Lab Pictures 7

August 12, 2008; Room 102-A, Research II

       NCSU, Raleigh NC

With the assistance of Chris Lease (courtesy of the Research Opportunities for Undergraduates program), who helped during June and July, I've made new antenna designs to test. The old open coils (as seen in the background of this page) were copper wire coated with ceramic, and caused plasma inside the coils primarily with little outside. Thus the next step was to fill the coils; that was done at first with polyclay, which then had a coat of high-temperature silicone. This was very provisional and only done because it was cheap and easy to test the basic geometry.

   The silicone burned and the polyclay was not durable, but it did show that the main part of the discharge was at the base, highly undesirable. Next came three different patterns of aluminum foil to shield the outside and help make the plasma form all along the antenna. This was especially effective when the foil then was coated with ceramic, and when the foil was in the form of triangles.

    Next comes the Mark 2 antennas; 10 ga. copper wire embedded in epoxy, forming a cone (much less truncated than the previous helix), then coated in a silica composite ceramic. This also fires off at the base, but in this case the base does not burn as it is thick copper pipe and plate. Then I added copper triangles to extend the plasma along the antenna. This shield functions as a kind of balun; it helps ensure that the impedance of the antenna varies along its length, thus matching the environment somewhere at all times. I found that this initial triangle pattern works well but would be improved if extended very near to the tip, so now I'll take 4 of the 8 triangles off, replace them with bigger and longer ones, and try again. Finally after that's optimized I'll try coating the shield with ceramic and see if it makes enough difference to merit the bother and expense.




Mark 1 base damage

What happens when plasma hit the Mark 1 base...not pretty

Mk 1 base

closeup of carnage (smelled bad too)

Mark 1 trial

with the grid added and foil shielding (which didn't work)

Mark 2 coil

in plaster of paris mold; this attempt to use boron nitride for mold release was a FAILURE

Mark 1 pattern trial

aluminum foil and aluminum tape shielding patterns; the middle one worked best

first pour epoxy

had to cure a bit at a time (four pours) to prevent overheating

second pour epoxy

Chris sanding cones

me with the first bare Mark2 cone

Close-up of epoxy coil

Mark 1 antenna

with triangular aluminum tape shield, ceramic composite about to be applied

blown Mark 1 antenna

showing polyclay, copper wire

casting Mark 2 cones

PVC plug on right, making plaster cast; completed pour on left

South hemisphere test

with three patterns including ceramic coating along with just black silicone

casting Mark 2 antennas

I used vaseline for mold release

looking down into mold

new copper bases

machined ceramic fits into copper pipe; copper plate at base of the cone

Chris with epoxy cones

new epoxy cones

S hemisphere with grid and some antennas

copper bases on blocks

2x4 blocks are very handy to hold the antennas

coat of ceramic composite on copper base plate

Cross-section of blown Mark 1 antenna

drilling ceramic for 10 ga. wire

epoxy cones glued to ceramic and base

epoxy cones on bases

ceramic composite coating over epoxy

Cones at home in the oven

cured 12 hours at 140 degrees F, otherwise water still in there making the ceramic opaque to microwaves

Cones in the oven

The only thing I've baked since moving to this apartment in 2004

Cones set to test in S hemisphere

First test pattern for shield

unshielded cones fire at the base of the cone; needs shielding to match impedance and make plasma generation all along the cone

side view of first test shield

set up to test in S hemisphere

test cone in place

Still from video

1/2 Torr pressure, 1/500 sec shutter speed; the bright one is the trial with triangle shielding

Still from video

1 ms shutter speed, 480 mTorr pressure, showing more detail (see unshielded antennas for comparison)