Alexey's fusor progress

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Dennis P Brown
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Re: Alexey's fusor progress

Post by Dennis P Brown »

I cooled my first fusor with water through copper tubing. I used conductive expoxy (silver based) to spot 'weld' various sections of the copper tubing to the fusor. Worked ok but was not inexpensive.
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

This is interesting! Perhaps the same effect would be achieved by mixing aluminium powder with epoxy resin.
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Re: Alexey's fusor progress

Post by Dennis P Brown »

Check on line and see what mixtures are acceptable for adding Al powder with an epoxy. I'd expect someone has already done this to avoid the silver epoxy cost issue.
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

I would like to write about the unusual operation of my scintillation dosimeter. When I am at a safe distance and apply a high voltage to the cathode, the dosimeter readings increase very slightly from 4 to 6 µR/h. But when I switch off the voltage, the dosimeter reads 0.0 for a few seconds. I suspect that this is due to the fact that the dosimeter is designed to detect gamma rays with energy more than 50 keV, but the fuser can generate X-rays from 20 keV. Since their energy is low, perhaps the dosimeter software corrects this signal to be noise, but when the voltage is turned off, the noise disappears and the dosimeter shows 0.0. If this is the case, I may be underestimating the background radiation in my lab.
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Richard Hull
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Re: Alexey's fusor progress

Post by Richard Hull »

A scintillation counter is never a good indicator of background, it tends to read everything in the 50kev and above. Noise is a common thing on the lowest range and the best such systems have a way of killing the noise if there is no signal above the noise. Once the thing senses anything above what it considers noise it reports that plus the largest noise peaks. In short, on the lowest range expect noise if there is the slightest trace of real photonic emission.

In a closed environment Radon and daughters are the big thing.. A 2-inch mica windowed pancake GM counter is what you want to tell of a real background. When you have the fusor running at full voltage, that is the time for the low range electronic ion chamber type system. A scintillator will always read high.

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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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Richard, I was going to say that maybe my scintillation dosimeter is underestimating the dose rate for photons below 50 keV. I always use it in pair with a good mica dosimeter and it too does not show excessive background. But the manufacturer declares the lower limit of quantitative registration of photons at 50 keV. Speaking about ion chamber type system do you mean Geiger counter? I thought it also works from 50 keV.
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Richard Hull
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Re: Alexey's fusor progress

Post by Richard Hull »

The tube you show in a Beta/Gamma Geiger tube. A ion chamber instrument is most often a photon direct dose rate instrument base on the true definition of air ionization for which the roentgen was established. The three instrument commonly used for alpha, beta, gamma are:

1 Geiger counter chosed always for Alpha and Beta with a mica window.
2. An ion chmaber instrument for direct dose readings of hard beta and Gamma
3. Scintillation counter for gamma only. Most often to sniff out big, bad gamma sources or in a special instrument, a gamma spectrometer.

Each has a purpose.

Hunting Uranium is best done with a portable scintillation counter swung over the ground as one walks held by a long leather loop.
A geiger counter is best used for quantifying actual radioactive materials under study in a laboratory situation. it is also handy in finding contamination on bench tops and around the lab.
The scintillation instrument, in a lab, is used to tell of gamma readings above a carefully recorded background. Most often in a gamma ray spectrometer to identify a specific isotope from an unknown source of radiation.

I only use my ion chamber to find out my x-ray dose rate from my fusor.

Click on images to enlarge, then back arrow to return to pictures.

Richard Hull
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A 2-inch pancake GM detector used in laboratory determination of alpha and beta radiation intensities.
A 2-inch pancake GM detector used in laboratory determination of alpha and beta radiation intensities.
ion chamber.  A direct reading gamma does rate meter
ion chamber. A direct reading gamma does rate meter
ion survey2.jpg (9.09 KiB) Viewed 1513 times
Using a TSA gamma scintillator to find a small Uranium ore sample in tall grass.
Using a TSA gamma scintillator to find a small Uranium ore sample in tall grass.
Lutetium gamma ray spectrum using a 3" scintillation detector.
Lutetium gamma ray spectrum using a 3" scintillation detector.
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
Alexey Khrushchev
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Richard, I really appreciate your such a detailed response!
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

I think I found what I need. Specialized dosimeter DRG3-02 is used for determination of X-ray dose rate (µR/s). This instrument contains a scintillator based on polystyrene and zinc sulfide. Here is its specification:

