Effect of He addition on the heating characteristics of substrate surface irradiated by Ar thermal plasma jet

Effect of He addition to Ar as the discharge gas on the substrate surface temperature during thermal plasma jet (TPJ) annealing is investigated. The maximum surface temperature (Tmax) increases from 1370 to 1470 K with increasing He fraction (RHe) from 0 to 28%, then decreases to 1040 K with increasing RHe to 86%. It has been confirmed that the TPJ is efficiently concentrated when He addition is around 30%, which suggests that the increase in Tmax is due to the increase in the power density induced by thermal pinch effect. By adding 30% He and increasing the total gas flow rate to 15.4 L/min, Tmax is increased to 1580 K.