Some low-power operational data is attached, and a couple more (better) pics. All this operation is still in air rather than deuterium.
I collected some beam current numbers via my Keithley 610 electrometer configured as an ammeter in the target power supply ground return. The beam current as a function of extraction voltage (with RF forward power held constant) is on top, while the beam current as a function of RF forward power (with extraction voltage held constant) is on bottom. (How much of the registered beam current is due to backstreaming electrons? I don't know, but the setup is designed in some simple ways to cut down on the secondary electron current off the target. It is made from graphite, not a very good secondary electron emitter. It has a 30-degree cone and a 1/4" drill hole along its centerline where the beam strikes, geometrically restricting the escape of electrons.) The anode is at 9 kV throughout.
Hard to know what conclusions are really suggested by the measurements here. The current-versus-voltage curve is upwardly monotonic like the Child-Langmuir law predicts it should be, but it either underperforms the V^(3/2) proportionality of the Child-Langmuir law at low voltages or overperforms at high voltages. Whatever the case, this trend clearly suggests that I need to kick the extraction sauce up a notch. The feedthrough for it is rated 5 kV, so that's probably my ceiling without resorting to a potted connection. The RF power curve has a bump in it at about 50W forward power. This probably indicates a new type of discharge mode becoming established that is a better source of ions. When the source is run in deuterium, beam current should go up by at least a factor of three (again a prediction of the Child-Langmuir law). I'm predicting a yield of 2 mA deuterons at 75 W / 5 kV extraction.
The photos both show operation at 75 W RF, 3 kV extraction, and about 300 uA. The beam is easy to see. Base pressure is about 0.1 mtorr and the gas valve is barely cracked. I really cannot do any better than that with the pumping system I have.
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2008-14-09 04:09 RF ion source sees first light 
(Carl Willis) [Latest: 2009-09-01 17:18]
2008-16-09 02:34 Re: RF ion source sees first light (DATA)