RF excited ion sources

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
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John Futter
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RF excited ion sources

Post by John Futter » Tue May 23, 2017 7:15 pm

This is answer some questions from Werner
"@John: You are right! But I did not use the controlling boards. The reason for choosing the BLF188XR was its robustness versus Price. The right device for a plasma generator! Are you also going to use it for this purpose - or just for ham?
I just read that you are very good in designing RF devices: I still do not know how to design the antenna for the plasma. My first idea was just trying to use a copper pipe with 14 turns and give it a try - using the tuner. I also thought about calculating a kind of resonance frequency resulting out of the geometry – but did not succeed. Next try was to use a spectrum analyzer with a VSWR bridge to measure the resonance frequency - did not work. What do you think will be the right way to focus on – from your experience?

BR,
Werner"

Werner looking at your coil it has too many turns about 4 -6 turns is normal. Also ICP systems usually make the coil from copper pipe that contains cooling fluid as the circulating current in the coil is hundreds of RF amps
No you cannot wind the coil on a copper pipe as the pipe acts as a shorted turn which will reduce your circuit Q to zero or like in ordinary transformer speak a shorted turn.
you can also think of using CCP instead of ICP. ICP generally is harder to get the plasma to strike where with capacitivly coupled plasma it lights the plasma staight away.
CCP and ICP ionize through different mechanisms the CCP works with the electric field and the ICP works on the magnetic field component of the electromagnetic wave.
The amplifier i'm making will be used for ham and rf ion source experiments @ work. There is now a new fet the MRF1K8 that is a drop in replacement for the BLF188XR which takes you to 1800 watt if you raise the VDD to 65 volts you can use the W6PQL boards as they are.
Of course you can get further improvement in your ion current by also using a permanent or solenoid coil magnet to help squeeze the plasma into a more concentrated state.

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Werner Engel
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Re: RF excited ion sources

Post by Werner Engel » Wed May 24, 2017 7:07 pm

John, I did use a pipe as antenna as I expected it to heat up – I already prepared an active cooling device with none conductive distilled water for this purpose. And I will change it to 4-6 turns – thanks to your suggestion.
As you see on the picture I did wind up the coil around a glas-pipe.
I think I will also stick to ICP, as it is easy to build (I found a nice picture of both methodes and attached it)
Changing the FET is not easy so I will try to stick with the BLF188XR based SSPA. I also thought about adding two magnets but did not find the right one yet. Maybe I will construct them out of several small ones. That’s the way how they do it at some of the Ion-Sources at CERN.

And what about my ideas regarding the spectrum analyzer? What do you think about this way to find the right geometry of the coil?
Linac 4 Ion Source Pres-IS-Review.pdf
Some Pictures of the Ion-Source of the new LINAC. The old one was a DuoPlasmatron.
(3.49 MiB) Downloaded 45 times
Attachments
ICP CCP difference.PNG

John Futter
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Re: RF excited ion sources

Post by John Futter » Thu May 25, 2017 7:02 pm

Normally you would use your vswr bridge to monitor the reflected power after tuning your matching unit.
no match means this is not the right frequency.
ICP is done commercialy at the industrial rf freqs (ISM Band) of 13.xx and 27.xxMHz
this is in case of leakage.
CCP is anywhere from 50MHz to 2400MHz
The biggest of these I have worked with is a 915MHz 25kW unit

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Werner Engel
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Re: RF excited ion sources

Post by Werner Engel » Sun Jun 04, 2017 8:55 am

OK - I see! Thanks!
As I'm using 13,56 MHz, so I think it will be ICP.
Within the next weeks I will be visiting http://isotopenforschung.univie.ac.at/en/vera/ and they have a lot of ion sources there.
I will have a special look at how they constructed them.

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Werner Engel
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Re: RF excited ion sources

Post by Werner Engel » Sun Jun 18, 2017 3:20 pm

Here are some of the ion source relevant pics I made at VERA.
Unfortunatly it was not an RF source.
Attachments
Tandem Pelletron Accellerator 3 MeV.jpg
Outside of the first accellerating cavity.jpg
IMG_6239.jpg
IMG_6238.jpg
Cs sputtering Ion Source.jpg

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Re: RF excited ion sources

Post by John Futter » Sun Jun 18, 2017 7:06 pm

Werner
Negative ion ceasium ion sources are not rf driven as you say
so why post these pics here
we have the exact same 40 sample NEC ion source on our NEC XCAMS C14, Be11, and Al27 dating accelerator

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