An Xin, Artemyev Anton, Angelopoulos Vassilis, Liu Terry Z, Vasko Ivan, Malaspina David
Department of Earth, Planetary, and Space Sciences, <a href="https://ror.org/046rm7j60">University of California</a>, Los Angeles, California 90095, USA.
Department of Physics, <a href="https://ror.org/049emcs32">University of Texas at Dallas</a>, Richardson, Texas 75080, USA.
Phys Rev Lett. 2024 Nov 29;133(22):225201. doi: 10.1103/PhysRevLett.133.225201.
In space plasmas, large-amplitude Alfvén waves can drive compressive perturbations, accelerate ion beams, and lead to plasma heating and the excitation of ion acoustic waves at kinetic scales. This energy channeling from fluid to kinetic scales represents a complementary path to the classical turbulent cascade. Here, we present observational and computational evidence to validate this hypothesis by simultaneously resolving the fluid-scale Alfvén waves, kinetic-scale ion acoustic waves, and their imprints on ion velocity distributions in the Earth's magnetopause boundary layer. We show that two coexisting compressive modes, driven by the magnetic pressure gradients of Alfvén waves, not only accelerate the ion tail population to the Alfvén velocity, but also heat the ion core population near the ion acoustic velocity and generate Debye-scale ion acoustic waves. Thus, Alfvén-acoustic energy channeling emerges as a viable mechanism for plasma heating near plasma boundaries where large-amplitude Alfvén waves are present.
在空间等离子体中，大振幅阿尔文波可以驱动压缩扰动、加速离子束，并导致等离子体加热以及在动力学尺度上激发离子声波。这种从流体尺度到动力学尺度的能量传递代表了一条与经典湍流级联互补的路径。在这里，我们通过同时解析地球磁层顶边界层中的流体尺度阿尔文波、动力学尺度离子声波及其在离子速度分布上的印记，给出观测和计算证据来验证这一假设。我们表明，由阿尔文波的磁压力梯度驱动的两种共存压缩模式，不仅将离子尾群加速到阿尔文速度，还在离子声速附近加热离子核心群，并产生德拜尺度的离子声波。因此，阿尔文 - 声能传递成为在存在大振幅阿尔文波的等离子体边界附近进行等离子体加热的一种可行机制。
