Subject RF ion source, modified, with deuterium
Posted by Carl Willis on 2008-21-10 01:00
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My original RF ion source was described here:
http://www.fusor.net/board/view.php?bn=fusor_ionguns&key=1221383383
It used a $100 glass-to-metal adapter as the discharge bottle, a capillary gas feed, and previously was only operated with air.
In the newer version, the glass-metal adapter is replaced with a $1, standard 19mm test tube, feeding the gas into the extraction gap via the anode flange as shown below in the drawing. To suit the very low discharge pressures favored by this source, I have cut down on gas flow considerably by adding a 4 micron laser-drilled septum purchased for $40 from Lenox Laser in the gas feed circuit. Also, although not shown in the drawing, I have placed a #8 ceramic washer (Small Parts, Inc.) over the extraction aperture to help shield the exposed copper in that region. Copper is good at recombining the atomic ions we want out of such a source and it should be shielded as much as possible.
The attached photos show the ion source operating in D2 gas, about 0.5 sccm, producing about 200 uA of current. I closed the throttle valve some so that the residual pressure is up around 10 millitorr and the beam is nicely visible in the gas. It has the characteristic red color of clean deuterium beams (contrast with the pale blue from an air beam in the previous thread), although the discharge in the bottle is a similar shade of pale grayish-pink. When the target is biased at -15 kV, some neutrons can be detected by a small He-3 tube (maybe a dozen CPM). I cannot run the feedthrough above 15 kV without putting it in oil, something I might do just for the heck of it to make more neutrons.
-Carl
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2008-21-10 01:00 RF ion source, modified, with deuterium 
(Carl Willis) [Latest: 2008-10-11 11:24]