  The goal of nuclear astrophysics is to measure cross sections of nuclear
physics reactions of interest in astrophysics. At stars temperatures, these
cross sections are very low due to the suppression of the Coulomb barrier.
Cosmic ray induced background can seriously limit the determination of reaction
cross sections at energies relevant to astrophysical processes and experimental
setups should be arranged in order to improve the signal-to-noise ratio.
Placing experiments in underground sites, however, reduces this background
opening the way towards ultra low cross section determination. LUNA (Laboratory
for Underground Nuclear Astrophysics) was pioneer in this sense. Two
accelerators were mounted at the INFN National Laboratories of Gran Sasso
(LNGS) allowing to study nuclear reactions close to stellar energies. A summary
of the relevant technology used, including accelerators, target production and
characterisation, and background treatment is given.
