The symposium participants offered in themselves cause for encouragement, as 15% of the presenters were women. While this is a long way from where it should be, it is a great improvement over most fusion science conferences, which are only about 5% women. The average age was also much younger than in many previous conferences, showing that a new generation of Chinese researchers was being drawn to the proton-boron fusion effort.
Perhaps the most exciting progress reported was the achievement of the dense hot, high-magnetic field plasmas needed for practical boron fusion. In two experiments using femtosecond lasers illuminating nanowires, large currents generated the pinch effect, compressing the nanowires to high density. One experiment at Peking University reported a record pB11 fusion yield of 10 billion alpha particles per J of laser energy. Assuming typical laser efficiency of about 1%, this works out to a total wall-plug efficiency of about 50 J out for every MJ of electric input. This is almost a factor of eight more than has ever been achieved with pure deuterium fuel. However, further gains in yield will require major increases in confinement time from femtoseconds to tens of picoseconds, which will not be easy with nanowires.
The other experiment at Jiao-Tong University in Xi’an achieved an estimated magnetic field of 10 giga gauss. This would be a world record if confirmed by measurements and would be well into the range where the Quantum Magnetic Field Effect (QMFE), pointed out by our research at LPPFusion, is expected to be important. Since the plasma density is as much as 100 times solid density, measurements will certainly be challenging, but worth trying.
Not only the accomplishments of our colleagues, but also the problems encountered were of interest. It was reassuring that the same problems we are dealing with—preventing the separation of hydrogen and boron, and keeping our plasma clean—are those almost everyone else is dealing with. In particular, the problem of keeping ENN’s spherical tokamak clean, where the machine is far too large to practically bake out and its periodic “disruptions” tend to vaporize part of the vessel wall, make our silicon cleaning challenges seem modest in comparison.
A third problem we all share is how to convert the energy produced to electricity. Here, both LPPFusion’s patented photoelectric approach to x-ray conversion and our inductive approach to beam energy conversion were a source of a good deal of discussion and interest.
The most surprising development of the Symposium was the news of a new debate about how the proton-boron reaction actually occurs. For decades, the standard description was that the proton and boron nuclei briefly merged in an excited sate of carbon-12. The state existed only for 13 zeptoseconds (a zeptosecond is 10-21 seconds) and then falls apart as the energy is too much for the carbon nucleus to contain. The nucleus flies apart into a helium nucleus (also termed an alpha particle) and a Beryllium 8 nucleus, which then decays into two more alpha particles in a more leisurely 82,000 zeptoseconds.
But a number of nuclear physicists, particular Panyang Dang of Beihang University, pointed out that this model does not really fit detailed data very well. Instead, they contend that the reaction proceeds directly, with the proton grabbing a tritium nucleus—a proton and two neutrons—, forming a helium nucleus in the process and traveling on without any pause. This reaction would only take 0.5 zeptoseconds, two dozen times faster than the excited C-12 process.
This debate is relatively new—and was certainly new to the plasma physicists at the conference—and no consensus has yet been reached. Other than the inherent interest in knowing how our reaction which was discovered back in 1933, actually works, the debate does have practical implications. Measurements of the overall reaction rate of pB11 fusion have changed over the years, leading to higher estimates of the rate. A good part of the problem is that it is not possible to measure the reaction products coming off in all directions. To go from incomplete measurements to a calculation of the total reaction rate requires knowledge of how many alphas go off in which directions. That in turn depends on the reaction model chosen—it’s different in the C-12 route then in the direction collision route. We’ll no doubt be hearing more about this debate as new data accumulates.
This exciting and productive conference opened up a number of potential avenues for collaboration between LPPFusion and other researchers. We’ll be reporting on those as they develop in the coming months. For now, I’m flying back home for a new round of experiments.