PSFC Seminar: Pedro Cabrera
Friday, February 21, 2020 at 3:00pm to 4:00pm
Building NW17, NW17-218
175 ALBANY ST, Cambridge, MA 02139
Title: Tokamak plasma edge studies by microwave short-pulse reflectometry and backscattering in TCV
Speaker: Pedro Cabrera, MIT Plasma Science and Fusion Center
Abstract: This talk will discuss two new diagnostics developed at the TCV tokamak: a Doppler backscattering (DBS) system and short-pulse reflectometer (SPR). Innovative experiments with the DBS diagnostic have demonstrated a new approach to generating and detecting multiple simultaneous frequencies using a digital AWG and direct sampling. Furthermore, the magnetic-field line pitch angle at the edge has been estimated by rotating the polarisation axis orientation of the probing beam while maintaining a constant ellipticity.
The SPR diagnostic is the first broad-band pulse reflectometer conceived which allows for flexible pulse output frequency, duration, and repetition rate. Such flexibility allows the instrument to overcome traditional SPR spatial sampling limitations while reducing hardware complexity. In order to measure the group-delay of short pulses (∼1ns), both traditional analog and digital sampling techniques have been explored reaching a group-delay resolution of 17ps (2.5mm) in average. First results will be presented of group-delay dynamics under various plasma conditions as well as density profiles reconstructed with micro-second resolution.