\begin{figure}
	\centering
	\includegraphics[width=12cm]{Images/t1upgrade-nocolors}
	\caption{An arrangement to replace the current \textbf{T1} CSC telescope of TOTEM \cite{pinto-cmsw}}
	\label{t1upgrade}
\end{figure}
The GDD group, and ours, conceived the \textit{``Large GEM''} as a replacement for the current \textbf{T1} forward telescope of the TOTEM experiment at the LHC, which is now made of Cathode Strip Chamber detectors. T1 consists of two arms, each of them precisely fitting in a gap around the beam pipe and inside the inner surface of the CMS detectors, in symmetric positions around \textit{Interaction Point 5}. It covers the pseudorapidity region $3,1 \leq\vert\eta\vert\leq 4,7$.\\

A renovation is needed for T1, as its CSC chambers may start ageing fast when the LHC machine will start to run at luminosity $ \mathcal{L}~\geq~10^{31}~\dfrac{1}{cm^2 \cdot s} $. In particular, it is expected that if luminosity overcomes that level by two orders of magnitude, the CSCs would age in a few months \cite{lami-cmsw}. However, according to informal reports of ongoing T1 data acquisition sessions, discharges are already being observed at a luminosity $ \mathcal{L}~\simeq~10^{30}~\dfrac{1}{cm^2 \cdot s} $.\\

The same structure can be built with large GEM chambers, arranging six discs for each arm, where a disc is made of two planes of 5 chambers in a back-to-back arrangement (\figurename~\vref{t1upgrade}). Overlap regions would ensure a 360\degree \ coverage and allow to adjust the radius of the six discs on demand \cite{pinto-lg}.\\

As an alternative \cite{lami-cmsw}, each disc may be made of six detectors on a single plane; they could be alternated in back-to-back configuration, each disc offset by 30\degree \ from the adjacent ones, to allow overlay. Four such sets would be enough to equip an arm of the future T1.\\

As in \figurename~\vref{padreadout}, readout boards would be pad based, like in the prototype, featuring $16 \cdot 64 = 1024$ pads of various dimensions.\\
\begin{figure}
	\centering
	\includegraphics[width=12cm]{Images/padreadout}
	\caption{Two readout board options for a large triple GEM detector}
	\label{padreadout}
\end{figure}

With respect to CSC, GEM chambers offer high rate tolerance, limited discharge probability (less than $10^{-12}$ at gain $G\simeq 10^4$), high time resolution. For the prototype analized in this thesis, $RMS \simeq 11.8 ns$ (see \figurename~\vref{tdc}), and it may be improved by adding CF\subscript{4}.\\

In conclusion, T1 had been designed for a bunch crossing rate $f \geq 75ns$ and luminosity $ \mathcal{L} \leq 10^{31}$, while in principle a GEM based substitute could survive for years at $\mathcal{L} = 10^{33}$ and would be suitable for faster bunch crossing by just adding a percentage of CF\subscript{4} to the internal gases \cite{lami-cmsw}.\\

The CMS experiment is also developing similar large GEM prototypes, with a compatible readout, foreseeing a project for muon detecting in the forward region. $50cm$ wide GEM foils are being produced with no need for splicing.\\

At the same time, the INFN section in Bari is working on LASER ablation of GEM foils, a technique that could make automation of mass-manufacturing easier, and possibly increase hole precision and density.\\

A new generation of GEM detectors has definitely been started. The large active surface and quite simple readout system of these new detectors will prove useful to better reveal high energy particles both from accelerators and cosmic rays. They might also bear significant improvements in different research fields, such as low-energy or medical physics, and path a way to possible new applications.