  The JSNS^2 (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron
Source) experiment aims to search for sterile neutrino oscillations in the eV
mass range. A 1 MW beam of 3 GeV protons incident on a spallation neutron
target produces an intense and pulsed neutrino beam from muon decay at rest.
The JSNS^2 detector is located at 24 m away from the neutrino source and began
operation from June, 2020. The detector contains 17 tonnes of gadolinium (Gd)
loaded liquid scintillator (LS) in an acrylic vessel, as a neutrino target. It
is surrounded by 31 tonnes of unloaded LS in a stainless steel tank. Optical
photons produced in LS are viewed by 120 R7081 Hamamatsu 10-inch
Photomultiplier Tubes (PMTs). In this paper, we describe the JSNS^2 detector
design, construction, and operation.
