Emma - Fusor Number 1. First deuterium run

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Emma Black
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Re: Emma - Fusor Number 1. First deuterium run

Post by Emma Black »

Yep there are two 50k's in parallel, normally its remarkably controllable. Those sapphire leak valves give you such fine control over the pressure.

However with some failed diodes its power supply was putting out AC only, it was behaving exactly like a fluorescent tube. Nothing for ages then it suddenly lit up with more current than normal and the pressure jumped at the same time.
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Dennis P Brown
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Re: Emma - Fusor Number 1. First deuterium run

Post by Dennis P Brown »

Sorry for the diode fails - again. I keep a NST on hand to test my diodes - very easy and fool proof to determine their status.

What Matt suggested is how I control my fusor. I get it to high vac (under 10^-4 torr), then throttle the turbo (or diffusion pump) to it is almost closed position (but the system does not experience a pressure rise.)

I then set my variac to about 10 to 15 kV. After this I slowly increase gas pressure via the leak value (For my system this is always four turns. But everyone's system is different but should be consistent once you set up your system.) When I see current flowing, I bump up my voltage up slowly. As I do that, I notice my current increasing. I stop increasing my voltage when I'm at max. current for my x-former. If below 25 kV, I lower my deuterium pressure by slightly turning the leak value down.

The current falls.

I then bump up the voltage a few kV. I repeat this process till get to full voltage (30 - 31 kV) and normal max current (30 ma.) Since my system is clean this tends to hold steady; however, after it has been exposed to air, I'll often get current spikes. Again, like you one has to be fast on the variac.

Aside: there is zero reason (and a lot of reasons not to) clean your fusor. Those metal deposits will do no harm and even are helpful to act as a "getter" on the surfaces. The window, however, is an other matter. Acetone and a soft lint free rag should work. If stubborn, I use a very fine steel wool (but that can scratch so be careful.)
Last edited by Dennis P Brown on Thu Sep 08, 2022 10:22 am, edited 1 time in total.
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Re: Emma - Fusor Number 1. First deuterium run

Post by Matt_Gibson »

What’s the peak current rating on your diodes? 25kohm ballast might be low enough to allow too much current during a “short”.

I bet your system is still burning off “junk”. I’d keep voltage low and let it do some cleaning runs where you let the cathode heat up, and remain hot, for longish runs. Eventually you’ll see just the faint reddish glow of deuterium.

I cleaned my viewport with a dremel, some 50k grit powder, and a felt bit. It did a great job in not much time.

-Matt
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Dennis P Brown
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Re: Emma - Fusor Number 1. First deuterium run

Post by Dennis P Brown »

Two 50 k's in parallel? That is a problem - two resistors in parallel operate such that most all current runs through the resister with the slightly lower resistance value - so using two doesn't buy you any reduce load on the resisters - one is already carrying 99+% of the current anyway. Those resisters need to be in series giving you 100 k-ohms. As you are seeing, 50 k-ohms is just too low.

Matt is likely correct that your system isn't clean enough, yet. Running the plasma at lower voltage (with some deuterium) is a good idea.
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Liam David
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Re: Emma - Fusor Number 1. First deuterium run

Post by Liam David »

Two resistors in parallel is not a problem... the current will flow in inverse proportion to their resistances. In fact, there is even a limited degree of thermal regulation. The lower resistance will dissipate more power (V^2/R), thus heating up, increasing in resistance, and so reducing the fraction of current it carries.
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Dennis P Brown
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Re: Emma - Fusor Number 1. First deuterium run

Post by Dennis P Brown »

Not an electrical engineer - simply learned from one that identical resisters in parallel do not carry similar currents. Rather one gets the majority of the load. Maybe not - never did the experiment myself but if you did, then that is the case.

Regardless, 50 k-ohms has proven inadequate (obviously the resisters in series have failed to protect in runaway conditions.) so it would appear they need greater resistance so placing the resisters in series is the better idea in order to protect her transformer and diodes.
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Re: Emma - Fusor Number 1. First deuterium run

Post by Matt_Gibson »

I think it’s diodes in parallel that don’t share load equally.

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Emma Black
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Re: Emma - Fusor Number 1. First deuterium run

Post by Emma Black »

Yeah I think i'll add this 100k monster while I'm diving into the oil tank, just to be on the safe side, as clearly 50k is not limiting the current enough. The old diodes said 2amps but take that with a huge pinch of salt.

Correction from earlier - It was two 100K's in parallel 50k total.

New ones are microwave type, but from a proper supplier with full spec sheet etc. 12kv @ 500ma. I will use many.

Anyway original issue it turns out was entirely due to my ineptitude. A usb cable had physically fallen and brushed past the feedthrough on its way down. Did not notice until I had a look today. There are tiny burns on the cable and the camera and power adaptor are both dead. The resistor value issue still applies though.

