158 research outputs found

    Formation of laser plasma channels in a stationary gas

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    The formation of plasma channels with nonuniformity of about +- 3.5% has been demonstrated. The channels had a density of 1.2x10^19 cm-3 with a radius of 15 um and with length >= 2.5 mm. The channels were formed by 0.3 J, 100 ps laser pulses in a nonflowing gas, contained in a cylindrical chamber. The laser beam passed through the chamber along its axis via pinholes in the chamber walls. A plasma channel with an electron density on the order of 10^18 - 10^19 cm-3 was formed in pure He, N2, Ar, and Xe. A uniform channel forms at proper time delays and in optimal pressure ranges, which depend on the sort of gas. The influence of the interaction of the laser beam with the gas leaking out of the chamber through the pinholes was found insignificant. However, the formation of an ablative plasma on the walls of the pinholes by the wings of the radial profile of the laser beam plays an important role in the plasma channel formation and its uniformity. A low current glow discharge initiated in the chamber slightly improves the uniformity of the plasma channel, while a high current arc discharge leads to the formation of overdense plasma near the front pinhole and further refraction of the laser beam. The obtained results show the feasibility of creating uniform plasma channels in non-flowing gas targets.Comment: 15 pages, 7 figures, submitted to Physics of Plasma

    Development of small scale soft x-ray lasers: Aspects of data interpretation

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    The widespread application of soft x-ray laser technology is contingent on the development of small scale soft x-ray lasers that do not require large laser facilities. Progress in the development of soft x-ray lasers pumped by a Nd laser of energy 6-12J is reported below. Some aspects of data interpretation and gain measurements in such systems are discussed. 11 refs., 11 figs

    Reaching the nonlinear regime of Raman amplification of ultrashort laser pulses

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    The intensity of a subpicosecond laser pulse was amplified by a factor of up to 1000 using the Raman backscatter interaction in a 2 mm long gas jet plasma. The process of Raman amplification reached the nonlinear regime, with the intensity of the amplified pulse exceeding that of the pump pulse by more than an order of magnitude. Features unique to the nonlinear regime such as gain saturation, bandwidth broadening, and pulse shortening were observed. Simulation and theory are in qualitative agreement with the measurements.open695

    The Effect of Neutral Atoms on Capillary Discharge Z-pinch

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    We study the effect of neutral atoms on the dynamics of a capillary discharge Z-pinch, in a regime for which a large soft-x-ray amplification has been demonstrated. We extended the commonly used one-fluid magneto-hydrodynamics (MHD) model by separating out the neutral atoms as a second fluid. Numerical calculations using this extended model yield new predictions for the dynamics of the pinch collapse, and better agreement with known measured data.Comment: 4 pages, 4 postscript figures, to be published in Phys. Rev. Let

    Radiated energy and impurity density changes during intensive hydrogen influx in the PLT tokamak

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    During a discharge a puff of hydrogen is admitted, sufficient to more than triple the plasma density, and the resulting changes in various plasma parameters are determined. The absolute densities of various wall and limiter (carbon) materials are found to decrease by a substantial fraction, probably as a result of lowered peripheral temperature. The radiation pattern deduced from spectroscopically determined plasma composition is in good quantitative agreement with direct bolometric measurements. In the interior of the discharge radiation constitutes only a small part of the power input. Neither the radiated power nor the power input changes very markedly as a result of the density rise, since the effects of temperature and plasma composition changes tend to compensate each other

    Coherence Enhanced Transient Lasing in XUV Regime

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    We report the effect of a coherent drive on transient lasing in three-level Λ\Lambda and Ξ\Xi configurations (c↔a↔bc\leftrightarrow a\leftrightarrow b). We show that the presence of a resonant coherent drive on the a↔ca\leftrightarrow c optical transition can yield an order of magnitude enhancement of the output laser energy on a a→ba\rightarrow b XUV or X-ray transition than with no coherent drive. We demonstrate the crucial role of coherence ϱac\varrho_{ac} for the laser power enhancement. Contrary to the forward direction (with respect to the pump), where forward gain can be enhanced for some choice of the drive Rabi frequency Ωc\Omega_{c}, coherent drive on the acac transition always suppresses the backward gain.Comment: 8 pages, 11 figure

    Toroidal plasma rotation in the PLT tokamak with neutral-beam injection

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    Toroidal plasma rotation in the Princeton Large Torus, PLT, has been measured for various plasma and neutral beam injection conditions. Measurements of the plasma rotational velocities were made from Doppler shifts of appropriate spectral lines and include data from both hydrogen and deuterium beams and co- and counter-injection at several electron densities. Without injection, a small but consistent toroidal rotation exists in a direction opposite to the plasma current (counter-direction) in the plasma center but parallel to the current (co-direction) in the plasma periphery. Using these measured velocities and the plasma density and temperature gradients, radial electron fields can be determined from theory, giving E/sub r / approx. = 40 V/cm near the plasma center and E/sub r/ approx. = 10 V/cm near the plasma edge. Insertion of a local, 2.5 percent magnetic well produced no observable effect on the beam driven rotation. Modeling of the time evolution and radial distribution of the rotation allows one to deduce an effective viscosity of the order of (1 to 5) x 10/sup 4/ cm/sup 2//sec
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