Arc plasma ablation of quartz crystals

TL;DR

This study investigates the use of arc plasma discharges to ablate quartz crystals, analyzing heat flux, ablation rates, and phase changes, highlighting potential applications in geothermal drilling.

Contribution

It provides a detailed analysis of quartz ablation by arc plasma, combining experimental measurements, spectroscopy, and simulations to understand heat transfer and phase transformation mechanisms.

Findings

Ablation rate up to 15 cm/h at 150 W/cm2

Linear correlation between power density and ablation rate

Phase transition from crystalline to glassy silica observed

Abstract

Spherical quartz stones of around 1 cm in diameter have been exposed to anodic arc discharges in a helium atmosphere at 300 Torr. The arc current flowing between the graphite electrodes was set either in continuous DC mode (30-150 A) or in pulsed mode at 2 Hz (220 A peak). The ablation rate in each sample was systematically measured after several seconds of arc plasma treatment. Optical emission spectroscopy (OES) diagnostics and 2-D fluid simulations of the arc discharge have shed light on the heat flux transport and the heating mechanisms of the quartz crystals. A linear correlation is found between the absorbed power density and the resulting rate of penetration, which yields a maximal value of 15 cm/h for approximately 150 W/cm2. The linear fit on the slope provides a specific energy of 40 kJ/cm3. The incident energy flux onto the sample surface promoted a phase transition from crystalline to glassy silica, as characterized via Raman spectroscopy. This study points out the strong potential of arc plasma technology for geothermal drilling applications.