  The SPIDER experiment, part of the Neutral Beam Test Facility (NBTF) at
Consorzio RFX (Padua, Italy), is the prototype of the negative ion source for
the ITER neutral beam injectors; the source is coupled to a 100 kV three-grid
acceleration system. A Beam Emission Spectroscopy (BES) diagnostic was
installed in SPIDER to study and optimize energy distribution, aiming,
uniformity and divergence of the H-/D- beam extracted from the source. The
diagnostic is based on the analysis of the Doppler shifted H{\alpha}/D{\alpha}
light emitted in the interaction between the beam particles and the H2/D2
molecules of the background. In 2019 the BES diagnostic in SPIDER was installed
and calibrated, and it allowed to characterize the first hydrogen beams
extracted from the SPIDER source, in cesium free conditions. The number of
active beamlets composing the beam was reduced from 1280 to 80, affecting the
BES diagnostic capabilities. This paper presents the BES diagnostic setup and
discusses the first collected results. Under limited extracted current density
($\sim$ 10 A/m^2) and ion energy ($\leq$35 keV), no significant vertical beam
deflection caused by the magnetic filter field in the source was detected. In
some cases the beamlets were observed to be elongated in horizontal direction;
beamlet divergence values down to 20 mrad and 30 mrad e-folding were measured
in vertical and horizontal direction, respectively; the intensity of the
Doppler shifted radiation was found to be strongly correlated to the beam
current and to the beam divergence. The progressive compensation of beamlet
deflections (caused by electron suppression filter fields) with increasing
voltage in the extraction gap was studied.
