Probe measurements on a shock precursor

Abstract

A shock front of speed Vs from 0.6 to 5×106 cm/sec is launched by a capacitor discharge in one end of a 10 cm i.d. Pyrex pipe 150 cm long. Initial gas pressures range from 0.05 to 1.35 Torr of argon and observations with internal probes are carried out at positions down the tube, z of 73 to 117 cm. A steady magnetic field is applied and the shock, detected by pressure traces, compresses the field by 1.7: 1. Ahead of this shock a precursor is found which produces a magnetic field change which is abrupt (risetime=0.7 μsec) and substantial (approximately 50% of the imposed field). The size of this diamagnetic field change increases with Vs in agreement with a simple diamagnetic model which includes substantial radial flow. The location of precursor field change moves upstream toward the shock with reduced Vs and the strength of the field change is reduced at radii nearer the tube walls. Measurements of excitation temperature yield values of kTe=2.0 eV for the shock and 2.5 eV for the precursor region.

Turbulent collisional ionising shock waves in argon

“…Although turbulence is not usually excited in a gas dynamic shock wave. turbulence and instabilities have indeed been observed in ionising shock waves in argon and krypton gas (Barach and Vermillion 1965, Pert 1968, Levine 1970, Barach 1979, Glass and Liu 1978and Houwing et a1 1986. The time-averaged relaxation processes behind ionising shock waves often can be adequately described by current numerical techniques (Kaniel et a1 1986).…”

“…The plasmas created here have contact discontinuities: at the interface between the post-shock plasma and the arc discharge heated expanding plasma (the 'blast wave'); and at the interface between the electron precursor and the shock front. At both of these discontinuities, pressure and flow velocity are continuous but temperature and density are discontinuous (Barach 1979 andZel'dovich andRaizer 1966). A classical Rayleigh-Taylor instability could develop (Taylor 1950); in this case, the stability property depends on the direction of OP and the direction of a pseudo-field which is equivalent to the gravitational field in the conventional Rayleigh-Taylor instability.…”