Hi all,
So I finally got my chamber assembled and pulled a vacuum on it about 3 weeks ago now. I got a plasma to light a few days ago and thought i would share my progress before I commit to fusion in a couple weeks. Here it is before assembly. I use a steel plate to secure it to my table.
My vacuum chamber consists of a 6 way 4.5" confalt cross. It is backed by a two stage alcatel 2002 pump. It relatively small but pulls a good vacuum (3 micron at the head). After pumping for 30 minutes, I get a pressure of 15 mTorr on my chamber. My turbo is a TPU050 that manages to get my chamber lower than 10E-5 and a day and night of operation. I use a sapphire valve as my gas input and an MKS901P gauge to measure the pressure inside the chamber. I had some bad knife edges but they were easily masked with some high vac grease. I will be using viton gaskets to help achieve a lower pressure later. The chamber isn't optimized for vacuum conductance but it works to the pressures needed. After fusion I will be changing the design since this chamber isn't only for the purpose of a fusor.
- chamber without HV hooked up.
My high voltage is supplied with a modified Xray transformer and the feedthrough is similar to Andrew Seltzmans. He was the one who actually sold me the feedtrhough components. I also had some help from Liam David in its design. Here is a photo of the Swagelok seal that I used. I was having problems coming up with a good seal, so I opted to ditch the ferrules and just use orings as the main method to seal. It worked fine and was confirmed with an alcohol test to have no leaks.
- the orings are squished between the top and bottom of the end cap
My voltage is measured with a HV probe (up to 40kv DC). I just got some 10 ohm 50W resistors so I haven't measured the current as of yet. I used a variac to control my voltage. My main goal being to just get a plasma to light. At about 500v I get a very faint plasma, but increasing it I manage to achieve a brighter and more clear one. I can't seem to measure more than 1kv (explained in detail below) so I keep it at that voltage, but it's clear that I have a demo fusor.
Here is a photo of the full set up:
Pressure is below 100 mTorr when lit and decreases to 30 mTorr using the mechanical pump only. The following photo is my plasma at 60mTorr. Please excuse the horrendous grid I will be making a better one for my real fusor. The chamber is grounded.
Issues to fix
At the moment, I haven't been able to measure more than a thousand volts because my meter seems to glitch after getting over that voltage. I can't tell what is happening and I'm concerned that in operation up to 30kv it won't do it's job. It's possible that the probe its self is defective but I can't really tell. I connect the positive side of the probe to the negative output and the ground side to earth ground. I have feeling this is the cause of the issue but there's really nothing to back that up.
I also have an issue with my gauge. Once I apply a voltage to the grid, my computer start glitching out and the gauge read out just freezes. I'll be checking the manual to see how to protect the gauge from HV but until then I cant tell what my pressure is exactly. As such, the pressure before operation is my closest guestimate.
At the moment, I need to make a good tungsten grid and I lack the wire to do so. My PEM cell has had some difficulty arriving to my destination because the sender put an incorrect address. I also have the need for a detection set up but that is a whole other beast.
I'm happy to finally get to this stage and ready to start fusing. I hope you enjoyed the read!
Regards,
AA