The dosimeter is designed to measure the exposure dose rate of X-ray and gamma radiation in laboratory and industrial conditions.
The range of measured dose rates of X-ray and gamma radiation of the dosimeter is from 0 to 100 µR/s.
This range is divided into the following sub-ranges:
- 0 to 0.1 µR/s,
- 0 to 0.3 µR/s,
- 0 to 1.0 µR/s,
- 0 to 3.0 µR/s,
- 0 to 10.0 µR/s,
- 0 to 30.0 µR/s,
- 0 to 100.0 µR/s.
The range of effective energies of quanta of registered X-ray and gamma radiation is from 20 to 3000 keV.
The limits of the basic error of exposure dose rate measurements are divided into subranges: - from 0.1 to 0.3 µR/s - 15% (other subranges - 10%).
Energy dependence of this instrument when measuring X-ray and gamma radiation energy in the range from 20 to 3000 keV is -25% relative to readings of 1250 keV (cobalt-60).

The dosimeter has radiation immunity to fast neutrons, which provides measurement of X-ray and gamma radiation dose rate at fast neutron flux of 20 neutrons/cm2*s with additional error not exceeding +/- 1% with respect to the maximum permissible X-ray or gamma radiation dose rate of 0.8 µR/sec
Radiation resistance of the dosimeter is determined by the limit value of the absorbed dose in the scintillating plastic of the detection unit and is not less than 1000 J/kg.

The dosimeter is powered from AC 220v or from 12 mercury-zinc elements.

Dimensions of the DRGZ-02 console are 200 x 160 x 95 mm,
Diameter of the detection unit - 50 mm,
Length of the detection unit - 330 mm,
Weight of the console - 2,3 kg,
Weight of the detection unit - 0,7 kg.


In practice, this device allows to measure dose rate from 18 to 360.000 µR/h. The device is of course old from 1980s, but it is still used in specialized laboratories and is included in the state register of measuring instruments. I can buy it for 50$ in good condition.
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

I plan to use a 40x40mm aluminum flow cell to cool the fusor. For better cooling efficiency it is necessary to ensure a tight fit of the cell to the fuser wall. As a thermal paste I decided to use plasticine in which I added 15% of aluminum powder. The mixture is still quite plastic, but it does not melt at 60C, so it is quite convenient to work with it. To evaluate the thermal conductivity, I molded two 5mm thick pancakes (in the thermograms P1-with aluminum, P2-source plasticine). I heated them on the 3D printer table to 44C (P1) and 41.8C (P2), and then placed them on the aluminum plate. After two minutes, the temperature of P1 was 31.9C and P2 was 35.2C. Thus the cooling rate of the aluminum plate in this experiment was 6 degrees*min-1, and that of the original plate was 3.3 degrees*min-1. As a measuring device I used InfiRay P2 Pro thermal imager. Thus, the addition of 15% aluminum significantly increased the thermal conductivity of the plasticine, and the cooling rate increased almost 2 times.
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Alexey Khrushchev
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

I have finally received my high voltage diode (150kV/1A). I have already installed it and tested it a bit, everything seems to work as it should. I also changed the layout of the high voltage system components a bit. The ballast resistor is now mounted on the high voltage input of the fusor. I had to print some adapters on a 3D printer to do this. Since my hydrogen cell finally broke down for tests I had to produce hydrogen by reacting calcium with water. The reaction is violent so I first dial the hydrogen into a syringe and then run it through the purification cartridge in my gas meter. I also tried a water cooling system. I used plasticine with 15% aluminum powder as a heat conducting paste. I noticed that the cooling worked quite well and at up to 100 watts of power, the temperature did not rise above 26 degrees. However, in the stress test at higher power (around 200 watts) the plasticine started to melt. Perhaps I should increase the aluminum content to increase the melting point.
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Dennis P Brown
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Re: Alexey's fusor progress

Post by Dennis P Brown »

Why not use epoxy with the Al powder? There are high temperature epoxies but even regular epoxies would likely hold up.

Your open air diode system could have major corona issues - especially above 45 kV.

