  The main task of the Top Tracker detector of the neutrino reactor experiment
Jiangmen Underground Neutrino Observatory (JUNO) is to reconstruct and
extrapolate atmospheric muon tracks down to the central detector. This muon
tracker will help to evaluate the contribution of the cosmogenic background to
the signal. The Top Tracker is located above JUNO's water Cherenkov Detector
and Central Detector, covering about 60% of the surface above them. The JUNO
Top Tracker is constituted by the decommissioned OPERA experiment Target
Tracker modules. The technology used consists in walls of two planes of plastic
scintillator strips, one per transverse direction. Wavelength shifting fibres
collect the light signal emitted by the scintillator strips and guide it to
both ends where it is read by multianode photomultiplier tubes. Compared to the
OPERA Target Tracker, the JUNO Top Tracker uses new electronics able to cope
with the high rate produced by the high rock radioactivity compared to the one
in Gran Sasso underground laboratory. This paper will present the new
electronics and mechanical structure developed for the Top Tracker of JUNO
along with its expected performance based on the current detector simulation.
