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Date: November 17, 2021, Virtual
Speaker: Stephen Obenschain, U.S. Naval Research Laboratory
Title: Progress Towards High-gain Inertial Confinement Fusion With Lasers
Time: 1:00 pm Eastern Standard Time (US and Canada). Attendees can sign in any time after 12:30 p.m.
Abstract: Inertial confinement fusion (ICF) involves the compression and ignition of frozen deuterium-tritium “fuel“ contained within several mm diameter pellets. The most advanced approach utilizes high-energy high-power lasers to drive the implosion. This is being attempted either by directly illuminating and thereby heating the pellet surface, or the indirect-drive approach where the laser beams heat the inner wall of a gold hohlraum containing the pellet and the x-rays from the heated wall drive the pellet implosion. Recently the National Ignition Facility (NIF) achieved a 1.3 MJ fusion yield using 1.9 MJ of laser light with the indirect drive configuration.* This achievement supports the basic viability of inertial fusion, and the fusion energy came close to matching the laser energy (gain =0.7). However, for the energy application one needs much higher gains (>100) so that most of the generated power is available to be distributed to the grid rather than to power the laser and other power plant systems. The direct-drive approach is more efficient and therefore more capable of reaching such gains. High-gain direct-drive implosions require uniform illumination of the target, and means to mitigate hydrodynamic and laser plasma instabilities. The electron-beam-pumped argon-fluoride (ArF) laser under development at the Naval Research Laboratory could be the ideal driver for such implosions.** Its short wavelength (193 nm vs 351 nm on NIF) and capability to provide multi-THz bandwidth light on target would improve the efficiency of the implosion and suppress instabilities. This presentation will discuss the status of laser inertial fusion research, and a potential path to practical inertial fusion energy (IFE) using the ArF laser.
Biography: Dr. Obenschain is Head of the Laser Plasma Branch and leads the laser fusion program at the U.S. Naval Research Laboratory. The laser fusion program includes research efforts in laser-matter-interaction experiments, in large-scale simulations of pellet implosions, and in development of high-energy excimer laser technology for inertial fusion. Dr. Obenschain was project manager for the design and construction of Nike, the world’s largest krypton fluoride (KrF) laser facility. The program has recently begun development of the shorter wavelength (193 nm) high-energy argon-fluoride (ArF”) laser which is projected to be a very attractive driver for inertial fusion energy. He was co-inventor with Dr. Robert Lehmberg, of the induced spatial incoherence (ISI) technique that provides uniform illumination of targets by high-energy lasers. He led the first experimental efforts that showed such laser beam-smoothing schemes help suppress deleterious laser-plasma instability. For this work, he was a recipient of the 1993 APS-DPP award for Excellence in Plasma Physics Research. He received the Fusion Power Associates Leadership award in 2012. In selecting Dr. Obenschain, the FPA Board recognized his many scientific and technical contributions to fusion development and the leadership he has been providing to the U.S. and world inertial fusion efforts, including the leadership and vision he has been providing to planning for a next-step inertial fusion test facility. He is a fellow of the American Physical Society. He received a B.S. degree in physics from the University of Virginia and a Ph.D. in physics from UCLA.
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