Properties of an Ablation Plasma at Very Low Target Temperatures

It has been long established that the intensity of the lines emitted by an ablation plasma increases monotonically when the target is heated above room temperature 1 . In this work we investigate if this trend continues at cryogenic temperatures such as those encountered in space exploration and in ablation-plasma thrusters. The experiment consisted in placing an aluminum target inside a vacuum chamber and in close contact with the cold finger of a helium refrigerator that operated in the temperature range 20-290 K. The focused beam of a nanosecond laser induced the plasma on the target's surface. The lines emitted by the plasma were recorded using both an echelle spectrometer and a monochromator. From the emission lines we obtained the electronic temperature and density of the plasma.