I have copied the full reportfrom Focus Fusion and we are seeing solid progress. An upgrade in hardware design should be veryrewarding this coming year.
My one thought here is that alarger robust design may be practical a lot sooner. The geometry may support just that and maymake success that much easier. A collapsingplasmoid may just need more room.
Often design processes latch onto an apparent economic solution that works against the physics. One recalls that the first aircraft werekites and never quite practical.
Lawrenceville Plasma Physics are working towards commercialnuclear fusion using dense plasma focus fusion. They have theirDecember, 2010 report. They have had problems with switches that has cost thema few months of time to resolve. They have repeatably fired the bank with 10 capacitors attached, giving reliable shots above 1 MAat 33-34 kV. They believe that they now clearly understand the previouspre-firing and insulator-breakage problems. This will enable them tocontinue gathering data and testing their theories while they prepare athorough ruggedization of the switches that will enable them in a few months toreach full power with all 12 switches at 45 kV, and push on to their goal of 2MA current. They are implementing a redesign which will take until March tocomplete because delays to get some components. So in April, 2011 they will beable to push ahead with 12 switches at 45 kV.
LPP has completed 3.5 of their 8 milestones. They are a year behind theoriginal schedule, which can mostly be blamed on the switch problems, but theyare making good progress. In 2011 their plan is to finish the trigger electroderevision, which will allow them to achieve 45kV and 2MA, optimize the gas pressure for that configuration with deuterium,switch to helium and nitrogen while continuing to optimize, then switch tohydrogen and boron. At that point they hope/expect to see a shot that generates33,000 Joules of fusion energy, and all of their milestones will becomplete. Unless they run in to more unexpected problems it is realistic thatthey might finish that by the end of the year.
We ran into a number of problems that had to be resolved in turn.Perhaps most importantly, we learned from our experiments that the pre-firinginevitably gets worse with more capacitors.
This is because the pre-firing is caused by a slow breakdown of the gas related to a phenomenon called “coronadischarge”. With more capacitors attached, the power supply’s fixed outputcharges the bank more slowly, so the switches stay longer at high voltage.Because of this problem, the present configuration of the switches will notwork with all 12 capacitors attached. Ten capacitors is our current maximum.
However we know the cure for this. We’ll move the electrodes in the switchesfurther apart (see the attached diagram for further explanation). We will bedoing this in our general redesign over the next few months. In addition, ifthe tungsten trigger rods get worn down so they are too thin or too rough,the field gets too concentrated, and this also leads to pre-firing.Temporarily, we have replaced the thinnest rods and are sanding the otherscarefully on a regular basis. In our re-design, we will use much thickerrods—probably one-quarter-inch diameter instead of one-eighth inch.
We also had trouble eliminating breakage. While our large stabilizer blockprevented any cracking of the insulator above the plate, the rapid movement ofthe tungsten rods was still breaking the Lexan insulators near the tip. Afterseveral tries, we have used a solid cylinder insulator to provide maximum strength. Sofar, they have lasted 40 shots with only two cracking, so this is adequate fornow, although too soon to tell their real lifetime. Again, we know the solutionto the mechanical breakage: making the rods thicker so they bend less, andmaking the insulators thicker so they are stronger. These changes require replacingthe top plates of all the switches and making the spark plug holes larger. This hole size haslimited our past efforts with the spark plugs.
Finally, to prevent the electrical break-down of the insulators, we also haveto make them thicker. All of this can be calculated, based on the experimentswe have done, and we hope to complete design work very soon, probably early inJanuary. However, there are considerable ordering delays on some items, such asthe tungsten rods, and some additional testing will be needed, so realisticallywe will not complete the new switches until March. Until then, we will berunning with the existing 10–capacitor bank.
