  We present the design, data and results from the NEXT prototype for Double
Beta and Dark Matter (NEXT-DBDM) detector, a high-pressure gaseous natural
xenon electroluminescent time projection chamber (TPC) that was built at the
Lawrence Berkeley National Laboratory. It is a prototype of the planned
NEXT-100 $^{136}$Xe neutrino-less double beta decay ($0\nu\beta\beta$)
experiment with the main objectives of demonstrating near-intrinsic energy
resolution at energies up to 662 keV and of optimizing the NEXT-100 detector
design and operating parameters. Energy resolutions of $\sim$1% FWHM for 662
keV gamma rays were obtained at 10 and 15 atm and $\sim$5% FWHM for 30 keV
fluorescence xenon X-rays. These results demonstrate that 0.5% FWHM resolutions
for the 2,459 keV hypothetical neutrino-less double beta decay peak are
realizable. This energy resolution is a factor 7 to 20 better than that of the
current leading $0\nu\beta\beta$ experiments using liquid xenon and thus
represents a significant advancement. We present also first results from a
track imaging system consisting of 64 silicon photo-multipliers recently
installed in NEXT-DBDM that, along with the excellent energy resolution,
demonstrates the key functionalities required for the NEXT-100 $0\nu\beta\beta$
search.

Instrumentation and Detectors;High Energy Physics - Experiment;Nuclear Experiment