Liam David Fusor Update

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Richard Hull
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Re: Liam David Fusor Update

Post by Richard Hull »

Nice work Liam! I hope to have you in the neutron club soon. You are going at this correctly. Good luck.

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: Liam David Fusor Update

Post by Liam David »

I still have a few things to work out, like the pesky ZVS driver for my 150kV x-ray transformer, a still broken vacuum convectron gauge circuit board, an the voltage and current metering stuff.
My HVAC backing pump runs blazing hot. I have to keep a rather large fan blowing on it for extended pump down.

-Liam David
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

Also, as a separate topic, I am working on a website. It is still a major work in progress.

http://liamdavid75.wordpress.com/home/

-Liam David
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Re: Liam David Fusor Update

Post by Liam David »

I let the system pump down using only the mechanical pump and switched on the power. The plasma appears exactly like the plasma with my diffusion pump on. The star doesn't become more distinct or star-like with the diff pump, so it doesn't appear like my diff pump is doing anything. Since my gauge is broken, I can't tell the pressure.
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Richard Hull
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Re: Liam David Fusor Update

Post by Richard Hull »

Without at least a known good TC gauge, you are dead in the water, vacuum wise. You will never know what you have or haven't got in the fusor environment.

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: Liam David Fusor Update

Post by Liam David »

Finally I bought a Granville Phillips Series 275 Convectron Gauge with digital display (part # 275538-GQ-T). I powered it up and is displays around 750 torr when in the correct horizontal orientation.The gauge has a 1/4" female VCR connection, and I do not want to buy some outrageously priced VCR to KF-16 adapter. I brazed a washer to a male NPT fitting to allow it to seal with the gauge.
Image
Image

I hooked it up to the chamber, and was not happy with what I saw. With the roughing pump, I got the chamber down to 450 millitorr. With the diffusion pump, the pressure first rose to over 600, then dropped to about 250 millitorr, and then rose to stabilize at about 350 millitorr. When I closed the ball valve between the chamber and diffusion pump, the pressure rose at over 100 millitorr/second. Crud. Next step is to find the outrageous leaks (probably the HV feedthrough with compression fitting and hose barbs in the vacuum line).
-Liam David
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Richard Hull
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Re: Liam David Fusor Update

Post by Richard Hull »

Suspect your gauge connection kludge first. Connect the gauge to the forepump directly before anything else and see where you are. Step by step process.

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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Rich Feldman
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Re: Liam David Fusor Update

Post by Rich Feldman »

Yes, what Richard said.

Previous threads have mentioned changes in plasma color
when a tracer chemical is sucked into a leak.
Alcohol, acetone, dust-off spray, butane? :-)

You have at least one massive leak, findable with more primitive methods.
For example, pressurize the apparatus and apply soapy water to suspected joints.
Or evacuate the apparatus and apply vacuum oil to suspected joints. Pressure will drop as oil temporarily plugs the leak.
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

After re-brazing a conflat to KF adapter and replacing part of my vacuum line with copper pipe, I got my chamber down to 35mTorr after 45 minutes of pumping(not great, but an improvement over 400mTorr). The pressure rises at about 1mTorr/sec when I close the valve. I cranked up the voltage and got a dull, white plasma without a distinct star in the center, compared to purple distinct plasma I achieved earlier. I'll buy a bottle of helium soon for leak testing.
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

I discovered that one of the gas ball valves I use leaks, so I immediately suspected all of them. I bought a new vacuum butterfly valve for dirt cheap and replaced the ball valve. Now I can vent the mechanical pump and keep the chamber under vacuum. It leaks at about 0.5mTorr/s, and rises to 13 torr after 12 hours. Pictures probably coming tonight.
I suspect that the leak is at the cap of the feedthrough. The Swagelok cap broke off the end of the alumina rod, which is now rough. I'm still on the lookout for a cheap turbo pump/controller package and am still having problems with the high frequency transformer.
-Liam
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Re: Liam David Fusor Update

Post by Liam David »

It's been a while since I last posted. I have bought a 6 way 2.75" conflat cross to serve as a new main chamber. It will get here next week. Also, when I'm roughing the chamber out, the pressure drops to ~55 mtorr (still leaks) and then starts to slowly rise to 56 and then 57 as the pump starts to warm up. I disassembled and cleaned the pump, including one of the rotary vane stages, and got the chamber down to 55 mtorr, a 20mtorr improvement from before the cleaning. The rise in pressure still happens. Any idea what could be causing this?
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Richard Hull
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Re: Liam David Fusor Update

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What can the pump do at the head? Put a gauge directly at the pump inlet.

