Potential Transformers

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Emma Black
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Re: Potential Transformers

Post by Emma Black »

The element on my diffusion pump seems to have issues, it trips the RCD after a few seconds. The manual suggests baking it in an oven for 8 hours at 180c to remove moisture, so we shall see how that goes.
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Re: Potential Transformers

Post by Luca Aldridge »

Good luck!
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Aidan_Roy
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Re: Potential Transformers

Post by Aidan_Roy »

Emma,

I had the same issue with my pump when first purchased. A good hot day in the sun insulated with fiberglass got er going again as I baked it out running on a 30 amp fuse. Once you get the water out of there, assuming its not a real short somewhere, all should be smooth sailing. Good luck!

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Emma Black
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Re: Potential Transformers

Post by Emma Black »

I tried it via a variac at half voltage for an hour, which seemed to do the trick. It can run for a couple of hours on full power now and seem to be getting a pretty decent vacuum already.

Chamber can take 40kV+ quite happily without any visible plasma or current draw. Now on to adding some gas back in!
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Dennis P Brown
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Re: Potential Transformers

Post by Dennis P Brown »

While a proper vacuum gauge will aid you far better, certainly when you get below 5 microns, plasma's do not occur. So you are achieving at least that level but without a high vac gauge, you will be in the dark to both the units real performance and ultimate vacuum - also, leak or out gas issues. Still, a good start. Be careful not to 'crack' the oil from any minor leaks (oxygen) or too high a temp (too much current draw or poor water flow.)
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Emma Black
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Re: Potential Transformers

Post by Emma Black »

I have a pirani gauge, which at the lowest point is saying 0.37 microns (from the voltage I’m reading). However this was an untested eBay purchase and so could be a mile out of calibration.
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Re: Potential Transformers

Post by Luca Aldridge »

If you have another gauge, try and see how they compare. I think Justin has sone Edwards Pirani Gauges, but check with him first.
I'm testing my diff pumps tomorrow, excited to see how that goes.
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Dennis P Brown
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Re: Potential Transformers

Post by Dennis P Brown »

Once you get below 1 micron, (and you might even be in the 10^-5 torr or lower range) any pirani gauge might default to a non-zero but near zero value - much as you are reading. You will need a proper high vac gauge that handles 10^-5 and lower.
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Emma Black
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Re: Potential Transformers

Post by Emma Black »

So even after an a few hours of pumping today the voltage, out of the gauge did not change at all, so either there is a constant pressure leak or more likely the gauge is bottoming out. Either way I have a freshly calibrated penning gauge on the way, hopefully good for 1 times 10 to the minus plenty. Apologies - this thread had wandered off high voltage discussions somewhat.
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Dennis P Brown
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Re: Potential Transformers

Post by Dennis P Brown »

We all do but since its your thread, and the primary topic is still relevant, no problem. Take it where you think most appropriate.
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Emma Black
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Re: Potential Transformers

Post by Emma Black »

Some progress. After around 30 mins after the diff pump got up to temp I indeed got below 10^-5 torr, very pleased. After another 40 minutes it very slowly dropped a little lower This is the first long pump down and to be honest I wasn't particularly meticulous with the chamber cleaning, so there must be a fair amount of off gassing, but its looking good so far.

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Dennis P Brown
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Re: Potential Transformers

Post by Dennis P Brown »

Congrats! No surprise with that massive DP. In the future, one can keep their fusor super clean by leaving it under vacuum and not opening it. Of course, one can't have a real leak - then this method doesn't work. I know that for a new system, it is impossible to do this when one first starts using a fusor - many add on's after the fact, and adjustments to make that require opening the system. But once things get settled, that is essential for a good operating system. I can turn my fusor on, set the gas flow & voltage and that's it. It is stable for the entire time of the runs I make (i.e. my tolerance to run the system till the cathode heats up too much - say fifteen to twenty or so minutes.)
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Emma Black
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Re: Potential Transformers

Post by Emma Black »

Yeah I need to open it again this week, to add the adaptor for the deuterium inlet, so I think thats where a deep clean with be useful. Also I reused a couple of con-flat gaskets from before, which if i have a leak will be the source, so have a brand new set to install. Really not a million miles away from letting some gas in and getting used to operating the thing before moving onto deuterium, considering I was aiming for the end of the year.

