A new ion source

Ways to make charged particles you can tug on with an E field.

A new ion source

Postby johnf » Mon Jul 04, 2011 5:07 am

Hey guys
been playing with a new ion source over the last few days
details will follow
managed to get 10mA of ion current out of it over several hours with a nice warm spot appearing on the chamber wall we were testing it in.
In this case a N+ or N2+ not sure of it yet until we do an RBS of the result into Al foil.
We are limited at this stage because of the self bias regime using KE1.5 400A CE diodes (5 in the string)to give 2kV to give the arc in the source

I have ordered KE 1.5 100A (20 in the string)diodes so that I can go to 40mA without the diodes unsoldering themselves while running.
So far I have been able to use 12kV from the supply @ 10mA, so thats 2kV drop for the arc and 10kV for acceleration so 10kV X 10mA gives 100 watts of ion current
Yeh hah!!!

watch this space!!
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Re: A new ion source

Postby Starfire » Mon Jul 04, 2011 3:38 pm

Way to go John! congrats :P - don't burn your fingers.
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Re: A new ion source

Postby Doug Coulter » Tue Jul 05, 2011 11:00 am

Yeah, that sounds pretty exciting, and on a topic I've got a great interest in just now. What's the pressure you're running to get this? Differential pumping?
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: A new ion source

Postby johnf » Tue Jul 05, 2011 2:42 pm

Pressure in chamber = 2 x 10 to the minus 4 millibar very little differential pumping due to the design of the source.
Source has run several days now with no noticeable damage. The source is cooled by a water circuit that does load the HV supply to around 0.5 mA @ 10kV due to using tap water ---conductivity issues.
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Re: A new ion source

Postby Doug Coulter » Tue Jul 05, 2011 3:40 pm

I'll be watching this space for details when you can put them up. Just so happens I'm building a beam device and haven't done that part yet...
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Re: A new ion source

Postby johnf » Sat Jul 09, 2011 3:26 am

Ok now at 250watts of ion current 25mA 10kV acceleration

Had to stop, some smoke problems external to the experiment and although the ion source has a water cooling circuit to a car radiator we had to invoke the radiator fan (here read a small 4 cylinder car radiator with 12 volt fan attached) to keep things cool.

specifics scant @ the moment IP issues to be sorted out
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Re: A new ion source

Postby Doug Coulter » Sat Jul 09, 2011 12:27 pm

How's the lifetime looking on this? Almost sounds like a duoplasmatron, which kinda ate itself (sputtering) due to using a huge amount of power in the basic arc (and needing water cooling).
You might want to check our library on ion sources for any prior art -- a heck of a lot of stuff has been tried and published. Not much of it makes me real happy for my application however. The uWave ECR source is nice, but not high current in the existing design due to the magnetic pinch where the ions would like to come out -- but it lasts "forever" -- I got maybe 1000 hours last time before taking it apart for other reasons. The issue for me putting it up at a HV terminal is how much raw power I need to get floated up there to run it - it's not real power efficient. In my app, I don't need a boat load of current -- just "enough". Since I'm going for super fine focus, I can't have too much space charge in the beam, or the focal lengths required are just too short to make the thing. A few uA tops. I'd prefer monatomic ions of course for this, and that's the hard one I think so far -- I don't want to have to select them out post acceleration. The uWave source scores on that fine, compared to most others but....has its own issues -- takes a couple hundred watts to run it, most of which winds up as heat in the magnetron (a better place than in the vacuum), but...

In my case, I'm trying to make something that's going to wind up looking like a miniature version of your implantation beamline + spin-flip trickery, times two -- with the emphasis on "miniature" and "focus". Pretty much all of the rest will be about the same (but smaller) -- physics is physics and what's practical and reliable doesn't vary much just because my ions are fusible.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: A new ion source

Postby johnf » Fri Nov 22, 2013 4:25 am

Okay
I haven't posted for a while
things are moving again
My STR series 150kV supply has arrived and I had to run a new 55mm crossectional area three phase cable down to the end of the lab (50m) where I'm setting up so I now have plenty of power. The STR is a Spellman unit rated at 6kW output ie 150kV @ 40mA.
Today I started conditioning the system but the ion source struck on the residuals in the chamber, pressure 3 x 10 to the minus 7 Torr giving around 0.6mA of ion current and a few hundred milli-rem of x-rays @50kV.
I now have to lock down the lab for radiation safety, invoke the lead sheild around the terminal end of the test setup and reduce the self bias chain voltage to stop the source running at these low voltages and pressures.
The STR supply has an ethernet port and i haven't checked yet but I hope to remote control it from my office so I do not get a sun tan

pics will follow soon
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Re: A new ion source

Postby Doug Coulter » Fri Nov 22, 2013 11:34 am

Wow, I'm not sure if even the microwave ECR source will strike that low, though it will go pretty darn low - e-6 mbar no problem, for example, once lit. But I always lit it off at higher pressure, say in the e-3 mbar range or above, then pumped down.
150kv isn't that hard to shield - fairly thin lead sheet handles it well, I'd have to look it up again, but someplace I have the guide radiologists use, and it'd be something like 1/8" or a little more, not too hard to put on (it solders easily if you need to make a bunch of odd shaped bits to cover your stuff - cuts with scissors). Wow, 6kw? Gee, when we use more than 1kw we have things melting here, and that's without anything like a fine "beam" - as you saw.

I guess I'd better get into cooling more. The new supply is many kw (we don't know how many, but the original rectifiers were 100kv at 300 ma) will destroy my tank, otherwise.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: A new ion source

Postby Starfire » Fri Nov 22, 2013 6:05 pm

look forward to the pic's John - and avoid the sun tan :lol:
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