Properties of BeD molecules in edge plasma relevant conditions

The A 2 Π– X 2 Σ + band (the Δ v = 0 sequence) emission of beryllium deuteride (BeD) molecules has been observed both in Be-seeded deuterium plasma and in front of Be targets exposed to deuterium plasma. The particle interchange reaction, Be + + D 2 → BeD + D + , is thought to be a dominant process for the BeD formation in the plasma. On the other hand, BeD observed in front of Be targets is a product of chemical sputtering of Be bombarded by deuterium plasma. The photon emission coefficient of the A – X band at λ ∼ 497.3–499.2 nm around the prominent Q branch is estimated to be ∼5 × 10 −14 m 3 s −1 for electron temperatures ≳8 eV as deduced from particle balance between Be, Be + , and BeD in D 2 neutral pressure scans. The surface temperature dependence of chemical sputtering of Be released as BeD is investigated, and the sputtering yield of BeD is found to peak at ∼440 K. This peak temperature is consistent with the onset temperature of the decomposition of BeD 2 , obtained from thermal desorption spectrometry of BeD 2 powder. Also, the chemical sputtering yield is observed to be decreased with increasing incident ion flux, similar to carbon. Vibrational ( T vib ) and rotational ( T rot ) temperatures of BeD molecules are evaluated by fitting a measured A – X band spectrum with a simulated spectrum. Spectra taken from BeD formed in the plasma are well fitted with a single pair of T vib and T rot , which increase linearly with electron density. However, the vibrational and rotational energy of sputtered BeD is found not to be consistent with a Boltzmann distribution.