Reply To: turn heat into electricity

[asymmetric_implosion]

Henning wrote:

Given that symmetry in the physical geometry of the electrodes appears to be important, is there any reason that the cathodes have to be separate rods? A solid piece, with projections to guide the plasma filaments, would mean that one never had to worry about individual cathode alignment. Is it necessary to have empty space between the individual cathode rods?

It’s not 100% clear why, but a plasma focus seems to work better with individual cathode rods. People speculate that some of the gas between the anode and the cathode needs to be pushed out while others cite debris as the reason. Groups have employed blades instead of rods that are mounted or welded to a single base piece that helps with alignment. The open area, rod diameter, etc seem to be able to cover a wide range of conditions and still achieve reasonable results. The cathode is not nearly as well studied in PF devices as the anode.

As far as I understood Eric Lerner et al, these rods help the creation of filaments. FoFu creates filaments already in the axial phase. This seems to be different to other DPFs. See also here: https://focusfusion.org/index.php/forums/viewthread/1045/#9674

I don’t know if we are talking about the same thing. The cathode rods, which are prominent in the pictures of the FoFu-1 electrodes, are common in plasma focus devices of the Mather Type. Rods or blades have been used for over twenty years. From my understanding, the initiation of the plasma focus and the tungsten pins near the anode that are installed in the cathode are new to FoFu. I can tell you that my plasma focus uses rods for the cathode and we generate a fairly uniform sheet from visible images. Other plasma focus device observations are similar. The filaments in FoFu-1 could be due to the operating pressure. Most devices even at the 2MA level operate in the 1-10Torr range. FoFu-1 operates at >20 Torr. I remember seeing something like 44 Torr and 80 Torr on some shots. Filaments are more likely to form at neutral high pressure.