Progress on my fusor

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MatthewL
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Progress on my fusor

Post by MatthewL » Fri Jun 23, 2017 3:31 pm

Hi all,

It took a little longer than anticipated, but I now have most of the parts for my fusor assembled and I feel like I am at a stage where I should make this update.
IMG_1004.PNG
I had my power supply working for awhile but when the output exceeded 20kv I had an arc over in the tank (luckily not between the windings). I had to move some wires around to avoid the arcing but I then got an oil leak in the tank, which was a large diameter PVC pipe with two .5 inch acrylic lids (I used this instead of a bucket because I didn't want an implosion under vacuum). To avoid leaks I just got a bucket with as thick a plastic I could find from McMaster (still imploded at 3/4 atmosphere, but I did get the bubbles out from the windings). With primary ballasting I can get to just over 40kv DC.
IMG_0985.JPG
My chamber is a four way reducing cross with two 6 inch CF flanges and two 2 3/4 inch CF flanges.
IMG_0998.PNG
IMG_1001.JPG
My grid is made from tungsten and is 1 inch in diameter
IMG_0986.JPG
IMG_0989.JPG
My foreline pump is an Edwards EDM12 pump that I have tested to 30 mTorr. My secondary pump is an Edward's Diffstak 63, which I haven't been able to test yet because I don't have the oil drain plugs or dipstick assembly. I have tried different sized acorn nuts both metric and customary but the size must be unique to Edward"s. I have ordered plugs from Edward's but they are out of stock with a lead time of 7 weeks, if anyone has any other ideas for what I could use in the mean time that would be greatly appreciated. For pressure measurement I am using an Instrutech convection enhanced pirani gauge which measures only to 10e-4 Torr. I hope to also use a an ion gauge (hot or cold cathode) if I find I good deal on Ebay.
IMG_0984.JPG
I am using D2O electrolysis for my deuterium gas source, I haven't fully completed building this part yet.
IMG_0988.JPG
For neutron detection I am using 2 BTI bubble dosimeters. If my neutron flux is high enough I will also be doing some activation experiments.

I need to do a little more work, but in the next few days I should be able to perform a demo test.

-Matthew

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Dennis P Brown
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Re: Progress on my fusor

Post by Dennis P Brown » Fri Jun 23, 2017 6:16 pm

Looks good; have you considered making your own for the DP? Edwards could tell you the thread type and maybe you could then machine (lathe) your own? You don't show a detailed image of what you need for the DP so can't really know what it is that you are missing - I assume it is a "cap" for that part on the lower section of the DP in the photo?

MatthewL
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Re: Progress on my fusor

Post by MatthewL » Sun Jun 25, 2017 9:05 pm

I recently completed doing a demo run of my fusor an got these photos:
IMG_6586.PNG
IMG_6585.PNG
I don't know if this is enough to be admitted into to the Plasma Club, because the plasma is not centrally confined as I would like, that is probably because the pressure in my chamber is just under 800 mTorr (with a voltage in the first photo of 6kv and the second 8kv). My mechanical pump that I spoke about in the previous post can get down to 30 mTorr but didn't this time because I later realized that one of the CF flanges wasn't fully tightened. My pump was working smoothly, but after the first 3 minutes of the run the pump stopped working. I let the motor cool off and I tried it again, it begins to pump correctly for the first few seconds of the run but it then begins to stop pumping and start pumping.......until it stops and makes a quit humming noise. It also draws a lot of current enough to flip a breaker. My guess is that there is a short somewhere. If anyone has had a similar problem or knows what this might be I'de appreciate the help. If not I may end up finding another roughing pump to use.

Also Dennis, here is a closer photo of what I was trying to find a plug for:
IMG_1007.JPG
I will call Edward's on Monday and ask about the thread size and if the lead time on the plugs and dipstick is still 7 weeks, If so I may have to machine my own. I don't own a lathe but I will see if any machine shops around me will help and are not unreasonably priced.

Thanks,
-Matthew

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Dennis P Brown
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Re: Progress on my fusor

Post by Dennis P Brown » Mon Jun 26, 2017 8:53 am

This type of pump startup issue happens to one of my pumps when 1) starts at near atmospheric pressure and 2) hasn't been run two weeks or more (which likely means it is near atm pressure since that might be the leak rate for that system ... .) I just make sure to run it once a week until I get a few milli-torr (microns - is the unit we tend to use here) before I shut it down and seal off the system.

Also, one should not run a system at nearly a full torr and expect a pump to work well; Do you not have a gauge that reads a few torr? Not a big deal with you don't but can be helpful. In any case, 30 microns, which is ok for a DP is rather high for a good two stage pump - maybe the oil is bad?

My next guess is that your pump struggles against near atmospheric pressure due to leaks; certainly leaks will not just cause a difficult start up but will also make the pump work very hard (large current load) as it pumps against the incoming air. A good system should have only "wall out gassing" (a micron or a few microns per second but the system should remain under ten torr or so for the day.) Maybe consider opening the pump body and cleaning it out (if you suspect contaminate build up. I've done this to pumps that have visible contamination in the sight glass. A rebuild kit might be needed - I've done it without but when the main body gasket broke, I had to use a "gasket sealant" to fix that - a kit, allows one to replace all gaskets and other critical parts that tend to wear out. Does require some skill. Not for the novice that isn't ready to learn by getting dirty ... .)

