Helium retention in tungsten under plasma and ion beam irradiation and its impact on surface morphology

Helium (He) is a product of deuterium-tritium (DT)-fusion reaction and will be a natural impurity in DT plasma in future fusion devices. He retention in tungsten irradiated by plasma and mass-separated ions in a wide temperature range (300-1200 K) was investigated by means of thermal desorption spectroscopy (TDS). He retention did not exceed the level of 1.5 x 10(21) He m(-2) for all investigated samples. A significant effect of air exposure on TDS spectra was demonstrated. In contrast to in situ TDS measurements, He release after interaction with the air started from similar to 400 K, even in the case of high temperature irradiation. Changes in surface morphology were analyzed by secondary electron microscopy. Blisters were found at the surface after ion irradiation at low temperatures. Acceleration of surface modification and more complex surface morphology was observed in the case of irradiation at temperatures above 1000 K.