Focus Fusion Report
December 30, 2010
Summary: LPP’s Focus Fusion project has demonstrated that ions withmore than 100 keV energy (equivalent to more than 1 billion degrees C) areconfined in a dense plasma focus. Thisbreakthrough is based on both new evidence from the past month and are-analysis of shots made earlier in the year, and resolves a long-standingcontroversy within the field on whether the ions are confined in a small space,and thus can potentially heat the fusion fuel up to ignition, or are in a beamrunning freely through the cold background plasma of the chamber. A combinationof evidence from many instruments, fit together like a jig-saw puzzle, hasdemonstrated that the ions are trapped in circulating beams in very dense plasma.The evidence ruled out the unconfined beam model. The 100-keV energy is sufficientto burn pB11 fuel, once we start running with that fuel in the coming year, andmakes us confident that we will be able to achieve at least significant pB11fusion yield. A press release on these results will be forthcoming shortly, andwill be submitted to the leading physics journal, Physical Review Letters.
In other key developments, we have repeatably fired the bank with 10capacitors attached, giving reliable shots above 1 MA at 33-34 kV. We believethat we now clearly understand the previous pre-firing and insulator-breakageproblems. This will enable us to continue gathering data and testing ourtheories while we prepare a thorough ruggedization of the switches that willenable us in a few months to reach full power with all 12 switches at 45kV, andpush on to our goal of 2 MA current. Demonstrating over 100 keV confinement ina dense plasma.
While researchers have known for a many years that the dense plasmafocus produces high energyions, with energies well into the range where pB11fuel will burn, some fusion
researchers have long held that the high-energy ions are not trapped,but travel freely in unconfined beams. These beams, according to this model,collide with the diffuse, cold background plasma in the vacuum chamber toproduce the observed fusion reactions. By contrast, we and other DPFresearchers have long contended that some of the high energy ions are indeedtrapped for relatively long times in dense plasma spots—the plasmoids. Bothsides agree that high-energy beams are also produced by the device. Thequestion is if any of the hot ions are confined—moving in closed loops, notstraight lines.
This argument is critical to the viability of the DPF as a fusion generator,because only if some ions are trapped, circulating around and around within adense plasmoid, can they heat the fuel up sufficiently to ignite aself-sustaining burn that will consume most of the fuel in the dense plasmoids.A diffuse beam alone, traveling on a one-way trip through cold and much lessdense background plasma, will not be able to do that.
Previous experiments by LPP at
in 2001, andby other groups of Texas A&M University
researchers, have accumulated evidence that the hot ions are indeedtrapped. But clear proof has been lacking that would rule out the unconfinedbeam model. LPP now has provided that clear proof. One big piece of that proofcame from a recent re-analysis of shots we fired back in March. These shotsachieved high fusion yield, over 1011 neutrons, but with relatively modest currents,between 600 and 700 kA. We wondered how these high yields could be explained bya beam running through the background plasma. How much energy would it take togenerate such a beam? Because the background plasma is diffuse, with a densityof only 6.6X1017atoms/cubic centimeter, a very powerful beam would be needed toproduce so many fusion neutrons. We calculated that at least 9 kJ of energywould be needed to produce such an ion beam, about onethird of all the energyfed into the capacitors.
But not all energy fed into a DPF is available at any given instant.Only the energy stored in the magnetic field created by the current is soavailable. In turn, only part of this energy is drawn into the pinch andtherefore can drive the beams. We found that the energy needed for this hypotheticalbeam was more than double all the energy available for forming it, so it couldnot exist.
We could measure the amount of this energy drawn from the DPF’s circuitduring the pinch by examining the drop in the current. The energy carried by acurrent is proportional to the square of the current times the inductance.(Inductance is a basic electrical quantity which is explained briefly at theend of this report.) From our Main Rogowski Coil, one of our instruments, we couldmeasure the drop in current. But what was the inductance of the total circuit?
In the past month, LPP engineer Fred van Roessel had measured theinductance of the entire DPF device by matching the current output curves fromseveral shots with standard electrical models. He checked those results bycalculating the inductance of some key components, such as the switches. So weknew how much inductance we had, and thus could calculate the total energy inthe pinch as less than 4 kJ—far less than was needed for the hypothetical beam,even at 100% efficiency. So a beam through the background gas could not producethis many neutrons.
The shots back in March only reached about 70 keV of energy. InSeptember, however, we had two shots that our time-of flight detectors showedhad over 100 keV ions. Could we be sure of this result? It came from measuringthe difference in the neutron arrival times at two detectors set at differentdistances—11 meters and 17 meters. The more the neutrons spread out, the greatertheir range of velocities and thus the greater the range of velocities of theions (deuterium nuclei) that fused to produce the neutrons. More velocity meansmore energy, so this is a measure of the ions’ energy.
