Ultrashort-pulse reflectometry for steady-state plasmas

Abstract

Design of an X-mode fast-scanning reflectometry for edge density profile measurement on HT-7 tokamak Rev. Sci. Instrum. 74, 1522 (2003; 10.1063/1.1527253 Millimeter-wave reflectometry for electron density profile and fluctuation measurements on NSTX Rev. Sci. Instrum. 72, 348 (2001); 10.1063/1.1329657 Ultrashort pulse reflectometry for electron density profile measurements on SSPX Rev. Sci. Instrum. 72, 332 (2001); 10.1063/1.1308999Preliminary electron density profile and fluctuation measurements on GAMMA 10 using ultrashort-pulse reflectometry Rev.An ultrashort-pulse reflectometry ͑USRM͒ has been applied to the inductively coupled steady-state plasma ͑ICP͒ for density profile measurement. A reflected wave from ICP is directly recorded into a digitizing sampling scope and is analyzed by the signal record analysis ͑SRA͒ method. From repetition of the measurement, we have obtained the time evolution of the density profile. In order to apply the USRM and SRA method to high density plasmas such as core region of the Large Helical Device plasma, generation of the pulse with higher frequency up to 90 GHz is essential. We have utilized a frequency upconverter and an active doubler for this purpose. We confirmed the generation of the upconverted pulse in the range of 60-90 GHz and the second-harmonic frequency in the range of 26 -40 GHz. Time of flight measurements have been preliminarily performed with a metal target.