Fusor 3.0 (small)

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Dennis P Brown
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Fusor 3.0 (small)

Post by Dennis P Brown »

Fixed the vacuum leak - bad seal on the home made window. Pumps down but a lot of outgassing (new epoxy.) Will plasma clean tomorrow and test under high vac. The electrode feed-thru is home made but it appears vacuum tight. Will see tomorrow on this complete system's overall performance under high vac.
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Fusor Electrode (completed)
Fusor Electrode (completed)
Fusor 3.0 (Small)
Fusor 3.0 (Small)
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Dennis P Brown
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Re: Fusor 3.0 (small)

Post by Dennis P Brown »

While the system gets down to the mid 10^-6 torr, there is a small but serious leak (micron/sec.) This started just after my first plasma burn out run. So while I currently can't locate it I am 95% convinced it is in the HV feed assembly. Alcohol testing yields no results even while under 10^-6 torr. Strange.

Hope I don't have to reconstruct my commercial HV plate to this small system. But if I can't locate and fix the leak, will have no choice.

Two steps forward, one, somewhat, big step back.

Another step - did a higher temp bake out of just the fusor and HV feed-thru at high vac. After cool down, the leak rate is down to less than 1 micron every fifteen seconds. Again, just doesn't follow logic of a real leak. But the plasma burn out shouldn't then make matters worse as it did that first iteration.

Will try another plasma burn out and see what happens to the leak rate.

Same result - leak rate returns to a few microns a second. Not sure what is causing this. Will remove the unit and add ceramic seal to the inside end. I do feel that I need to shield my vacuum detectors from the plasma with a metal screen. At times it certainly is causing issues. However, that would only occur during ignition so isn't the fundamental factor.

Also, tried the pancake Geiger probe I recently received and used my bench type RM-24 Eberline unit (instead of the Ludlum Mod 3 with the std Geiger tube). The Pancake probe measures a sight increase in background around the fusor body when the fusor is powered up to 32 kV. However, at the fusor window (about 6 inches away), it soars to 120 mRem/hr. So, more inline with what should be expected at that voltage. Also, having a uranium sample to further test the device is also useful (and people getting started should consider having some for cross checking detectors for that reason.)

Grateful to both Rich and Richard when they correctly pointed out the issue with my old Geiger unit - while it was never a safety problem since the fusor window points away (I use a mirror system to view the cathode), and I shield the fusor over and above what the fusor case protection factor provides, it is essential to confirm that these safety devices are providing what is expected. Further, it is reassuring to know that my setup is safe and the x-ray system is properly working.
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Richard Hull
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Re: Fusor 3.0 (small)

Post by Richard Hull »

It is to be remembered that x-rays at 32kv applied voltage are not all at 32kv energy. The Maxwellian tail of energy of x-ray energy vs. applied voltage, shows only a tiny fraction of 32kv x-rays. The bulk of x-rays are well below 32kv energies. Most stock CF fittings and tubing are .060-inch thick SS. We have long known that mid thirties kv voltages will produce a penetrating tail of x-rays at that voltage. In short, most fusor chambers go transparent to x-rays of 35kv actual energy. Higher voltages mean more energies above 35kv penetrate the shell and serious x-ray emissions are an issue above 45kv.

Common glass ports are very transparent to x-rays over 15kv energy.

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: Fusor 3.0 (small)

Post by Dennis P Brown »

As for ports and their x-ray threat, Richard you are so very correct even through my max voltage is 'just' 32 kV. My new port window is 5/8's inch thick fused quartz and the x-ray emission thru it is certainly very high. My fusor housing shows little above background at the same time. Again, grateful for the advice making me aware of this serious problem with my then 'new' Geiger tube.

Fusor 3.0 has serious running issues. I'll include a pic of the plasma seen through the small window and the overview of the installed system.

I found that controlling the discharge is essentially impossible for any time period longer than ten to thirty seconds for the most part. My Fusor 1.0 was easy to run (and by volume, far larger.) Ditto my previous very large chamber (largest to date), fusor 2.0. In fact that was extremely stable and would run indefinitely without any inputs by me.

Apparently size does matter ... ;) The stability of the fusor appears to improve with 'size'. Though that effect, I bet, isn't just size alone but that geometry also matters. A small spherical fusor I'd think is more stable than a 'T' shaped fusor of identical volume. Maybe not but considering the issue of least resistive path combined with 'sharp' corners, the plasma would discharge more readily to those closer/abrupted shaped corners but depending on minor 'unstable' discharge, jump and surge. I'd think a spherical chamber would create a better plasma due to the discharge being more uniform and would tend to lend itself, I believe, to a more stable current and hence, operation.

In sum, I am seriously considering abandoning Fusor 3.0 today and just re-assembling and running fusor 2.0 - the change over would take, at most, an hour. I really enjoy a stable plasma even if the neutron count is significantly lower. Yes, when fusor 3.0 was managing to run for a few tens of seconds, my He-3 detector went wild - easily 15 k neutrons and greater per min. But never once got it to run stable for a full minute - ugh.

Rather than try activation, guess I'll return to fusor 2.0 and focus on the fast neutron detector and also, see if I can get my ancient BF3 detector tube operational. Furthermore, deal with trying some repairs on two black boxes. Finally, deal with the noise issue on my remade ultra-sensitive preamp (the CSA, not the Ortec. That appears fine but isn't in the same league of detection compared to the CSA - the Ortec is better suited for a PMT system.)
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Plasma - Note Jet
Plasma - Note Jet
Fusor 3.0
Fusor 3.0
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Richard Hull
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Re: Fusor 3.0 (small)

Post by Richard Hull »

You note that I tried the smaller chamber and failed due to control and arcing issues. I just refused to tolerate the intolerable. I went back to a larger chamber for ease of control and even to accepting a 1 micron sealed leak rate per 30 seconds. I'm just too tired of trying to seal leaks I can't find readily. I can hit the mega mark at 45kv.

You can activate easily at 32 kv in a good system using the counter detector/activated material bound method I have described and shown in countless posts after 2020. Silver is best for this within the small purse crowd. One only needs a cheap $20 "Russkie" STS-5 GM tube wrapped in silver foil 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
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Dennis P Brown
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Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: Fusor 3.0 (small)

Post by Dennis P Brown »

I so agree with you, Richard. I reinstalled my large chamber fusor. Can't say enough about a fusor that is stable, and response to extremely well to D2 input leak valve control in order to adjust current. No unsteady current flow or voltage swings.

I discovered the turbo isn't really needed for operation of the large fusor. Have to admit, I didn't even think to try that out till someone here mentioned that type of operation (my fore pump reaches sub-micron; I'd guess 0.2 - 0.4 micron via an uncalibrated meter.)

I've pumped it out in order to check for gross leakage - none - but haven't tried running it yet. Should look into that tomorrow.

I will reread the simple activation methodology some more that you cover. I am still determined to get my fast neutron PMT working again - should never have disassembled it - ugh.
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