Way further down the line, assuming I get things working with a modest flux, I'm quite interested in exploring chamber cooling & even pre-heating in relating to wall loading effects.
To that end and some may hate this idea, but considering a fully submerged tank design that can be heated or cooled as needed to a precise temperature.
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Liam David
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Re: Potential Transformers

Post by Liam David »

I think that a deep clean will make a disproportionate difference when you attempt fusion later on. Hydrocarbons are evil.

You can get away with reusing copper gaskets if you tighten the flange only part way the first time, leaving a gap of a millimeter or so. On the second assembly, tighten until the flanges meet. Just keep it clean and the orientation unchanged between uses. I've had many such gaskets hit 1e-6 and two on my current system that is in the low e-9 without issue. Others here have had similar successes. The cost of new gaskets can add up fast, especially for larger flanges.

Submerging the device in a tank is not as crazy as some here make it out to be. It would make determining the absolute yield a little more challenging, but the cooling potential and moderation would be hard to beat. Don't forget about galvanic corrosion in conductive liquids, if you go that route.
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Richard Hull
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Re: Potential Transformers

Post by Richard Hull »

I have mused over the fully submerged fusor idea. So this is not a folly, but would demand a number of extreme measures. The beauty is water is a great moderator for scattering neutrons. All you would need is to sink the neutron detector underwater! (A very easy task as I used a water summerged 3He tube in a tank as my neutron moderator and detection system from 2003-2019)

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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: Potential Transformers

Post by Emma Black »

I'm glad it's not a completely crazy idea, although its a long way off. As you said light water with total coverage would make for a nice moderator. You could potentially use it for the diff pump cooling reservoir as well, with a chiller.

In my head I'm picturing a thick polycarbonate tank, reinforced with a metal frame, an extended feedthrough sticking out the water, a large diameter dump type valve so you can get rid of the water quickly if needed, plus lots of other measures to deal with catastrophes.

Question are some 3He tubes temperature sensitive?

Also - I did some cleaning on the chamber today and found that two bolts on of the conflats was only finger tight - opes. This plus the clean has improved the vacuum further. I used a hairdryer on the chamber to gently warm it up with the idea of speeding up the off-gassing. It was quite surprising how little heat it took for the gauge to start to climb.
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Re: Potential Transformers

Post by Matt_Gibson »

I wonder if (instead of a tank of water) we could use a stream/s of water with a catch pan underneath?

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Liam David
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Re: Potential Transformers

Post by Liam David »

I think if you go through the hassle of making a catch-pan system, ensuring that the falling water cools everything properly and routing numerous tubes, you might as well submerge it. I'd rather have a quasi-static tank system than a source of splashing. Also, without turbulent mixing that is supported in a container, your heat transfer coefficient will suffer.

3He tubes are almost entirely temperature independent. Since the volume is constant, the gas density and hence macroscopic cross-section remain unaffected. I've never so much as seen a response vs. temperature curve.

It takes very little temperature shift to affect the partial pressures of things. For example, the night vs. day pressure difference for my system is ~4e-9 vs. ~8e-9, albeit I live in a desert so it gets quite toasty in a garage. Now think what plasma bombardment and heating would do to outgassing, and you start to see why contamination can be a major inhibitor... Thorough cleaning and bakeout are necessary if you want to get the extra mile out of your system later on.
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Richard Hull
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Re: Potential Transformers

Post by Richard Hull »

Heavy gauge PE water tanks are readily available. They are found in farm supply stores. They are used as water troughs, water tanks, etc. They need no re-enforcement against the water pressure. The walls are designed to support the internal load of water against the walls.

There are also PE sinks like laundry sinks, etc. I think a suitable fusor friendly PE tank could be easily located as a stock, relatively low cost item of commerce. It would just take a search by someone interested enough to follow up on the concept of a submerged fusor system.

https://www.google.com/search?q=Farm+us ... e&ie=UTF-8

Local Northern Tool and Equipment stores might just have the ticket here

https://www.northerntool.com/shop/tools ... lsrc=aw.ds

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: Potential Transformers

Post by Emma Black »

I was thinking about the farm tanks as well, there are about 30 of them currently stacked at the farm next to us. Other option would be custom aquarium type of thing. I have made several out of glass as well as plastic for fish and are fairly easy to do, obviously much smaller water mass and less access etc.

