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\section{The MEMPHYS detector}
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The MEMPHYS (MEgaton Mass Physiscs) detector is a Megaton-class water \{C}erenkov in the straight extrapolation of the well known and robust technique used for the SuperKamiokande detector. It is located at Fréjus, so 130~km from CERN and it is an alternative design of the UNO \cite{UNO} and HyperKamiokande \cite{HyperK} detectors and shares the same physics case both from Non Accelerator domain (Nucleon Decay, Super Novae Neutrino from burst event or from Relic explosion, Solar \& Atmospheric Neutrinos) and from Accelerator (Super Beam, Beta Beam) domain. For the physics part not covered by this document, this kind of megaton Water detector can push the Nucleon decay search up to $10^{35}$~yrs in the $e^+\pi^0$ channel  and up to few $10^{34}$~yrs in the $K^+\bar{nu}$ channel, just to cite these benchmark channels. MEMPHYS can register as many as 150,000 events from a SN at 10~kpc from our galaxy and 50~events or so form Andromeda. To detect Relic Neutrinos from past Super Novae explosion one can use pure water and get a flux of 250~evts/10~y/500kT or increase this number by a factor 10 by adding Gadolinium salt.

A recent civil engineering pre-study to envisage the possibly of large cavity excavation located under the Fréjus mountain (4800~m.e.w) near the present Modane Underground Laboratory has been undertaken. The main result of this pre-study is that MEMPHYS may be build with present techniques as 3 or 4 shafts modular detector, $250,000~\mathrm{m}^3$ each with 65~m in diameter, 65~m in height for the total water containment. Each of these shafts correspond to about $5$ times the present SuperKamiokande cavity. For the present physical study, we have chosen on a fiducial volume of 440~kT which means 3 shafts and an Inner Detector (ID) of 57~m in diameter and 57~m in height. Each ID may be equipped with photodetectors (PMT, HPD,...) with a surface coverage at least 30\%. The Fréjus site 4800~m.w.e offers a natural protection against cosmic rays by a factor $10^6$.
\begin{figure}
\centering
\includegraphics[width=0.45\textwidth]{MEMPHYS.eps}
\caption{\label{fig:MEMPHYS}Sketch of the MEMPHYS detector under the Fréjus mountain.}	
\end{figure}

The decision for cavity digging is fixed at 2010 after an intense Detector Design Study (eg. cavity excavation, vephotodetector R\&D) performed in parallel of the digging of at least a Safety Galery in the Fréjus road tunnel. One may notes that this key date may also decisive for SPL construction as well as the choice of the EURISOL site. After that, the excavation and PMT production are envisaged to take seven years or so, and the Non accelerator program can start before the rise up of the accelerator program (Super Beam and Beta Beam) which may start before 2020.     