Alexey's fusor progress

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Alexey Khrushchev
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

If the problem is gas contamination, I don't know how to fix it. I get the deuterium in a PEM cell, then the gas goes through a silica gel cartridge (with color indication) to remove water. The gas is then bubbled through vacuum oil over a layer of granular KOH. Should I install an activated carbon cartridge to remove traces of oil?

Yeah, I noticed by the way that the color of the plasma has turned blue lately, without the red tint like it used to be.
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Dennis P Brown
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Re: Alexey's fusor progress

Post by Dennis P Brown »

No expert but I think your deuterium is fine (red or blue is typical for deuterium discharge color.) I would avoid bubbling through oil or KOH; no real need. Some here don't bother to dry their PEM cell D2 either.
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Liam David
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Re: Alexey's fusor progress

Post by Liam David »

The arc that you're describing is absolutely caused by some kind of field enhancement, and in your case the triple junction is to blame. The path from triple junction to ground is across the flat glass surface and surfaces have lower breakdown thresholds than volumes.

I don't have enough experience with PEM cell deuterium to really comment on its purity (I use bottled gas only), but it may not be the gas itself that is to blame. Consider, for example, the adsorbed gases on the surface of your stalk and cathode. Under plasma bombardment, that gas will be driven off which will locally enhance ionization and thus a positive feedback loop forms. Locally, the current density becomes large and you see a brief arc. This is one of the reasons conditioning is important. Running a lower-energy plasma helps remove this gas, which corroborates Dennis' explanation of his system misbehaving unless brought up slowly. In fact, this is the main issue plaguing my system, especially with my cathode design.
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Rich Gorski
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Re: Alexey's fusor progress

Post by Rich Gorski »

Alexey,

I agree with Dennis and Liam on this arcing issue. It may be worth redesigning your HV feedthrough to increase the surface path length along the glass. Maybe look at a commercial HV feedthrough like from K Lester vacuum to get a look at their proven design. They have one that claims to handle 100kV.

Good luck,
Rich G.
Alexey Khrushchev
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Thank you all for the discussion!

Vacuum oil is the working fluid of my gas storage system. It is an inverted dividing funnel that is placed in a wide vial. Initially the funnel is filled with oil and when I feed deuterium the oil is forced out of the funnel into the vial. In this way I can store up to 125ml of pure deuterium. Underneath the oil layer are KOH pellets to remove traces of water.

I agree that the breakdowns are a consequence of having a triple point, but I can't find a professional insulator at the moment.

I always burn the chamber before working, for this I increase the pressure to 50 microns and set the current to 20-30 mA, the cathode is white hot. I think all adsorbed gases fly out of the chamber as a result of this procedure.

If it is not the purity of the deuterium, why do breakdowns occur at high gas flow rates? Again, at 1 ml/min and 20 micron pressure, the plasma is stable, but at 10 ml/min and 20 micron pressure, there is no plasma, and when I try to increase the voltage, breakdown occurs.
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Rich Gorski
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Re: Alexey's fusor progress

Post by Rich Gorski »

Why should the D2 flow rate change the arcing and plasma formation in the chamber when the pressure is constant 20 microns? Could there be a pressure differential in your chamber? Is the gas inlet close to the HV feedthrough while the vacuum gauge is far away? Just a thought. Strange indeed!

Flashover due to the triple junction at the glass/metal/vacuum interface is caused by electrons hopping along the glass surface from cathode to anode which cause secondary electrons to be emitted from the glass surface eventually resulting in a runaway situation ending in a flashover. Some techniques used to help this in HV application are:

1: Roughen the surface (increases path length and helps to clean the surface.
2: Apply a coating on the glass surface of a material that reduces work function and secondary electron yield such as a metal oxide. I know that Cu2O has been used.
3: Redesign the geometry of the glass surface to increase path length from anode to cathode.

If you Google "flashover across solid insulators" you might find other ways to reduce this problem

