KrF Lasers, Direct Drive, and Inertial Confinement: a path to fusion energy

John Sethian

Fusion powers the Sun and the stars.  If harnessed on earth it would be a source of clean, abundant energy.  In the fusion reaction, two forms of hydrogen, deuterium (D) and tritium (T), are brought together to form a helium ion and release large quantities of energy.  Because the D and T are brought together and “fused,” the process is called fusion.  The fuel is plentiful: the deuterium in one gallon of sea water has as much energy as 300 gallons of gasoline, and the Tritium is bred from lithium, which is an abundant element in the earth’s crust. The fusion reaction produces no greenhouse gasses or chemical pollution, so it is a very clean and “green” energy source.  While fusion does induce radioactivity, it is only in the surrounding structure, and is at a low enough level to be readily handled. So if fusion is so good, why don’t we have it?  The answer is simple: it has turned out to be very tough to get it to work!  The main challenge is holding enough DT together, for a long enough time, and at a high enough temperature, to initiate the fusion reaction. Researchers have been worldwide investigating and developing several approaches to fusion energy for almost five decades.

One promising approach to fusion is to use a powerful array of lasers to quickly compress and heat a pea-sized pellet of deuterium and tritium "fuel." The approach that is the simplest and most energetically efficient is to illuminate the pellet directly with the laser beams. This "direct drive" approach is being investigated in the US by the Naval Research Laboratory (NRL) and the University of Rochester's Laboratory for Laser Energetics. Another approach, considerably more complex approach is to use the lasers to heat the inner walls of a small cavity to produce x-rays to drive the pellet. This is the path chosen for the National Ignition Facility in California.

NRL has developed an electron beam pumped the Krypton Fluoride (KrF) gas laser for direct drive laser fusion. These lasers have inherent unique advantages that are predicted to make it easier and more efficient to achieve the high performance (energy produced) needed for a power plant. Recent advances in the pellet physics, the laser technologies, and the other key parts for a power plant make this a very promising approach.

This talk will discuss this technical progress, as well as the path to a clean, fusion based, power source.

This lecture is sponsored by the Institute of Electrical And Electronic Engineers (IEEE) Nuclear and Plasma Sciences (NPSS) Distinguished Lecturers Program.

Research has been by the US Department of Energy, Defense Programs

Biography

Dr. John Sethian recently retired from The Naval Research Laboratory as the head of the Electron beam Science and Applications Section of the Laser Plasma Branch in the Plasma Physics Division.  He was born in Washington, DC and attended public schools in Arlington County, VA. He received an A.B. degree in physics from Princeton University in 1972, and a Ph.D. degree in applied physics from Cornell University in 1976. He has worked as a scientist at the Naval Research Laboratory (NRL) since 1977.

At NRL, Dr. Sethian worked on a broad range of topics in plasma physics, electron beam physics, pulsed power, lasers, and all approaches to fusion: inertial, magnetic and z-pinch based.  His most recent contribution was founding and directing the national “High Average Power Laser” (HAPL) Program.  This program was directed to develop the technological underpinnings for practical fusion power based on lasers and the direct drive.  The program brought together more than 60 researchers from national labs, universities, and private industries. The key science and technologies were developed in concert with one another as a part of coherent system. Credible solutions for most all the key components were developed.

As part of the HAPL program, Dr Sethian developed the science and technologies needed to build a repetitively pulsed, large area, high energy electron beam source.  He first applied the technology to develop a durable and efficient electron beam pumped krypton fluoride (KrF) Laser to meet the requirements for fusion energy.  He later applied the technology to a wide range of applications, including material surface modification, fuel reformation, and most recently, the elimination of NOx in fossil fuel power plants.

Although officially retired, he still remains active in several scientific disciplines.  He is an adjunct professor at Washington State University, with the role of deploying a high energy laser facility on the Dynamic Compression Sector of the Advanced Photon Source at Argonne National Laboratory. He also serves as an advisor on several research projects throughout the US.

Dr. Sethian is a Fellow of the American Physical Society, has received four NRL invention/technology transfer awards, four patents, three NRL publication awards, and has published over 80 archival papers. He has received the Fusion Power Associates Leadership Award, the American Nuclear Society’s Annual Outstanding Achievement Award, and the US Navy Meritorious Service Medal.