2 research outputs found
Validating and optimising mismatch tolerance of Doppler backscattering measurements with the beam model
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