Radio Frequency Heating Coils for Shock Wave Experiments

Abstract

Radio-frequency eddy current heating of metallic samples in shock wave, ultrasonic and diamond anvil apparatus provides a methodology for obtaining hot samples or hot metallic gaskets (containing a sample) and yet not heating the entire target, ultrasonic assembly or diamond cell. Analysis of a previous design of a radio-frequency (~0.5 MHz) coil demonstrated that the center of 13 mm diameter shock wave experiment sample discs were underheated and the experimental temperatures achieved resulted from conduction of heat from the overheated sample edges relative to the center of the sample. We show, using the Biot-Savant law, that the ratio of magnetic field in the center to that at the edge of the sample, f, can be maximized to a value of f=1.8, by decreasing the radius of the heater coil, relative to the 13 mm diameter of sample. A simple analysis provides the thermal gradient across the sample thickness. An electric skin depth for iron of ~1 mm for the 0.45 MHz frequency of the heater power supply of our system is obtained. This leads to a maximum temperature gradient of ~52 K over the 4 mm thickness of the shock wave sample discs.

Shock compression of liquid silicates to 125 GPa: The anorthite‐diopside join

“…The ceramic plate was attached by a 0.5″ × 0.25″ × 6″ Macor™ bar to a brass block clamped onto the outer 1″ diameter Cu cylinder of a vacuum‐sealed coaxial support rod whose inner and outer cylinders were connected to the two terminals of the final transformer (Lepel model LCT‐4) of a Lepel 10 kW radio frequency (RF) generator. The brass block also provided the attachment point for both ends of a Cu‐tube induction coil [ Chen and Ahrens , 1998] and cooling water inlet and outlet ports.…”

High Pressure and High Temperature Equation-of-State of Gamma and Liquid Iron

“…The pure iron targets are in the shape of a single machined disk, the "driver plate" is 2mm thick and 38 mm in diameter, the central "top hat" is 4 mm thick and 13 mm in diameter [6]. The target is heated via an induction coil (see Chen and Ahrens [6]) placed around the top hat.…”

“…The target is heated via an induction coil (see Chen and Ahrens [6]) placed around the top hat. The temperature is monitored until just before impact with a two-color infrared pyrometer (Williamson 8120S-C-WD2) which in turn was calibrated against a thermocouple (Figure 2).…”

“…To summarize, the pyrometers were able to determine the sample temperature to within about 10 K after thermocouple calibration. The spatial variations in temperature in target is estimated and measured to be about 52 K at a pre-shock temperature of 1573 K [6].…”

“…With initial density at 1573 K of 7.413(0.012) Mg/m 3 [10] (the uncertainty is estimated from the pre-shock temperature uncertainty of about 52 K [6]), and using the relations between c 0 , s and K os , K′ os [14],…”