New Calibration Confirms FF-1’s High Fusion Yields

After six months of modifying the switches, LPP finally achieved the firing of all 12 switches within 25 ns of each other in four shots on April 26. At a charging voltage of 30 kV, we achieved our first pinch at over 1 mega-amp (MA). The fill pressure of the deuterium gas was 40 torr, which is a record for a pinch in a DPF. We were deliberately using a pressure about twice what we believe is optimal for this charging voltage in order to avoid a pinch so we could test the electrical characteristics of the device. But the plasma pinched anyway, although well after the higher current had passed. The 1.03 MA current is a record for us when creating a pinch, but the 40 torr is a record for a pinch in any DPF.

During the month of May, we will be replacing the automotive spark plugs in the switches (which had been leading to the prefiring) with custom-built tungsten-rhenium rods from which we will make our own spark plugs. We expect them to have a very long life and practically eliminate prefiring in future testing.

Finally, a joint team from LPP and the Focus Fusion Society has produced a 70 ns simulation of the formation of a single plasma filament as part of the plasma sheath in the DPF. It showed a filament pinching itself down from a radius of about 300 microns to around 50 microns, a first step in compressing the plasma and its magnetic field. The simulation team consisted of John Guillory, Jeff Schoen, Henning Burdack, and Luis Angulo.  FFS volunteer Burdack, who lives in Germany, provided the implementation that actually ran. Previous versions of the algorithm used had shown numerical instability where the values oscillated wildly. The new runs are the first to be stable and appear to show the filamentation process. In time, such simulations will complement our experimental observations and analytical theory, and may find applications in other fields of plasma physics as well.

At the beginning of March, good shots (those without pre-firing and with pinches) were a bit under 50% of the shots we fired. Since mid-month, we have increased that to 90% good shots. The two time-of-flight neutron detectors have produced more evidence that we are already duplicating the high ion energies achieved with higher currents in the Texas experiments. In our best shots, ion energies were measured in the range of 40-60 keV (the equivalent of 0.4-0.6 billion degrees K). The electron beam carried about 0.5 kJ of energy and the plasmoid held about 1 kJ of energy, nearly half that stored in the magnetic field of the device. So, this is evidence that a substantial part of the total energy available is being concentrated in the plasmoids and transferred to the beams.

We found that the control shots (with the magnetic coil turned off) were increasingly producing more neutrons (up to about 10 times) as the control shots in the beginning of our testing.  It turns out the steel flanges that attach the vacuum chamber to the inner lower bus plate and the bus plate itself were both becoming permanently magnetized. This provides additional (though unintended) evidence that the predicted angular momentum effect is working. In the future, we may find it necessary to replace the flanges and bus plate with those made from non-magnetic alloys, but that will have to wait for now.

On March 18, Lerner gave an invited presentation on the DPF to an audience of physicists and engineers at Princeton Plasma Physics Laboratory, the nation's largest fusion lab. The Princeton physicists responded with interest and some friendly questions. The atmosphere was one of collaboration, not competition.

Finally, we received enough investment money to carry us through the end of summer, with additional funding pledged. This means we are almost halfway to our goal of raising $900K in this capital drive.

We have obtained the first preliminary evidence that the injection of angular momentum into the DPF considerably increases the efficiency of energy transfer into the plasmoid, the size of the plasmoid and thus the fusion energy yield. On Feb. 19 and 22, we fired Focus-Fusion-1 at 24 kV with a pressure of 8 torr of deuterium in the vacuum chamber. In some shots, we connected the angular momentum coil (AMC) to the power supply, so current could flow through it. In other shots, we left the coil circuit open, so no current could flow. The shots with the AMC connected have a neutron yield 8-10 times that of those with the AMC disconnected, so this is a large and very promising effect.
 
What we believe is happening is that the current in the coil is producing a small magnetic field along the axis of the device. The interaction of the currents with this field induces angular momentum (spin) in the plasma sheath. This in turn diverts the current in the sheath in the same direction as the current in the coils, amplifying the field. The angular momentum, conveyed ultimately to the tiny plasmoid, creates a centrifugal force that balances the compressive magnetic forces. The bigger the centrifugal force, the bigger the magnetic field that can be balanced and the bigger the plasmoid. However, if the centrifugal force is too big, it will prevent the plasmoid from forming at all. Thus only small fields are effective.
 
In the few shots we have taken, so far we have not seen a difference in the neutron yield with the power supply to the AMC providing different levels of current. This may be because the current induced in the coil by the DPF’s own current pulse is higher that the imposed current. We will need to investigate this with more shots under varying connections.  However, the fact that we have already obtained a factor of ten improvement in yield through the use of the AMC is very encouraging and is an initial confirmation of the proposal that LPP VP Aaron Blake made four years ago. It is also a further confirmation of our general theory of the DPF.

Effect of AMC - Logarithm of neutron yield plotted against logarithm of peak current. Blue (upper) points are with AMC connected.  Red (lower) points are with AMC disconnected.

We have obtained the first preliminary evidence that Focus-Fusion-1, like the Texas A&M machine and PF-1000 in Warsaw, is producing high-energy ions.  This evidence indicates that,  even operating well below its intended current, FF-1 has produced ions with an average energy of at least 45 keV, the equivalent of half a billion degrees C.

The evidence was obtained on a single shot on January 8.  This shot was with 10 torr of deuterium in the vacuum chamber, by far the highest pressure for which we have good data with the FTF detector.  LPP’s theory predicts that higher gas densities will lead to higher temperatures within the plasmoid.  In this shot the bank produced 0.56 MA at 30 kV, well below its ultimate potential.

We deduced this energy from the timing of the X-ray and neutron pulses observed by the FTF.  The first very sharp peak was the X-ray pulse, caused by radiation from hot electrons in the plasmoid and arriving at the FTF at the speed of light, 30 cm per ns.  The second group of peaks was the neutrons, traveling much slower and arriving later.  We know that the neutrons are produced by DD fusion reactions and should have a velocity of 2.2 cm per ns and should arrive 719 ns after the X-rays.  We also know that the fusion reactions only occur once the electrons have heated up the ions.

But in this shot (1/08/10-05), the first burst of neutrons arrived only 682 ns after the beginning of the X-ray pulse.  These neutrons, traveling faster than would be expected from the fusion energy alone, must have additional energy imparted to them by the motion of the nuclei that collided to produce the reaction.  From this data we can deduce that the average ion in the plasmoid had at least 45 keV of energy.  If the neutrons actually originated later in the pulse, then they traveled faster and the average ion energy could have been higher.