Do you have heavy water (D2O)?
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Epoxy will glue it down. I want to be able to redo the cooling system if something goes wrong.
The diode is over 20cm long, I don't think I'll have any problems with the arc, plus the voltage drop across the diode is only 180V. As for the corona, I haven't seen it forming on the diode ends or terminals yet, but it's something I keep thinking about. Maybe I will attach metal balls over all terminals, or fill all bare contacts with a thick layer of paraffin. Thanks for pointing out this important issue.
I have heavy water. My wife gave me 50ml for my birthday. But I will use it when all the fusor components are working perfectly.
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Re: Alexey's fusor progress

Post by Matt_Gibson »

I wonder if you could make some sort of thermal conductive putty? That might help with the flat surface of a waterblock mounted to the round surface of the chamber?

-Matt
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

I wrote above that I use a mixture of plasticine and aluminium powder (15% by weight) as thermal conductive putty. This works well, but I need to experiment more with the composition to increase the melting point. Perhaps there is a more suitable bonding base, better than plasticine.
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Re: Alexey's fusor progress

Post by Matt_Gibson »

Another thought might be using some copper tubing (wrapped several times around the chamber) and the putty instead of the waterblock.

-Matt
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

The 6mm copper tube is very stiff I couldn't wrap it around the chamber.
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Re: Alexey's fusor progress

Post by Matt_Gibson »

You should be able to get some softer tubing. I’ve wrapped coils around soda cans for a can crusher. I used refrigerator copper tubing.

-Matt
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

How would you estimate the cooling efficiency of the copper tube? How many watts of heat can be dissipated from the chamber?
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Re: Alexey's fusor progress

Post by Matt_Gibson »

No clue :-)

I’d imagine it would be much better than the waterblock assuming the putty does a good job interfacing the round tubing to the chamber. You would have much more surface area for heat to conduct across/through with multiple turns of tubing.

You could probably just wrap some copper tubing around without putty and do a before and after to see if you need putty at all. I’d expect it to be better, but just not sure how much better. It might be good enough to extend your runs a bit before the thing overheats.

-Matt
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

My chamber is made from a KF50 cross, I don't see how it can be wrapped with tubing. Most of the heating is in the centre of the cross, so I think a tube would be worse at dissipating heat than a waterblock.
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Re: Alexey's fusor progress

Post by Matt_Gibson »

Good point. If you’ve thermal scoped your chamber and it has a hotspot, the waterblock probably is the way to go.

-Matt
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Perhaps the best solution would be to print two hemispheres on a 3D printer and then glue them together with silicone sealant. In this case the cooling efficiency will be maximised.
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Re: Alexey's fusor progress

Post by Ryan Ginter »

As far as the copper tubing is concerned, you might consider annealing it to improve its formability. Heating the metal with a torch and then submerging it in water to rapidly cool will significantly soften the metal. You'd need to be mindful of how you bend it though, as it's possible to pinch closed if done without the correct tools.

I would agree with Matt however, if your seeing a hotspot it's likely better to just place a water block over it. Perhaps you would find better success using Indium metal to transfer the heat between the chamber and water block. The thermal conductivity of Indium is 86 W/mK, which is much better than most thermal compounds. The metal is about four times softer than lead, so it should be possible to crush it between the cross and the heat block to completely fill the gap.

I think the ideal setup would be two heat blocks, one on each side of the cross. Metal plates could be placed over each of the heat blocks and bolts would pass through, allowing you to mechanically tighten the blocks against the chamber. A piece of Indium of slightly greater thickness than the gap would be placed between the heat blocks and the cross, and the pressure from tightening the bolts would force it to deform and fill the gap. Bear in mind that Indium melts around 150 degrees Celsius, so you would need to ensure there is a sufficient flow rate of water to keep its temperature down.

Your idea of a 3D-printed enclosure would likely also work. Be mindful how you design it. Just like electricity, water will want to take the path of least resistance. If you just surround the cross in a sphere without directing the flow of water over it, most of its volume will likely remain stagnant, reducing its effectiveness. This is why heat exchangers such as the water block use a winding flow path to cover the full surface of the block. At a very minimum, I would make sure the inlet and outlet ports are as symmetrical as possible and placed on opposite ends of the cross.
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

The indium idea is interesting, I have about 30g. But it is quite expensive metal and hard to get, I was planning to use it in activation experiments.

About the stagnant zones in the 3D cooling circuit. I don't think that it will significantly affect the cooling efficiency, the flow rate is high enough, besides the hot water will go upwards so where the outlet connection is located. But thank you for pointing out this issue, I will think how I can design a winding circuit inside the sphere.
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