  In this Technical Design Report (TDR) we describe the NEXT-100 detector that
will search for neutrinoless double beta decay (bbonu) in Xe-136 at the
Laboratorio Subterraneo de Canfranc (LSC), in Spain. The document formalizes
the design presented in our Conceptual Design Report (CDR): an
electroluminescence time projection chamber, with separate readout planes for
calorimetry and tracking, located, respectively, behind cathode and anode. The
detector is designed to hold a maximum of about 150 kg of xenon at 15 bar, or
100 kg at 10 bar. This option builds in the capability to increase the total
isotope mass by 50% while keeping the operating pressure at a manageable level.
  The readout plane performing the energy measurement is composed of Hamamatsu
R11410-10 photomultipliers, specially designed for operation in low-background,
xenon-based detectors. Each individual PMT will be isolated from the gas by an
individual, pressure resistant enclosure and will be coupled to the sensitive
volume through a sapphire window. The tracking plane consists in an array of
Hamamatsu S10362-11-050P MPPCs used as tracking pixels. They will be arranged
in square boards holding 64 sensors (8 times8) with a 1-cm pitch. The inner
walls of the TPC, the sapphire windows and the boards holding the MPPCs will be
coated with tetraphenyl butadiene (TPB), a wavelength shifter, to improve the
light collection.
