🚀 go-pugleaf

A little more than a week ago, I related of the problems I had to get
a van de Graaff generator running. Things are much better now, and I
would like to compare its performance with others.

As suggested by Ron V. Parsons <parsons@sequent.com>, I replaced the
bottom PVC roller, with an aluminium one. That made the charging current
settle to about 2.5uA after a few seconds. I noticed however, that the
charging current was much higher initially, and that much charge was
left on the belt when it came down again. So I changed the top roller
for an aluminium one too. That did it. The current is now up to 9uA
and the thing starts spitting discharges all around about a second
after I switch it on. It works fine for both polarities.

The high voltage electrode is still the same aluminium foil covered
plastic ball, and it leaks corona discharges all over. In spite of
that, I now get the nice fat sparks I wanted. With a proper polished
metal ball, performance is likely to be far more impressive still.
I'm trying to find one...

I have a few more questions too:

Would some generator owners take the trouble to measure the charging
current of their van de Graaff? I.e. connect an Ampere meter between
ground and the high voltage electrode and then switch on. Not the other
way around: You might damage your meter.

Can anyone suggest a method to measure the output voltage? I do not
think suitable probes exist. The best I can get is a 40kV 1000MOhm
probe, which is clearly insufficient. I have considered using some
sort of Kelvin electrometre arrangement, but, one of the electrodes
being a ball, calibration is a problem. Yet I think that's the way to go.

So far, I get fat sparks from a polished 4cm diameter metal pipe over
a little more than 10cm. The more diffuse sparks from the pipe's end
easily exceed 50cm. You can make you own voltage estimates from that.

Jeroen Belleman
jeroen@dxcern.cern.ch
jeroen@cernvax.cern.ch