High School Fusor: Fusor 1 Construction Completed!

Max E.
4 min readOct 20, 2021


Last week, the rest of the fittings, adapters and other parts for Fusor 1 arrived! I put the chamber together last week, but due to a shipping mistake with Kurt J. Lesker (KJLC), did not receive a Conflat to KF adapter that I had ordered for another few days. Additionally, the leaded viewport that I ordered from them would not arrive until late December, so I cancelled that order and bought a non-leaded port on eBay. This might create some problems in the future, but I can add lead shielding if need be when I switch to the 30kV supply.

Some of what I got from IdealVac, LDS, and Stephen Haid laid out on my IC workbench. I definitely don’t have plans to turn the Nerf gun in the background into a <1W laser gun.

I decided to assemble and seal the chamber inside instead of in the workshop, because I wanted to avoid dust contaminating the inside of the chamber or interfering with the HV seals.

Everything (except for the viewport) set up for assembly on the table. The blue tape on my PC (bottom) is to cover the hole where the DVD burner that I definitely didn’t cannibalize for laser diodes used to sit.

I went with Viton gaskets instead of copper ones because I knew that I will end up disassembling the chamber repeatedly in the near future as I iterate and improve the system and copper gaskets cannot be re-used more than 3 times.

Me inserting the grid feedthrough into the chamber.

One of the 6" to 2.75" CF flanges came preinstalled on the chamber and I was able to attach the other 6" to 2.75" CF flanges without much difficulty. If I get significant leakage, I will consider opening that connection and replacing the gasket, but if I do not encounter a problem I see no reason to worry about it.

The grid inside of the chamber after the flange was attached.

The grid stalk is too short for my chamber so the grid does not sit in the middle of the chamber. I am a little worried that that will increase the chances of arcing to the chamber walls, but I do not think that the likelihood of this occurring outweighs the risk of elongating the stalk and permanently damaging the feed-through. In any case, I highly doubt that this arcing will occur at the (comparatively) low potential difference generated by the NST.

The chamber fully assembled except for the viewport which had not arrived yet. I had not yet tightened the flanges when this picture was taken, hence the incomplete connections.

When I realized that the KJLC leaded viewport would take too long to arrive, I canceled the order and found a significantly cheaper unleaded viewport on eBay. Although this means that I will be dealing with a significantly worse attenuation constant¹ for x-rays exiting through the glass, I can simply angle the viewport (which will become a potentially deadly source of x-rays) away from myself and use extra lead shielding.

Is this a workable solution? Certainly.

Is this a good solution? No comment.

The chamber with the eBay viewport attached. After the fact, it bothers me that I did not align the flanges so that the bolts were even, but this is a purely cosmetic non-issue that I am not going to wast time fixing.

On Monday, the viewport arrived and I attached it to the chamber and tightened the bolts on all flanges. At this point, I believe that aside from the KF inlet for the thermocouple and the NPT insert for the vacuum line² the chamber is fully sealed.

I plan to do a pump-down test tonight to figure out how well the chamber is sealed. Although I know that there will be leaks between the chamber and pump (and inherent within the pump) that will likely prevent me from reaching below 1 torr, I think that the chamber itself will be relatively well sealed and that it will reach a lower vacuum than Fusor 0 as a result.

I am very excited to begin working on Fusor 1 in the coming days. As I’ve said before, the upgrade from my borosilicate tube Fusor 0 to the new Fusor 1 is monumental!

Notes & Citations:

¹ https://www.nist.gov/pml/x-ray-mass-attenuation-coefficients

² For more information as to why I am using this demonstrably leaky system, see my last post.



Max E.

Hi, my name is Max and I’m a freshman at Columbia SEAS! This blog is where I document my progress designing and building a FarnsworthHirsch IEC nuclear fusor :)