Development of a neutrino tracking detector using gas electron multiplier avalanche light production in neon

We describe a prototype time projection chamber for tracking recoil electrons from low energy neutrinos down to 100 keV using Gas Electron Multipliers (GEMs) in supercritical neon below the critical temperature. Under this condition, electron drift and diffusion approach the low values of the electron bubble state. Light output produced by Townsend avalanches in a stack of three GEMs operated in mixtures of neon and hydrogen has been measured as a function of the GEM operating voltage, hydrogen partial pressure, and total gas pressure at room temperature in this stage of measurement. The next step will be below the critical temperature. Light from avalanches in neon-hydrogen mixtures has not been observed previously. Using commercially available low cost CCD-based imaging devices, the tracks of electrons can be recorded. The light output contains strong emission of neutral atomic neon (Ne I), and most of the allowed transitions connecting the 10 2P states to the 4 1S states (in Paschen notation) are observed. A broad band of emission from about 560 nm to the cutoff of the optical system at 225 nm is also observed, especially at low hydrogen concentrations and high total pressure. The origin of this emission is discussed. The ratio of the number of photons emitted to the number of avalanche electrons is greater than 1 at low hydrogen concentrations, and is essentially independent of the GEM voltage at fixed total pressure but, due to the Penning effect, decreases monotonically with increasing partial pressure of hydrogen for all mixtures studied. A plasma-kinetic model of the neon-hydrogen system has been developed to explain the measurements and to estimate the charge gain and light production in supercritical conditions. The implications of these observations are discussed to use the light output from avalanches in GEMs to implement a high density, large volume, time projection tracking detector for low energy solar neutrinos from pp fusion which are 99.5% of all solar neutrinos and has not been extensively and completely measured so far.