An experimental study of magnetic fields in plasmas created by high intensity one micron laser radiation

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Abstract
Magnetic fields generated in plasmas formed by focusing intense picosecond (∼20 psec) duration Nd: laser pulses onto disk targets have been studied using simultaneous polarimetry and interferometry for a wide range of laser and plasma parameters. Megagauss fields, which extend throughout the plasma corona, have been observed during the pulse, but subsequently these decay rapidly and are unobservable only 100 psec after the pulse peak. The general morphology of the field together with this rapid decay suggests a role for the superthermal particles in magnetic field generation and saturation (via convection). Hard x-ray (∼20 keV) imaging has been used to relate the regions of energy deposition by superthermal electrons to the magnetic field structure. The results are compared with the predictions of recent two-dimensional (2-D) computer simulations.