagramming the voltage divider, and sort of morphed from there to show the relationship of the parts. I have since erased it from my classroom whiteboard as I needed the space, but the students used to love it!
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Richard Hull
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Re: Demo Fusor Progress Update

Post by Richard Hull »

Follow Liam's advice!!!! you need 1gig ohm 1000 million ohms!!! Ten series connected 100meg resistors to make your 50ua meter read 50kv.
Using the 2 500k resistors would not draw all those 900 watts. Sure, it would try, but within a few milliseconds your meter's coil would have gone off like a photo-flash bulb.

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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Dennis P Brown
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Re: Demo Fusor Progress Update

Post by Dennis P Brown »

Liam is spot on - my 45 kV high voltage probe is nothing more then a micro-amp meter (not sure of its range - 50 u-A might be it) and a 1.1 G-ohm resister (a few watts rating) in a handle assembly. However, it is used only as a probe, not for continuous service.

My 1 G-ohm resister broke (age, again, surplus) so I got a nice Chinese 1.1 G-ohm resister to replace it (a bit shorter.) These resisters are available (but now, back order and delay might be the rule) and fairly inexpensive. I do not know if a ballast resister is required for that supply - someone here should know.

Your HV vacuum feed-thru looks perfectly fine for air operation, rather than oil. I use oil for my ballast resisters and frankly, a mess; service is not fun with oil. Adding it when essential is one thing, adding it if not necessary is making a lot of extra work.

A voltage divider is extremely simple: for example - using a 100 M-ohm and 1 M-ohm resisters placed in series. Then read the voltage between the common ground and the node between the 100 and the 1 meg-ohm resisters. Your drawing is not a voltage divider.
Jim Enright
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Re: Demo Fusor Progress Update

Post by Jim Enright »

Liam, thanks for the insight! What you, Richard and Dennis all said makes sense to me now. I am going to purchase 10 of the 100 M ohm resistors to wire in series. It will take some time to get them, so in the meantime we are going to start chasing down our leak(s). For right now, we will have to keep using the smaller, home-built feed through until we get a small inner grid of titanium done and attached to the commercial feed through we purchased. At that point, I think we are going to move everything over to the 6-way cross so that we can start working through leaks and have the metering system installed once rather than trying to move it over.

Dennis, for shielding you mentioning using slate. Is that as effective for shielding as lead?
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Dennis P Brown
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Re: Demo Fusor Progress Update

Post by Dennis P Brown »

I use slate but it (quickly looks up densities using google) has about 1/4 the density of lead. So if you want 2mm of lead equivalent, then you need about 8 mm of slate. For my current project I had a stack of floor tiles so I used them but slate is better; it is easy to drill (dry cermet drill -cheap) and a dry abrasive saw blade (again, cheap) cuts right through it. Non-toxic, insulates, and is extremely inexpensive. Disposal is easy - normal trash.

An important point with series resisters: when you solder those resisters together in line, learn how to do proper ball solder joints.
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Re: Demo Fusor Progress Update

Post by John Futter »

Jim
I gave that diffusion pump to Steven you can buy a 110 volt heating element for it
your glass 100 meg ohm resistors are not suitable for the voltages you are using they are range resistors out of an electrometer or similar
look on this site there are very cheap 7kV resistors available from Element14 RS components Mouser ETC I have put the part type up on this site several times i use the 68meg ohm variant for my dividers 10 in series to give some margin for 50kV
Jim Enright
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Re: Demo Fusor Progress Update

Post by Jim Enright »

John, thanks for the insight! For the diffusion pump, the outside noted that it is a 240V system. Can I just replace out the heating element for the 110V without issue? Any thoughts on where I could find that heating element? It looks like a great pump and we were excited to have Steve give it to us! We drained the oil, cleaned it up inside and out, and purchased new oil for it. We are anxious to get it up and running!

