30keV Deuteron Source

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
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Scott Moroch
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30keV Deuteron Source

Post by Scott Moroch » Fri Dec 06, 2019 3:35 am

I have been working on developing a Capacitively coupled ion source and Einzel lens for generating 30keV deuterons. Right now the source is being operated in DC discharge mode with just air. The anode is floating at 17kV and the cathode at 15kV. A chain of 400 volt zener diodes are used to self bias the cathode at 15kV, followed by a 2 MOhm resistor to ground (a technique discussed by John Futter on here numerous times).

For higher beam currents we will likely need to replace the 400 V zeners with 100 V or less to reduce power consumption. First test went very well today though and I would like to thank John for the advice on this topic.

More to come, as always.
Scott
Attachments
Test stand.jpg
Test stand without Einzel Lens
Lens.jpg
Einzel Lens (soda can for reference, it does not add to functionality)
Plasma.jpg
Ion Source in DC discharge.
Beam on Screen.jpeg
"In the middle of difficulty lies opportunity"
-Albert Einstein

ian_krase
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Re: 30keV Deuteron Source

Post by ian_krase » Fri Dec 06, 2019 5:28 am

I'm a bit unclear on how this very impressive system all goes together.

What's the white ceramic material?

Scott Moroch
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Re: 30keV Deuteron Source

Post by Scott Moroch » Fri Dec 06, 2019 7:31 pm

Ian,

The ceramic is a high voltage break, electrically isolating the ion source from ground and allowing it to float at 20kV. See the full CAD rendering with a circuit below. The voltage drop across the diodes allows for a DC plasma discharge, and the voltage drop across the resistor is the extraction voltage (~20 kV).

The ions are extracted through the capillary tube (inside the glass) which is differentially pumped to reduce back-streaming from the source to the beamline.

Scott
Attachments
Screenshot (488).png
Screenshot (488).png (110.38 KiB) Viewed 1126 times
"In the middle of difficulty lies opportunity"
-Albert Einstein

Roberto Ferrari
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Re: 30keV Deuteron Source

Post by Roberto Ferrari » Fri Dec 06, 2019 10:20 pm

Hi Scott
Really a beautiful setup.
What is that knob at the lower end of the glass tube?
Deuterium imput or one of the points for differential pumping you mentioned?

ian_krase
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Re: 30keV Deuteron Source

Post by ian_krase » Sat Dec 07, 2019 2:55 am

I meant the ceramic disk holding the middle element of the einzellense.

Scott Moroch
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Re: 30keV Deuteron Source

Post by Scott Moroch » Sat Dec 07, 2019 6:22 pm

Ian,

The ceramic on the Einzel Lens is Macor. The first and third electrodes of the lens are grounded and the middle is at a positive potential (400-1kV depending on desired focal length).

Scott
"In the middle of difficulty lies opportunity"
-Albert Einstein

Roberto Ferrari
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Re: 30keV Deuteron Source

Post by Roberto Ferrari » Tue Dec 10, 2019 9:21 pm

Hi Scott

Beside my earlier question, I have another one.
Einzel lens designs almost always have a gap of 0.1 D between lenses.
Why you gone further, enlarging the space between lenses? It is almost 0.5 D (being D the lens diameter)

Scott Moroch
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Re: 30keV Deuteron Source

Post by Scott Moroch » Wed Dec 11, 2019 12:42 am

Roberto,

To your first question: yes, the bottom of the glass tube is the gas inlet

Second question: Yes, I have read about those ratios. The spacing was increased for that photo to demonstrate variability. Ultimately the spacing will be based on a SIMION model I have built of the entire beam line. This simulation accurately models the specific geometry of the lens.

I will post that simulation when I finish with my final exams.

Scott
"In the middle of difficulty lies opportunity"
-Albert Einstein

Roberto Ferrari
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Re: 30keV Deuteron Source

Post by Roberto Ferrari » Wed Dec 11, 2019 3:53 pm

Understood!
Thanks

John Futter
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Re: 30keV Deuteron Source

Post by John Futter » Wed Dec 11, 2019 6:24 pm

Looking good Scott

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