  (abreviated) We aim to study the inner-wind structure (R<250 Rstar) of the
well-known red supergiant VY CMa. We analyse high spatial resolution
(~0".24x0".13) ALMA Science Verification (SV) data in band 7 in which four
thermal emission lines of gaseous sodium chloride (NaCl) are present at high
signal-to-noise ratio. For the first time, the NaCl emission in the inner wind
region of VY CMa is spatially resolved. The ALMA observations reveal the
contribution of up to four different spatial regions. The NaCl emission pattern
is different compared to the dust continuum and TiO2 emission already analysed
from the ALMA SV data. The emission can be reconciled with an axisymmetric
geometry, where the lower density polar/rotation axis has a position angle of
~50 degrees measured from north to east. However, this picture can not capture
the full morphological diversity, and discrete mass ejection events need to be
invoked to explain localized higher-density regions. The velocity traced by the
gaseous NaCl line profiles is significantly lower than the average wind
terminal velocity, and much slower than some of the fastest mass ejections,
signalling a wide range of characteristic speeds for the mass loss. Gaseous
NaCl is detected far beyond the main dust condensation region. Realising the
refractory nature of this metal halide, this hints at a chemical process
preventing all NaCl from condensing onto dust grains. We show that in the case
of the ratio of the surface binding temperature to the grain temperature being
~50, only some 10% of NaCl remains in gaseous form, while for lower values of
this ratio thermal desorption efficiently evaporates NaCl. Photodesorption by
stellar photons seems not to be a viable explanation for the detection of
gaseous NaCl at 220 Rstar from the central star, and instead, we propose
shock-induced sputtering driven by localized mass ejection events as
alternative.
