Fusor Forums

Hi all! Much has changed in the past few months. I have not been working on my fusor as much in the past few months due to me attending college. I don't exactly have space in my dorm for a fusor. I am discussing with my professors about the possibility of continuing my work here at school.

A few months ago I performed a brief run of my fusor with deuterium gas, however I do not feel I have enough evidence to claim that fusion occurred. The gas line needs significant work, there is still an infuriatingly elusive leak in the chamber which resulted in lots of wasted deuterium, and my power supply could use a bit of improvement. When I return home for spring break Ill be disassembling the chamber and inspecting all of the knife edges and likely working on the power supply's improvements.

I suspect the leak I have been chasing may in fact be outgassing. There is a small amount of JB Weld that is securing an insulator to the HV feedthrough. I have found mixed information on whether or not JB Weld is vacuum safe. Any ideas on whether this is the issue? I did replace all the copper gaskets with laser cut viton O-rings and the leak still persisted. Does anyone have any experience with JB weld? I dont see what else the pressure increase could be.

What kind of vacuum gauge do you have? Hopefully it is one that changes reading depending on what gas is in the chamber. If so, go to an office supply store and get some "canned air". It's not actually air but a gas such as trifluoroethane. Pump your system down to vacuum until the reading is more or less stable. Then spray suspected joints. When you find the leaky one, the vacuum reading will change noticeably. If you don't find any leaking joints, then the problem could be outgassing.

There is another message here re: JB Weld High-Vaccum safe at viewtopic.php?t=8547. Unfortunately the nasa.gov link there is no longer valid.

On the broken NASA link in the earlier post that Bob referenced...
I think I saved the NASA data. I have posted what I saved as a zip file here:

www.xertech.net/pub/NASA_Outgassing.zip

In that zip are two files:
NASA Outgassing Database.xls -- which is a spreadsheet of the NASA data.
Outgassing_NASA_Key_Fields.pdf -- which is a description of the column contents in the spreadsheet.

If you print out the pdf it should be easier to track what is in each column as you scroll down through the data.

From the outgassing data for J-B Weld it is ok but not great. TML = Total Mass Loss = 3.37%, good would be < 1%.

So maybe not great for use in deep vacuums. Also, being an epoxy, I would think not good if exposed to plasma.

I do like J-B Weld for vacuums down to low microns, like out of a good 2-stage mechanical pump.

Here's a link to a post where I used J-B Weld as part of a mod to the input port of my Welsh 1402
"Convert Welch Duo-Seal Hose Nipple to KF-25"
viewtopic.php?t=14401

Keeping the exposed surface area of J-B Weld also helps. Note that in that mod the exposed J-B Weld is just a small ring.

Nice review of the old post. One need only have a small lathe and such KE/barb adaption is a snap. The recent adventure by Joe Ballantyne is an example of the hard way. I too, like Rex, machined my inlet on the precision pump's barb to accept a KF 25 nipple. I used Hysol to secure the weld and it has held since 2006. Prior to that I had a short length of rubber hose to the barb and then to a KF 25 to barb adapter. I never had a problem with the rubber hose bit, but in 2006 I pulled the Precision pump for what was a, not needed, KTO double load flushing fluid cleansing followed by new oil and replacement back into my system.

While out of service, I decided to machine the inlet barb to accept the KF 25 nipple.

Alas, upon reinstallation I did not lose or gain a single micron of bottoming pressure. Since then only two simple oil changes and zero pump removal from the system is just fine. That 2002 hamfest, for free, locked up, 5CFM precision pump is a good ole sleepin' dog now, doing a steady 5 micron bottom end.

As regards TC gauge tube issues, I do indeed, on rare occasion, remove my foreline TC gauge tube and flush it twice with acetone and MEK to avoid any back-streaming pump oil from creating a shellac residue over the thermocouple pair.

Richard Hull

I actually only have a rough analog vacuum gauge currently. I am guessing it is necessary to invest in a proper TC gauge. I will begin searching for such a device. It still baffles me that the leak rate has stayed constant despite my re-tightening and replacement of every single gasket. I am praying that my turbo is not at fault. I think I will also remove the JB Weld and replace it with Hysol 1C. JB Weld seems to be perfectly fine based off the NASA sheet, however Hysol 1C looks to be vastly superior.

If your turbo is spinning, it is working! Now it may be contaminated with outgassing interior deposits. Not likely, long term, in a sealed system. it would be the last place I would look to for issues. Virtual hidden leaks tend to abound in new systems that are not holding a vacuum.

Yes, you must have at an absolute minimum a reliable TC gauge or you know absolutely nothing about your vacuum.

Richard Hull

That is very reassuring Richard. I will attempt to clean the interior chamber once it arrives at school. I am meeting with the physics chairperson at my college on the 14th of February to discuss continuation of my project. He will likely be able to help me find this leak and properly seal the chamber. Do you think the laser-cut viton gaskets I made are an issue?

True viton is a good gasket material for most fusor type vacuum systems. It is how the gasket is applied. No piece of the gasket should ever be exposed directly to the inside of the vacuum chamber or plasma. It will outgas if exposed to any plasma.

Richard Hull

As long as it's adequately compressed and cleaned, viton can be good down to high-UHV. Sometimes rubber sheets like viton or buna-n can come with manufacturing gunk covering the surface, so make sure you clean them well. If absolutely necessary, you can use a very small amount of vacuum grease to help the seal, but if the viton is properly compressed and sealing surfaces are smooth and clean, it can hurt more than it helps.

Thank you Richard and Liam. I will stick with the viton gaskets in that case. The JB weld must be the issue, I see no other possible point of failure, however I can only be sure once I have the fusor back in my possession. I will be meeting with the physics chairman at my school on the 14th, we will discuss when and where my parents can deliver the fusor. Afterwards I will post yet another update.