Onset of turbulence in an autooscillating complex plasma

Abstract

Turbulence is one of the last unresolved issues of modern theoretical physics. In conventional experiments on turbulence, the carriers of the interaction are not directly observable. Instead, typically tracer particles are used - a method that might not produce reliable results [1]. Here, we present an experiment performed in the PK-3 Plus Laboratory on board the International Space Station [2] which allows investigating the fundamental particles in turbulence directly. First, the complex plasma cloud was stabilized with an alternating electric field. Once the stabilization was switched off, a heartbeat instability developed, and the microparticles started oscillating radially. We show that the kinetic energy spectra develop a double cascade once the cloud becomes unstable, see Figure 1. This double cascade has been predicted by Kraichnan [3] and Leith [4] for forced two-dimensional turbulence, but has only seldomly been observed in experiments [5]. We also show that the reduced rates of energy and enstrophy transfer can be used to infer the excitation wave number kexc, in good agreement with kexc obtained from the energy spectrum. [1] V. Mathai et al. Phys. Rev. Lett. 117, 024501 (2016). [2] H. M. Thomas et al. New J. Phys. 10, 033036 (2008). [3] R. H. Kraichnan. Phys. Fluids 10, 1417 (1967). [4] C. E. Leith. Phys. Fluids 11, 671 (1968). [5] G. Boffetta and R. E. Ecke. Ann. Rev. Fluid Mech. 44, 427{451 (2012)