Validating and optimising mismatch tolerance of Doppler backscattering measurements with the beam model
Abstract
We use the beam model of Doppler backscattering (DBS), which was previously derived from beam tracing and the reciprocity theorem, to shed light on mismatch attenuation. This attenuation of the backscattered signal occurs when the wavevector of the probe beam's electric field is not in the plane perpendicular to the magnetic field. Correcting for this effect is important for determining the amplitude of the actual density fluctuations. Previous preliminary comparisons between the model and Mega-Ampere Spherical Tokamak (MAST) plasmas were promising. In this work, we quantitatively account for this effect on DIII-D, a conventional tokamak. We compare the predicted and measured mismatch attenuation in various DIII-D, MAST, and MAST-U plasmas, showing that the beam model is applicable in a wide variety of situations. Finally, we performed a preliminary parameter sweep and found that the mismatch tolerance can be improved by optimising the probe beam's width and curvature at launch. This is potentially a design consideration for new DBS systems.
Keywords
Cite
@article{arxiv.2209.15303,
title = {Validating and optimising mismatch tolerance of Doppler backscattering measurements with the beam model},
author = {Valerian H. Hall-Chen and Julius Damba and Felix I. Parra and Quinn T. Pratt and Clive A. Michael and Shi Peng and Terry L. Rhodes and Neal A. Crocker and Jon C. Hillesheim and Rongjie Hong and Shikang Ni and William A. Peebles and Ching Eng Png and Juan Ruiz Ruiz},
journal= {arXiv preprint arXiv:2209.15303},
year = {2022}
}