Jack and Scott's Fusor-First Light at NJIT

[Scott Moroch]

Jack and I recently moved all our of equipment to a small lab at NJIT. As out school year has come to an end, we have begun to assemble our equipment and begin to test for leaks. The first thing we did was attached our TC gauge to our mechanical pump and the lowest it would pull is 450 millitorr. We then proceeded to attach the TC gauge to the chamber and we managed to pull the entire chamber down to 470 millitorr. The company that sent us the pump said it was tested down to 2 millitorr, so we knew the NPT fittings were leaking. We decided to blank off the port with the port with the TC gauge and see the pressure based on the plasma. We assembled a pretty horrible meiro grid the first day and managed to get pretty nice plasma. Today we added a spherical grid and we do believe we saw a weak star mode and, depending on the pressure, we saw a bugle jet. As expected with our NST, as soon as we pull any current the voltage drops. When we open our bellows valve all of the way and pump down the chamber, we see no plasma and the voltage is around 2,800 volts. We do have a small leak, which we believe is in our feedthrough. In order to see plasma again we close the valve all of the way, let a little air leak back in, and then turn on the NST. The voltage will drop down to 1,550 volts. I have attached images of the plasma we have seen.

Scott Moroch

[Jim Kovalchick]

Nice work so far guys. Keep working on your vacuum. It is the key to enabling voltage and gas inlet control.

[Dennis P Brown]

Low milli-torr is the worst place for leak detection since there are few easy methods. Your situation, however, appears a bit easier since your rate appears higher: read greater volume of air entering so it should be more audible. Turning off the pump and listening closely at the suspected site should allow detection of such a large leak. A stethoscope (cheap one - auto parts shops often have these) can be a great device to hear small leaks and may even help with lower end milli-torr leaks. Are these home made feed through's? I've made a few that hold to low 10^-6 torr. Just use as little epoxy as possible will often prevent issues.

[Ryan Catalano]

Congrats on first plasma! You guys might want to try using loctite 290 on that TC gauge. I used to have a similar problem with all the NPT fittings on my system until I switched from teflon tape to loctite. I have been using it on my TC and I can consistently pump down to rough pressures of around 15 millitorr no problem and it holds a vacuum very well.