O-mode reflectometry on Aditya-U

Abstract

Density profile measurements using a FMCW reflectometer have been done for the first time on Aditya-U tokamak at IPR. Fast swept frequencies in the K-Band (18–28 GHz) were transmitted in 10 μs and the reflected waves were collected via a high gain (20 dBi) pyramidal horn placed outside the vacuum vessel in O-Mode of operation. System was synchronised with the tokamak control using an custom trigger engine with each trigger generating a non-linear ramp of 0–20 V in 10μs and output I and Q data recorded at high speeds of 200 MSps with a memory depth of 1 GS of 16 bits each. Reflections from the viewport which masked the plasma signal were mitigated by tilting the viewport to 25 degrees. Beat frequencies were estimated using the spectogram method and inversion was done by Bottolier-Curtet algorithm. First results from the profile measurements on Aditya-U are presented.