Need pro comments before building ICP

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
steve_rb
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Need pro comments before building ICP

Post by steve_rb » Wed Jan 13, 2010 7:30 am

Everything is now ready (RF, HV, Vac, ...) but before get my hands dirthy and starting my first ICP experience I want to ask for proffesional comments not to damage myself or equipments and get hassle free results. The subject is building my first ICP ion source with cylindrical chamber with an ion extraction aperture.

1- 13.56 MHZ RF via maching network (variable power) will feed the 3 turn copper antenna (3cm long X 2cm diameter) with water running inside the antenna.

2- Plasma chamber will be cylindrical made of steel (10 cm long X 6cm diameter)
3- First chamber will be evacuated to 10-7 torr
4-Then needle valve will be opened leting H2 gas slowly flows inside the chamber till 10-3 torr
5- turn on RF and see if ignition happens. If not use pre installed (gas stove type or a spart plug ) ignitor to help ignition start
6- watch return RF power on Bird 43 power meter and minimize it by adjusting the capacitor
7- obtaine stable plasma condition by playing with the capacitor and run it for a few minutes and check beam sputtering effect on the copper target installed in about 6cm from the exit hole.
8- cross fingers and hope for fist time stable plasma condition

post any advice or comment you may have

Chris Seyfert
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Re: Need pro comments before building ICP

Post by Chris Seyfert » Wed Jan 13, 2010 2:45 pm

Steve,

Am I correct in that your RF antenna will be wound around a steel vacuum chamber? If so, I am afraid it will not work. The steel will shield the RF and you will not get any inductive coupling to the inside - instead, you will just heat the steel tube wall.

This is why most RF ion sources (Carl Willis', for example) have quartz or pyrex glass tubes under the antenna.

Some more details on your source would be welcome.

myID
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Re: Need pro comments before building ICP

Post by myID » Wed Jan 13, 2010 7:33 pm

Hi-

as Chris already pointed out- more details on the construction would be fine.
My first thought also was: will not work with coil outside a steel chamber..
Or is the coil in the chamber? Otherwise you will need a (quartz) glass tube to contain the plasma.

Greets

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Carl Willis
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Re: Need pro comments before building ICP

Post by Carl Willis » Wed Jan 13, 2010 8:30 pm

Steve,

The only concern that comes to mind in general would be about protecting your RF supply. Maybe you have that issue covered. If not though, I suggest putting a long length of lossy coax between it and your load. The losses go up with the VSWR, and just a few dB of loss will help even out the load presented to the generator.

Like your other respondents, much depends on the specifics of your construction and it's hard to offer advice without a fuller understanding of what you have. I doubt there is likely to be any immediate or significant damage from just jumping right in and trying it, no matter how it is configured.

-Carl
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Dustinit
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Re: Need pro comments before building ICP

Post by Dustinit » Wed Jan 13, 2010 10:49 pm

I also assumed the coil was outside the steel but then I read the dimensions.
Now I assume the coil is immersed in the plasma. If you are water cooling the coil then I guess you intend to pump some serious power into it then Carls words are sage. I would guess the plasma will strike in the single digit watts. Immersion of the coil in the plasma may sputter the coil itself as plasma may occur between turns in the electric field. Last thing you want is to etch through the tubing wall releasing water into the vacuum but I like the "suck it and see" approach.
I'm sure everyone would appreciate some eye candy to get a handle on your setup.
Dustin

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Chris Bradley
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Re: Need pro comments before building ICP

Post by Chris Bradley » Wed Jan 13, 2010 11:44 pm

Roman Radtke wrote:
> as Chris already pointed out- more details on the construction would be fine.
> My first thought also was: will not work with coil outside a steel chamber..
> Or is the coil in the chamber? Otherwise you will need a (quartz) glass tube to contain the plasma.

Evidently inside, note the clues:

steve robinson wrote:
> 1- 13.56 MHZ RF via maching network (variable power) will feed the 3 turn copper antenna (3cm long X 2cm diameter)
> 2- Plasma chamber will be cylindrical made of steel (10 cm long X 6cm diameter)

steve_rb
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Re: Need pro comments before building ICP

Post by steve_rb » Sat Jan 16, 2010 8:53 am

As Chris said Coil is inside. I know it will sputtered but for know I want it to work and later I am planing to cover the coil with something like quartz to prevent coil damage. At the moment I have following concerns:

1. Dimensions are all what I have gussed and I haven't done any calculations and I need confirmation/advice on dimensions?
Chamber: 10(L)X6(D)?
Target distance : 6cm for 100-120 Kv target negative voltage?

2. Procedure I described are from my readings. I need comment on starting procedure?

3.Carl said it is better to use lossy coax for RF protection. I guss this should be between RF and impedance matching box. What lenght of the cable should I use?

RF generator is ENI-OEM28 which is 0 - 2.5 Kw

Steve

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Doug Coulter
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Re: Need pro comments before building ICP

Post by Doug Coulter » Sun Jan 17, 2010 7:53 pm

Sounds like you've determined what you're going to do regardless of any comments.

I find this

viewtopic.php?f=12&t=5022#p32330

works really well for the amount of monatomic ions I happen to need for what I'm doing. Maybe not if you're wanting a really huge amount of them by comparison. It solves the sputtering and other problems nicely, though, it's very reliable and trouble free compared to all others I've tried.

What are you doing that needs kilowatt amounts? Could be of interest here.
Why guess when you can know? Measure!

steve_rb
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Re: Need pro comments before building ICP

Post by steve_rb » Mon Jan 18, 2010 4:41 am

I haven't planned to use kilowatts I just was lucky to find some nice HV and RF (0-3Kw) for very low price about 6 month ago and din't hesitate to buy them. What I am planning to do is an interesting device I found (viewtopic.php?f=6&t=3003#p12513) and I am seriously looking at it. It is different with what I want to do but since it is simple and easy to build it can give a lot of experience to one like me with almost no practical experience on fusor. Anyone willing to participate is welcome comment. I will need a lot of advice to make this successful, specially in terms of calculations I may need since I am not good at all in theory and calculations.

Steve

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Re: Need pro comments before building ICP

Post by John Futter » Mon Jan 18, 2010 6:20 am

Steve
I would suggest building one of Carl's ion sources first. It has the benefit of being able to see what is going on with all bits more or less readily accesable.
Gas pressure is proportional to watts input --so for the ten to the minus four millibar range 20 -100 watts should be plenty. Going this path first and getting a feeling for what happens will help when you make your enclosed one. For RF the air and vacuum are the same so why not keep the RF outside of the plasma tube.
You have enough Rf power there to ionise a difficult gas like argon in air --and yes this does take a kilowatt or two and needs an ignitor to get it going.

For what you are doing you do not need an ignitor just vary one of three things
gas pressure
RF drive
mag field for plasma confinement

and the source should strike
if it doesn't--- vary any two of the above and it should go

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