With the vacuum pump working again, I assembled the fusor and attempted a fusion run last night. It was a day frought with challenges, but in the end the bubble meter saw 4 bubbles in 2 hours and 40 minutes:
Previously we were having problems with transient voltages spikes or EMFs crashing the data acquisition (DAQ) card. Today was a big test for the new transient voltage suppression system . It FAILED big time. But I learned something in the process.
I began by intentionally creating an unstable plasma to test the transient voltage system. This crashed the DAQ every time.
Next I disconnected all wires to the DAQ to determine if the interference is coming through the wires or the air:
This proved to work very well.
To control the high voltage from a distance I used the emergency stop button:
This also worked very well. At this point the reactor is completely under manual control. No computer necessary. Which will turn out to be a good thing.
So now we can test the DAQ with no physical connection to the reactor.
Quinn noticed the USB hub flickering during the plasma sparks and suggested it may be the failure point. I removed it, and indeed the system seemed less vulnerable to crashing:
At this point the DAQ seems to remain running in the face of sparking plasmas. Good.
Next I tried connecting one channel to the DAQ… a digital output channel to turn the high voltage on and off. I created a duty cycle function in labview to make it easy to bake out the chamber without melting the fusor grid. This is what it looks like running:
At first the computer controlled bake out was running smoothly. About 15 minutes in I get a computer crash. Restart. It runs for about 7 minutes and crashes. Try again. 5 minutes and it crashes. The crashes in increase frequency until I am getting nowhere.
At the point I switch the system over to full manual control and begin the metered fusion run. A fresh bubble detector was unboxed and activated.
(so fresh and so clean)
For the main fusion trial the deuterium atmosphere was at 10 mtorr, high voltage set to it’s maximum: 30Kv @ 10mA. The procedure was to run the system at full power until the plamsa became unstable and started sparking. This instability seems to correspond to the grid becoming red hot, so the plasma instability may be due to thermionic emission.
The bubble detector was activated for 2 hours and 40 minutes. The plasma was running for some unknown fraction of that time. 4 bubbles were detected.
Challenges remain for controlling this wily beast with a computer.