Zeff profile measurement system using a Thomson polychromator

To measure the effective ion charge Z(eff) profile, most plasina machines are equipped with a bremsstrahlung measurement system as a filter-scope diagnostic device. In Korean Superconducting Tokamak Advanced Research (KSTAR) machine, a new type of bremsstrahlung measurement system, called hybrid-type polychromator system, was developed and tested at a single position during the 10th KSTAR plasma campaign [I]. The main idea of this hybrid-type polychromator system is to combine a polychromator system, which can measure the Thomson scattering signal, with a bremsstrahlung signal measurement system. The advantages of this hybrid-type polychromator system include the reduction of diagnostic vacuum windows in the Tokamak or Stellarator, and the measurement of the Z(eff) parameter with electron temperature (Te) and electron density (ne) at a same position. In this study, we improve last year's hybrid-type polychromator system. A major improvement is the change in the structure of the optical system. This allows measuring the bremsstrahlung signals more clearly, and four hybrid-type polychromators were equipped to measure the Z(eff) profile preliminarily. In this paper, we explain the structure of the hybrid-type polychromator and the system's measurement results. (C) 2017 Elsevier B.V. All rights reserved.