  The preponderance of matter over antimatter in the early universe, the
dynamics of the supernovae that produced the heavy elements necessary for life,
and whether protons eventually decay -- these mysteries at the forefront of
particle physics and astrophysics are key to understanding the early evolution
of our universe, its current state, and its eventual fate. DUNE is an
international world-class experiment dedicated to addressing these questions as
it searches for leptonic charge-parity symmetry violation, stands ready to
capture supernova neutrino bursts, and seeks to observe nucleon decay as a
signature of a grand unified theory underlying the standard model.
  Central to achieving DUNE's physics program is a far detector that combines
the many tens-of-kiloton fiducial mass necessary for rare event searches with
sub-centimeter spatial resolution in its ability to image those events,
allowing identification of the physics signatures among the numerous
backgrounds. In the single-phase liquid argon time-projection chamber (LArTPC)
technology, ionization charges drift horizontally in the liquid argon under the
influence of an electric field towards a vertical anode, where they are read
out with fine granularity. A photon detection system supplements the TPC,
directly enhancing physics capabilities for all three DUNE physics drivers and
opening up prospects for further physics explorations.
  The DUNE far detector technical design report (TDR) describes the DUNE
physics program and the technical designs of the single- and dual-phase DUNE
liquid argon TPC far detector modules. Volume IV presents an overview of the
basic operating principles of a single-phase LArTPC, followed by a description
of the DUNE implementation. Each of the subsystems is described in detail,
connecting the high-level design requirements and decisions to the overriding
physics goals of DUNE.