If the concept proves useful and something permanent is wanted, a below ground indoor pond type of thing, using a liner, would be cool. The water couldn't flood the lab and you could have a huge volume. Be fairly cheap other than the manual labour involved.
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Dennis P Brown
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Re: Potential Transformers

Post by Dennis P Brown »

Why not wrap the chamber using flexible copper tubing and conductive epoxy every few centimeters? I did this with a previous chamber and it worked great. You could even use a fluro-based coolant to get extremely low temps and much higher room temps using a simple compressor system. I did this in college for a cold trap for a DP (of course, the heated side was fan cooled.) Extremely safe and getting a old refrigerator (or a new window unit) can be done rather cheaply. Modification is trivial (even the old Sci. Am. Amateur Scientist discuses converting these units for cooling. Adding a heating feature is simple as well.)
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Emma Black
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Re: Potential Transformers

Post by Emma Black »

I like that idea a lot, way less hassle - plus all the materials are on hand.

In other news, after a re-configure did another deep clean today and did a long pump out, hitting 3x10-6 torr quickly now. Then experimented with adding some argon back in, fair amount of learning needed to get the throttle the diff pump, gas inlet valve and the voltage right.

Did detected my first x-ray emissions to, wow they really stream out of the viewport! With the thick tempered glass server rack door closed however, it drops the rate right down as you would expect.
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Richard Hull
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Re: Potential Transformers

Post by Richard Hull »

Yes jockeying the valves to achieve a stasis in gas, versus voltage and current in part of the long touted artifice that exceeds the science and trains the mind and hands.

In many FAQs on radiation. The viewport is the killer orifice. Point it away from all living things. Above 35kv the entire device goes somewhat transparent to the high energy x-ray spectrum.

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: Potential Transformers

Post by Emma Black »

I may attempt some xray photographs using some large format film I have, not of anything alive obviously.

As often is the case though, two steps forward and one step back.

One (or maybe all now) of my cheap diodes from China seem to have blown. The PT is now trying to draw huge currents on its primary as the variac voltage is increased, without the fusor even connected.
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Dennis P Brown
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Re: Potential Transformers

Post by Dennis P Brown »

I lost one (pair) of my diodes in my bridge a few months back (after over ten years of on/off operation) - and like your occurrence it was to the ground side. Never expected diodes so inexpensive to be all that good so I got extra when I ordered them the first time. Stuff happens.

Since my fusor's power supply can't go above 31 kV (generally 29-30 kV), I have never been able to measure any x-rays (even from the port window.) That all said, I still use a thick ceramic shield between me and the fusor to play it safe.

Once the chamber is truly clean, operation of a fusor can become nearly automatic and highly stable (assuming no leaks.)

In my case, once I start my mechanical pump, and turbo I pump my system down. Then I mostly close the turbo's gate valve. Next, open the deuterium leak valve four turns (discovered from past operation to be almost the exact value needed every time) and check the system's pressure. Next I slowly raise the voltage and somewhere between 19 kV and 28 kV strike a plasma. Then I use very small changes in the leak valve to set the desired current at the voltage I want to operate at.

I recently experimented and discovered that once I pull the system below 10^-4 torr (I have a fairly large chamber; KF seals), I can turn off the turbo and operate the fusor for decent periods of time (15 minutes to date; likely longer but have no reason to do that yet) - and the mechanical pump alone holds the proper pressure in the system. Apparently, my system is leak tight and outgassing is mostly deuterium from the wall loading.

So making the fusor leak tight offers a lot of advantages - such as stable operation being the primary one. Known, repeatable settings being another. No runaway current issues to deal with that hurts the power supply is nice. Finally, the fusor becomes the least concern in your set up and then one can focus on other issues/projects* for the fusor.

*And this can be both a good and a bad situation, too. As I've discovered by increasing my objectives - that is, doing other ideas/projects that others here have mastered can be a challenge. This is because one then discovers there are vast areas one needs to understand and learn that dwarf simple fusor issues. This in turns creates all new types of problems to tackle - these can be both fun and frustrating. Thank goodness for this forum and experts like Richard who has the patience to deal with people like me asking these questions.
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