低Z流体的单次冲击波压缩极限是判断各种研究高压物态方程理论和实验正确与否的重要参数。维里定律和Hugoniot方程表明, 单次冲击波压缩率是由各种因素的相对重要度决定的, 包括平均势能、平均动能、内部自由度的激发度和逆幂函数型势能曲线的幂指数。如果幂指数大于2, 相互作用势能使流体变得比理想气体更难压缩, 否则流体就比理想气体更容易压缩。内部自由度的激发总是让流体变得更容易压缩。在各种不同因素起主导作用的压强段, 低Z流体的单次冲击波压缩极限不同。用一个简单的单次冲击波压缩极限的表达式解释了低Z流体在离解区域和电离区域的行为。

Compression limit of low-Z fluid is the most important criterion of theoretical and experimental study of equations-of-state at high pressure. Virial theorem and Hugoniot equation show that the shock compression ratio is decided by the excitation degree of internal degree-of-freedom, average potential energy, average kinetic energy and the scaling exponent of the potential in inverse-power law. If the scaling exponent exceeds two, the interaction effects make the fluid less compressible than an ideal gas, otherwise the interaction effects make the fluid more compressible. The excitation of internal degree-of-freedom makes the fluid easier to compress.Accordingly, the low-Z fluid has different compression limits at different pressure ranges where different effects work. A simple function for single-shock compression limit is derived to discuss the behaviors of low-Z fluids in the dissociation regime and in the ionization regime.