I was astonished when I started up PADEX this morning. Suddenly, it was very hard to get a plasma, and I couldn't match above 80 Watts input power - which is not too good considering I want to go to 500 Watts now and maybe beyond eventually.
I fiddled around with the matchbox, installed another coupling capacitor - nothing. I had a good look at the RF signal on the 'scope, and there I noticed strange peaks, like you would get when there is arcing. So I shut off the lights, thinking that maybe there were some tiny sparks in a corner of the reactor which I couldn't see with the lights on.
I saw sparks alright, but from below the experiment. PADEX has been in use in one form or the other since the 80s, and the cabling is... suboptimal. I had avoided changing the cabling, because it involves taking everything apart again, and is a hassle, and it worked. Well, up to now. The RF power line goes through an old aluminium box that is not in use anymore, and when I opened the box I was greeted by a cloud of smoke that electrical elements use to indicate their displeasure.
It took me the whole day, but now it's fixed.
1 week ago