With just twodetectors of neutrons, we could not be positive that something was notintroducing an error. For example, what if there were really two neutronspulses? We needed data on neutrons as measured closer to the source.
On our last day of shots in December, on December 24, we got clearneutron signals from one of our PMTs located at only 1.3 meters from the axisof the machine. Thanks to a reduction of noise, to 6 mm of copper shielding tocut back on the X-ray signal, and to the reliable firing of the device (more ofthat below), we have clear evidence that we are not getting double neutron pulsesand that our measurements of ion energy are reliable. (see Fig. 1) This is asecond major piece of the evidence for the confinement of 100 keV ions.
Our ICCD images, obtained in October, show that the region where theions are confined is only about 120 microns or less in radius.
In addition, our neutron bubble detectors, located along the axis ofthe device, as well as
horizontally, show that there definitely are somewhat more neutronsmoving in the axial
direction than horizontally. This means that the motion of the ionscannot be totally random as in a thermalized plasma with no circulating beams.Instead, the only explanation of all the data is a circulating beam of ions,constituting a large fraction of the ions in the plasmoid, that encounters themost dense plasma as it flows up along the central axis of the plasmoid, thus producingthe most neutrons in the axial direction, but many in all other directions.
This model has allowed us to calculate the plasma density in our bestshots to be in the area of 1-4 X 1020 ions/cubic centimeter, more than 100times the fill pressure of the gas we started with.
We will be working on the technical paper describing this importantresult in January and hope to complete it during the month. We think that itwill add considerably to the credibility of the Focus Fusion project, and thusease future fundraising.
Reliable firing of bank with 10 capacitors
On the last day of firing this year, we finally achieved reliablefiring with 10 capacitors—all fired together six times in a row with nopre-firing. We now are confident that we understand the remaining two problemsof the switches, their pre-firing and the breakage of the spark plug insulators.Unfortunately it has taken us a total of three months to get this understanding,from the time that we solved the first problem of achieving simultaneous firingin late September. We simply have not had enough reliable shots to optimize thepressure and axial field to obtain the higher yields we are seeking. While weare able to continue firing the bank in its present configuration, to go to all12 capacitors firing at 45 kV will require some additional work on the switches.But we know what we must do.
We ran into a number of problems that had to be resolved in turn.Perhaps most importantly, we learned from our experiments that the pre-firinginevitably gets worse with more capacitors.
This is because the pre-firing is caused by a slow breakdown of the gasrelated to a phenomenon called “corona discharge”. With more capacitorsattached, the power supply’s fixed output charges the bank more slowly, so theswitches stay longer at high voltage. Because of this problem, the presentconfiguration of the switches will not work with all 12 capacitors attached.
Ten capacitors is our current maximum.
However we know the cure for this. We’ll move the electrodes in theswitches further apart (see the attached diagram for further explanation). Wewill be doing this in our general redesign over the next few months.
In addition, if the tungsten trigger rods get worn down so they are toothin or too rough, the field gets too concentrated, and this also leads topre-firing. Temporarily, we have replaced the thinnest rods and are sanding theothers carefully on a regular basis. In our re-design, we will use much thickerrods—probably one-quarter-inch diameter instead of one-eighth inch.
We also had trouble eliminating breakage. While our large stabilizerblock prevented any
cracking of the insulator above the plate, the rapid movement of thetungsten rods was still breaking the Lexan insulators near the tip. Afterseveral tries, we have used a solid cylinder insulator to provide maximumstrength. So far, they have lasted 40 shots with only two cracking, so this isadequate for now, although too soon to tell their real lifetime. Again, we knowthe solution to the mechanical breakage: making the rods thicker so they bendless, and making the insulators thicker so they are stronger. These changes requirereplacing the top plates of all the switches and making the spark plug holeslarger. This hole size has limited our past efforts with the spark plugs.
