Multichannel ultrashort pulsed radar reflectometer on LHD

An ultrashort pulsed radar reflectometer with 24 channels in the K_a band and four channels in the X band is used for the electron density profile measurements in the Large Helical Device. An ultrashort pulse has broadband frequency components. However, we have usually utilized the discrete frequency components because we apply a filter bank system in a time-of-flight measurement. To utilize the whole frequency spectrum of the impulse we apply the switching technique of the intermediate frequency signal and the frequency modulation of the local oscillator. A more detailed reconstructed electron density profile, compared to that of the previous system, is obtained by using an Abel inversion method from the profile of the delay time as a function of the probing frequency

Raman calibration of the LHD YAG Thomson scattering for electron-density measurements

We have calibrated the LHD yttrium aluminum garnet (YAG) Thomson scattering system by using anti-Stokes rotational Raman scattering from air for the measurements of absolute electron-density profiles of LHD plasmas. The air Raman calibration was carried out at near atmospheric pressure and room temperature. Total uncertainty in measured electron densities is estimated to be ±15% or less. Electron densities obtained with the calibrated YAG Thomson scattering show good agreements with those measured by the LHD millimeter-wave interferometer