Demo Fusor close to first light

[Larry Upjohn]

Hi All;
I have not quite kept up with my development schedule due to few extra fusor minutes. I have been continuously pumping my chamber now fitted with both a TC gauge and a 15 torr Baratron capacitative manometer. I have done an Excel spreadsheet to sort out my observations and see how the two gauges correlate. I have noticed an interesting effect as the ambient temp goes down (unheated garage area) the vacuum indication creeps upwards. I suspect it is a complience issue with the base gasket material (red rubber gasket) and as noted the teflon in the ball valves probably including the shaft packing as noted earlier. I have now collected three pneumatic bellows valves and will build them into the "real" fusor system. By the way thanks for the observations on the grid. The following thread:
viewtopic.php?f=6&t=2863&hilit=shaker#p12373

was my inspiration. I picked up the shaker bottle at GNC for around $8.00USD. This is clamped to a SS bolt threaded on the other end to the Sparkplug. This is
a non-resistor Model A Ford sparkplug (new) from Antique Ford Parts of Sacramento.
They have a website and these can be ordered online for around $4.00USD. The plug is a standard 1/2" NPT thread. Thanks again for your encouragement. I will keep plugging away.....Larry Upjohn.

[John Futter]

Two modern sparkplugs with no internal resistor come from NGK

standard size D7EA

small size (approx 10mm thread) C7HSA

We use dozens of these @ work on ion sources and implanters.
We have a test setup for the leak detector to test them--- none have leaked --so now we just take one out of the box and use it without testing

Edit
you can select what you want from here --just avoid the R type plugs from NGK
http://www.ngk.com/sparkplug411_manufac ... cturerID=1

[adrian.f.h]

Nice effort!
I think the first post in this set was made when I had my first success on demo fusors. Sort of inspiration for my first tests as can be seen on this picture http://www.adrian-homelab.de/bild55.JPG from my website.

I use sparkplugs too but with the plug facing in. But using them the other way seems to be even better regarding isolation and the connection with the inner grid. On the outside of the chamber epoxi seals are not such a problem. Some are using epoxies in their vac system and I do so for an improvised flange connection on the rotary pump but I personally don't trust them especially when the chamber becomes fairly hot during operation.

This spurkplug thing is by far one of the most professional low cost improvised feed through solutions I found.
I'm really interested what's the maximum voltage rating, as I never heard of failures?

[Richard Hull]

The spark plug useage goes back to my fusor I and fusor II in 1997. They do indeed fail once voltages rise to what anyone might consider "useful levels". For demo only fusors, they are quite servicable, but that is pretty much their limit.

I did do my first low level, moderately detectable fusion in 1998 using a spark plug in fusor III, but within days, it arc'd over and that was that.

Much discussion on this can be found in the old songs forums. The spark plug more or less dropped from sight in fusor construction until just recently.

Richard Hull

[Doug Coulter]

That's good info John, thanks. We'd only found the super old and hard to find Ford plugs so far.

I have also had decent success with just sealing a thick wall ceramic tube through a hole in a CF flange with Hysol, as long as it doesn't get too hot, it's fine, and should you need to, you can smash the ceramic back out and replace it. Cheezy but functional.

For real high volts though, it's hard to find a thick enough walled piece of ceramic, which is why the pro HV FT's are made the way they are -- a long very open space on the inside, so at no point does the wall thickness alone have to stand off the full volts. In a fusor, with space charges etc I've had troubles with these though, and now use my own design with quartz tubing, which at least is cheap by comparison to replace should you need to. (ten bucks for a new piece of quartz vs the cost of a new 50-100kv FT looks real good to me).