RF Power Supply for ICP Purposes

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
Erik smith
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RF Power Supply for ICP Purposes

Post by Erik smith » Tue Dec 26, 2017 9:51 pm

I have seen multiple members on this forum use professional 13.56 MHz RF power supplies for their ion sources. However since these supplies are very expensive and difficult to transport, I'm looking to see if their is an easier way to generate an inductively coupled plasma. Recently I have been seeing a lot of designs posted by several radio enthusiasts for multi-kilowatt RF class AB amplifiers that utilize extremely rugged power transistors. I've also seen some users like Werner Engle and John Futter briefly discuss building class AB RF supplies for use in their ion sources. Since there is very little information on these supplies for ICP purposes I was wondering if these have been used, or could be used to generate an inductively coupled plasma?

Homemade RF Amplifier
Image
http://www.qsl.net/kf8od/ldmos.html

Purchasable RF Amplifier
Image
https://eb104.ru/internet-magazin-shiro ... for-blf578

Werenr Engel RF Supply
Image
viewtopic.php?f=12&t=11456

ian_krase
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Re: RF Power Supply for ICP Purposes

Post by ian_krase » Wed Dec 27, 2017 3:32 am

Thomas Rapp has (in german) this tube based ICP source, though it looks like it needs changes to put it in an ISM band.

Erik smith
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Re: RF Power Supply for ICP Purposes

Post by Erik smith » Wed Dec 27, 2017 3:58 am

Ian, I have seen that post by Thomas. However, I like the idea of using one of these RF amplifiers since the frequency can be chosen manually and the power level can be adjusted. I just simply want to know If these RF amplifiers could be used in ICP sources?

John Futter
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Re: RF Power Supply for ICP Purposes

Post by John Futter » Wed Dec 27, 2017 6:47 pm

Erik
Of course these can be used for an ICP ion source.
I do not know why you would want to use ICP (inductively coupled plasma) as it usually needs a high voltage RF kick to get it started.
Most accelerator based ion sources use CCP (Capacitively coupled Plasma) which is inherrently high voltage and self starting and yes the amplifiers pictured will do just fine.
more info at https://www.qrz.com/lookup and type in my callsign ZL2TUD

Erik smith
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Re: RF Power Supply for ICP Purposes

Post by Erik smith » Wed Dec 27, 2017 7:23 pm

John, thanks for the reply but before I invest $200 on the BLF578XR transistor and amplifier components, I found this little 100W amplifier for an extremely low price. I might try to see if I can generate an ICP with this amplifier. My only concern is that I dont know if the transistors can handle the inital high VSWR conditions.
Attachments
Rf amp3.JPG
Rf amp2.JPG
RF amp1.jpg

ian_krase
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Re: RF Power Supply for ICP Purposes

Post by ian_krase » Wed Dec 27, 2017 8:22 pm

Can you create a DC discharge through the chamber to start?

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Richard Hull
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Re: RF Power Supply for ICP Purposes

Post by Richard Hull » Wed Dec 27, 2017 10:53 pm

It is tough to beat an old fire bottle, glow FET, linear ham amplifier that can handle VSWR issues that might kill silly-con based stuff.

Blowing up silly-con is just part of the cost of using them in power circuits that can suffer great instablities or bursts of very bad behavior on the part of the load.

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.

Erik smith
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Re: RF Power Supply for ICP Purposes

Post by Erik smith » Thu Dec 28, 2017 12:22 am

Richard, here is a link to a supplier of the transistors used in the amplifier. Looking on other forums. They seem to be very hard to replace.
https://www.rfparts.com/rftransistors/t ... t9784.html

I have also seen multiple posts on how to modify cheap amplifiers found on eBay with extremely rugged transistors.
https://sm6vfz.wordpress.com/2015/10/06 ... at-144mhz/

But right now, I'm deciding whether to use the old ham radio amplifier for ICP generation or invest in the new, extremely rugged, LDMOS amplifiers.

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Re: RF Power Supply for ICP Purposes

Post by John Futter » Thu Dec 28, 2017 1:32 am

Erik
Make a 1dB attenuator to put on the output - you lose 20% of your output at the gain of not blowing the devices
This immediately means the VSWR can not go over 8.7:1
which should bew ok for that very old design Bipolar PA you have
The one I linked to before with the BLF188XR can run VSWR of 65:1 indefinately

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Re: RF Power Supply for ICP Purposes

Post by John Futter » Thu Dec 28, 2017 1:34 am

Erik
Make a 1dB attenuator to put on the output - you lose 20% of your output at the gain of not blowing the devices
This immediately means the VSWR can not go over 8.7:1 with a dead short or open on the output (the two worst possible cases)
which should be ok for that very old design Bipolar PA you have
The one I linked to before with the BLF188XR can run VSWR of 65:1 indefinately

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