Latest FF-1 tweaking aims to eliminate small tilts
Tweaking tilts for maximum plasmoid compression. Reprinted from the LPPX November 23, 2011 Report.
In LPP’s continuing effort to improve the symmetry of FF-1’s electrodes, we made modifications to the central o-ring and insulating Mylar sheets to eliminate a small tilt we had detected in the alignment of the electrodes. The alignment of the electrodes is critical in producing a symmetric current sheath, which in turn is needed to get the highest compression of the plasmoid where the fusion reactions occur. There is only a 15 mil (thousandths of an inch) clearance between the insulator and the cathode, or outer electrode, so this distance must be kept constant to within one mil around the whole circumference of the insulator. While previous efforts have accurately centered the insulator at its base, any slight tilt in the large steel plate holding the anode can create a misalignment when the insulator passes close to the cathode.
LPP’s team did detect such a tilt. The cause was a small error in the dimensions of a rubber o-ring that surrounds the anode and provides a vacuum seal to prevent air from entering the vacuum chamber. Because the ring was too thick, it did not compress enough under the weight of the upper steel plate (which is attached to the anode) to rest securely on the Mylar plastic insulating layers and the lower steel plate (which is attached to the cathode). Instead, the o-ring carried the main weight and allowed the steel to tilt slightly. A reduction in the o-ring thickness as well as adding more lead weights to increase the compression will cure this problem, and the solution was tested by assembling the electrodes, insulator, and plates on our work table. After a breakdown earlier in November, improvements are underway to protect the inner assembly to electrical breakdown at the 120 kV levels that we expect to reach during future shots. LPP’s team expects that the elimination of the tilt will improve symmetry and increase fusion yield.