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: Liam David Fusor Update

Post by Liam David »

At the moment, I am unable to deadhead the gauge. I got my new chamber in the mail today- it's a 6 way 2.75" conflat cross. Here is it assembled with used copper gaskets just for reference.
Image

Image

On a separate note, my school is building a 1MeV cyclotron starting next year. The project will be guided by Tim Koeth from UMD, and I had the pleasure of talking to him briefly after the school interest meeting for the cyclotron was over. Hopefully I will be fully involved in the project over the next few years- I am probably one of the more vacuum and high voltage knowledgeable students at my school currently (though I'm mostly still a newb), and I am sure that my "experience" building a fusor will help earn me a spot on the team.
-Liam
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Re: Liam David Fusor Update

Post by Nick Peskosky »

Just a quick note: I see that you're using some type of NPT threaded elbow adapter to connect the VCR flange on the 275 Mini, you did use a metal gasket seal between the VCR flange and the VCR->NPT coupling? These connections require silver plated SS crush discs which must be seated (and ideally centered) between the Male/Female VCR connections. I had a minor leak on my gas line which was affecting my ultimate pressure with the turbo on and the fix was as simple as utilizing vice grips and a wrench to tighten each VCR connection. Try placing ~90% isopropyl alcohol (denatured) or acetone on the flange seams and if you see the pressure climb even further than you've found your leak.

Just some food for thought.
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

Yeah, it's not the right fitting. I used it earlier by brazing a washer to the end to act as a rudimentary seal surface along with a cast solder gasket. It undoubtedly leaked and I'm replacing it with a VCR to KF adapter soon. It's just in the picture for "show". Do I need silver plated SS gaskets or can I use copper?
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Re: Liam David Fusor Update

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It think the gaskets are typically AG plated copper. The VCR fitting is a close relative of the old, much larger, Curvovac fittings that tried to work around the old conflat patents. I have some old 2.75 curvovac stuff hanging around the lab. In many ways, to my mind, it seemed like it would be better than conflats, but is just not seen now.

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: Liam David Fusor Update

Post by Liam David »

Hmm. I guess LDS vacuum sells only plain VCR copper gaskets, which I assume will work fine.
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Re: Liam David Fusor Update

Post by Richard Hull »

Sure, they will do just fine. Just make sure to really tighten the fitting down good and firm. They make centering rings for those gaskets.

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: Liam David Fusor Update

Post by Liam David »

It's been a while since I last shared my progress. I finally found a turbo pump! It's a Pfeiffer TPU 040 pump with TCP 040 controller, which was described as not working. Opening it up revealed a loose relay, and a quick atmosphere test confirmed that it was the problem. I now have a fully functional turbo system, and it only cost $150. All things considered, I made out like a bandit. Once a KF-40 to KF-16 adapter gets here, I'll test the pump on the chamber.
I'll post progress on my HV transformer soon.

-Liam David

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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

Anyone know if I can run the TPU-040 pump horizontally, or will it destroy the pump? I have been unsuccessful in finding a manual.
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Re: Liam David Fusor Update

Post by Roberto Ferrari »

Hi David

Manufacturer claims it can be mounted in any position.
I will leave a manual at Files forum.
Good luck!
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Liam David
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Re: Liam David Fusor Update

Post by Liam David »

Thanks!
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Re: Liam David Fusor Update

Post by Alex_Nicholas »

That's a nice looking setup Liam. As someone looking to move from a demo fusor into neutron production your fusor has just become my goal. It looks so clean/simple and well organised. Great work to date and I look forward to seeing your progress.
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Re: Liam David Fusor Update

Post by Liam David »

There are some less professional parts of the setup that I'm not too proud of and that you can't see in the pictures, but thanks for the compliments. Smaller 2.75 conflat fusors don't produce as many neutrons as a 6" sphere or other larger chambers, but I went with this chamber because of costs.
-Liam David
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Re: Liam David Fusor Update

Post by Alex_Nicholas »

Cost is a big concern for me as well. I'd love to be able to nail a large fusor but something in the 3" sort of realm is far more walletable. I can do a lot of the work myself although finding materials here can be difficult. Namely high voltage gear. It's seemingly not very common in Australia. I will figure something out. As we always do in this field.

As a very wise man once said, Physics is like sex. Sure, it has some practical applications... But thats not why we do it.
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