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An investigation of the transient characteristics for a high power high-pressure argon arc stabilized by vortexing gas and water wall in LTE is presented. The 30 cm long arc is operated in a current range from 50 to 400 A and is short circuited for brief durations (typically 100 ps to 2 ms) such that the arc does not extinguish. Transient arc voltage, arc current, and radiant intensity at 900 nm resulting from this arc lamp notching are recorded. The arc is shorted using a crowbar circuit consisting of several high power IGBTs in parallel, chosen for their ruggedness and fast response times in the order of 500 ns. The arc is operated in such way that a quartz envelope is cooled on the inside by a spiraling film of deionized water. This effective cooling allows for electrical input power into the arc lamp of up to 300 kW. The experimental setup is described, with reference to electrical, water, and gas system design and results are interpreted with reference to expected arc behaviour. Experimental results are compared to a numerical model describing transient characteristics of a cylindrical argon high-pressure arc column. Resonance lines are assumed fully trapped in this model. All other arc radiation losses are assumed optically thin in this model. The numerical modeling approach is discussed and verified by comparison with experimental results. A close agreement between theoretical results and experimentally observed transient radiation characteristics and arc voltage is found. This indicates the radiation loss term in the model is represented with sufficient accuracy. This study is aimed at determining a maximum "arc-interruption-interval" that does not require re-ignition of the plasma. Such brief interruption of the radiative output allows for various in-situ diagnostics on samples during processing with the high-power Vortek arc lamp.A numerical model is presented to investigate the influences of cathode and nozzle geometries on the characteristics of transferred arc torches for waste melting process. The arc plasma is described in the atmospheric condition by a two dimensional magnetohydrodynamic (MHD) model with the assumptions of steady state, axisymmetry, local thermodynamic equilibrium (LTE) and optically thin plasma. In order to simulate the realistic torch configurations with complex nozzle and cathode arrangements, the unstructured triangular andlor quadru-lateral grid systems are used with a finite volume discretization, gradient reconstruction procedure and a SIMPLE-like pressure-correction algorithm[ 11. For the self-consistent prediction of temperature profiles on the anode workpiece and heat transfer rates to it, the energy conservation and current continuity equations are solved not only in the thermal plasma region but also in the anode region with the special treatment of electric conductivity and energy balance at the interface of plasma and anode material. By the suggested numerical model, the temperature and flow field distributions of argon plasmas and the heat flux rates to anode materi...