Figure 1: Schematic layout of the WANF beam line pointing out its main
elements (not drawn to scale).
Fig. 1 shows a schematic layout of the present WANF beam line.
Up to 
protons are extracted per spill using a
fast/slow extraction
from the SPS at 450 GeV in each of two 4 ms long spills separated by 2.6 s.
Neutrinos are mainly produced by decays in flight of the
secondary pions and kaons originating from proton interactions in a beryllium
target (T9). Positive (negative) 
and 
are focused
(defocused) towards the neutrino detectors
by a horn and a reflector in front of a 290 m long vacuum
decay tunnel. Protons which have not interacted,
hadrons and muons are
absorbed by a 400 m shield of iron and earth. The neutrino detectors
are housed in the BEBC Hall, about 820 m from T9.
The 
and 
flux at the detectors are predicted by detailed Monte Carlo simulations.
The largest uncertainties in such
simulations, i.e. particle production spectra in hadronic interactions,
are expected to be reduced by the CHORUS and NOMAD data and by the
results of the SPY experiment [46].