Detailed wave profiles for Kinosaki basalt at pressures up to 25 GPa are measured using a laser velocity interferometer in order to determine the dynamic properties. The results indicate a Hugoniot elastic limit of ∼2 GPa and a relationship between shock velocity (U s ) and particle velocity (U p ) approximated by U s (km/s) = 3.5 + 1.3U p (km/s) in the low-pressure plastic region (U p below ∼4 km/s). These data are compared with the known data for rocks with basaltic compositions, and tensile strength of the basaltic rocks was found to be about one tenth of that of compression strength.
Ions accelerated in z-pinch experiments with either positive or negative discharge were measured by using a Thomson Parabola analyzer in order to understand the directional tendencies of the ion acceleration. Ions having energy on the order of MeV were observed in both positive and negative discharges. The velocity and energy of each ion species were measured to be considerably similar in magnitude, in spite of the difference in the polarity of the power supplies. The highest-velocity ions with different charges in each measurement lay on the constant velocity line. The model independent of the current direction should be considered as the main mechanism of ion acceleration in this study. Accelerated ions having energy on the order of MeV have been observed in many studies of high current experiments, particularly in the plasma foci [1, 2] and z pinch systems [3,4]. Charged voltages of the main power supplies of these systems are several tens of kV, thus the understanding of any acceleration mechanism is required. Some acceleration models are discussed as the potential mechanisms of the acceleration, such as an induced electromotive force caused by increase of inductance [5,6] and/or resistivity [7,8], the kinematic effect under the calculated electric fields [9,10], and a displacement current caused by the blocking of the conduction [11]. In all the above theories, the direction of the accelerated ions are assumed to be the same as that of the electric currents. The models of these theories are collectively called the "current-directional electric field model" in this study. Although few experimental observation [3] have reported the reversed acceleration of ions, no comparative experiments have been carried out. Because it is difficult to measure the electric field in the fast and microscopic phenomena of pinch, the nature of the particle acceleration process by the electric field still remains undefined. Experimental observations using another approach are needed. Assuming that the above-mentioned current-directional electric field model is the main mechanism, the reversal of polarity of the power supply should reverse the acceleration direction of ions. Accordingly, either positive or negative power supplies were examined in the same gas-puff z-pinch experiment system in this study.
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