Sandia National Laboratories is pursuing a variation of Magneto-Inertial Fusion called Magnetized Liner Inertial Fusion, or MagLIF. The MagLIF approach requires magnetization of the deuterium fuel, which is accomplished by an initial external B-Field and laser-driven pre-heat. While magnetization is crucial to the concept, it is challenging to couple sufficient energy to the fuel, since laser-plasma instabilities exist, and a compromise between laser spot size, laser entrance window thickness, and fuel density must be found. Nonlinear processes in laser plasma interaction, or laser-plasma instabilities (LPI), complicate the deposition of laser energy by enhanced absorption, backscatter, filamentation and beam-spray. Key LPI processes are determined, and mitigation methods are discussed. Results with and without improvement measures are presented.
A hybrid fs/ps pure-rotational CARS scheme is demonstrated in the product gases of premixed hydrogren/air and ethylene/air flat flames. Near-transform-limited, broadband femtosecond pump and Stokes pulses impulsively prepare a rotational Raman coherence, which is later probed by a high-energy, frequency-narrow picosecond pulse, generated by sum-frequency mixing of linearly chirped broadband pulses with conjugate temporal phase. Spectral fitting is demonstrated for both shot-averaged and single-laser-shot spectra. Measurement accuracy is quantified by comparison to adiabatic-equilibrium calculations for the hydrogen/air flames, and by comparison to nanosecond CARS measurements for the ethylene/air flames. Temperature-measurement precision is 1-3% and O2/N2 precision is 2-10% based on histograms constructed from 1000 single-shot measurements acquired at a data rate of 1 kHz. These results indicate that hybrid fs/ps rotational CARS is a quantitative tool for kHz-rate combustion temperature/species data.