Abstract: Spacecraft have long used ablative heat shields for protection during entry into planetary atmospheres. Past heat shield testing approaches using lasers, plasma jets, and hypervelocity projectiles suffered from the problem that no single method could simulate the exact heating conditions present during a high-speed atmospheric entry. Consequently, past models of heat shield behavior have sometimes over-or under-predicted ablation of the heat shield, with potentially disastrous results. Future missions to the outer solar system will need more sophisticated materials than currently exist. In our experiments at DIII-D tokamak, we demonstrated that the hot plasma created by a fusion reactor during operation offers a novel and potentially improved way of modeling heat shield behavior, especially for entries into Venus or the gas giants like Jupiter. Three types of samples were used for the experiments: stationary graphite rods protruding from the vessel's floor, 1-mm-diameter porous carbon spheres, and 700-micron-diameter glassy carbon spheres injected from the floor into the scrape-off layer and edge plasma. In the graphite rod experiments, the mass-loss rates as a function of heat fluxes determined from an extensive array of spectroscopic measurements agree with semi-empirical ablation models obtained from spacecraft flight data. Experimental results for the porous and glassy carbon pellets' trajectories and mass-loss rates are confirmed using the UEDGE-DUSTT simulations. These pellet experiments are also compared against simulations of meteorite atmospheric entries for different velocities, initial masses, and angles of entry. The scaling between DIII-D experimental results, available flight data, and numerical models can be used to address questions ranging from optimization of ablation heat shields for future planetary missions to understanding extraterrestrial delivery of organic material to planet surfaces.
Bio: Dmitri Orlov is an associate research scientist in the Center for Energy Research at the University of California San Diego. He received my B.S. and M.S. from the Moscow Institute of Physics and Technology and a Ph.D. from the University of Notre Dame, where he did pioneer research on the aerodynamic plasma actuators for aerodynamic flow control. He worked at the Department of Physics at the U.S. Air Force Academy before joining the U.C. San Diego's Center for Energy Research in 2008, where he is presently working at the DIII-D National Fusion Facility. His research is focused on the control of the edge instabilities in high-confinement regimes in present-day tokamaks and future plasma burning devices, including ITER, transport in the core and edge of the tokamaks under 3D non-axisymmetric perturbation fields, and heat and particle transport to the diverter surfaces. He is a member of the APS DPP and US TTF Executive Committees and a Vice-Chair of the Coalition for Plasma Science.