Achived - Henry & Fergus' first plasma

[henryhallam]

We hooked up the new chamber to the system, put in a simple quick-and-dirty 2.5" spiral grid, pumped it down and applied around 4kV, 2mA at about 60 microns.
Having trouble getting a more focused plasma because whenever we lower the pressure and raise the voltage, the USB webcam crashes! Hanging grounded aluminium foil everywhere didn't seem to help much, so we may have to go with an analogue camera unless anyone has any ideas?
Fergus built a really clever little dohickey with a servo to turn the needle valve under computer control, and programmed it so that we can set a pressure and it will hold it automatically to within about 4 indicated microns (this is probably only within ~30% of the real pressure though). I've bought a baratron on eBay so we should get better accuracy when that arrives.

P.S. Richard, do we qualify for Plasma Club membership now?

[henryhallam]

Hi, thanks for the advice,
The computer is a laptop and has a totally isolated power supply, but unfortunately is grounded through its serial connection to the control PCBs which share a common ground with the fusor system for metering reasons. It might eventually be necessary to opto-isolate everything, could be quite a hassle
Adam, I did try wrapping the camera USB cables in grounded Al tape and that didn't help at all. I'm beginning to suspect it may not be the camera itself that's crashing, as much as the USB hub it's connected to (this also runs a USB->serial converter for communication with the PIC on the control board). Opto-isolating just the serial connection may help here.
I didn't try putting a conductive shield actually in front of the camera though, and I'll give that a shot.

Cheers

Henry

[colinheath]

hi henry,
glad to see your on the way with the fusor! is that the x ray transformer running it?
cheers
colin

[3l]

Hi Henry:

Congratulations!
Looks great guys,you are well on your way.
I think you have entered the plasma zone.
When I tried out a Usb cam ,I had the same disaster.
Fiber is the only way I know to prevent heck from breaking loose.
Varactors might do it but it would interupt the signal during the overvoltage.
Nice touch with the servo valve.

Happy Fusoring!
Larry Leins
Fusor Tech

[fergus]

Hi colin,
yes it is your xray tranny, its doing its job wonderfully, although we have had to brave a dunk in the gunk a couple times (due to our own mistakes )Here are some photos of our first neutron producing run. 28kV, 10mA, pressure uncertain.

[Brian McDermott]

Congratulations guys! Have you determined an isotropic emission rate yet?

[henryhallam]

Thanks

Only trying to estimate a rough rate here...
We were counting about 20cpm and the counter needle was hovering around 0.8 mrem/hour. According to Richard's FAQ (we need to consult the calibration data properly) this equates to around 5 n/cm^2/sec of flux at the counter tube.
Taking the radius of the "sphere of neutron flux" to be 25cm since this is the approx. distance between the centre of the poissor to the centre of the counter tube we get a total surface area of around 7800cm^2, giving a total neutron flux of ~35000 neutrons/sec. This seemed surprisingly high for a first run but we were operating at 28kV and 10mA so there was a pretty good ion flux.

Will need to take more accurate measurements and consult calibration data to be sure.

Cheers

Henry