MAGNETIC AND ELECTRIC-CURRENT MORPHOLOGY IN THE PLASMA EJECTED BY A LASER-IRRADIATED FOIL

A quasisteady model for the plasma ablated from a thick foil by a laser pulse, at low phi-a-lambda-L2 and R / lambda-L2 within a low, narrow range, is given (phi-a is absorbed intensity, lambda-L wavelength, R focal-spot radius). An approximate analytical solution is given for the two-dimensional plasma dynamics. At large magnetic Reynolds number R(M), the morphology of the magnetic field shows features in agreement with recent results for high intensities. Current lines are open: electric current flows toward the spot near its axis, then turns and flows away. The efficiency of converting light energy into electric energy peaks at R(M) approximately 1. Both the validity of the model and accuracy of the solution are discussed. The neighborhood of the spot boundary is analyzed in detail by extending classical Prandtl-Meyer results.