The fusor itself is fine and after a pump out I'm getting down to 2x10-7mbar now, the lowest its ever gone.

Denis - my previous operating procedure was pretty much identical.
Let it hit below 10^-5torr. Throttle back the pump. I have also my moved my deep pressure gauge between the fusor and the pump, so you have an idea of how much gas is leaving the chamber. The other gauge will stay put. Then slowly build the voltage and pressures adding the deuterium, while watching the current.

I was more interested in how oddly a chamber filled with low pressure deuterium behaves, when exposed to HV AC current. Nothing for ages then brightly flashes to life in a fraction of a second and acts like a dead short.

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Last edited by Emma Black on Thu Sep 08, 2022 2:54 pm, edited 1 time in total.
Matt_Gibson
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Re: Emma - Fusor Number 1. First deuterium run

Post by Matt_Gibson »

2A peak rated diodes would definitely struggle with a short, especially if you have a capacitor in there.

Take a look at the 2CL2FM diodes. They are rated for 20kV, 100mA, and can run up to around 35kHz. They are able to take up to a 10A spike (non repetitive).

-Matt
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Emma Black
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Re: Emma - Fusor Number 1. First deuterium run

Post by Emma Black »

Thanks Matt - the ones I have picked up are 12kv 500ma and can deal with 30A surge. A local store had these for £18.50 ($21) for a 100 pack.

https://www.tme.eu/en/details/by12-dio/ ... ctor/by12/
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Re: Emma - Fusor Number 1. First deuterium run

Post by Matt_Gibson »

That’s a solid deal right there!

Edit- Btw, sorry for your loss, the Queen was a truly classy woman and great leader!

-Matt
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Emma Black
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Re: Emma - Fusor Number 1. First deuterium run

Post by Emma Black »

Thanks Matt, yeah I know. I only met her the once very briefly but she came across as genuinely nice with a very quick sense of humour.
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Richard Hull
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Re: Emma - Fusor Number 1. First deuterium run

Post by Richard Hull »

Diodes in parallel are indeed a no-no.

Resistors of identical value100k @5w, in parallel, share all currents perfectly 50:50. Their total would be 50k @10watts. With 10ma flowing through this combo would subtract 500 volts from the supply voltage to the fusor. The 10 watts would be double what a 10ma would demand (5W) and would be nice.

Two 25k 5w resistors in series would do the same thing yielding a 50k @10watts. Again, this combo would do the same thing as the above example.

Resistors of any equal value but of a fixed wattage will have their wattages in either series or parallel combination sum.

A100k resistor would drop 1000volts from the supply at a fusor current of 10ma. The wattage would be 10 watts demand so a 20 watt resistor would be better.

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: Emma - Fusor Number 1. First deuterium run

Post by Dennis P Brown »

Well, that settles the matter on parallel resisters.
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Emma Black
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Re: Emma - Fusor Number 1. First deuterium run

Post by Emma Black »

Though I had replied already, thanks for the clarity Richard Is there any real benefit for large wattage resistors for use in fusors i.e. 100W+ ?

Have also been getting ready for some activation attempts - lots of HDPE, from Amazon cutting boards. I was going to use wax, as I have a massive bag but the fire and melting risk is not worth the hassle.

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Richard Hull
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Re: Emma - Fusor Number 1. First deuterium run

Post by Richard Hull »

Wattage only comes in handy with dead short conditions. 25 to 50 watts will handle most anything up to a longish short like 3 seconds or more. (time to reach the kill switch.)

Most fusor supplies are whimpy. 20 ma is a death point at full tilt. Monster supplies that will handle 60kv @100ma will need the higher wattage ballasting as the supply is quite happy vaporizing a central grid in pressure bumps or electron runaway conditions.

Compute a good resistor value that you can tolerate under a load of say 30ma to a running fusor. Let us say 50K . Now figure the power rating.
P = I^2 x R .030 X.030 = .0009 X 50,000 = 45 watts Double that to 100 watts or so. Now, few power supplies will supply 30ma at full voltage. Still be prepared for near short conditions. Most likely 20ma would be more normal as max current before the supply blows up. .0004 X50,000 = 20 watts and a 50 watts would be OK.

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
Matt_Gibson
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Re: Emma - Fusor Number 1. First deuterium run

Post by Matt_Gibson »

The higher wattage resistors are probably larger/longer and might handle higher voltages than smaller ones. That might be a reason to go for one of those.

