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The parametric decay of finite-size Alfv\'en waves in nonperiodic low-betaplasmas is investigated using one-dimensional hybrid simulations. Compared withthe usual small periodic system, a wave packet in a large system under theabsorption boundary condition shows different decay dynamics, including reducedenergy transfer and localized density cavitation and ion heating. The resultingAlfv\'en wave dynamics are influenced by several factors of the instabilityincluding the growth rate, central wave frequency, and unstable bandwidth. Afinal steady state of the wave packet may be achieved when the instability doesnot have enough time to develop within the residual packet, and the packet sizeshows well-defined scaling dependencies on the growth rate, wave amplitude, andplasma beta. Under the proper conditions enhanced secondary decay can also beexcited in the form of a narrow, amplified wavepacket. These results may helpinterpret laboratory and spacecraft observations of Alfv\'en waves, and refineour understanding of associated energy transport and ion heating.

Parametric decay of Alfv\'enic wave packets in nonperiodic low-beta plasmas