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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]

We report spatially and temporally resolved measurements of self-generated multi-megagauss magnetic fields produced during ultrahigh intensity laser plasma interactions. Spatially resolved measurements of the magnetic fields show an asymmetry in the distribution of field with respect to the angle of laser incidence. Temporally resolved measurements of the self-generated third harmonic suggest that the strength of the magnetic field is proportional to the square root of laser intensity (i.e., the laser B-field) during the rise of the laser pulse. The experimental results are compared with numerical simulations using a particle-in-cell code which also shows clear asymmetry of the field profile and similar magnetic field growth rates and scalings. [ABSTRACT FROM AUTHOR]

Two experiments studying the interaction of high intensity laser pulses (1×1019–5×1020 W/cm2) with underdense plasma are compared. The experiments used lasers that differed in power and focused intensity but had similar pulse duration (∼1 ps). Spectroscopic measurements of the forward scattered light (sidebands) near the fundamental laser frequency produced by the self-modulation instability were performed and the energies of electrons accelerated in the interaction are measured and compared. It is found that at high intensities the sideband intensities and the electron energies were not directly correlated, implying that relativistic plasma wave generation is not the most important mechanism for electron acceleration in the ultrahigh intensity regime. Simulation results for the forward scattered spectrum agree well with experimental results. [ABSTRACT FROM AUTHOR]

The interaction of an intense laser pulse (intensity, greater than 10 19 W cm -2 ) has been studied with underdense deuterium plasmas. The laser pulse is found to be self-modulated at the plasma frequency by the Raman forward-scatter instability. Wave breaking of the resulting plasma wave causes high-energy electrons to be accelerated beyond 100 MeV. [ABSTRACT FROM AUTHOR]

Experiments have been performed using high power laser pulses (up to 50 TW) focused into underdense helium plasmas (ne ≤ 5 × 10[sup 19] cm[sup -3]). Using shadowgraphy, it is observed that the laser pulse can produce irregular density channels, which exhibit features such as long wavelength hosing and "sausage-like" self-focusing instabilities. This phenomenon is a high intensity effect and the characteristic period of oscillation of these instabilities is typically found to correspond to the time required for ions to move radially out of the region of highest intensity. [ABSTRACT FROM AUTHOR]

Presents an experimental study of optical probing of a dense z-pinch plasma. Ways to evaluate the plasma density profiles; Reasons for the rapid plasma expansion; Effects of the lower hybrid instabilities in fiber z-pinches.

Discusses the use of a two-dimensional magnetohydrodynamic simulation incorporating cold start conditions to explain the early phase of carbon fiber Z-pinch experiments. Reproduction of the rapid development of large scale, nonlinear perturbations in the plasma corona; X-ray bright spot formation in the necks of the instability.

Studies the interaction of a picosecond laser pulse with a solid target. Maximum energy cutoff; Range of the hot electron temperatures; Observation of the collimation of the plasma flow.

Picosecond resolution shadowgraphy is a powerful tool for measurement of high-intensity laser propagation instabilities through underdense plasma. It is shown that as the plasma density increases, the laser beam is subject to severe filamentation instabilities-likely due to the effect of stimulated Raman side-scattering. At higher plasma densities, scattering and absorption are so severe that the propagation distance of the high intensity laser pulse is reduced. [ABSTRACT FROM AUTHOR]