Thanks for the info about the resistors. I had waited to buy the ones I had shown in the image, thinking that they weren't quite right. I will search for the correct ones. Richard noted that I could hook up 10 of the 100 Meg ohm to reach the required ohm. We are still figuring out some of the resistor technology - how will the 10 count of 68 Meg ohm resistors equate to 50kV on the gauge?
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Re: Demo Fusor Progress Update

Post by John Futter »

Jim
A bit of a pity you replaced the oil
I had cleaned it and put a new charge of santovac 5 in it ( a light straw coloured oil)
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Re: Demo Fusor Progress Update

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No matter what, in the end, you must think not only of the resistance, but how you achieve it. This means the resistors must not "bridge-arc" at your voltage impressed over the string. You are not in Kansas anymore toto. You are in a world of electrostatics. A world of intense electrostatic fields where no power need exist to create electric arc bridges, where Tritchel pulses in the fields can form ionized regions, where real surface currents can travel freely over smooth insulating surfaces. 50 kv is not a really high voltage at all at the extreme end of electrostatic field work, but at the amateur level where soldered leads and disjoint non-continuous surfaces abound, the choice of resistors and their assembly is critical.

I will show a 50kv resistor divider in air that works which I built and tested. You will notice the 100meg resistors are long in length. The solder joints and discontinuities are are encased in RTV. No 50kv arc on earth will jump this string. You will also note that it is in air and potentially, (no pun intended), deadly if approached in an operating system. I stressed this to the buyer. It is up to the user to isolate this from idiots who like to fondle things. I call this species Tactillian-Electrocuriotis an ancient form of life with weak brainstems they will never suffer complete extinction, but die one by one.

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Calibration.JPG
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
Jim Enright
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Re: Demo Fusor Progress Update

Post by Jim Enright »

John, unfortunately by the time I got it, there wasn't much oil left and what was in there was pretty thick. I'm not sure if it had been used much before Steve sent it to me, but it definitely needed a cleaning. It was shipped to New Hampshire so I'm assuming that the oil was drained before being shipped.

Richard, thank you for the information! I had previously bookmarked the metering thread that you referenced, which included the images that you have shown. We are trying to digest the information, and hope to start working on the build in the upcoming weeks.
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Re: Demo Fusor Progress Update

Post by John Futter »

VR68 series resistors about US$40 per hundred
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Re: Demo Fusor Progress Update

Post by Jim Enright »

John, thank you so much for the resistor information! We have a 50uA gauge that we are intending to use for a 50kV meter. In looking at Richard's diagram of a voltage meter, he had 10 of the 100Meg ohm resistors in series and spaced out between a threaded rod and a piece of plexiglass, which results in resistance of 1,000,000,000. Using the 68 Meg ohm resistors would require 14 or 15 and the math doesn't work quite as evenly. I'm probably missing something or not understanding what you are trying to tell me. Would it be easier to use 10 of the 100 Meg ohm resistors? Thank you John, we truly appreciate your help!
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Richard Hull
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Re: Demo Fusor Progress Update

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My stack was 5 200 megohm resistors count them.... five resistors.

There are other ways to skin the cat.... Resistor shunt the meter to turn the 50ua meter into a 100 ua meter and use only 5 100 meg resistors. It would still read as a 50kv meter, just draw twice the current from your supply (100ua at full scale = 50kv). Critical thinking and a good bit of electronic metering experience and simple algebra need to be brought to the problem.

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
Jim Enright
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Re: Demo Fusor Progress Update

Post by Jim Enright »

Thanks Richard, I see the error of my ways about the number of resistors! In the text boxes, 100 Meg ohm resistors had been mentioned, and I just quickly looked at the image of your design and continued referring to 10 resistors. But I do understand that it needs to get to the 1,000 million resistance so either 10 @ 100, 5 @ 200, etc. We will start tackling this metering problem as soon as we can get the resistors. Thank you!
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Dennis P Brown
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Re: Demo Fusor Progress Update

Post by Dennis P Brown »

My HV probe is a standard looking HV probe rated for 45 kV (where it has a 'safe' range to 45 kV so that I treat as its upper limit. It scale reaches 50 kV.) It had a single 1.0 G-Ohm resister inside (now 1.1 G-ohm) that connects to the 50 um-A meter. The resister is about 6.5 inches long and inside an enclosed plastic case that has a handle with an upper 'shield' on its opposite end and a metal tip on the 'business' end. The meter is housed between the two just below the plastic 'shield'. There are no long strings of 100 M-Ohm resisters. I had no issue buying the long 1.05 G-ohm resister new from a Chinese supplier - as to checking it, I had a known voltage supply and it tracked it like my original resister so it was certainly accurate in its ohms value.

That all said, if I decided to use that for continuous service, yes, I'd submerge the resister under oil both to prevent arcing and to dissipate possible heat build up.

Still, why use a string of resisters that require careful soldering (ball is best) and big oil containing system if one could get a single, very long 1 G-ohm resister or are none now available?

