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RF Power Supply for ICP Purposes

Posted: Tue Dec 26, 2017 4:51 pm
by Erik smith
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
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http://www.qsl.net/kf8od/ldmos.html

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

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

Re: RF Power Supply for ICP Purposes

Posted: Tue Dec 26, 2017 10:32 pm
by ian_krase
Thomas Rapp has (in german) this tube based ICP source, though it looks like it needs changes to put it in an ISM band.

Re: RF Power Supply for ICP Purposes

Posted: Tue Dec 26, 2017 10:58 pm
by Erik smith
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?

Re: RF Power Supply for ICP Purposes

Posted: Wed Dec 27, 2017 1:47 pm
by John Futter
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

Re: RF Power Supply for ICP Purposes

Posted: Wed Dec 27, 2017 2:23 pm
by Erik smith
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.

Re: RF Power Supply for ICP Purposes

Posted: Wed Dec 27, 2017 3:22 pm
by ian_krase
Can you create a DC discharge through the chamber to start?

Re: RF Power Supply for ICP Purposes

Posted: Wed Dec 27, 2017 5:53 pm
by Richard Hull
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

Re: RF Power Supply for ICP Purposes

Posted: Wed Dec 27, 2017 7:22 pm
by Erik smith
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.

Re: RF Power Supply for ICP Purposes

Posted: Wed Dec 27, 2017 8:32 pm
by John Futter
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

Re: RF Power Supply for ICP Purposes

Posted: Wed Dec 27, 2017 8:34 pm
by John Futter
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

Re: RF Power Supply for ICP Purposes

Posted: Thu Dec 28, 2017 12:02 am
by Erik smith
I have seen a lot of RF attenuators on ebay and Ali Express. My only concern is the very low VSWR (~1.2:1) rating for most of the 1dB attenuators widely availabel.

https://www.aliexpress.com/item/100W-N- ... 92558.html
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Re: RF Power Supply for ICP Purposes

Posted: Thu Dec 28, 2017 2:21 am
by ian_krase
Low VSWR is what you want, right?

Re: RF Power Supply for ICP Purposes

Posted: Thu Dec 28, 2017 12:47 pm
by Erik smith
Ian,
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)
8.71:1 indicates the maximum VSWR the amplifier can see with a 1db attenuator on the output. Here is more info on it
(http://www.rfcafe.com/references/electr ... uction.htm). But you are right about the desired VSWR. For maximum power transfer, you want a VSWR of 1:1. However since ICP sources have been known to be very unstable. This means that the VSWR can change. Since the 1dB attenuators listed online can only withstand a maximum VSWR of ~1.2:1, I might need to build my own. There are many designs for RF attenuators however since 1dB reduction means a 20W power loss when the amplifier is at its maximum output (100W), I need to find high power carbon resistors (low reactance) which is no easy task. Does anyone know if it would be a good idea to still use the attenuator listed online?

Re: RF Power Supply for ICP Purposes

Posted: Thu Dec 28, 2017 1:35 pm
by John Futter
Erik
That VSWR figure is for the attenuator it is not its with stand rating
ie the attenuator matches nearly 50 ohms resistive
more here from my web site
http://www.iel-rf.com/AttenuatorsDescription.html

all you need is a 1dB 25 watt dissipation attenuator