Rich G.
Alexey Khrushchev
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Today I was able to confirm that my fusor is producing neutrons. As I wrote earlier I had a problem with my neutron detector (MKS-01R) it was reacting to X-rays. Recently I was able to purchase a large scintillation crystal for neutron detection - SDK.02, 40x63mm in size.
Crystal 1.jpg
Crystal 2.jpg
I don't know much about this crystal, it is quite rare, as far as I know it contains the isotope lithium-6, and is virtually unresponsive to x-rays and gamma rays. It cost me about 35 dollars. My dosimeter kit has several detection units: neutron, gamma, beta, and alpha radiation. I disassembled the alpha unit as it was the easiest and replaced its 150mm diameter scintillation plate with an SDK.02 crystal. I had to print some parts on a 3D printer to do this. Of course, now the detector will not give the true neutron flux value, I don't have a reference neutron source for calibration. The only thing I could do was to check the value of the natural neutron background. The neutron detection unit showed a value of 0.15 neutrons*cm2/s, and the modified unit showed 0.06 pulses*cm2/MIN. The diameter of the crystal (40 mm) is 3.75 times less than the diameter of the plate, but the microprocessor of the dosimeter does not guess about the substitution) For myself I decided to be guided by the dosimeter readings and consider that it shows not pulses*cm2/min, but neutrons*cm2/s. Of course, I realize that my device in its present form is only an indicator of neutron radiation. I have done many experiments and found that the detector now only responds to neutrons. Today I set the following parameters: voltage 34 kV, current 6.0 mA, pressure 20 microns, deuterium flow 1 ml/min. I recorded 15.9 "neutron*cm2/s" at a distance of 17 cm from the center of the chamber, which conventionally corresponds to 2.2E+5 n/s.
16ns.jpg
Moder.jpg
After removing the neutron moderator, the detector showed an almost background value of 0.2 "neutron*cm2/s".
02ns.jpg
WoModer.jpg
The background in this measurement mode (averaging over 10s) was 0.1 "neutron*cm2/s".
BGD.jpg
Next, I wanted to do the activation of the indium plate. I set it to 35 kV and 8 mA at a pressure of 25 microns. This raised the neutron yield to a notional 4.0E+5 n/s.
Plazma.jpg
However, the cooling system of the fusor is not capable of dissipating such amount of heat and after 4 minutes it heated up to 100C. Besides this my variac (power up to 1 kW) was working at the limit, I felt the smell of insulation and turned off the device. I placed the plate in a lead house (5mm thick, inside covered with copper sheet) and turned on my gamma spectrometer (Atom nano-3, CsI 3cm3). I expected to see photo peaks of In116m1 138 keV and 417 keV, but unfortunately nothing was detected. I am in the process of building a new 100mm diameter chamber, hopefully I can solve the housing heating problem, then I can increase the neutron yield and do activation experiments.

I have made some improvements to the gas flow control system. I installed a geared motor on the deuterium fine control valve. I printed a handy bracket on a 3D printer, which allows me to quickly remove the motor and manually adjust the valve. I placed the motor control unit on the operator's table. Now it is very convenient to adjust the pressure in the chamber by giving short pulses (2-3 s) to the motor.
Valve.jpg
Ctr.jpg
By the way, I installed a giant capacitor 50 kV/0.025 µF weighing 10 kg. And it looks cool) The thing is, my voltmeter didn't work well with the pulsing voltage and I wasn't sure of its readings. I realize this is a big risk, so I made a checklist for myself on how to work with HV. I never go near the work bench when HV is applied; after turning off the voltage I wait 30s until the capacitor has discharged to 1-2kV, then put on dielectric gloves (up to 10kV), stand on dielectric rubber carpet and discharge the capacitor with a metal rod attached to a 1m length of plastic tubing. Even after that I only touch the fuser with gloves on.
cap.jpg
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Richard Hull
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Re: Alexey's fusor progress

Post by Richard Hull »

Alexey,
You have been admitted to the neutron club. The fine report coupled with the moderator/no moderator report showed you were making neutrons.
Good work and I am glad you have hung in there to make it happen.

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
Alexey Khrushchev
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Thank you so much, Richard!
It means a lot to me. Thanks to your efforts, many people around the world have discovered the fusion universe.
Alexey Khrushchev
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Rich, thanks for the interesting information!
I have been thinking and working a lot about the breakdown problem in my chamber and came to this conclusion: maybe at high deuterium flow rate my thermocouple vacuum gauge shows an overestimated pressure value. For example, it shows 20 microns, but actually the pressure in the chamber is 2 microns. In this case I can't ignite the plasma at normal voltage, charge build up on the cathode and eventually breakdown in the triple junction. I don't have any other vacuum gauge yet, so I can't test this assumption. I just decided to operate at a flow rate of no more than 2 ml/min. By the way this helped to avoid pressure pulsation, as my diffusion pump does not handle high flow rates well.
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Dennis P Brown
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Re: Alexey's fusor progress

Post by Dennis P Brown »

Congratulations on the success; certainly overcame many issues using clever methodologies.
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Rich Gorski
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Re: Alexey's fusor progress

Post by Rich Gorski »

Alexey,

Congratulations on producing neutrons and your induction into the neutron club. With a bit more work and time spent understanding the idiosyncrasies of your setup and some minor improvements (like getting to 40kV) it appears capable of activating elements. I might suggest trying to activate Silver instead of Indium. Based on the half life of the two isotopes I think Silver 108 with it 2.3 minute half life will be easier to detect than Indium 116 with its 54 minute half life.

