High Energy Concentration by Spherical Converging Shocks in a Shock Tube with Conically Shaped Test Section

摘要

Spherical shock waves were created in a regular circular shock tube using a smooth converging transformation section of the tube wall designed to shape the plane shock into the form of a spherical segment. Numerical calculations were made to find a shape of the transformation section that achieved that goal. Shock tube runs using argon and nitrogen as test gas were made. The light created at the implosion focus was measured with photomultipliers and a spectrometer. For a series in argon at initial Mach number M_S = 3.9 blackbody spectra with apparent temperatures of up to 27,000 K were measured. Ionization relaxation at the high pressures and temperatures involved is such a fast process that equilibrium ionization might have already been established when the measurements were made - about 250 ns after reflection. An upper limit of the shock Mach number is taken from the simulations and yield M ≈ 25 - 30 close to the collapse instant, indicating efficient shock amplification.