Path to higher fusion yields—avoiding the pre-schock

Posted by Lerner on Sep 15, 2010 at 05:50 PM
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As reported last month, we have observed for some time that the X-ray pulses from the DPF have a three-pulse structure.  The third pulse is always the one associated with the fusion reactions.  We can tell this because of their timing relative to the neutron pulse.  What we have now observed is that while there is a correlation between the size of the third X-ray pulse and the number of neutrons produced, the first pulse can lead to a smaller fusion output.  In addition, we have observed that in many of the recent shots, there is a little “hiccup” in the current about 45 ns before the pinch maximum, when the plasmoid forms (Figure 3).  This drop indicates absorption of energy in some process.  What is particularly interesting is that this drop is simultaneous with the first peak in the X-ray pulse and must be associated with it.  However, in the earlier shots back in March, where we achieved our highest fusion yields, there is no such hiccup in the current (Figure 4).

While we need far more data, we have hypothesized a possible theoretical explanation of this data.  We believe that the first pulse is created as the filaments of the sheath converge into the pinch and annihilate each other, forming a single filament.  The second pulse occurs when the kinks converge to form the plasmoid, and the final one is the heating and compression of the plasmoid itself.  If there is insufficient angular momentum, the filaments crash into each other, causing a shock and absorbing much of the energy in the pinch, leaving too little left over for the plasmoid.  If there is too much angular momentum, the filaments circle around each other without fully merging.  But with just the right amount (the Goldilocks point!), the filaments spiral smoothly into each other, allowing the maximum energy to be transferred to the plasmoid.  This would explain the sensitivity of the axial magnetic field adjustment and the lower-than-expected yields.

If this hypothesis is valid, we should be able to double the radius of the plasmoids and thus increase their volume and fusion yield by 8-10 fold, through precision adjustment of the axial field.  This investigation will take time, but we will be starting it in September.