超流$^4$ He中台面形声子脉冲的形成
Formation of a mesa shaped phonon pulse in superfluid $^4$He
摘要：
本文提出了超流$^4$ He中台面形声子脉冲的形成理论。从超流氦的流体力学方程出发，得到了描述强各向异性声子系统演化的方程组。这样的系统可以通过实验来创建。方程的解是简单波，它对应于运动声子脉冲中的第二声。利用这些精确解，我们描述了零温下超流氦中声子脉冲的膨胀。这一理论给出了一个解释的台面形状观察到的声子角分布。几乎所有的台面形状对系统参数的依赖关系可以定性地理解。
英文摘要：
We present a theory for the formation of a mesa shaped phonon pulse in superfluid $^4$He. Starting from the hydrodynamic equations of superfluid helium, we obtain the system of equations which describe the evolution of strongly anisotropic phonon systems. Such systems can be created experimentally. The solution of the equations are simple waves, which correspond to second sound in the moving phonon pulse. Using these exact solutions, we describe the expansion of phonon pulses in superfluid helium at zero temperature. This theory gives an explanation for the mesa shape observed in the measured phonon angular distributions. Almost all dependencies of the mesa shape on the system parameters can be qualitatively understood.
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