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Laser-driven magnetic reconnection is investigated using proton deflectometry. Two laser beams of nanosecond duration were focused in close proximity on a solid target to intensities of I∼1×1015 W cm-2. Through the well known ∇ne×∇Te mechanism, azimuthal magnetic fields are generated around each focal spot. During the expansion of the two plasmas, oppositely oriented field lines are brought together resulting in magnetic reconnection in the region between the two focal spots. The spatial scales and plasma parameters are consistent with the reconnection proceeding due to a Hall mechanism. An optimum focal spot separation for magnetic reconnection to occur is found to be ≈400±100 μm. Proton probing of the temporal evolution of the interaction shows the formation of the boundary layer between the two expanding plasma plumes and associated magnetic fields, as well as an instability later in the interaction. Such laboratory experiments provide an opportunity to investigate magnetic reconnection under unique conditions and have possible implications for multiple beam applications such as inertial confinement fusion experiments. [ABSTRACT FROM AUTHOR]

Measurements of the bidirectional plasma jets that form at the surface of a solid target during a laser-generated driven magnetic reconnection are presented. Resistivity enhancement of at least 25× the classical Spitzer value is required when applying the Sweet–Parker model of reconnection to reconcile the experimentally observed reconnection time scale. Analytic calculations show that a fast reconnection model, which includes a priori the effects of microturbulent resistivity enhancement, better reproduces the experimental observations. [ABSTRACT FROM AUTHOR]

Changes in the poloidal magnetic field around a tokamak magnetic surface due to different values of triangularity and ellipticity are analyzed in this paper. The treatment here presented allows the determination of the poloidal magnetic field from knowledge of the toroidal current density. Different profiles of these currents are studied. Improvements in the analytic forms of the magnetic surfaces have also been found. The treatment has been performed using a recent published system of coordinates. Suitable analytic equations have been used for the elliptic magnetic surfaces with triangularity and Shafranov shift. [ABSTRACT FROM AUTHOR]

Significant departures from standard transport coefficients [e.g., Sov. Phys. JETP 6, 338 (1958)] have been found for the electron current and heat flux in a fully ionized plasma. These have been discovered by carrying out a direct and accurate numerical solution of the linearized Fokker–Planck equation using a Cartesian tensor expansion of the distribution function. The results, which were carried out for plasmas of various atomic numbers, show the presence of major inaccuracies (errors of up to 65%) in Braginskii coefficients β[larger_closed_square], κ⊥, and κ[larger_closed_square] (as conventionally defined) for Hall parameters ωτ in the range 0.3<=ωτ<=30. Surprisingly, α[larger_closed_square] and β⊥ are found to depend on τ/(ωτ)2/3 and 1/(ωτ)5/3, and not on τ/(ωτ) and 1/(ωτ)2, respectively, as ωτ→∞. An analytic expansion for large ωτ verifies this result, showing that the relatively cold unmagnetized electrons in the distribution function play a dominant role in the cross-field transport. The numerical results are fitted to within 15% to a polynomial in ωτ for various values of Z. [ABSTRACT FROM AUTHOR]

A transverse magnetic field B is found to be convected by the electron heat flux qe because of the Nernst effect, i.e., with a velocity VT(∼2qe/3neTe). The mechanism is clarified by the two-electron-fluid model. In laser-driven ablation the convection is toward the overdense region and B can be amplified by 10–100 times because ∇ · VT<0, making B/ni almost constant for λmfp>c/ωpe. [ABSTRACT FROM AUTHOR]

Experiments reporting magnetic-field generation by the ablative nonlinear Rayleigh–Taylor (RT) instability are reviewed. The experiments show how large-scale magnetic fields can, under certain circumstances, emerge and persist in strongly driven laboratory and astrophysical flows at drive pressures exceeding one million times atmospheric pressure. [ABSTRACT FROM PUBLISHER]

The magnetic fields generated at the surface of a laser-irradiated planar solid target are mapped using ultrafast proton radiography. Thick (50 μm) plastic foils are irradiated with 4-kJ, 2.5-ns laser pulses focused to an intensity of 4 x 1014 W/cm2. The data show magnetic fields concentrated at the edge of the laser-focal region, well within the expanding coronal plasma. The magnetic-field spatial distribution is tracked and shows good agreement with 2D resistive magnetohydrodynamic simulations using the code draco when the Biermann battery source, fluid and Nemst advection, resistive magnetic diffusion, and Righi-Leduc heat flow are included. [ABSTRACT FROM AUTHOR]

Magnetic fields generated by the nonlinear Rayleigh-Taylor growth of laser-seeded three-dimensional broadband perturbations were measured in laser-accelerated planar targets using ultrafast proton radiography. The experimental data show self-similar behavior in the growing cellular magnetic field structures. These observations are consistent with a bubble competition and merger model that predicts the time evolution of the number and size of the bubbles, linking the cellular magnetic field structures with the Rayleigh-Taylor bubble and spike growth. [ABSTRACT FROM AUTHOR]

Magnetic fields generated by the Rayleigh-Taylor instability were measured in laser-accelerated planar foils using ultrafast proton radiography. Thin plastic foils were irradiated with ~4-kJ, 2.5-ns laser pulses focused to an intensity of ~1014 W/cm2 on the OMEGA EP Laser System. Target modulations were seeded by laser nonuniformities and amplified during target acceleration by the Rayleigh-Taylor instability. The experimental data show the hydrodynamic evolution of the target and MG-level magnetic fields generated in the broken foil. The experimental data are in good agreement with predictions from 2-D magnetohydrodynamic simulations. [ABSTRACT FROM AUTHOR]