Damages of hot-pressed boron carbide during solid target boronization in Uragan-3M torsatron

Abstract

The investigation of hot-pressed boron carbide erosion caused by the arc-regime of a solid target boronization (STB) procedure was carried out. The sample had a high density (2.44 g/cm 3, B 78.2 a.m.%, C 21.5 a.m.%) and was used as a head plate of the movable limiter during the pulsed discharge cleaning campaign in the Uragan-3M (U-3M) torsatron. The total number of pulses during STB was about 2 × 10 4 ( n e=2 × 10 12 cm −3, T e=10–15 eV, B=0.035 T, the plasma pulse duration t=50 ms, the negative pulsed biasing of B 4C-plate with an amplitude of up to 200 V had a time duration of 10–50 ms). As was shown by an optical examination of the surface morphology of the exposed sample, the character and intensity of damages of the limiter surface strongly varied depending on the distance from the plasma column axis. The most damaged sites were covered with many craters of 0.1–1.2 mm in diameter and spallings with a size up to 5 mm. The possible physical mechanisms of these damages and erosion behavior of hot-pressed in vacuum boron carbide caused by the arc-regime of STB are discussed.