The Inverse Faraday Effect In Plasma

The existence of axial magnetic field 1-3 induced by the interaction of circularly polarized laser light with plasma is reported. Axial magnetic fields from 500 Gauss up to 2.17 MegaGauss were measured using a Nd:YAG laser with a pulse duration of 7 ns for irradiance from 109 to 1014 W/cm'2 accordingly. Up to 5 - 1013 W/cm2, the results are in agreement with a nonlinear model of the inverse Faraday effect dominated by the ponderomotive force. Two diagnostic methods were used to measure the axial magnetic field. At low irradiance (109 - 101'1 W/cm2) the axial magnetic field induced by the circularly polarized laser light (CPLL) in a ferrite target was measured from the voltage signal induced by the magnetic field in an output coil. At higher irradiance the axial magnetic field was measured using the Faraday rotation diagnostic. The scaling law of the measured axial magnetic field B from the experiments performed with CPLL, in the intensities range of 109 - 1013 W/cm2, is B ∼ I /1/2. At higher intensities of the order of 3 . 101'4 W/cm2 a sudden increase of the axial magnetic field beyond the above scaling law is observed in the experiments performed with CPLL. This study might have interesting implications in creating a mini tokamak configuration in laser produced plasmas, with intermediate plasma densities (1022 cm3) and confinement times (100 ns). Such an approach to fusion circumvents many of the complexities of inertial confinement fusion where very symmetric implosions using many laser beams are required. Intermediate fusion density may also overcome severe requirements of tokamak fusion