Reply To: turn heat into electricity

[asymmetric_implosion]

Sorry to hear the insulator went. I guess it will be 4-8 wks before more data is taken while the insulator is made unless you have a better supplier than I do. I use the hat insulator design as well.

Only one material that I know of has better properties for a plasma focus insulator than alumina and it is far from cheap; diamond. Many other materials have been tried but each has a problem. If you are looking for a cheap solution that works OK, I suggest alumina silicate. I’ve use it in my PF as a cheap alternative to alumina when I’m trying something new. Alumina silicate is easy to machine but it is not as mechanically robust as alumina. You need to be careful about weight distribution on the disk part of the hat. I’ve broken more insulators installing them than by running the machine when using alumina silicate. Other materials that might be useful are zirconia but last I checked no one could make it in the shape you need. Diamond has the same problem. I know people love glass and quartz as an insulator but I’ve never had a good experience with either. Quartz needs to be heat treated properly and no one has gotten it right for me. Glass works OK but more fragile and more expensive than alumina silicate. I can suggest a vendor but again, some change to the cathode might be required because glass cannot be made with a tight corner at the disk-cylinder interface and be strong.

My best suggestion is thicken the alumina wall where it is breaking. I know it’s a pain for the pulse power design but it does help. I’ve run a single alumina insulator at 0.25 MA for over 25,000 shots from ~5000 shots by increasing the wall thickness by 20% in the vertical section of the hat. If you are breaking on the flat disk section, you have a tolerance problem or a weight distribution problem. Both are a pain to resolve. To my knowledge very few machines above 0.5 MA have an insulator lifetime of more than 1000 shots. Nasty plasma environment coupled with shocks is not a recipe for a long insulator lifetime. High grade alumina (>99.6%) might have some benefits as well given that it is closer to sapphire, but I use >93% with great success.