First experimental demonstration of magnetized fast laser isochoric heating for efficient creation of high-energy-density states

Shinsuke Fujioka, Institute of Laser Engineering, Osaka University
January 26, 2018, 11:00am - 12:00pm, SERF Room 232



The quest for the inertial confinement fusion (ICF) ignition is a grand challenge, as exemplified by extraordinary large laser facilities like National Ignition Facility (NIF). Although scientific break-even, the energy released by fusion reaction exceeds the energy contains in the compressed fusion fuel, was achieved on NIF, the pathway to the ignition is still unclear. Fast isochoric heating of a pre-compressed plasma core with a high-intensity short-pulse laser is an attractive approach to create ultra-high-energy-density states like those found in inertial confinement fusion ignition sparks. This avoids the ignition quench caused by the hot spark mixing with the cold fuel, which is the crucial problem of the currently pursued ignition scheme.Relativistic-intensity laser-plasma interactions efficiently produce relativistic electron beams (REB). However, only a small portion of the REB collides with the core because of its large divergence. Here we have demonstrated enhanced laser-to-core energy coupling with a magnetized fast isochoric heating method. The method employs a kilo- tesla-level magnetic field that is applied to the transport region from the REB generation point to the core which results in guiding the REB along the mag- netic field lines to the core. 7.7 ± 1.3 % of the maximum coupling was achieved even with a relatively small radial area density core (ρR ∼ 0.1 g/cm2). A simple model shows 6.2% of the coupling with the experimentally measured parameters, this value is fairly consistent with the coupling measured in the integrated experiment, and the simple evaluation reveals that higher area density core leads to higher laser-to-core coupling. An energy density increment of the heated core is about 1 Gbar, which corresponds to 50 J of the energy deposition in a 100 μm-diameter spherical volume. An ultra-high-energy density state could be efficiently created by the magnetized fast isochoric heating. Finally, plasma hydrodynamics, generation and transport of electron/ion beams, thermal conduction and α particle transport will be able to be controlled by the externally applied strong magnetic field. There is no doubt that laser-plasma experiments with strong magnetic fields contain a lot of unexplored physics, therefore this research also stimulates spin-off sciences in the field of atomic physics, nuclear physics, and astrophysics which act to broaden inertial fusion sciences and high energy density sciences.



Shinsuke Fujioka is a professor of Institute of Laser Engineering (ILE), Osaka University, Japan since 2015 and a visiting scientist of Lawrence Livermore National Laboratory in 2017. He received Doctor degree from Graduated School of Engineering at Osaka University (Osaka, Japan) in 2005 for his studies on "Suppression of hydrodynamic instability on ablation surface of laser-driven fusion pellet". Since 2004, he joined ILE as an assistant professor and he worked on development of laser-based extreme ultraviolet (EUV) light source for the next-generation photo-lithography application, x-ray spectroscopy of photo ionized plasma generated with high-power laser, and fast isochoric heating of inertial confinement fusion. He also acted the leader of the FIREX (Fast Ignition Realization EXperiment) project in Japan from 2013 to 2016. He was awarded the young scientists' prize from the Minister of Education, Culture, Sports, Science and the technology in 2011 and also from Japanese Society of Physics in 2010. He is author of 237 journal papers according to Web of Science database.

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