Lab Pictures 11

early March to June 1, 2009;

       NCSU, Raleigh and TUNL, Duke, Durham NC

The main challenge now is getting low enough pressure. The antennas included composite ceramic with many gas pockets, resulting in totally unacceptable outgassing and poor vacuum. I took the antennas home to NCSU, stripped them down, and cast them in solid slow-curing epoxy. This filled up much of the remaining voids and sealed off any remaining gas pockets behind thick plastic. (Ideally the antennas would be made of low-expansion metal like Invar, encased in solid baked ceramic.)

To protect the surface against flashes of plasma, I coated the antennas with BN paint. However adhesion was spotty and after some minor use, several antennas showed flaking. I left fixing that until later.

I moved the reactor to a small adjoining room since access to the shielded target room is sometimes interrupted for days at a time. Here I checked for leaks. The homemade windows were a problem, so I put in flanges and one has a store-bought window that works well. Eventually I got down to as low as 30 mTorr and could run a turbo pump; however I accidentally allowed the pressure to go up unexpectedly while running the turbo which damaged its power supply. A replacement turbo didn't work so well...



Antennas in carrying bag

Going back to NCSU for major overhaul

NH gear

Showing extra thermocouple pressure gauge, turbo pump

Stripping antennas

The antenna ceramic was outgassing; I took them home to NCSU, tore off the exterior and prepped for dipping in epoxy

Removing ceramic

which was an expensive composite

Spreading the tip

had to get under the shield at the tip

Gluing shield tips

Put in 1/8 inch PVC spacers to keep the distance correct, at the tips and also at the bases to fit the epoxy mold

Close up PVC spacers, tip

Shield tip

Making plaster molds

For casting the antennas into solid epoxy, I made plaster molds, liberally coatin inside with vaseline, from traffic cones

Casting antennas

Used slow cure epoxy in four pours each to keep from overheating

Antennas ready to cast

Gluing tips

had to keep them in place

BN first coat

After pulling the antennas I gave them BN paint, which ultimately did not work well, peeling in many places

Fresh out of mold

Later antennas in an ideal future would be of low-expansion metal cast in solid ceramic and fired

Tip of new cast antenna

you can just see the inner coil

Base of cast antenna

All these pop rivets are now solidly sealed (after much bubbling)

Side view cast antenna

1/8 thick coating over shields

Side view cast antenna

With the Inventor's thumb

Close up tip

showing inner coil, kinda cool

Another close-up of tip

BN first coat

Unpainted and painted

Bag painted antennas

Close up painted tip

After removing BN paint from brass electrodes; need to have current from grid land here

Mounted N. Hemisphere

With BN coated antennas

N. Hemisphere with antennas

NH with antennas

BN peeling after firing

After some use, several antennas showed peeling off the plastic

Close-up peeling BN

Window replacement

I had originally had home-made windows; replaced with a custom aluminum flange epoxied into the window holes

External window flange

The windows mate with KF-40 flanges as you see here

Flange on SH

One on each hemisphere

Window o-ring

Window port NH

with protective tape over the window

Complete window

Worked much better, allowed lower pressures; the SH leaked some but plugged with Q putty

New KF25 adapter port SH

Can switch these; only bought one window ($$!) so one port is a new access, very handy

Laser room, TUNL

Put the reactor in here for leak chasing (see helium tank and white leak chaser gear)

John Dunham chasing leaks

John helped a great deal during my stay at TUNL

Leak chasing NH

Got down to 30 mTorr! Ten times better than before