Also, why not a simple voltage divider under oil? Use a single long 100 m-ohm and wire to a 1 M-ohm. Read between ground and the other end of the 1 M-ohm resister (so you have a 100:1 reduction in voltage) It will be a lot smaller then a chain of 100 M-ohm resisters and any cheap voltmeter will work (here I'd definitely place that assembly under oil or encased in silicon (cleaner)). Not very difficult to build that system either and far more compact.

Now if you are going above 50 kV, that is another matter and very tricky. There I'd certainly consider a long chain under oil.
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Re: Demo Fusor Progress Update

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The simple 100 meg system sounds nice for 50kv but that resistor would need to be a 25 watt resistor! 50,000/100e6= 500ua.... 500e-6 X 50 e3 = 25 watts demanded and wasted from your 50kv supply just to measure the voltage with a single simple resistor! Not many 25 watt 100meg resistors on the market. To limit heating and drift you might look for a 75 watt 100 million ohm resistor! Good luck!

Gotchas all over the place here. What sounds so simple, the math and the availability crush to dust.

5X10E4/10E9 ohms = 50ua.....50X10E-6 X 5X10E4 = 2.5 watts. With 5 200meg resistors in series 0.5 watt resistors demanded. With 10 100meg resistors in series only 0.25 watt resistors demanded. The thermal drift in high ohm resistors being heated by dissipation is terrible and thus the measurement accuracy suffers. In this paragraph, 2 watt resistors would be ideal.

Smart money does the math and matches it against the resistors you can actually buy and the amount of power you are willing to lose from you 50kv supply just to measure the voltage output.
High voltage measurement demands a bit of consideration.

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
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Re: Demo Fusor Progress Update

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The difference between an engineer's solution and a physicist's; so, the cow being assumed spherical does not work in reality! ;)
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Richard Hull
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Re: Demo Fusor Progress Update

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I'll never forget my fellow engineer, Tom Ligon, Doc' Bussard's lab rat, telling me he was Bussard's set of "gravity boots".
physicists feel if it can be imagined, surely, there is kit to make it happen. An engineer needs to be there to say, "they haven't invented that yet or they don't make something that is that big or that capable." Material science has stopped many a project or idea from getting out of the starting gate.

In this case it just crushed the idea of a single resistor 50kv metering effort. But there are always clever methods and workarounds that can make it happen. You just gotta' make some extra space and use what is readily at hand.

I have 2 electrostatic volt meters... Rather giant contrivances with infinite resistive loading that go to 40kv in the largest reading. It has U.S. Atomic Energy Commission marked on its case. (Hamfest buy)
They work on the needle moving across the scale as two chorme-plated plates are being electrostatically moved into various physical alignment based on coulombic action. Most all GM service manuals prior to 1980 stipulate the use of an electrostatic voltmeter to set the high voltage. (effective zero loading)

I attach an image of such a meter. They contain zero electronic parts being 100% capacitively based electro-mechanical action in nature. These leviathans weigh about 20 - 30 pounds. One of mine has three ranges changed by pulling a knob out of the case at three detents which vary the static plate to three precisely determined positions. I own both of these style meters

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ESV meter range.jpg
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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Dennis P Brown
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Re: Demo Fusor Progress Update

Post by Dennis P Brown »

Impressive instruments. Yes, being practical is both a necessity and part of training for engineer's. But spherical cows could have some advantages ... wonder if biologist have considered that issue?

Understand the effect of a high voltage electric field all too well; my 100+ kV voltage multiplier created a field (while under oil) that really impressed me (in a bad way.) Even my high voltage probe responded without contact. I gained a powerful respect for voltages in those ranges.
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Re: Demo Fusor Progress Update

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Electrostatic fields of intense magnitude within a high dielectric constant fluid insulator can actually mechanically stir and move that media. Intense Amperian currents within a highly conductive molten metallic media can likewise stir and move it as is seen in molten aluminum reduction operations where tens of thousands of ampere currents are common. Such studies and rarely seen events are far outside the gaze of virtually all living beings. It is enough to know that they occur in singular high field events. Electrostatic fields where the currents are in the picoamp range with potential differences of many thousands of volts with almost no magnetic field present create motion within a medium. We also observe motion within intense surrounding magnetic fields in suitable conductive media where the potential difference is almost non-existent within the medium.

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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