High di/dt silicon controlled rectifier (SCR) / phase control thyristor (PCT) module, "hockey puck" style, manufactured by ABB (model# 5STP 0365D0002). Rated at 6.5kV blocking voltage, 6.5kV reverse blocking voltage, 1.5kA for 50us pulses, 1.1 kA/us di/dt, without trigger unit. Previously used. A .pdf datasheet for a similar part number is available,
here (we could not find a datasheet for this exact part number). Approximately 2" diameter by 1" thick.