One of the main purposes of the Deep Underground Neutrino Experiment (DUNE) is to measure the CP-violation
phase in long-baseline neutrino oscillations with a liquid argon detector of unprecedented size.
In order to constrain the systematic uncertainties from the flux, neutrino interaction cross section, energy scale and so on, a near detector is needed to measure the un-oscillated neutrino spectra. In the near detector complex, a three dimensional projection scintillator tracker, also called 3DST, located downstream of
the liquid-argon detector, is proposed and being studied. 3DST is comprised
of a large number of 1 cm x 1 cm x 1cm scintillator cubes. We expect this tracker to have full solid
angle coverage for charged particles, as well as good energy and angular resolutions.
3DST provides a unique opportunity of carbon cross section and flux measurements in DUNE,
and a great potential of neutron tagging and nuclear effect extraction in the neutrino interactions.