When I was working at Sandia National Laboratories, my fusion research began with a concept of highly-focused, high-current electron beams. After a few years, my colleagues decided that the energy deposition of ions would be more favorable than electron beams for target coupling and implosion. This changed our approach to ion beam focusing. It also led us to propose construction of a new pulsed power machine, which we decided to call Particle Beam Fusion Accelerator or PBFA.

In addition, the researchers emphasized the use of radiation coupling, which years later would become the key to the recent fusion breakthrough at Lawrence Livermore National Laboratory’s National Ignition Facility. We thought radiation coupling would be essential to driving a spherically symmetric implosion.

In our original plan, we thought we would need an electron beam pulse of 100 trillion watts, which was 100 times more than what we had in the lab at that time. As it turned out, that tremendous increase was still not enough. My colleagues at Sandia went through many iterations struggling to get to the 100 trillion-watt level. After many experiments, many decisions and several critical government reviews, we felt convinced that the ion approach was going nowhere. In the mid 1990s, our program was on the edge of termination. 

Then a technical miracle happened. We discovered a more promising approach to creating the radiation source. We could use a multiple wire Z pinch. We redirected all of our resources to the Z pinch. In 1998, I wrote about this effort in a Scientific American article entitled “Fusion and the Z pinch.” 

To succeed with this approach, it seemed that a much higher current pulsed power machine would be needed. I proposed a new machine called X-1, which meant yet another large increase in funding. The Department of Energy was not entirely amused, but agreed to upgrade the Z machine. With the upgrade, the program continued with improved computer simulations, diagnostics and machine performance all focused on radiation-driven targets.

Recently, Steve Slutz, a Sandia scientist, and his colleagues, came up with a theoretical breakthrough. They suggested using the Z pinch to directly compress the fusion fuel embedded in a strong magnetic field. To lower the power requirement for ignition, a laser is used to achieve the pre-heat needed to start the burn. Aided by the applied magnetic field, the laser preheats the cold fuel. The next step will to achieve ignition and then high gain. We are unsure how much energy will be needed to get a successful high gain from the fusion explosion. There are several theoretical estimates, and Sandia is now considering building a next generation Z machine to deliver 10 megajoules to a fusion target.

The quest for fusion represents decades of research. In my next post, I will discuss the contributions the Russians made to fusion research. For now, I’ll conclude by pointing out how the path to scientific breakthroughs is often littered with false starts, setbacks, disappointments and then startling breakthroughs. I describe this process in my new science fiction novel, The Dragon’s C.L.A.W., which will be released May 16, 2023. Like the fusion researchers at the real national laboratories, my characters are seeking the ultimate clean, safe, unlimited energy source. Will they succeed? Preorder the first novel in this series to find out.