Finally, to prevent the electrical break-down of the insulators, wealso have to make them
thicker. All of this can be calculated, based on the experiments wehave done, and we hope tocomplete design work very soon, probably early inJanuary. However, there are considerable ordering delays on some items, such asthe tungsten rods, and some additional testing will be needed, so realisticallywe will not complete the new switches until March. Until then, we will berunning with the existing 10–capacitor bank. Derek Shannon is ably assistingwhile Dr. Subramanian is on vacation.
IEEE Green Engineering to support FFS video on Focus Fusion
Dr. Paul G. Ranky, the Senior Editor of IEEE’s Green EngineeringSeries, has offered to
collaborate with the Focus Fusion Society in producing an eight-hourvideo series on Focus Fusion technology. The IEEE (
and Electronic Engineering), with nearly half a million membersinternationally, is the largest technical organization in world. The series willbe available to all IEEE members, so this will be very good for raising FocusFusion’s profile in the technical community that is most likely to beinterested in our work. Institute of Electrical
The offer came about when Dr. Ranky attended a Focus Fusion Society-LPPJoint Solstice Seminar in
, on Dec. 21. Thanks to LPPDirector of Business Development Derek Shannon for organizing this! Somerset, NJ
On the lighter side—inter-species technical cooperation
Our efforts are already getting help from the international communityof DPF researchers. So what’s the next step—get help from another intelligentspecies? Maybe the dolphins can lend
As Focus Fusion fans know, our device produces tiny plasmoids which area plasma version of a phenomenon also found in fluids—the vortex ring. Humanscan produce a primitive version of the vortex ring—the smoke ring. However suchsmoke rings are very unstable, so they’re not very interesting (as well ashaving health hazards associated with producing them!).
Dolphins, however, produce highly stable vortex rings and then playwith them, as seen in this
video (http://www.youtube.com/watch?v=5us-v4bntP).The vortex ring is formed in the water by the way the dolphins blow air fromtheir blow-hole. Since the vortex has its lowest pressure at the core, the airstays there. The motion of the much more massive water ring overcomes thebuoyancyof the air and prevents the rings from rising.
But how do the dolphins learn to produce such thin and stable rings?Perhaps we can learn something of interest from their play. Dr. Diane Reiss ofHunter College, a leading researcher on dolphin communication and intelligence,and LPP’s Eric Lerner are discussing ways of studying this fascinatingbehavior. Her long-term research program is also attempting to try tointerpretthe intricate songs and sounds that dolphins use to communicate with eachother. (Dolphins have the second largest brain-to-body-mass index of any animalon earth, comparable with that of our Homo erectus ancestors). So perhaps oneday the dolphins will be able to explain to us their vortex ring techniques!
We apologize for the lateness of the report, but at times, it is morecritical to continue the
experiments than take out time for the report. A year-end report willfollow shortly and we will then resume the regular schedule, reporting again inearly February.
Technical note: What is Inductance?
Inductance is a measure of how much magnetic energy is stored in acircuit (or part of a circuit)for a given amount of current. All currentsproduce magnetic fields, and these fields contain energy. The current itselfsupplies the energy to build these fields. The inductance of an object is theratio of the amount of magnetic energy to the square of the current (to be precise,twice that ratio). The bigger the inductance, the large the magnetic field of agiven current, so the slower that current must build up. Inductance is affectedby how strong the magnetic field produced is—and thus how concentrated thecurrent is—but also by the total volume of space affected by the field.
Happy New Year to ALL!
Figure 1. Ready for its close-up. This graph shows the output of thephotomultiplier tube (PMT) located only 1.28 meters from the machine’s axis.This is close enough so that the neutrons from fusion reactions do not havetime to spread out due to their different velocities, so they reveal the shapeof the neutron pulse as it originated. This shot, 12241009, has a single x-raypeak, the one on the left. It is filtered heavily by 6mm of copper so onlyrelatively high-energy x-rays, above 80 keV, can get through. This reduces thex-ray peak enough so we can see the neutron peak, the broad one on the right.We can identify it as a neutron pulse because of its timing relative to theneutron pulses observed at the same time at a much greater distance by the nearand far Time-of Flight PMTs. This graph shows clearly the single-pulse shape ofthe neutrons and confirms the high energy that we have calculated for the ionsproducing the neutrons. This particular shot achieved “only” over 40 keV, butother shots in September achieved over 100 keV.