Temperature control system for laser heating: Application for minute asteroidal materials

A temperature control system for a laser heating has been developed to extract noble gases from minute material samples recovered from the asteroid Itokawa by the Hayabusa spacecraft. An ultra-fine thermocouple was produced from 3% Re-W and 26% Re-W wires 25 μm in diameter, and its electromotive force was calibrated. A temperature control program was originally produced using LabVIEW 2011 in which proportional-integral-derivative (PID) control was not adopted as an algorithm of the program. Particle samples smaller than 60 μm in diameter were set in conical depressions in a sample holder made of fused silica and irradiated by a slightly defocused Nd-YAG laser. The temperature of the samples was recorded by the thermocouple that passed through a small hole 50 μm in diameter because the sample and the thermocouple always came into contact during laser heating. The program controlled the temperature of the tiny samples appropriately. The average temperature during heating was slightly lower than the setting temperature and the standard deviation and the maximum overshoot were lower than 2.5% and 6.0% of the setting temperature, respectively. The performance of the temperature control system is high enough to conduct the stepwise heating experiment for minute extraterrestrial material samples.