Experimental ablation processes study on an electrothermal launcher
An experimental parametric study has been performed to analyse the influence of time on the ablation processes in the capillary of an electrothermal launcher. A 600 kJ, 16 cells pulse forming network (PFN) was used. The time discharge was varied from 350 /spl mu/s to 100 /spl mu/s by changing the cell number (from 16 to 4) and then the capacitance (from 1760 /spl mu/F to 440 /spl mu/F). The parametric study has been performed at a constant voltage level (13 kV). The ablated masses have been measured for different time discharge and the results have been compared with a 0-D code.
Characterization of Short Intense Pulsed Electrothermal Plasma Capillaries for Use as Fusion and Launchers Heat Flux Sources
Electrothermal plasma sources operating in the confined capillary arc regime are characterized by the magnitude and shape of the discharge current. The desired plasma parameters at the source exit, especially the pressure and heat flux, are highly dependent on the arc due to the effect of the arc radiant energy that ablates the inner wall of the source. These sources have applications in fusion as drivers for pellet injectors and as high heat flux sources for fusion materials studies. The high-pressure high heat flux flow is also of application in mass accelerators and launch technology systems. The 1-D, time-dependent ETFLOW capillary code models the plasma generation and flow inside the capillary discharges and determines the plasma parameters. The input file to the code is the discharge current density providing the Joule heating in the energy equation. A circuit module has been developed and incorporated in the code to generate desired current shapes and magnitudes. The current pulse length was varied between 5 and 100 μs at constant amplitude of 50 kA, and then the pulse amplitude was varied between 10 and 200 kA at a constant pulse length of 20 μs. Increasing the pulse length while maintaining its amplitude increases the plasma density and the total ablated mass, which have accumulation behavior by increasing the pulse length, and subsequently increases the exit pressure from 60 to 410 MPa in the cases studied herein. The pressure increase allows the thermalization of the plasma particles through more collisions, which reduces the plasma temperature by about 0.2 eV. The bulk velocity follows the trend of the plasma temperature, but at shorter pulse lengths the total ablated mass is lower and enables the plasma to carry the particles with increasing velocity. Increasing the pulse amplitude up to 200 kA increases the density to about 18 kg/m3 and the bulk velocity, which varies between 6.1 and 10.7 km/s. A sharp increase in most plasma parameters occurs as a result of the increase in the pulse amplitude.
A theoretical model for the physical processes in the confined high pressure discharges of electrothermal launchers
Different physical processes in confined high-pressure discharges are analyzed. The energy transport inside the discharge tube yields a radial temperature profile which has sharp gradients only near the tube walls. The regime at which such discharges can operate at a steady state is determined. For a given discharge ablation rate and plasma pressure, the tube length is limited. An analytical model is developed for confined high-pressure discharges operating in a quasi-steady-state in which the resulting plasma jet characteristics are steady at hydrodynamic timescales. This model allows the calculation of all the discharge parameters, such as ablation rate plasma temperature, resistivity, density and pressure as functions of the slowly varying current and the tube dimensions. The scaling laws obtained in this model are important for determining the impedance matching between the discharge and the power source and upgrading the discharge energy in electrothermal launchers to hypervelocities. Good agreement is obtained between the analytical model and experimental results at energies up to 100 kJ. >