Reply To: Bang or no bang

[TimS]

Clearly, if the knife edge on the new electrode plate works, then this problem is solved.

EDIT: I proposed bending the pins inward toward the anode to fix the asymmetry if it persists. After checking the photo in the article, I see that I misunderstood where it said that the problem pins were higher than the others. It looks like they are longer, not shorter (or more eroded). In the article, it says that they fire first because the tips are closer to the end of insulator, not the base as I had thought. In this case erosion of the pins would have gotten rid of the asymmetry even with straight pins, but that does not seem to have happened. The ends of the pins do not look eroded away to me. I wonder what feedback mechanism is making the asymmetry worse as more shots are fired? Perhaps the filament of current leading from the pin to the anode generates a force which pulls the pin further downward? Perhaps the asymmetry is caused by a tiny diffusion of some conductor from the plasma filament onto the surface of the insulator? Maybe a different composition of insulator would help.

If the problem persists with the knife edge, I wonder if there would be some way to add a slight inductance at the base of the main electrodes so that the current sheath could be created to the knife edge (or pins) all around before lifting off to the electrodes? Perhaps returning to pins and adding a slight inductance in each would slow the current rise through the first pins and allow other pins to become active? I should go back to my old basic electronics class and work out the inductance and timing of the pins as they are…

Although the previous poster’s suggestion of using ‘laser spark plugs’, completely removing the need for high speed synchronized switches and the knife edge or pins, sounds pretty cool.

I had initially thought that the negative side of the capacitors was switched into the cathode electrodes separately, instead of having the positive side of the capacitors switched and then tied together to the anode. That way the shot energy would always be divided evenly between the electrodes. I had thought the circuit worked this way when I saw all those switches, specifically in order to avoid this problem of asymmetric current through the electrodes. I spent some time yesterday confusedly looking at the focus fusion pictures on flickr (aren’t they cool!) trying to figure out why the problem occurs before I realized I had it backwards. I had been wondering how all those separate circuits were synchronized so precisely… A schematic of the focus fusion device would be great.