Coherent Vorticity Holes from 2D Turbulence Decaying in a Background Shear Flow

Abstract

Freely decaying 2D turbulence in magnetized electron columns has been measured using a phosphor screen/CCD camera diagnostic. The relaxation towards axisymmetric equilibrium is hindered by medium-sized coherent vorticity holes which persist for hundreds of column rotations despite the strong negative rotational shear. These holes tend to settle into symmetric configurations in the column, give a negative skew to the measured vorticity fluctuations, and are eventually destroyed due to a slow outward radial creep.