end-hall ion source

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
Jeroen Vriesman
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end-hall ion source

Post by Jeroen Vriesman » Sat Jan 02, 2016 9:11 pm

pictures of a home made end-hall ion source.

I'm trying to make a small ion source, the test model in the pictures doesn't have a gas feed.

The cathode wire is from a 12V 5W light bulb, emission is more than expected, when I run it at 10V, 0.3A it gives 5mA emission with the anode at 200V. (it can probably do more, but I didn't try it at 12V yet).
The ion current collector is at a negative potential of -500V...-6 kV, the ion current (3uA) doesn't depend much on the collector voltage and is constant at -U > 500V.

For the construction I used an aluminium anode, M2 inox bolts and nuts, a piece of Macor as insulator (thanks for the Macor, Roberto Ferrari! just enough left for one ion gun experiment...).
The reflector is a "dubbeltje", an old Dutch 10 cent coin which is ferromagnetic, it keeps the CoSm magnets in place.
With the magnets reversed it doesn't give any ion current, so I'm quite sure the ion current is really caused by the hall effect.

I have a few questions:

a) is 3uA ion current to be expected, or is it very low?
b) if it's too low, any ideas?
c) is it ok for the reflector ("het dubbeltje") to be magnetised?
Attachments
end_hall_construction.jpg
ion_current.jpg

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Steven Sesselmann
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Re: end-hall ion source

Post by Steven Sesselmann » Sat Jan 02, 2016 10:25 pm

Jeroen,

This looks nice, do you have a section diagram of the ion source?

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG

Roberto Ferrari
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Re: end-hall ion source

Post by Roberto Ferrari » Sat Jan 02, 2016 10:51 pm

Hi Jeroen

Glad to learn the fate of that Macor slab.
Super nice set up!
It is evident you invested all your Dutch coins...
Good luck and a great Year!
Roberto

Jeroen Vriesman
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Re: end-hall ion source

Post by Jeroen Vriesman » Sun Jan 03, 2016 11:52 am

Steve,

quick sketch attached. (the real design will be drawn with medusa4, this is just a test model)

The first ion source I tried was a doughnut shaped anode with a doughnut shaped CoSm magnet, and the cathode in the hole. That didn't work, emission was ok, but when the negative voltage was applied to the collector, al electrons were pushed through the hole an emission current diminished, no ions. That is the reason for the reflector in the end-hall design, it will get just enough negative charge to make the electrons got to the anode, independent of the external negative potential on the collector.
The next thing I tried was simply a cathode and an anode, with the emission current passing through a magnetic field (perpendicular to the line cathode-anode), the idea was that the hall effect would create a charge separation and ions could be collected at one side perpendicular to both the magnetic field and the cathode-anode current.
That didn't work either, it did something, but the strong magnetic field created so much more path-length for the electrons between the cathode and the anode that a very high voltage was needed to get some emission current, at 350V there were sparks between the magnets and the anode and the cathode... some ions, but hard to measure.

But the end-hall design works, the limit of my current test model seems to be about 8uA ion current when the emission is 10mA and the anode is at 300V. The improvements I have in mind:

a) more emission current, might need anode cooling
b) gas feed
c) closing the magnetic circuit so that the gap is just between the reflector and the edge of the anode (looking a bit more like the magnetic field used in a hall thruster)
d) any other ideas from people here?

The goal is about 100uA ion current, but at least 50uA is needed to use it for my other experiments.
Attachments
end_hall_sketch.gif

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Werner Engel
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Re: end-hall ion source

Post by Werner Engel » Wed Jan 06, 2016 12:19 pm

Hi Jeroen!

Did you already see the seminars and handouts of UNI Frankfurt regarding Ion-Sources?
http://acc.physik.uni-frankfurt.de/vorlesung/WS1112/
I recently visited a university lecture about accelerator physics here in Vienna. The handout there was not so much focusing on ion sources but there are some usefull links to be found at the end of the skriptum: http://tulectures.web.cern.ch/TULECTURE ... 040901.pdf

Two learnings I had:
1) Ion sources are “black magic”
2) It’s all about “focusing the beam”

Have fun reading!
I’m also in the design process for a deuteron source, but I think I will use the HF approach using 13,56 MHz and a pyrex glas tube.

BR,
Werner

Jeroen Vriesman
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Re: end-hall ion source

Post by Jeroen Vriesman » Wed Jan 06, 2016 2:12 pm

Thanks Werner,

it's a lot of information...

For as far as I can see now, my ion source is very inefficient, from what I found the ion current of an end-hall ion source should be al least 0.2 x cathode emission current at 300V anode voltage. In my case it's about 0.001 x cathode emission.
But most of the data is for at least 1A of cathode-anode current, while I'm working with 10mA, I didn't find any examples of "milliamp range end-hall ion sources".

I think the inefficiency in mainly caused by not having a magnetic circuit. I hope to finish one with a closed magnetic circuit today, this will make the magnetic field at the anode about 100 times stronger.

What do you mean by "black magic"?

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Werner Engel
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Re: end-hall ion source

Post by Werner Engel » Wed Jan 06, 2016 4:28 pm

"Black Magic" means, that the calculated numbers may be up to 75% away from real data, when it comes to theory and real measurement at ion sources.
Only very few people at CERN can handle and adjust the ion sources in the right way.

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Re: end-hall ion source

Post by Andrew Seltzman » Wed Jan 06, 2016 6:51 pm

Here's a fantastic reference on hall current / anode layer ion sources

http://www.wiley-vch.de/books/sample/3527410295_c01.pdf
Andrew Seltzman
www.rtftechnologies.org

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Richard Hull
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Re: end-hall ion source

Post by Richard Hull » Fri Jan 08, 2016 8:35 am

In the end, in real science experiment, certain apparatus are often of a nature that they approach black magic operation. Often, only a few people skilled in the art of construction of specific devices and their critical needs and setup to warrant a desired operational performance can make the difference in an outcome of an experiment. We often call them by the crude term, "technicians". Such super specialists are so indrawn to a specific skill set and limited but highly focused knowledge base, often possesed of capabilities hard won through experience that they seem to perform magic that no one else can summon forth. They are not really technicians nor are they magicians, they are artisans within science and technology. As the theoretical physicist cannot move forth on a solid base without the experimental physicist, so the experimental physicist cannot move forth without a cadre of these highly focused artisans of design and operational experience.

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.

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Re: end-hall ion source

Post by Jerry Biehler » Sat Jan 09, 2016 10:29 am

I was looking at building a ion source for my deposition system to do Ion Assisted E-Beam and was never able to find a source of magnetically permeable stainless tubing to make the housing out of to complete the magnetic circuit. Steel is bad enough in a chamber and it gets worse since I may need to run oxygen plasma. One option is get some magnetically permeable stainless sheet and roll it into a cylinder with a slip roll.

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