Experiments this month gave further confirmation of our basic theoretical model of the DPF (Dense Plasma Focus). ICCD images showed the pinched filament kinking into a plasmoid and gave us clearer estimates of the plasmoid radius and density. X-ray emission energy continues to increase, giving us more confidence for our spin-off X-ray generator applications. Our replacement trigger heads were completed and tested, making us ready to return to 12-capacitor firing. Aaron Blake and Derek Shannon are joining the LPP team full time.
For the first time, LPP have captured images of the kinking process that leads from the pinched filament column to the formation of the plasmoid. This process, portrayed in the Focus Fusion Society animation of DPF functioning, is critical to our theoretical understanding of how the plasma in the pinch region gets further concentrated into the donut-like plasmoid.
X-ray energies continue to increase to hundreds of keV. Shots taken at the end of October have shown very high X-ray energies. LPP can’t yet say precisely how hot the electrons producing the X-rays are, but it is clear that the typical X-rays emitted must have energies of around 150 keV, with large fractions at 200-300 keV, above the minimum goals we have set for our spin-off X-ray inspection application. The total amount of X-rays emitted (tens of mJ) are still far short of the goals for this application, and more data will be needed to get a precise measurement of the X-ray spectrum and the electron energy distribution, but we are excited about the progress thus far.
As reported last month, optimal fusion yields seem to require short times to pinch, so that the current is still rising when the pinch process beings. On first consideration, it seemed that getting to that short pulse time would be a simple matter of reducing the fill pressure in the vacuum chamber. However, resistence went up and times did not go down much at low pressure. Overall this is an optimistic conclusion, since as we move to higher currents with more capacitors on line and higher voltage, we will use higher fill pressure and thus resistance will decrease.
More rugged spark plug designs are being manufactured.
Dr. Michael Brown, Professor of Physics at Swarthmore University, was asked by the Abell Foundation to prepare a progress report on LPP’s project. The review was very thorough and the report is quite favorable: “I was generally very impressed with the operation at LLP,” Brown wrote in his summary. “The group has clearly made significant progress in the past year. The operation is very professional and the procedures they follow are scientific. I feel that this work is worthy of support.”
Dr. Brown’s basic concern was with the indisputable fact that our current results are several orders of magnitude away from demonstrating the scientific feasibility of net energy. We addressed that gap in our comments on the report. Dr. Brown made several useful recommendations concerning better statistics, determining the isotropy of the neutron emissions, better graphical presentation, and better marshalling of evidence. We are taking these recommendations seriously and should be able to implement them quickly
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