Good luck & continue reporting on your efforts.
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Alexey Khrushchev
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Rich, Dennis, thanks for the congratulations!
I'll try to find a suitable silver plate and try to activate it.
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Richard Hull
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Re: Alexey's fusor progress

Post by Richard Hull »

Activation is a world unto itself! Fusors do not produce much of a usable neutron flux for activation. Activation is also a temporal exposure issue for we fusor operators. In a given neutron flux, to activation saturate an element one must maintain a maximal neutron output for 5-6 full half lives. This places a seemingly impossible burden on the beginning fusioneer.

I put up an activation FAQ in the radiation forum a few years ago.

viewtopic.php?t=12251

We can rarely run our fusors at the mega mark for more than 10-15 minutes due to heating and control issues. Thus, we need to expose an element of giant activation cross section, almost always to less than one or two half life periods! There are only 2 or 3 elements suitable for short run activation that make one feel great for their effort with decent, easily detectable, radiation emission after activation.

In order:
Rhodium- The very best and easily exposed for 6 full half lives of 54 seconds. Problem? $10,000 per troy ounce. I currently use Rhodium
Silver- The very best for the poor man. at 99.99% purity a full troy ounce is currently under $30. My first element to activate in the early 2000s.
Indium - The only other element that is low priced, (under $50/ounce). Takes longer to activate and tough to active over even one half-life.

Advance fusioneers here have activated gold, manganese and some of the rare earth metals and oxides.

Primary beta emitters are to be desired as a geiger count is all you need after activation. Gamma emitters are usually chosen by those who have a gamma ray spectrometer or a PMT counter system.

I use rhodium only because I bought for only $600 a tiny strip of Rhodium foil when Rhodium was only $3000/ounce. I also devised an arduino based geiger counter that begins counting in 5 second collection intervals to create a 600 second count of 5 second intervals in a file I can roll into Excel and create a rhodium activation exponential decay graph. (attached)

All the best on your efforts.

Richard Hull
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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
Alexey Khrushchev
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Richard, I read your great article on activation. It has pretty much all the information I need to start experimenting.

I have an indium plate and manganese dioxide. I realize that these are not the best elements for activation, the price of rhodium is discouraging, so I will look for silver. By the way, I have a colloidal solution of silver nanoparticles, bright blue in color, it would be interesting to expose it to neutrons, maybe that would change the color.

I also have some metallic gadolinium. A natural mixture of its isotopes has a very high neutron capture cross section of 46000 barns.
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Re: Alexey's fusor progress

Post by Ryan Ginter »

One mole of any element contains 6.022x10^23 atoms.The very best amateur fusors produce 1x10^8 isotropic neutrons per second, but most will emit below 1x10^5, and only a portion of that flux will pass through a sample.

Even if we are to assume the neutron absorption cross-section were so large that 100% of the neutrons passing through the sample will cause activation, the shear difference in magnitude between the number of atoms in the sample and the neutrons passing through it means you will never see macroscopic evidence of activation from an amateur reactor. The only means of knowing that activation has occured is by measuring the sample with a radiation detector.

The fusor could irradiate the target at peak output power for one million years and you still wouldn't have activated even one tenth of a percent of the original material.
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Re: Alexey's fusor progress

Post by Richard Hull »

Piling on...., Beta emitters, (GM friendly activation detection), will only show surface activation and then only 180 degrees of the surface! No one exposes a mole of any element to a fusor and dreams of total activation. The best is a foil sample of the element to be activated. 90% silver coins and even pure silver bullion coins or bars do no better than a .010-inch foil.

Gamma emitting activation products often do much better before a scintillator as some depth detection will be collected and indicated. Gamma spec instruments just prove activation to a specific new isotope with the count distributed.

Do well with a silver foil and GM counter, then branch out from there as the neutron numbers go up as your fusor operational regime gets perfected.

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
Alexey Khrushchev
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Ryan, the silver nanoparticles I mentioned are triangular in shape and about 50 nm in size. Activating a small number of atoms in each particle can change its structure or ionic environment. This will result in a color change due to aggregation or a shift of the plasmon resonance band. So you don't need to activate all the silver atoms to see the effect of neutrons. This is something I want to test in the near future.
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

I noticed that when the walls of my chamber are heated to 100 degrees there is a dramatic increase in neutron flux, about 10 times more. What could this have to do with? The first thing that comes to mind is the desorption of deuterium from the chamber walls. But I don't fully understand the mechanism.

