Parametric Decay of Alfvenic Wave Packets in Nonperiodic Low-beta Plasmas

The parametric decay of finite-size Alfven waves in nonperiodic low-beta plasmas is investigated using one-dimensional (1D) hybrid simulations. Compared with the usual small periodic system, a wave packet in a large system under the absorption boundary condition shows different decay dynamics, including reduced energy transfer, localized density cavitation, and ion heating. The resulting Alfven wave dynamics are influenced by several factors relating to this instability, including the growth rate, central wave frequency, and unstable bandwidth. A final steady state of the wave packet may be achieved when the instability does not have enough time to develop within the residual packet, and the packet size shows well-defined scaling dependencies on the growth rate, wave amplitude, and plasma beta. Under the proper conditions, enhanced secondary decay can also be excited in the form of a narrow, amplified wave packet. These results may help to interpret laboratory and spacecraft observations of Alfven waves, and to refine our understanding of the associated energy transport and ion heating.

Automated summary

The parametric decay of finite-size Alfven waves in nonperiodic low-beta plasmas is investigated using one-dimensional (1D) hybrid simulations. The results show that a wave packet in a large system under the absorption boundary condition exhibits different decay dynamics compared to the usual small periodic system, including reduced energy transfer, localized density cavitation, and ion heating. Several factors relating to the instability, such as the growth rate, central wave frequency, and unstable bandwidth, influence the resulting Alfven wave dynamics.