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October 06, 2010

Lawrenceville Plasma Physics Achieves Reliable Firing

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Shot 9-09-10-02, 0.225 microsec before pinch

Right - Shot 9-15-10-07, magnified plasmoid at the pinch. We see the plasmoid on axis, which is about 150 microns across. The small dots are individual pixels, and do not represent actual fluctuations in intensity.




On September 29, Lawrenceville Plasma Physics finally achieved repeatable dense plasma focus nuclear fusion firing of all attached capacitors. That day, and on September 30 and October 1, we fired all eight attached capacitors in 11 successive shots with only three pre-fires.

* Even with this partial bank, we achieved over 1 MA current, which is very encouraging.
* We are now rebuilding the four missing trigger heads to a new and more rugged design, a task that should be completed in October. We are confident that we will then be able to repeatably fire all 12 capacitors together.
* DPF researchers have long known that it is important to match the time that the pinch occurs with the time that the current from the capacitors peaks. Last month, we plotted the fusion yield for FF-1 against the time of the pinch (see Figure 1). We found that for the shots in March and early April, the yield was tightly correlated with pinch timing, and there was a sharp peak right around the time of greatest current, close to 1.8 microseconds. All the high-yield shots had short pinch times, and none of the lower yield shots did. The same pattern was followed at the higher pressures and currents that we used in September, but the whole curve was shifted upwards by about a factor of 5. This shift implies a good scaling with current to the fifth power.

* What was particularly significant was that only shots with the axial field coil turned on had the short pinch times
* In our experiments this month, we intend to vary the axial field together with the gas pressure to achieve pinching at a time very close to that of peak current. We expect to avoid the “hiccupping” shock waves observed in the lower yielding shots (described in last month’s report) and move up to a yield approaching or exceeding 10^12 neutrons (over 1 joule of fusion energy).

Highest ion energy observed, over 100 keV

In both of the shots with yields over 10^11 neutrons, we observed average ion energies over 100 keV for the first time with FF-1, getting us into the range useful for pB11 fusion. In shot 93002, we measured an average ion energy of 143 keV, and in shot 100102, we measured 108 keV (equivalent to 1.6 billion degrees K and 1.2 billion degrees K respectively). The important thing is that we are confining ions of this energy for tens of ns. If we can achieve the same conditions with pB11 as we did with D in shot 93002, we would expect a pB11 fusion yield of about 0.5 J.



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