Edge plasma density reconstruction for fast monoenergetic lithium beam probing

Two types of plasma density reconstruction methods for fast Li0 beam probe diagnostics have been developed for edge profile measurements in the CHS helical device, in which density dependence of atomic processes such as ionization, excitation/deexcitation and charge exchange is introduced by the use of effective rate coefficients calculated from collisional radiative model. These methods enable us to get plasma density profile well inside the last closed flux surface (LCFS) for various range of plasma densities with considering attenuation of the fast Li0 beam and using effective rate coefficients. A new method (method-I) can unfold the plasma density profiles from a fractional part of emission profile of Li I resonance line. The second method (method-II) reconstructs the density profile from the whole range of emission profile including signal tail-off region due to the beam attenuation. These two methods, which introduce density dependence of atomic processes and the beam attenuation caused by ionization, noticeably improve the precision of the measurements and extend the applicable density region of the plasma. Density profiles reconstructed by these two different methods have shown good agreement each other and are consistent with the result of ruby laser Thomson scattering. (author)