Highly charged tungsten ions generated by nanosecond pulsed laser and influence of magnetic field on ion charge state

Ions emitted from the laser generated tungsten plume were investigated with the help of ion collector (IC) and electrostatic ion energy analyzer (IEA) operating in time-of-flight configuration. Plume was generated by irradiating a plane W target with 6 ns pulsed Nd:YAG (λ = 1064 nm) laser. Laser fluence at the target was varied in the range of 3.0-19.4 J/cm2. IC measurements showed that the amplitude of tungsten ions pulse increases with the laser fluence. IEA spectra indicate that the number of available Wn+ ions charge states increases from 1 to 6 when laser fluence at the target was varied in the range of 3.0-19.4 J/cm2. With the application of 0.23 T axial magnetic field at the target surface, the number of available Wn+ ions charge states increases from 1 to 10 in the similar range of the laser fluence. In addition, molecular oxygen ions O2n+ were also observed when magnetic field is applied at higher values of the laser fluence. The ion charge state enhancement is presumably due to the magnetic trapping of electrons in front of the target surface, which intensifies electron impact ionization process.