Reply To: Bang or no bang

[markus7]

Rezwan wrote: Your thoughts on the asymmetry of tungsten pins, the knife edge solution, and other factors of symmetry.

As I understand it, the source of the plasma sheath asymmetry problem is in the asymmetry of the initial current sheath on the surface of the insulator before it gets “kicked off” and driven down the annulus.

I am wondering if such asymmetries are inevitable with all designs that initiate the current sheath across an insulator as the present test model does. Even with a ‘perfect’ knife edge, I expect current filaments (even full up vacuum arcs?) will progressively pit the cathode, creating cathode ‘hot spots’, and deposit the vaporized metal on the insulator surface adjacent to the pits. The longer the device runs, the more asymmetric the initial current sheath is likely to be.

Have other methods of initiating the current sheet, perhaps “spark plug plasma jets” of some kind ever been tried? I am imagining one “spark plug plasma jet” for each cathode outer rod (16 total) aimed to fire across the annulus to the anode to initiate sheath current flow. Thus, the initial current sheet is created across the annulus, not across the surface of the insulator.

My preference, of course, would be for the simple knife edge cathode base to work.

EDIT: I wonder if such an arrangement of 16 “spark plug plasma jets”, in addition to improving current sheath symmetry, might make it possible to eliminate using the main capacitor switches to trigger pulses. That is, the 16 outer cathode rods would, while running, be connected to the capacitors, and the “spark plug plasma jets” would take over the function of the vacuum switches, making them redundant. The function of the vacuum switches would be part of the fusor unit.

EDIT 2: Mainly for people like me who are new to this forum, relevant previous threads include Spark Plugs? https://focusfusion.org/index.php/forums/viewthread/471/ and Laser spark Plugs https://focusfusion.org/index.php/forums/viewthread/855/. Both of these threads focus on initiating the external switches. But they might also be applicable to the idea of reducing the asymmetry problem in the initial plasma sheath in the main fusor, while, as a secondary effect, eliminating the need for high tech external switches.