RF Magnetron Ion Source (A Carl Willis Clone)

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
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RF Magnetron Ion Source (A Carl Willis Clone)

Post by RobertTubbs » Thu Jan 31, 2013 9:38 am

This was my take on Carl's most recent RF Ion Source (seen here: viewtopic.php?f=12&t=5047#p32355 ), admittedly mine isn't quite as easy on the eyes but it does the job.

I started out the summer with a spare guide and ran through the math on calculating the guide-wavelength before chopping and drilling holes spaced 1/4 wavelengths apart. I added the same three stub tuner as well as the shorting sleeves to prevent too much leakage and found myself with a very nice source that could operate within a useful level with only one of the tuning screws about 1/4 of the way in. By using two MOTs, one for the filament and one for the HV driving the thing at much lower power was substantialy easier since maggies need that filament at 3V for the thermionic emission.

I had originally used a Pyrex test tube but that ultimately got a local hotspot from an arc and melted through, later switching to Quartz helped a bit but what seemed to have cured arcing off of the burrs was wrapping the tubing in plumbers teflon tape which is reasonably transparent to microwaves.

This was part of the eventual plan to get a little electrostatic linac going, when the Van De Graaff revealed it's sucky nature I built that ludicrous multiplier seen here: viewtopic.php?f=11&t=4915#p27753

Included are some pictures of the trainwreck and a video link to it operating:

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Doug Coulter
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Re: RF Magnetron Ion Source (A Carl Willis Clone)

Post by Doug Coulter » Sat Feb 02, 2013 12:00 am

Nice work! Are you running the usual microwave oven power (pulsed once per cycle) or a filtered DC there? I managed to get my own version of this working, different design, with ECR magnets yet just one microwave transformer, with pure DC. I just ran a variac on the MOT, and that was good enough, as I was getting close to 3v on the filament anyway with the variac at 89v indicated which is where the sweet spot was for operating mine CW.

I suppose one possible advantage of pulsed is that you should hear a correlation between the 60 hz pulse rate and any neutron (or other counter) output, and that the maggies will, yes, put out quite a lot more peak power in pulse mode than CW. That would make light-off easier, I suppose.

Once I get my ECR version lit off - takes maybe e-4 or so mbar in D, it'll run all the way down to below e-6 millibar. And of course, at more normal fusor pressures, it's not a problem ever.
I'm considering it for beam work, since it will run so low in pressure I won't need differential pumping.

Mine is discussed here on this thread:

and on my own forums here in much more detail:


It's a little simpler and more compact.
Why guess when you can know? Measure!

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