Fig. 1. Schematic diagram of the experimental setup

Fig. 2. V_p, I_dis and discharge images under different argon content
The argon content is 10% (a), 30% (b), 60% (c) and 80% (d), respectively; V_p is fixed at 1.75 kV

Fig. 3. Argon spectral line intensity vs.argon content
V_p is 1.75 kV (a) and 3 kV (b), respectively

Fig. 4. Argon spectra intensity vs. V_p
Argon content is 10% (a), 30% (b), 40% (c), 50% (d), 60% (e), 80% (f), 90% (g) and 100% (h), respectively

Fig. 5. T_excvs. argon content under different V_ps