LASER BLOW-OFF LITHIUM BEAM PROBING WITH HIGH TEMPORAL RESOLUTION FOR EDGE PLASMA DIAGNOSTICS

Laser blow-off neutral lithium beam probing with high temporal resolution has been developed to measure edge electron density profiles in a plasma. A new electron density reconstruction method, taking account of the transport of a laser blow-off beam in the plasma, improves the accuracy of the density measurement. The use of a camera system with a gate function makes it possible for us to measure the density profile with a high temporal resolution of 10-50 mus. The optimum condition for shutter timing and period to observe the Li I emission profile is discussed from the viewpoints of the beam penetration into the plasma and the accuracy of measurement. A rapid temporal evolution of the edge electron density profile during limiter biasing in a small tokamak HYBTOK-II was successfully obtained by this system.