Low Tech Gas Feed Solution

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.

Re: Low Tech Gas Feed Solution

Postby prestonbarrows » Sat Jan 21, 2017 2:27 am

I would imagine a 'U-trap' like this would lead to unstable operation where a volume builds up on the high pressure side then 'burps' over to the low pressure side sporadically. The magnitude of such surges may be acceptable, but they will always fundamentally be present.

The best approach to have a controlled flow of gas at high voltage is to locate a mass flow controller at the floating potential. You can still keep your feed bottle at ground in most cases. As the feedline across the potential drop will be at ~15 PSI, you can bridge that up to hundreds of kV without Paschen biting your ass or needing to jump though any ridiculous hoops for tubing path length.

Just keep above 1 Torr-cm and you should be OK.

If you absolutely can't deal with that, you can always float a lecture bottle at operating voltage. This gives zero potential drop across any gas lines but requires some thought about where the bottle and regulator will live.

The main rub for all of this is getting an analog signal and DC power to the floating MFC. For hobbiest situations, you can get away with a floating supply such as a battery or supercap for significant periods of time. Beyond that, you need to resort to motor generators and fiber optic communications.
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Re: Low Tech Gas Feed Solution

Postby Steven Sesselmann » Sat Jan 21, 2017 10:03 pm

Preston,

Thanks for advise, everything you say makes perfect sense, the only problem is I have been there and done that. (see my thread here) viewtopic.php?f=6&t=10479

Tried floating the MFC, tried powering it with batteries, tried optical connections, etc.etc. nothing stays up when the reactor starts fusing, huge voltage spikes mess with the electronics, which is why I am heading down the road with my "flux capacitor" invention.

I tend to agree with you that the gas on the low pressure side will have to build up quite a bit before burping a bubble, so I will be making it a little bit differently with a tiny hole at the bottom of the oil side.

I also have another idea I want to try, which is simply to put a bit of dry sand in the U trap, this will allow the gas to flow through, but prevent electrons ionising the gas through the sand, because the mean free path would be too short. This solution will be less messy and possibly work better. This is all R&D and I am at the point where I will try any simple idea.

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
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Re: Low Tech Gas Feed Solution

Postby Richard Hull » Sun Jan 22, 2017 11:50 pm

It is to be remembered that the fusor, the FICS and any other device that supports what is, in effect, a Townsend arc breakdown in a partial vacuum will be a great noise source across a rather broad spectrum, whether the device is doing fusion of not. Many great custom noise generators are constructed with this type of device at there core. Yes Virginia they do make expensive noise generators for sale in the world of electronics and RF engineering.

It is the devil's own work trying to float or remote sense, sensitive instrumentation in a noisy 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
Retired now...Doing only what I want and not what I should...every day is a saturday.
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Re: Low Tech Gas Feed Solution

Postby Dennis P Brown » Mon Jan 23, 2017 4:02 pm

Richard, when you point out

Townsend arc breakdown in a partial vacuum will be a great noise source across a rather broad spectrum
,

All I can say is, and this is from recent experience, I've learned this to be an understatement compared to the reality! Also, when the star ground configuration is used (and always a good idea to use this for safety!), one is also "piping in" huge voltage surges into the ground system which all your electronics can easily "see". My poor counter ran at the 120 Hz from the fusor!

I am slowly gathering together and assembling the equipment to have a battery supplied 2 kV DC and 120 AC power supply (for my counter) to operate/read my fully shielded Russian neutron counter. I will use a shielded cable/detector and locate the HV & counter some distance away (alas, shielding the car battery and HV x-former & variac is not practical as of yet.)

I do not think this subject in the detector FAQ's section is sufficiently emphasized as it so richly deserves.

My fusor - which easily achieves fusion conditions and (finally!) is highly stable - is, currently, as you correctly point out is just a very complex noise machine. Further, at least this aspect of a real fusor is its easiest property to demonstrate - LOL!
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Re: Low Tech Gas Feed Solution

Postby Richard Hull » Mon Jan 23, 2017 9:44 pm

In general well shileded cables running to properly shielded instruments is more than adequate to reduce noise to a windowable level. If using NIM gear you need to remember to terminate the line with the characteristic impedance...For most NIM this is 94 ohms, however, common 75 ohm terminators seem to do OK. Still, a 94 ohm terminator is easy enough to fabricate using a BNC male connector.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.
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Re: Low Tech Gas Feed Solution

Postby Steven Sesselmann » Wed Feb 22, 2017 8:43 pm

Looks like I finally invent something that works :)

The plasma backdraft arrestor (Flux Capacitor) actually works. My local glass blower Ken (Custom Blown Glass in Sydney) made up the airlock from borosilicate glass. What is not seen on the sketch is that the U shaped connector comes to a fine point with a tiny hole on the high vacuum side, which makes tiny bubbles as the gas is vented in.

airlock.png
Sketch


I found an eBay supplier in india selling small bottles of silicone oil for Diff pumps for $6.00 ( http://www.ebay.com/itm/272518309957 ) can't complain about that price, and it arrived fast.

Here is a pretty picture before adding the oil.

fics - 1.jpg
Flux Capacitor


The connections are 1/4" Swagelok hose barbs mating with 6 mm glass barbs, and the hose is special high vacuum hose.

After adding the oil, the plasma stopped and I can bring the chamber down to sub micron pressure yet I can still vent in the gas which bubbles up nicely. The only thing I might have to improve is the HV stand off on the outside of the Flux Capacitor, I should have made it longer, possibly with a few coils.

I can now mount the mass flow controller and deuterium cylinder at ground potential and hook it up to the DAQ in the same way as the other equipment, thereby eliminating the nightmare of trying to float the gas supply. Thanks to Doc Brown for the inspiration on this one...

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
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