Paper

Effect of mismatch on Doppler backscattering in MAST and MAST-U plasmas

Shi, Peng, Crocker, Neal A, Juan Ruiz Ruiz, Freethy, Simon J, Pratt, Quinn T, Trisno, Jonathan, Hillesheim, Jon C, Hong Son Chu, Ronald, Kevin, Storment, Stephen, Hall-Chen, Valerian H, Kogan, Lucy A, Parra, Felix I, Speirs, David C, Scannell, Rory, Peebles, William A, Rhodes, Terry L

2024

Overview

The Doppler backscattering (DBS) diagnostic, also referred to as Doppler reflectometry, measures turbulent density fluctuations of intermediate length scales. However, when the beam's wavevector is not properly aligned perpendicular to the magnetic field, the backscattered power is attenuated. In previous work, we used beam tracing and reciprocity to derive this mismatch attenuation quantitatively. In this paper, we applied our model, in the small but finite mismatch limit, to a several new cases. We compared our predictions with multiple O-mode channels for the first time. We then identified a \\( 3^\\) error in the MAST Q-band's quasioptics, showing that our model is useful for commissioning DBS diagnostics. For both O- and X-mode, we compared experimental data with our model's predictions at multiple times during the shots, unlike our previous work, where only a single time was analysed. Finally, we analysed other contributions to the backscattered signal, evaluating how much they affect our measurements of mismatch attenuation, giving comparisons with data from both MAST and MAST-U. This paper's detailed study systematically validates and demonstrates the usefulness of our model for quantitatively interpreting DBS data from spherical tokamaks.

• Publisher: Cornell University Library, arXiv.org
• Subject: Attenuation / Backscattering / Doppler effect / Quasi-optics / Reciprocity / Tokamak devices / Wave propagation