Lab Pictures 8

September, 2008; Room 102-A, Research II

       NCSU, Raleigh NC

Spent the month of September trying a likely antenna shield pattern, improving it, then applying the copper shields to all twenty antenna cores shown in Lab Pictures 7. By the end of the month all the antennas had shields, waiting for another coating of ceramic. The tips of four of the eight triangles forming the shield are not coated with ceramic, which allows current to flow from the -6kV outer grid to flow to these grounded tips.



Early cone shield

trial pattern, without external ceramic

Early shield

end view

Removing bad magnetron

Blew one up...

Bad mag

Everything is made to be replaced--I toast things

Trial of early shield

Other antennas unshielded, all the power goes out from the base as a result; note grid rings

Early shield mounted

Constructing base of shield

Used rivets to attach triangles to 1/16" copper disk

Me with trial antenna

Shield hoop

Wire required to hold triangles tight against ceramic and to connect ground at microwave frequencies, soldered to each triangle (it won't be getting hot)

Coated with ceramic

Using silica composite ceramic sheet that does not require heat curing

End view Mark II antenna

Inner tips of shield are bare to allow current from the grid to the tips

Mark II mounted for test

Close up mounted Mark II

First completed antenna ready to test: turns out this ceramic kicks up a lot of dust when in contact with plasma

Triangle stack

Getting ready to make the other 19 antennas

Shaping triangles to fit

Putting a bit of conical curve to the triangles

Shaping triangles

Took a long time!

Mounting shields

The white cones are the epoxy cores with the conical helix of copper wire inside, coated with the silica ceramic composite

Drilling for rivet holes

Used aluminum pop rivets; worried a bit about trapped gas; ideally the whole thing would be monolithic, cast, and fired with low-expansion metal

Riveting triangles to base