DC-HVDC Converters for Sustaining Ion Pumps

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
Post Reply
RobertTubbs
Posts: 209
Joined: Thu Mar 05, 2009 6:49 pm
Real name:

DC-HVDC Converters for Sustaining Ion Pumps

Post by RobertTubbs » Thu Jan 31, 2013 8:16 am

It's been awhile since I posted, and by the looks of things around here I figured you folks could use something neat.

I needed to get an ion pump (some kind of ion diode pump, normal or standard I don't know which (or really care)) operating to sustain a guide while it sits around waiting for it's next life and was provided an EMCO E40 from my Mentor. Rather charming things really, a little blackbox proportional DC to HVDC converter. The E40 takes +0-15V and proportionally spits out +/-0 to 4000V to the tune of about 0.75mA max. The nominal +12V is supplied by a hacked up ATX supply from the local PC-Recycle shop, providing the +3,200 to make the ion pump happy.

I don't really dare butcher the thing since it's my only one, but perhaps one of these days I'll come back to this thread with a torn up one to show the insides of. Otherwise if someone else has a clean shot of the guts then that would make for some good oggling.

Included are afew shots of the mess and the PDF for the DC-HVDC Converter.

(1) The Brick
(2) Brick in the Box
(3) Durpy Homebrew "Stinger"
(4) Overall Mess

-RT
Attachments
.jpg
.jpg (7.53 KiB) Viewed 1733 times
.jpg
.jpg (5.34 KiB) Viewed 1733 times
.jpg
.jpg (7.18 KiB) Viewed 1733 times
.jpg
.jpg (7.42 KiB) Viewed 1733 times
emco.pdf
(259.41 KiB) Downloaded 112 times

User avatar
Richard Hull
Moderator
Posts: 12201
Joined: Fri Jun 15, 2001 1:44 pm
Real name: Richard Hull

Re: DC-HVDC Converters for Sustaining Ion Pumps

Post by Richard Hull » Thu Jan 31, 2013 4:25 pm

Hmm.... Ion pumps, normal ion pumps, are very high current devices. Currents of 1 amp are not uncommon, but the norm is more like ~3-5kv at 500ma for medium-small pumps. Even tiny ion pumps need over 100ma. Current more of less controls pumping speed if you plan on reduced current operation.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

RobertTubbs
Posts: 209
Joined: Thu Mar 05, 2009 6:49 pm
Real name:

Re: DC-HVDC Converters for Sustaining Ion Pumps

Post by RobertTubbs » Thu Jan 31, 2013 7:46 pm

Richard,

This little guy is drawing a matter of microamps at +3,200V.

RT

richnormand
Posts: 287
Joined: Sat Aug 27, 2005 12:30 pm
Real name: rich normand

Re: DC-HVDC Converters for Sustaining Ion Pumps

Post by richnormand » Sat Feb 02, 2013 12:16 am

Hi Robert,

Your PS may be OK, provided you are at a sufficiently low pressure when you start I think.
I run an old Varian triode (negative supply) ion pump 911-5030 20l/s off a NIM bin Bertan 4000V supply. Since the PS is only 5mA max I have to pump it to mid 10^-5 Torr prior to starting it. I used a current limiting resistor so that 5 mA is the max current it can draw under a short circuit to protect the PS. Starting at low pressures also very much increases the pump lifetime.

Make sure your PS is safe under a short circuit. Since my pump is old a titanium flake sometime will short the pump. As it was from e-bay it was full of oily crud bits and shorted. Probably why I got it cheap... I had to completely flush it with acetone and there was a flood of small Ti bits then used DI water and baked the whole thing at 300C for about three hours at atmosphere. Do NOT go at this temperature if the magnets are still attached. They will lose strenght at high temperatures and will not recuperate afterwards. I did all this to the "naked" pump and only introduced the magnets after cooling.

I then plugged it in to the vacuum system (turbo pump) and restarted the baking with a hot plate for another half day (NO magnets!!!) until the pressure stabilized. Looks like the Ti can absorb lots of water. It took a long time before I was able to close off the ion pump off the main system and self-pump to about 8.10^-8 (after putting the magnets back at room temperature). I also measured the field strength of the magnets at 1200 gauss in the pump gap. If you have access to a gaussmeter you might want to make sure they meet specs also. Pumping speed is directly related I think.

I use the current limit resistor dropped voltage to read the pump current and used the Varian specs sheet graph to infer the internal pressure. For a pressure at 10^-5 is about 10 mA and at 10^-7 is 30 uA, down to 10 uA at ultimate 5.10^8 Torr. Been going for about a month and it is great to keep the system clean between uses.

Hope that answers some of your questions.

John Futter
Posts: 1604
Joined: Thu Apr 22, 2004 2:29 am
Real name: John Futter
Contact:

Re: DC-HVDC Converters for Sustaining Ion Pumps

Post by John Futter » Sat Feb 02, 2013 4:25 am

Robert

all ion pumps use very few mA when finally down at vac

its the getting there that hurts. I have used systems with 10kV 2 amp supplies that feed 6 ion pumps and the supply is soggy so that the pumps do not get damaged ie 10 -4 vacuum 2 amps but 3-4kV 10 -9 millibar = 6uA.

So as long as you can evacuate to 10-4 to -6 millibar before you start you have a chance. The 10-4 end will need serious power 10-6 two orders of magnitude less

all for now

RobertTubbs
Posts: 209
Joined: Thu Mar 05, 2009 6:49 pm
Real name:

Re: DC-HVDC Converters for Sustaining Ion Pumps

Post by RobertTubbs » Sat Feb 02, 2013 7:35 am

Rich, John,

Very useful primers, thanks for the commentary. I'll review them when I bring the Therac down to vacuum.

For now, however, the ion pump in question is on a 6MeV Guide that has been at vacuum, RF baked/processed and with the ion pump happily chugging along for about a decade.

This just chronicled an easy fix for a PSU to keep it happy while it sits around until I find a home for it.

Thanks,
RT

Post Reply