First light from near 180 degree, dual circumferential ion sources

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
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Rich Gorski
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Location: Illinois

First light from near 180 degree, dual circumferential ion sources

Post by Rich Gorski »

The photo below show the first light up of dual near 180 degree anode layer type sources energized at a D2 pressure of 1 micron. The two bright half circle ionization regions occur in the 0.125” gap between the two pole pieces which are 1/16” thick, low carbon steel bars bent into a 2.7" radius circular shape. These pole pieces are the cathode of the source and have a -1000V applied potential. The pole pieces are spaced about 0.13” from the wall of the vacuum chamber which also acts as the anode of the source at a potential of 0V. Thus the radial directed electric field and the vertical directed magnetic field form the crossed ExB fields needed for an anode layer ion source. The discharge current for each ion source was 60mA at -1000V and provided by a simple 60Hz, full wave, MOT based power supply driven by a variac. The planar ion beam can be seen as a pink fog protruding about one inch out from the ionization region.
360-1.jpg

A magnetic field of about 0.25T is created in the gap of the pole pieces by 6 pairs of N42 neodymium permanent magnets fixed the outside wall of the chamber. The magnetic field couples to the pole pieces through the 304 SS of the chamber.
360-2.jpg

Photo of the dual 180 degree ion sources with the glass top plate of the vacuum chamber removed. The curved carbon steel pole pieces can be easily seen.
360-3.jpg
Better view of a single near 180 degree ion source.
360-4.jpg
This is the first step in the development of a planar ring accelerator fusor using near 360 degree ion sources. If all goes well it should be capable of generating a full planar disk of ions that are converging at the center of the chamber, accelerated to fusion relevant velocities and having a total ion current near 100mA. At my planned operating potential of 30kV this will be at the limit of my HV PSU dumping some 3kW into the vacuum chamber. Things will get hot very quickly so I will need to severely limit the run time to only 1 minute or less. Just long enough to get a neutron flux count.

The next step in the build is to include the suppressor grids on the ion sources and then add the focus grid rings and accelerating grid rings.
JoeBallantyne
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Re: First light from near 180 degree, dual circumferential ion sources

Post by JoeBallantyne »

Very cool RIch! That last picture was particularly helpful in understanding the configuration of the ion source.

What diameter ISO vacuum nipple are you using? What material are you using for the top and bottom seals for the aluminum base and what appears to be a plexiglass lid?

Joe.
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Rich Gorski
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Real name: Rich Gorski
Location: Illinois

Re: First light from near 180 degree, dual circumferential ion sources

Post by Rich Gorski »

Thanks Joe,

The nipple is ISO160 size. The bottom seal is a standard ISO160 viton o-ring with centering ring. The bottom aluminum plate has been machined with a ISO160 o-ring grove. The top seal is a rectangular cross section, 1/4" thick viton o-ring with a ISO160 centering ring to keep the o-ring from getting sucked in. This top plate is 3/4" plate glass (not plexiglass). The 1/4" o-ring thickness is sufficient so there is no touch between the glass plate and the aluminum centering ring when compressed under vacuum. The glass plate will eventually be replaced by a proper aluminum top plate that contains the HV feed through. The long screws protruding radially through the pole pieces are 6-32 size and actually penetrate the wall of the ISO160 chamber. The 6-32 screws have small viton o-rings that seal on the outside of the SS chamber wall. Not a very good vacuum seal but sufficient to reach into the 10-5 Torr range. The 6-32 screws are electrically isolated from the pole pieces using ceramic standoffs.

Rich G.
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