Utilization of D2 molecular band emission for electron density measurement

D 2 molecular band emission observed at a wavelength range of λ ∼ 557 − 643 nm is utilized to measure electron density, n e , in D plasmas of the PISCES-A and PISCES-RF linear plasma devices. The D 2 band is divided at λ = 593 nm to make an intensity ratio, D 2L ( ∼ 557 – 593 nm )/D 2R ( ∼ 593 – 643 nm ), where D 2L consists predominantly of the g 3 Σ g + 3 d σ , h 3 Σ g + 3 s σ , i 3 Π g 3 d π , j 3 Δ g 3 d δ → c 3 Π u 2 p π transitions, while D 2R mainly includes the d 3 Π u 3 p π → a 3 Σ g + 2 s σ Fulcher band emission. It is experimentally found that D 2L /D 2R depends strongly on n e with little T e dependence in ranges of n e ∼ ( 0 . 031 − 6 . 1 ) × 1 0 18 m −3 and T e ∼ 2 . 3 − 13 . 9 eV . This observed trend is consistent with collisional-radiative model calculations using Yacora on the Web. • An intensity ratio of D 2 molecular bands, D 2L ( ∼ 557 – 593 nm )/D 2R ( ∼ 593 – 643 nm ), is defined. • D 2L /D 2R is sensitive to electron density. • D 2L /D 2R depends little on electron temperature.