For this energy application, the KrF laser amplifiers require very high-energy, high-voltage and durable pulse power systems that far exceed any previous state of the art capabilities. It requires operating many millions of continuous shot cycles at 5 to 10 pulses per second. With peak power capability more than 10 times higher than that of any other all solid-state pulse power system, this system is the prototype for still higher power and voltage systems that will be developed for NRL’s high performance electron beam pumped KrF lasers. The prototype system produces 300 nanosecond duration electrical pulsed of 200,000 volts at 5,000 amps and operates at 10 pulses per second.
In recent tests it has run continuously for 11,500,000 shots over 319 hours of nonstop operation. This is 100 times longer than possible with existing sparkgap switch-based systems of similar energy and repetition rate.
The National Academy of Sciences (NAS) has been conducting a major review of the prospects for inertial fusion energy. Currently, the U.S. Fusion Energy Sciences program is almost entirely focused on magnetic confinement fusion, while the inertial confinement fusion (ICF) program is funded by NNSA, whose mission is nuclear weapons physics and Stockpile Stewardship. NRL scientists have been actively involved in this review process and have made numerous presentations to the NAS review panels.
NRL presentations to the NAS Panel on Prospects for Inertial Confinement Fusion Energy Systems were made at panel meetings in San Ramon, CA (January, 2011) and at the University of Rochester (June, 2011). These overview presentations described the KrF laser direct drive approach to IFE and the numerous attractive features of this approach. Some of the advantages are specific to KrF laser technology and the interaction of the laser pulse with the target, while others are applicable to any direct drive target approach. On 2 November 2011, the panel visited NRL for a half day of tours and in depth discussions. Dr. Steve Obenschain presented the primary overview of NRL IFE efforts. The tours of the Nike and Electra facilities were enhanced by short briefings by individual staff members conducted in the experimental areas. Also presented was a history of the High Average Power Laser (HAPL) program, which supported research on a wide range of science and technology requirements for a commercial fusion electric power plant based on repetitively-pulsed lasers and direct drive targets. HAPL was a congressionally mandated program led by Dr. John Sethian that coordinated and funded S&T efforts at dozens of universities, national laboratories, and private companies before funding ended in 2009.
NRL has been even more directly involved in the NAS Sub-panel on Assessment of Inertial Confinement Fusion (ICF) Targets. Dr. Andrew Schmitt summarized direct drive target physics research at NRL at two subpanel meetings in Washington, DC (February, 2011 and September, 2011). This work focused on experimental studies of laser plasma instabilities (LPI) on Nike and the substantial potential increases in target gain from using shock ignition on direct drive targets. At the latter meeting, Dr. Steve Obenschain reviewed the NRL program and Dr. Sethian summarized past results from the HAPL program.
NRL also participated in the EPRI Fusion Energy Assessment (FEA) Workshop in July, 2011. The Electric Power Research Institute (EPRI) is an industry-funded nonprofit organization that supports research related to the generation, delivery, and use of electricity. Drs. Obenschain, Sethian, and Dr. Max Karasik outlined the NRL program and described the advantages and recent advances in KrF laser technology, direct drive targets, and other technology components. Active involvement by the electric power industry at an early stage will be essential if inertial fusion energy is to fulfill its promise.