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Abstract: Plasmas confined by a dipole magnetic field exhibit interchange and entropy mode turbulence causing bursty intermittent transport of particles and energy. On the Collisionless Terrella Experiment (CTX), this turbulence is dominated by low-frequency, long-wavelength modes with amplitudes and phases that vary chaotically in time. We present a new paradigm for characterizing this turbulence by measuring the time-evolution of the fluctuation power spectrum and the instantaneous bispectrum using the continuous wavelet transform and computing the statistical properties of turbulent wave kinetics. We observe that both the fluctuation power and the energy transfer by three-wave coupling, or bispectrum, between these fluctuations can be intermittent. When antenna are used to actively launch waves into the turbulence, the intermittency of the driven waves decreases, while the intermittency of other waves increases. Similarly, application of active feedback to amplify the turbulence decreases the intermittency of the wave energy, while suppressing feedback increases this intermittency. Measurements based on this new paradigm show that the transfer of wave energy to larger and smaller scales in a turbulent plasma is not steady but occurs in short and intense bursts, analogous to the better-known short bursts of particle transport in magnetized plasma.
Bio: Mel Abler is a Postdoctoral Research Associate at the Space Science Institute focused on experimental studies of the nonlinear behavior of Alfven waves. They recently completed their doctoral work characterizing turbulent wave kinetics and energy transfer via three-wave coupling in a dipole-confined plasma at Columbia University. Mel is a passionate advocate for improving inclusion in physics, and currently serves as the Secretary-Treasurer of the APS DPP Pride Committee. Outside the lab, Mel is an avid theater goer, union organizer, and competitive rower.