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[en] In this paper, three different experimental configurations designed to study jet propagation physics are presented. Each configuration uses a different target design: conical dimples in solid surfaces, hollow cones filled with foam and angled thin foils. When irradiated with a laser, these targets result in the launching of a plasma jet, the properties of which can be controlled by judicious choices of the target and laser parameters. Experimental results from these targets are shown, and the physics which may be studied with each of these targets is briefly discussed.
[en] The behaviours of a nitrogen plasma jet operating at pressures between 10 torr and 35 torr has been spectroscopically investigated. The relative intensity has been plotted against the pressure, plasmatron power and the plasma jet length for different pressures. The radial distributions of relative intensities for the same spectral lines against the plasma jet length have been plotted too. The measurements have been taken for two wolfram spectral lines and two heads of second positive nitrogen molecular bands. (author)
[en] A new plasma jet (PJ-100) plasma spraying torch with a fixed minimal arc length was tested and the basic working parameters were measured and evaluated. The velocity of the plasma exiting both the cylindrical and the conical anode nozzles was assessed by measuring the thrust generated by the plasma jet and by photographing the translation of plasma clouds (parts with different brightnesses) in the last third of the length of the plasma plume. The basic characteristics of the argon/hydrogen plasma jets (enthalpy, mean temperature, mean plasma velocity and effective exhaust thrust velocity) were determined for different working regimes, for both the cylindrical and the conical nozzles. The thermal efficiency of the new plasma torch is between 70% and 74% for the plasma generation power up to 90 kW. The plasma plume generated in the cylindrical nozzle has a homogeneous radial temperature (and velocity) distribution with a full laminar flow.
[en] The plasma column ignition seems to be one of the main difficulties associated with the different devices for the production of permanent high power plasma flows. The ignition conditions of power superposition on argon jets produced by two plasma generators (D.C.) have been studied. Their evolution depends: on the surroundings of the column (free atmosphere or cylindrical cavity), on the electrical conductivty of the cavity material, its length and its diameter, on the electrical power, gas flow rate in the two plasma generators as well as their distances from the cavity, on the flow type (laminar, transitory and turbulent) which governs the jet length
[fr]L'amorcage de la colonne de plasma semble etre l'une des difficultes essentielles des differents dispositifs de production d'ecoulements permanents de plasma a forte puissance. On presente ici une etude systematique des conditions d'amorcage de la superposition de puissance (courant continu) sur des jets d'argon produits par deux generateurs a arc souffle et leur evolution en fonction: du milieu (air libre ou cavite cylindrique) ou se cree la colonne de gaz, de la conductibilite electrique du materiau constituant la cavite et de sa geometrie, de la puissance electrique, du debit gazeux et de l'ecartement des deux generateurs a plasma antagonistes, du mode d'ecoulement (laminaire, transitoire ou turbulent) qui conditionne la longueur du jet de plasma
[en] Experimental and computational analyses of jet formation at the boundary of a decaying pulse discharge in an ambient quiescent air at 1 atm are presented. High velocity jets are observed attributed to the channel curvature set during the initial breakdown phase. The general convex-to-concave jet direction is explained, and the mechanisms of jets formation are discussed.
[en] The linear and nonlinear evolution of the plane magnetized jet, a magnetohydrodynamic configuration consisting of a plane fluid jet embedded in a neutral sheet, is examined. At low Alfvacute en number (A=ratio of the characteristic Alfvacute en speed to the characteristic flow speed), two ideally unstable modes are found that correspond to the sinuous and varicose modes of the fluid plane jet. Increasing A leads to a stabilization of both of these modes. For large A there is a separate resistively unstable mode. The ideal varicose mode and the resistive varicose mode are distinct modes with similar properties in a given range of A. A magnetohydrodynamic generalization of the Howard semicircle theorem indicates that a strong enough magnetic field will damp out all ideal modes. The stability properties of the two modes are studied in terms of their perturbation energy balances. The nonlinear evolution is quite different for the three modes in terms of time scales and of the properties and spatial location of the small-scale structures that strongly modify the initial configuration. The two ideal modes have in common the capability of accelerating the fluid initially at rest in a much more efficient way than the resistive one. copyright 1998 American Institute of Physics
[en] An anomalous kind of the positive corona - a linear corona torch discharge - is investigated. The discharge is nearly steady-state and operates with various electrode configurations, e.g., wire-plane, needle-plane, wire-cylinder, and two or more wires placed in parallel. It is found that the discharge exists in the form of a pulsed corona or an ordinary positive corona, which alternatively change each other under the action of a spark-gap switch
[en] Experiments were carried out on how laser radiation affects both the shape of an escaping plasma jet and the formation of a luminous object after the jet has been ejected from the electrode. It is shown that a 1-mW laser beam with an intensity as low as 0.001 W/cm2 can change the shape of the jet and its propagation direction. In applying laser diagnostic methods, it is necessary to take into account possible change in the configuration of such objects when they interact with laser radiation. It is confirmed that the temperature of a luminous object decreases sharply with time.