Pseudospark Switch Construction
Here is a drawing of my design for a first attempt at a pseudospark
switch. The vacuum chamber is made from a 3" length of 4" OD X 3.75"
ID polycarbonate (PC) tubing, capped with two 5" square X 1/2" thick PC
sheets. (Note: polycarbonate is not an ideal material for vacuum service,
being rather permeable to gasses.) Each end cap has a center hole
to accept the copper electrodes, a 1/4" deep X 4" OD X 3.75" ID groove
(made with a router and compass attachment) to accept the 4" OD PC tubing
and four 1/4" holes near each corner to accept threaded nylon rod (originally,
I had intended to assemble the vacuum chamber using o-ring seals, but the
grooves were not smooth enough to make a good seal). The inner (ground)
electrode is made from a 5" length of 1.125" OD X 0.995" ID copper (alloy
122) tubing (1" type K water tubing). The outer (high potential)
electrode is made from a 4" length of 1.375" OD X 1.245" ID copper (alloy
122) tubing (1 1/4" type K water tubing). Each electrode has four,
equally spaced, 1/2" long X 3/32" wide slots cut parallel to its long axis.
The trigger electrode is made from a 6" length of 1/8" OD tungsten rod,
insulated with a 5" length of 1/4" OD X 1/8" ID fused alumina (sapphire)
tubing and centered in the outer electrode with a 1/2" thick X 1.245" OD
X 1/4" ID PC disk. The inner electrode is capped with a 1/2" npt
to 1" water tubing copper adapter and 1/2" plug valve (Swagelok,
part number SS-8P6T2). The opposite end of the plug valve is fitted
with a 1/2" npt to NW25 vacuum flange adapter (Kurt-Lesker,
part number QF25XFNPT8) for connection to the vacuum
pump. Both electrodes are fitted with clamp-on shaft collars,
which are drilled and tapped to accept 3/8"-16 bolts (for electrical connections).
Except where noted, all materials are from McMaster-Carr
supply company.
This photo shows the fabricated parts, ready for assembly.
Picture of electrodes in place.
