  We present the Sejong Suite, an extensive collection of state-of-the-art
high-resolution cosmological hydrodynamical simulations spanning a variety of
cosmological and astrophysical parameters, primarily developed for modeling the
Lyman-Alpha (LyA) forest. The suite is organized into three main categories
(Grid Suite, Supporting Suite, and Systematics Suite), addressing different
science targets. Adopting a particle-based implementation, we follow the
evolution of gas, dark matter (cold and warm), massive neutrinos, and dark
radiation, and consider several combinations of box sizes and number of
particles. With additional enhancing techniques, we are able to reach an
equivalent resolution up to 3x3328^3=110 billion particles in a (100 Mpc/h)^3
box size, ideal for current and future surveys (e.g., eBOSS, DESI). Noticeably,
for the first time, we simulate extended mixed scenarios describing the
combined effects of warm dark matter, neutrinos, and dark radiation, modeled
consistently by taking into account the neutrino mass splitting. In addition to
providing multicomponent snapshots from z=5.0 to z=2.0 in intervals of dz=0.2
for all of the models considered, we produced over 288 million LyA skewers in
the same z-range and extended parameter space. The skewers are well suited for
LyA forest science studies, for mapping the high-$z$ cosmic web and the
matter-to-flux relation and bias, and for quantifying the critical role of
baryons at small scales. We also present a first analysis of the suite focused
on the matter and flux statistics, and show that we are able to accurately
reproduce the 1D flux power spectrum down to scales k=0.06 [s/km] as mapped by
recent high-resolution quasar data, as well as the thermal history of the
intergalactic medium. The simulations and products described here will be
progressively made available.
