Before fusion work began, I first made a small system which ran on air at low voltages. This allowed me to learn how to operate a system where the parameters were not as exacting and radiation and high voltage flashovers were much less of a problem.
The vacuum chamber is built around a 4" diameter pyrex oil cup glass. The ends of this cylinder are sealed with 6" diameter, 0.5" thick aluminum plates and flat neoprene seals. The outer grid diameter is about 3.5" in diameter, and the inner grid about 1.2". Both grids are constructed from 0.025" 304 stainless steel wire. The high voltage feedthrough is a modified sparkplug which is epoxied into a hole in the top plate. The chamber is connected to a direct-drive vacuum pump by a rather crude arrangement of copper pipe and rubber tubing.
The system is powered by a homebuilt HVDC supply. The supply is built from a 2.4 kV potential transformer and HV capacitors and diodes pulled from microwave ovens. Output voltage is varied by adjusting the input voltage to the transformer with a variac. When configured as a full-wave voltage doubler the maximum output was over 6 kV.
The entire setup can be seen in Fig. 1. Two shots of the system in operation are shown in Fig. 2 and Fig. 3. Although the vacuum system was a kludge of hardware store items, it would easily pump down to extinction of the glow discharge. Operating voltages of 0.5 - 6 kV were used, at currents of between 1 and 10 mA. The system served as an important learning tool before work was started on my second system, which was a much more complex and expensive stainless steel set-up.
| Fig. 1. View of my first system. The large black object behind the meters is a 2.4 kV potential transformer. The vacuum pump is farther to the right and not shown in the photograph. All the high voltage connections were made with alligator clips - certainly not a recommended practice! |
| Fig. 2. System operating at about 2.5 kV. Note the strong electron beam and bright central region. |
| Fig. 3. System operating at about 6 kV and a lower pressure than the previous photograph. The electron beam has faded away at this pressure. |