Also, (but not necessarily likely) is that the oil could have some water in it (allowing for a rapid rise in system pressure) but that can be removed if the pump has a built in purge valve; if so, allow the pump to run (with the inlet closed off) and allow the oil to heat up (5 minutes) then open the special valve (if the pump has one) allowing a controlled amount of air to "purge" the oil of water for a few hours. If this feature isn't available, might try replacing the oil (once you are sure all leak issues have been addressed.)

Others may have more/better ideas.

That cap design for the DP could be machined if you have access to a lathe - also, the tread size/type looks a lot like some lecture bottle hardware I've seen (not that that is very helpful with one does not have access to such hardware ... .)
Last edited by Dennis P Brown on Mon Jun 26, 2017 9:08 am, edited 1 time in total.

John Futter
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Re: Progress on my fusor

Post by John Futter » Mon Jun 26, 2017 9:05 am

Matthew
Any local fitting and turning shop will be able to make your Nut in half an hour. you will need to take the pump to them so as to measure the thread parameters
But that nut had a dipstick attached that gave you the oil level.
These pumps need the o-ring replaced top and bottom on that oil level / drain every year or better still every six months of continuous running otherwise the o-ring goes hard and jams the dipstick down the hole. The service guy then uses a large slipgrip wrench and F#$#$$cks the nut and dipstick. We have around 30 of these pumps at work and replace the viton o-rings six monthly.

MatthewL
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Re: Progress on my fusor

Post by MatthewL » Wed Jun 28, 2017 6:37 pm

I disassembled my entire roughing pump and cleaned out everything that needed to be cleaned. I assembled it and changed the oil and it can now run continuously without over heating. My pump can only pump the chamber down to 70 microns with a leak rate of around 1 micron/second. It may be that the rubber tubing I use to connect the pump to the chamber outgasses too much; I will be trying some different tubing to see if there is any change.
I called a machine shop and gave them details for the threaded end cap I need machined and they said it would cost a couple hundred dollars and recommended that I find a place that sells metric sized threaded caps. I will see if there are any other machine shops that could do it for less, or I will look into the lecture bottle hardware that Dennis recommended.
I just completed doing another demo fusor run at 100 microns and 8kv and got much better results than the first run I did at 800 microns:
Screen Shot 2017-06-28 at 12.40.57 PM.png
Screen Shot 2017-06-28 at 12.40.57 PM.png (91.75 KiB) Viewed 2573 times
Screen Shot 2017-06-28 at 12.40.11 PM.png
Screen Shot 2017-06-28 at 12.40.11 PM.png (74.44 KiB) Viewed 2573 times
I have a few more things I need to accomplish before I can achieve real fusion, but I hope to do so within the coming month.

Regards,
-Matthew

ian_krase
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Re: Progress on my fusor

Post by ian_krase » Thu Jun 29, 2017 6:09 am

At that level I suspect you have a real leak. Glow discharge plus Dust Off can tell you much.

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Dennis P Brown
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Re: Progress on my fusor

Post by Dennis P Brown » Thu Jun 29, 2017 9:35 am

First, glad you cleaned the pump and it runs far better; besides better operation, you've learned a great deal about pump maintenance and have a better understanding of the pump. Your leaks don't appear serious if you see 1 micron/sec. That can be out-gassing from contaminated walls - your pump was rather dirty after all. Maybe clean the chamber. Do you have an anti-back flow system for the vacuum pump between the pump and chamber? If not, than likely a lot of dirty oil vapor got into your system. Use as close to absolute alcohol that you can obtain (Isopropyl or ethyl; never methanol!)

If you want to prevent this problem and don't want to get such an item, then you either need a valve between the pump/chamber or need to back fill your system to atm every time you turn the pump off. I do all three - I have made a dry air supply, have a valve and anti-back flow device (which was surplus so I cleaned it out. Dirty at first but it was cheap ... should have just replaced the packing inside ... .)

I assume you are allowing the chamber to operate at 800 microns? If not, is that pressure achieved when the plasma ignites of is your leak rate far above 1 micron/sec? That pressure and your leak rate don't agree. If the pump is running and your chamber remains at 800 um then that is a serious leak and your stated leak rate can't be correct. In which case that sounds like a bad sealing surface like an o-ring or Cu gasket or a similar issue. That high a rate should be audible. So, maybe a picture of your connector system and a better call on the leak rate.

As for the cap, yes, metric might be the issue but that doesn't help unless you know the spec's so that a correct one can be ordered cheaply and fast on line. Having one made will be pricey since labor isn't cheap.

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Richard Hull
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Re: Progress on my fusor

Post by Richard Hull » Thu Jun 29, 2017 4:08 pm

Matthew, I have added your name to the Plasma club listing.

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.

MatthewL
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Re: Progress on my fusor

Post by MatthewL » Sat Jul 01, 2017 5:03 am

Here is a photo of the connection made from my pump to my chamber:
IMG_1013.JPG
There is a right angle valve in between the pump and chamber. While my pump is running I am able to get down to a vacuum of around 70 microns, I then close the valve to isolate the chamber and I can then turn off the pump. At that point the leak rate in my chamber is around 1 micron/second. There must be a leak before the valve or the silicone rubber tubing I am using to connect the pump to the chamber outgasses too much (this probably isn't the problem). If I did not close the valve and I turned off the pump my chamber would be brought to about .5 atmosphere, because when the pump stops running air rushes in through the pump outlet (I don't think that is supposed to happen because it doesn't happen on my single stage HVAC pump, it still retains a vacuum when off)
I have been using acetone to clean the inside of my chamber, would the alcohol have the same effect?

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