Abstract: Proton beams accelerated by short-pulse lasers rapidly deposit energy into dense targets, making them ideal for creating uniformly heated warm dense matter (WDM) samples. The properties of WDM are crucial to both inertial confinement fusion (ICF) and astrophysics. Besides, after the demonstration of ignition at the National Ignition Facility, the quest to achieve higher gains to make fusion energy suitable for future power plants is renewed. One promising method to increase gain is to separate the compression and heating phases, which is referred to as Fast Ignition (FI). Heating by protons is particularly appealing because they are not prone to transport instabilities like electrons and can be focused using curved geometries. Although a series of experiments have shown performance of proton focusing and heating, direct temperature measurements within proton-heated targets remain scarce. Moreover, it remains unclear how the compression drive would impact proton acceleration and transport in a FI scenario. We have carried out a series of experiments at the OMEGA facility to understand the focusing, transport, and energy deposition of laser-generated proton beams. In these experiments, the EP laser (450-900 J, 6-12 ps) is focused onto a cone-enclosed partial hemisphere to generate and focus an intense proton beam into cold solid material or more recently into imploded plasma. Our findings include novel measurements of x-ray fluorescence emission of solid copper slabs promptly heated by a laser-generated proton beam. Results show proton-heated temperatures exceeding 100 eV in under ~50 ps. Particle-in-cell simulations of proton transport and energy deposition closely matched the observed heating dynamics, which is consistent with the energy deposition of a proton beam of ~5 MeV characteristic temperature focused to a ~100 μm spot and containing ~2% of the laser energy (for protons >1 MeV). Preliminary results of a first integrated experiment, where the intense proton beam is directed towards a Cu-doped CH spherical capsule imploded by 54 UV beams (~18 kJ), hint at a preserved proton acceleration despite the harsh environment generated by the capsule implosion. Radiation-hydrodynamics simulations will be compared with data from this latter experiment and plans for the next integrated experiment scheduled in 2025 will be discussed.

Beam time on OMEGA was supported through the National Laser Users’ Facility (NLUF) program with support from U.S. DOE/NNSA for the University of Rochester under award number DE-NA0004144. This work was also partially supported by Shao-Chi and Lily Lin Chancellor’s Endowed Chair funds.

Bio: Mathieu Bailly-Grandvaux received his Ph.D. degree in 2017 from the University of Bordeaux, France, specializing in Astrophysics, Plasma and Particles. In 2017, he relocated to California to work as a Postdoctoral Researcher in the High Energy Density Physics (HEDP) group of Professor Farhat Beg at the University of California San Diego, where he is currently an Assistant Project Scientist. Mathieu received an award in 2018 from the University of Osaka, Japan for his outstanding contribution in the field of HEDP and Inertial Fusion Energy (IFE). His research focuses on the study of energy transport and particle acceleration in plasmas, with a particular interest in magnetized environments and applications in IFE and laboratory astrophysics. He has over 30 publications in prestigious journals (>1000 citations) and presented his work to major plasma physics international conferences. As sole principal investigator (PI), his research has been funded by the U.S. Department of Energy, and he is co-leading projects funded by the National Nuclear Security Administration, the University of California, and the Defense Threat Reduction Agency. Mathieu’s recent work includes the study of magnetized cylindrical implosions and intense proton heating for applications in astrophysics and inertial confinement fusion.