Amplification of magnetic fields in radiative plasmas

PI: Prof. Gianluca Gregori, Department of Physics, University of Oxford, UK

Status: Performed in October 2017.

Publications: https://arxiv.org/abs/2008.06594

Inefficient magnetic-field amplification in supersonic laser-plasma turbulence

A.F.A. Bott,et al,

Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK

arXiv:2008.06594v1 [physics.plasm-ph] 14 Aug 2020

Keywords: magneto-hydrodynamics, small-scale turbulent dynamo

Abstract: We report a laser-plasma experiment that was carried out at the LMJ-PETAL facility and realized the first magnetized, turbulent, supersonic plasma with a large magnetic Reynolds number (Rm ≈ 45) in the laboratory. Initial seed magnetic fields were amplified, but only moderately so, and did not become dynamically significant. A notable absence of magnetic energy at scales smaller than the outer scale of the turbulent cascade was also observed. Our results support the notion that moderately supersonic, low-magnetic-Prandtl-number plasma turbulence is inefficient at amplifying magnetic fields.

Upper panel: annotated photograph of the target. Aluminum foils (separated by 8 mm) are irradiated by the LMJ drive-beam lasers. An annular, CH washer is placed over the foil to aid jet collimation. The grids (located 2 mm away from each foil) are made of polyamide. The proton source is a gold foil, located 3 cm from the turbulent plasma’s center. The RCF stack used to detect the protons subsequent to interacting with the plasma is placed 10 cm away on the opposite side. Lower panels: 8.5 MeV proton images (obtained on different experimental shots) at 15.7 ns (left), 19.7 ns (middle) and 22.7 ns (right) after the initiation of the LMJ drive beams