I tried to activate the silver, but to no avail. For this I bought a 1mm thick coin with a diameter of 38mm. I ran the fuser at full power (500W at the cathode) for 5 minutes, but then the chamber got hotter than 100 degrees. The measurement on my mica dosimeter showed nothing. I assumed a more sensitive detector was needed, so I bought a drgb01 with a giant beta-5 counter (an improved analog of the SBT-10a). Hopefully I'll have success next time.

And I finally got around to testing my scintacor ND 40x40mm scintillation plate (contains lithium-6) as a neutron detector. I just replaced the crystal in my detection unit with this plate. Yes, it detects neutrons and does not react to x-rays. However, the number of pulses is about a factor of 2 lower compared to my large 40x63mm crystal. Someday I dare to break the plate into pieces and add them to the crystal.
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Richard Hull
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Re: Alexey's fusor progress

Post by Richard Hull »

When activating silver you must work very fast with a mica windowed geiger counter as one of the best beta emitters will decay very fast. The degree of activation depends a lot on exposure time within the polyethylene moderator. You will have to get the silver item out of the moderator quickly after shut down and place it as close to the mica windowed GM tube 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
Alexey Khrushchev
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Yeah, every second counts! Unfortunately, due to the peculiarities of my system, I cannot start measuring earlier than 30 seconds after the high voltage is switched off. You remember my giant capacitor?) A large part of the activated silver will have already lost its activity. I need to figure out how to place the dosimeter in the retarder unit, this will save precious seconds. But to do that, I'd have to disassemble the dosimeter and move the counter outside the housing. Then I can turn the dosimeter on immediately after the HV is shut down without going anywhere near the fuser. However, I am afraid that the X-rays may damage the meter even when it is off.
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Dennis P Brown
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Re: Alexey's fusor progress

Post by Dennis P Brown »

Maybe, place the instrument very close to the sample that will receive the neutron flux to be activated. Then shield the instrument with lead sheet and when the high voltage is turned off, remove the lead sheet.
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Alexey Khrushchev
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Yeah, that's a good one.
I recently read a book about neutron detectors based on the activation method. In a nutshell, thin sheets of various metals can be used to measure neutron field characteristics - neutron flux density and even neutron energy. Each metal has a unique neutron activation profile. Some absorb thermal neutrons only well, others have resonance with intermediate neutrons. In the described works, thin metal films about 10 µm thick were used, this avoids the effect of self-shielding of atoms. However, I have never been able to understand what thickness of silver foil should be for the most effective detection of activation. Thin foils will let some neutrons through, while thicker plates will block beta particles arising deep in the metal. I wonder if the radioactivity will be different on different sides of my coin? After all, 1mm of silver is guaranteed to absorb beta particles emitted from the reverse side.
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Rich Gorski
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Re: Alexey's fusor progress

Post by Rich Gorski »

Alexey,

You might want to check out my link below showing silver activation with my ring accelerator device. Some detail there on how the time between fusor shut off and turn on of the GM counter was minimized. Shut down and GM turn on were simultaneous. Only had to wait 10 or so seconds for the counter which was set in slow mode to start detecting. The neutron count using a B10 tube was around 150-200/s at 44kV - 20mA. I think the B10 sensitivity is something like 0.1 or 0.2 of a He3 tube of the same size so we might say the count was more like 1000/s and at a distance of 21cm. Maybe the total isotropic reached close to the mega mark but I have no official calibration. Exposure time was 7 minutes.

viewtopic.php?t=15233

As far as the x-ray issue and danger of hurting the detector, in my case the detector was shielded from the fusor with 1/16" thick lead sheet. I didn't run the math but I think the neutron absorption was very low in the lead sheet. The lead shielded the detector quite well from the X-ray. As Dennis said take advantage of 1/R^2 and get the detector as close as possible to your chamber.

Good luck.
Rich G.
Alexey Khrushchev
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Re: Alexey's fusor progress

Post by Alexey Khrushchev »

Rich, thanks so much for the link! I think it's just what I need. The idea of connecting the oscilloscope to the dosimeter is great! I don't fully understand if it can be done on my dosimeter, I'll look into it. Did you use a resistor for connection?

I noticed you used a lot of polyethylene behind the silver bar. Have you checked how much this affects activation compared to a moderator that is just in front of the silver?
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