-Matt
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Bob Reite
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Re: Emma - Fusor Number 1. First deuterium run

Post by Bob Reite »

During an arcing event, figure the impedance is close to zero, even though the duration is short, so you need at least a 100 watt resistor. You can find 225 watt wirewound resistors at hamfests. I plan to bring some extras to sell to HEAS.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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Richard Hull
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Re: Emma - Fusor Number 1. First deuterium run

Post by Richard Hull »

That's great Bob! I dare not think how many fusors have benefitted and been brought to life within a budget via the hamfest route. Hamfests are hit-and-miss related to fusor construction, but very viable. The HEAS flea market is the only place where you can see, touch and feel what is for sale and also be talking to a knowledgeable person selling his fusion related wares. E-bay is far more vast and has most anything you might need, but remote at best, with sellers ranging from idiots to the very helpful, but rarely knowledgeable in your area of need.

Fortunately, most arriving and staying on fusor.net know how to use real tools in their hands to assemble materials and build things. What they don't know, they pick up through self-directed learning, reading, seeing and then the doing. The materials needed range for hardware store found materials to the most complicated of scientific materials and instruments. As always, the true go-getters, go and get.

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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Emma Black
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Re: Emma - Fusor Number 1. First deuterium run

Post by Emma Black »

I'm off to a hamfest next month to take a look for useful stuff, never been before we shall see what crops up.

Anyway - rebuilt the bridge using 6x4 12kv diodes, installed a new 225w resistor and we are back in business. Pressure and current is nice and stable again. Neutron counts are around 0.6-1.0 mrem/h, so some I think some reconditioning needed.
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Emma Black
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Re: Emma - Fusor Number 1. First deuterium run

Post by Emma Black »

I did not appreciate how much the weather can play a part in HV systems. Today we have thunderstorms and the humidity in the workshop is crazy. All sorts of discharge sounds coming from cables and connectors.

The video (for sound only) was taken at around 30KV (with the fusor disconnected) via a iphone recording on top of my potential transformer, sound is mostly from the transformers HV connectors.

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Emma Black
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Re: Emma - Fusor Number 1. First deuterium run

Post by Emma Black »

Update
Somewhat predictably my feedthrough has started arcing at voltages over 30kv. Out of the other two I though I had, one arcs even worse and the other wont hold a vacuum.

Its failed where the ceramic goes through the conflat, as seems to be common with other posts on here about failed feedthroughs. Running things in high humidity can't have helped at all. I now realise what may have been obvious from the previous post and that the discharge noise was being caused by condensation on the cables, due to the humidity and low temps.

Fixes & Changes
I've added a dehumidifier & heater to the workshop and re-routed the HV cables. They are now all sitting in PVC pipes filled with oil and wrapped in some shielding tape. Also spent some time dealing with all the sharp points, now no more audible corona. I've also changed the oil - was previously using fully synthetic motor oil, now switched to proper transformer oil (it was on offer on amazon)

New cable routing:
Image

So figure it's time to build a new better feedthrough.

Thinking of building something close to the excellent post by Liam David around building a custom feedthrough using quartz and compression fittings. I could just use borosilicate glass and heat to seal. Making my own ceramic is also an option, but the main issue I think is going to be the material shrinkage 10%+ after firing and I'm not sure how I could get that to seal. Maybe something like this:
Image

Or get another 30KV feed through and modify it to cope with higher voltages, perhaps by adding an "oil jacket" to the air side of the ceramic. Either way I'm currently playing around with Ansys Maxwell to experiment with some simulations.

A few of the posts around very high voltage feedthroughs discuss two stage biased designs (I'm not thinking of building this) maybe a silly question but how does this work?
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Re: Emma - Fusor Number 1. First deuterium run

Post by Matt_Gibson »

That’s too bad. I’ve got three of these feed throughs and have been able to way exceed their voltage ratings. I do use some 99% isopropyl alcohol on them before use…

Were you getting your feed through really hot? I haven’t pushed much beyond 700w and I have a fan blowing across, so maybe that’s a thought?

-Matt
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Richard Hull
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Re: Emma - Fusor Number 1. First deuterium run

Post by Richard Hull »

I have a large box fan blowing across my insulator so that any small corona ozone/air ions that might cause or support an air arc via rising heat columns are blown laterally away from the insulator. Corona in air can be subtle and unseen even in the dark. It doesn't take much in a rising heat column to establish an air arc. The fan also helps cool the fusor, too. Many tricks out there when pushing the limits of materials.

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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Liam David
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Re: Emma - Fusor Number 1. First deuterium run

Post by Liam David »

Could you post a picture of the insulator failure, and the one that arcs worse? My personal sample size is one, but even with a toroid, the failure mode is typically arc-over on the air side. Getting the voltage high enough to puncture the insulator, or arc along the vacuum insulator surface, would typically require an oil socket. Unless something in your commercial part is much different from mine, I don't see how anything other than contamination, or perhaps a problem with the stalk, can cause a problem.
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