  The low wind effect (LWE) refers to a characteristic set of quasi-static
wavefront aberrations seen consistently by the SPHERE instrument when
dome-level wind speeds drop below 3 m/s. This effect produces bright low-order
speckles in the stellar PSF, which severely limit the contrast performance of
SPHERE under otherwise optimal observing conditions. In this paper we propose
the Fast & Furious (F&F) phase diversity algorithm as a viable software-only
solution for real-time LWE compensation, which would utilise image sequences
from the SPHERE differential tip-tilt sensor (DTTS). We evaluated the
closed-loop performance of F&F on the MITHIC high-contrast test-bench under a
variety of conditions emulating LWE-affected DTTS images, in order to assess
the expected performance of an on-sky implementation of F&F in SPHERE. The
algorithm was found to be capable of returning such LWE-affected images to
Strehl ratios of greater than 90% within five iterations, for all appropriate
laboratory test cases. These results are highly representative of predictive
simulations, and demonstrate the stability of the algorithm against a wide
range of factors including low image signal-to-noise ratio (S/N), small image
field of view, and amplitude errors. It was also found in simulation that
closed-loop stability can be preserved down to image S/N as low as five while
still improving overall wavefront quality, allowing for reliable operation even
on faint targets. The Fast & Furious algorithm is an extremely promising
solution for real-time compensation of the LWE, which can operate
simultaneously with science observations and may be implemented in SPHERE
without requiring additional hardware. The robustness and relatively large
effective dynamic range of F&F also make it suitable for general wavefront
optimisation applications, including the co-phasing of segmented ELT-class
telescopes.
