Characterization of helium retention in the inhomogeneous co-deposited layers using a long pulse laser induced ablation-quadrupole mass spectroscopy

Abstract

• The 2D-resolved quantitative characterization of the He retention in the inhomogeneous co-deposited layers has been carried out using 750 microsecond pulse laser induced ablation-quadrupole mass spectrometry (LIA-QMS). • The concentration of He atoms in the co-deposited layer has been determined based on the measured He mass spectral intensity and the ablation mass of laser ablated crater. • LIA-QMS approach has a significantly potential for the 2D-resolved quantitative diagnosis for the He or D/T retention in the non-uniform co-deposited layers on PFMs in nuclear fusion devices. In this work, a spatially lateral-resolved study of the co-deposition of helium (He) and aluminum (Al) in non-uniform layers is carried out by a long pulse Laser-Induced Ablation-Quadrupole Mass Spectrometry (LIA-QMS) approach. He was co-deposited with Al on the silicon (Si) substrate by Pulse Laser Deposition (PLD) method at He ambient pressure of 4.0 Pa. The Al is a proxy of beryllium (Be) because the Be is toxic. The thickness of the He-Al co-deposited layers decreases from approximately 3.9 µm to 0.2 µm with increasing lateral distance measured using white light confocal 3-D profilometer. The areal number density of He-retention in the inhomogeneous co-deposited layers decreases from 5.8 × 10 21 to 7.5 × 10 19 He/m 2 along the lateral distance, which is consistent with the variation trend of the deposition layer thickness. The 2-D imaging of the He atomic areal density measured by LIA-QMS shows that the He-retention in the co-deposition layer is significantly inhomogeneous. The maximum and minimum of the He concentration in atom ratio in the co-deposited layer are about 4 % and 0.4 %, respectively. The results indicate that LIA-QMS diagnostic approach has a significantly potential for the 2D-resolved quantitative characterization of the He (or D/T) retention in the co-deposited layers on Plasma Facing Materials (PFMs).