Time-resolved fast turbulent dynamo in a laser plasma

Abstract

Understanding magnetic-field generation and amplification in turbulent plasma is essential to account for observations of magnetic fields in the universe. A theoretical framework attributing the origin and sustainment of these fields to the so-called fluctuation dynamo was recently validated by experiments on laser facilities in low-magnetic-Prandtl-number plasmas ($\mathrm{Pm}<1$). However, the same framework proposes that the fluctuation dynamo should operate differently when $\mathrm{Pm}\gtrsim 1$, the regime relevant to many astrophysical environments such as the intracluster medium of galaxy clusters. This paper reports a new experiment that creates a laboratory $\mathrm{Pm}\gtrsim 1$ plasma dynamo for the first time. We provide a time-resolved characterization of the plasma's evolution, measuring temperatures, densities, flow velocities and magnetic fields, which allows us to explore various stages of the fluctuation dynamo's operation. The magnetic energy in structures with characteristic scales close to the driving scale of the stochastic motions is found to increase by almost three orders of magnitude from its initial value and saturate dynamically. It is shown that the growth of these fields occurs exponentially at a rate that is much greater than the turnover rate of the driving-scale stochastic motions. Our results point to the possibility that plasma turbulence produced by strong shear can generate fields more efficiently at the driving scale than anticipated by idealized MHD simulations of the nonhelical fluctuation dynamo; this finding could help explain the large-scale fields inferred from observations of astrophysical systems.

12 pages, 9 figures

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Cited by in corpus (13)

• Quasi-Periodic Erupters: A Stellar Mass-Transfer Model for the Radiation
• Retrieving transient magnetic fields of ultrarelativistic laser plasma via ejected electron polarization
• Fundamental scales in the kinematic phase of the turbulent dynamo
• Strong suppression of heat conduction in a laboratory replica of galaxy-cluster turbulent plasmas
• High Repetition Rate Exploration of the Biermann Battery Effect in Laser Produced Plasmas Over Large Spatial Regions
• Fundamental MHD scales -- II: the kinematic phase of the supersonic small-scale dynamo
• Persistent mysteries of jet engines, formation, propagation, and particle acceleration: have they been addressed experimentally?
• Growth or Decay -- I: universality of the turbulent dynamo saturation
• Insensitivity of a turbulent laser-plasma dynamo to initial conditions
• A systematic route to subcritical dynamo branches
• Impact of Electron Transport Models on Capillary Discharge Plasmas
• Turbulent dynamo in the terrestrial magnetosheath
• Scaling of Small-Scale Dynamo Properties in the Rayleigh-Taylor Instability