ABSOLUTE MEASUREMENT OF NEUTRAL DENSITY PROFILE IN A TOKAMAK PLASMA USING THE PRINCIPLE OF LASER-INDUCED IONIZATION

An application is discussed of a new method based on laser induced ionization that is an alternative to the laser induced fluorescence diagnostics. Here ionization of the hydrogen upper atomic states gives the local hydrogen densities in a plasma. On the basis of a rate equation analysis for a diffusion dominated plasma a probe saturation flux density of a few MFCT/cm(2) was introduced and appropriate values were used for the plasma diagnostics. A multipulse neodymium laser was designed for plasma probing on the FT-1 tokamak to measure the neutral density profiles along the plasma diameter. Local neutral densities as low as 1 x 10(8) cm(-3), which is close to the sensitivity limit of the employed device, have been detected in a single tokamak discharge. The experimental results obtained on the FT-1 tokamak are presented and discussed.