AVS 64th International Symposium & Exhibition
    Plasma Science and Technology Division Thursday Sessions
       Session PS-ThM

Paper PS-ThM10
Optical Emission Spectroscopy of a Spark-coupled Laser Aluminum Plasma for Multicharged Ion Generation

Thursday, November 2, 2017, 11:00 am, Room 22

Session: Plasma Sources
Presenter: Md Mahmudur Rahman, Old Dominion University
Authors: M. Rahman, Old Dominion University
O. Balki, Old Dominion University
M. Shaim, Old Dominion University
H.E. Ali, Old Dominion University
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A spark-coupled laser plasma is used to generate multicharged ions. A Q-switched Nd:YAG laser (λ = 1064 nm, , τ = 8 ns, pulse energy ≤ 100 mJ, repetition rate 1 Hz) ablates an aluminum target creating a laser ion source, while the spark discharge further enhances ion generation. A high-voltage pulse-forming network produces up to 12 kV, ~1 µs pulse across the spark electrodes. Line emission from neutrals and ions are probed by optical emission spectroscopy. These spectral lines are used to obtain time-integrated, spatially-resolved electron temperature (Te) from the Boltzmann plot and electron density (ne) from Stark broadening. The pulse forming network is triggered with a thyratron through a delay in order to optimize the timing between the laser pulse and the spark discharge for best spark energy coupling to the laser plasma. A delay of 100 ns is found to produce the best coupling of the spark energy to the laser plasma. For a spark energy of 1.5 J, the intensity of the Al IV 372.6 nm and Al III 361.2 nm lines increases by a factor of ~10 and ~ 6, respectively compared to that from the laser plasma alone. The effective ion temperature (Tieff) associated with translational motion along the plume axis is calculated from the ion time-of-flight (TOF) signal and compared with Te. The results show that Tieff is much larger than Te, although the plasma is considered to be in local thermodynamic equilibrium. This result is explained in view of the different regions of the plasma probed by ion TOF and optical spectroscopy.