Machining challenges lead to new cathode designMarch 23, 2012
Will new “Fusion Crown” make FoFu-1 king of clean energy?
Time will tell, but in any case “The Teeth that Chew the Sheath” are getting an updgrade!
Since FoFu-1’s ceramic insulator broke in late January, damaging the nearby cathode base, we’ve been working to make the ceramic more robust while also improving the cathode design to provide bettery symmetry for plasma compression.
While we had hoped to replace the broken cathode plate by mid-February, with only a small change from 100 to 96 tungsten pins (since 96 is a nice even multiple of the 16 cathode rods), the tiny (40-mil, or .040″) holes that held the tungsten pins on the inside edge of the plate proved extremely challenging for our regular machinist, due to their size and the softness of copper. The tungsten pins are critical to the functioning of FF-1, as it is from them that the current starts to flow and forms into filaments and the overall plasma sheath. Hence our nickname for them: “The Teeth that Chew the Sheath.”
Image: FoFu’s gaptooth smile after the ceramic insulator damage in late January
As a result of the machining difficulties, the plate was not completed until mid-March. Unfortunately, while the machinist had in the past been able to level the tungsten pins successfully, on this attempt many were seriously bent, rendering them useless. However, during the long delay, LPP research team members Aaron Blake and Derek Shannon designed a more robust substitute for the pins—a serrated ring of tungsten, with the saw tooth points substituting for the points of the pins. We also have located a much larger machine shop which uses electrical discharge machining (EDM), a highly precise method of machining with intense electric currents–A very appropriate method for high voltage-happy FoFu!
We now expect the new shop to complete the new cathode plate by early April, allowing us to resume firing, confident that we will have a highly symmetric set of electrodes. This symmetry is essential to achieving good compression of the plasma and producing higher fusion yields.
Thanks is also due to Focus Fusion Society volunteers such as Chris Kuether and ZapKitty for their CAD assistance.
Below, a preliminary model of FoFu’s new tungsten sawtooth ring, or more dramatically: “The Fusion Crown!”