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Flammability limits of hydrogen-oxygen-diluent mixtures were determined in a 5-cm diameter, 1.8-m long tube, for upward, downward and horizontal prop agation of the flame. It was found that for fuel-lean mixtures, upward limits were nearly independent of the diluent type and concentration; downward limits showed a slight dependence on diluent type and concentration. Limits for fuel- rich mixtures were independent of the direction of propagation of the flame. In all cases, to a good approximation, horizontal limits lay midway between the upward and downward limits. It was also found that limits for fuel-rich mixtures were dependent on the oxygen volume fraction. Empirical correlations are presented to estimate the limits.

Ion acceleration in electrostatic collisionless shocks is driven by the interaction of the high-power laser with specially tailored near-relativistic critical density plasma. 2D EPOCH particle-in-cell simulations show that the ion acceleration is dependent on the target material used. In materials with low charge-tomass ratio hZ=Ai, proton beams with high flux and low energy spread are generated. In multi-ion plasmas the ions with different hZ=Ai acquire different velocities under a non-oscillating component of electrostatic field in the upstream region. This relative drift between the protons (hZ=Ai ¼ 1) and the lower hZ=Ai ions leads to the excitation of electrostatic ion two-stream instability. This in turn generates a low-velocity component in the upstream expanding protons. The velocity distribution of the upstream expanding protons is further broadened toward the higher velocity by the electrostatic ion two-stream instability between reflected protons, which results in large number of protons being accelerated by the shock.

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