标题： 一种使用反向传播波测量阿尔芬波参量衰减不稳定性增长的新方案 显示英文标题

标题： A novel scheme for measuring the growth of Alfven wave parametric decay instability using counter-propagating waves

摘要： 阿尔芬波的参数衰减不稳定性（PDI）——其中泵浦阿尔芬波衰减为一个向后传播的子阿尔芬波和一个向前传播的离子声波——是一种基本的非线性波-波相互作用，并对空间和实验室等离子体具有重要意义。 然而，迄今为止，还没有直接的实验测量PDI。 在这里，我们提出了一种新颖且实验可行的方案，使用一个大泵浦阿尔芬波和一个小的反向传播种子阿尔芬波，在线性装置上量化阿尔芬波PDI的增长，其中种子波的频率被调整以匹配标准PDI产生的向后阿尔芬波。 通过混合模拟，我们展示了从泵浦波到种子波的能量转移减少了后者的空间阻尼。 通过比较有无泵浦波时的种子波振幅，这种阻尼减少可以作为PDI增长的直接且可靠的代理。 该方法在我们的模拟中针对一系列等离子体和波参数进行了验证，并与理论预测相符。 值得注意的是，该方案对于PDI的激发没有阈值，并且原则上在当前实验室条件下很容易实现。 该方案是解决实验研究阿尔芬波PDI挑战的关键一步，并提供了一种优雅的方法，可用于在受控实验室环境中验证参数不稳定的 fundamental 理论。 显示英文摘要

摘要： The parametric decay instability (PDI) of Alfven waves -- where a pump Alfven wave decays into a backward-propagating child Alfven wave and a forward ion acoustic wave -- is a fundamental nonlinear wave-wave interaction and holds significant implications for space and laboratory plasmas. However, to date there has been no direct experimental measurement of PDI. Here, we propose a novel and experimentally viable scheme to quantify the growth of Alfven wave PDI on a linear device using a large pump Alfven wave and a small counter-propagating seed Alfven wave, with the seed wave frequency tuned to match the backward Alfven wave generated by standard PDI. Using hybrid simulations, we show that energy transfer from the pump to the seed reduces the latter's spatial damping. By comparing seed wave amplitudes with and without the pump wave, this damping reduction can be used as a direct and reliable proxy for PDI growth. The method is validated in our simulations across a range of plasma and wave parameters and agrees well with theoretical predictions. Notably, the scheme exhibits no threshold for PDI excitation and is, in principle, readily implementable under current laboratory conditions. This scheme is a critical step toward solving the challenge of experimentally accessing Alfven wave PDI and provides an elegant method that may be used to validate fundamental theories of parametric instabilities in controlled laboratory settings.