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\title[]{Precision Muon Tracking Detectors and Read-out Electronics for Operation at Very High Background Rates at Future Colliders}

\author[]{S.~Nowak \and O.~Kortner \and H.~Kroha \and R.~Richter \and K.~Schmidt-Sommerfeld \and Ph.~Schwegler}
\institute{Max-Planck-Institut f\"ur Physik, Munich}
\date{Frontier Detectors for Frontier Physics - 13th Pisa Meeting on Advanced Detectors}

\begin{document}
	\begin{frame}
		\begin{block}{Abstract}
			\centering
			\begin{minipage}{0.98\linewidth}
				\small{The experience of the ATLAS muon spectrometer shows that drift-tube chambers provide highly reliable precision muon tracking  over large areas.
					The ATLAS muon chambers are exposed to unprecedentedly high background of photons and neutrons induced by the proton collisions.
					Still higher background rates are expected at future high-energy and high-luminosity colliders beyond HL-LHC.
					Drift-tube detectors with 15 mm tube diameter (30 mm in ATLAS) and improved read-out electronics optimized for high rate operation have been developed for such conditions.
					Tests at the Gamma Irradiation Facility at CERN showed that the rate capability of sMDT chamber is improved by more than an order of magnitude compared to the ATLAS chambers as space charge effects are strongly suppressed and operation with minimal electronics dead time becomes possible. Studies of the new readout electronics are shown.
					Several full-scale chambers have been constructed with unprecedentedly high sense wire positioning accuracy of better than 10 micron. The chamber design and assembly methods have been optimized for large-scale production, reducing considerably cost and construction time while maintaining the high mechanical accuracy and reliability.
					}
			\end{minipage}
		\end{block}
		\vfill
		\begin{columns}
			\begin{column}{0.49\textwidth}
				\parbox[t][\columnheight]{\textwidth}{%
					%MDTs and sMDTs
					\begin{block}{MDT and sMDT Chambers}
						\small{
							\begin{minipage}{0.96\textwidth}
								\begin{columns}
									\begin{column}{0.47\textwidth}
										\begin{center}
% 											\hspace{-3cm}
											\includegraphics[width=0.9\textwidth]{mdt_and_smdt_tube_end}
										\end{center}
										\hspace{28mm}$\diameter$30\,mm MDT\hspace{30mm}$\diameter$15\,mm sMDT
% 										\vspace{2.5cm} 
										\vfill
									\end{column}
									\hfill
									\begin{column}{0.47\textwidth}
										\textbf{Assembled sMDT chamber}\\
										\vspace{0.5cm} 
										\includegraphics[width=0.9\textwidth]{sMDT_chamber}
									\end{column}
								\end{columns}
								\vspace{1.0cm}
								\begin{columns}
									\begin{column}{0.47\textwidth}
										\textbf{MDT chambers:} drift tube detectors with 30\,mm tube diameter accounting for the majority of precision tracking chambers in the ATLAS Muon Spectrometer\\
									\end{column}
									\begin{column}{0.47\textwidth}
										\textbf{sMDT chambers:} newly developed drift tube detectors with 15\,mm tube diameter
										\vspace{1.5cm}
									\end{column}
								\end{columns}
								\vspace{0.5cm}
								\begin{columns}
									\begin{column}{0.03\textwidth}
									\end{column}
									\begin{column}{0.4\textwidth}
										\includegraphics[width=\textwidth]{resolution_curves}
									\end{column}
									\begin{column}{0.57\textwidth}
										\begin{itemize}
											\item Each particle hit causes space charge consisting of the slowly outwards drifting ions created in the charge multiplication in the vicinity of the wire
											\item Space charge effects due to the altered electric field leading to a decrease of the gas amplification: $\sim R^3$ for $\gamma$ and $\sim R^4$ for charged particles\\
											$\Rightarrow$ Rate capability in terms of gain drop by almost an order of magnitude higher for sMDT compared to MDT tubes \cite{smdt}
										\end{itemize}
									\end{column}
								\end{columns}
							\vspace{1cm}
							\textbf{Space charge effects are strongly mitigated in sMDT chambers and do no longer limit the performance}
							\end{minipage}
						}
					\end{block}
					\vfill
					\begin{block}{Occupancies at Maximum FCC Luminosity (ATLAS Geometry)}
						\small{
							\begin{minipage}{0.96\linewidth}
								\begin{columns}[T]
									\begin{column}{0.48\textwidth}
										\includegraphics[width=1.0\textwidth]{future_rates}
									\end{column}
									\begin{column}{0.48\textwidth}
										\vspace{1cm}
										\begin{itemize}
											\item Maximum sMDT occupancy at FCC is half the MDT occupancy  at HL-LHC
											\item FCC detectors are not limited to ATLAS operating parameters and geometry\\Further optimization of
											\begin{itemize}
												\item Tube length depending on $\eta$
												\item Drift gas parameters                                                                                                
												\item \textbf{Read-out electronics}
											\end{itemize}
										\end{itemize}
									\end{column}
								\end{columns}
							\end{minipage}
						}
					\end{block}
					\vfill
					\begin{block}{sMDT Design}
						\small{
							\begin{minipage}{0.96\linewidth}
								\vspace{0.5cm}
								\begin{columns}[T]
									\begin{column}{0.03\textwidth}
									\end{column}
									\begin{column}{0.65\textwidth}
										\begin{itemize}
												\item sMDT chamber design and assembly procedures optimized for mass production
												\item Simple and cheap drift tube design with high reliability
												\item Special plastic materials selected to prevent outgassing and cracking
 												\item Industrial standard Al tubes
 												\item Wire positioning accuracy better than \textbf{10 $\mu$m}
										\end{itemize}
									\end{column}
									\begin{column}{0.35\textwidth}
% 										\textbf{End-plug}
										\vspace{0.5cm}
										\includegraphics[width=1.0\textwidth]{end-plug3}\\
										\vspace{0.5cm}
										\hspace{2cm}
										\tiny{Schematic of an sMDT end-plug}
									\end{column}
								\end{columns}
								\vspace{0.5cm}
								\begin{columns}[T]
									\begin{column}{0.03\textwidth}
									\end{column}
									\begin{column}{1\textwidth}
										\begin{itemize}
											\item No wire aging observed up to 9 $\frac{C}{cm}$ charge on wire (15 x ATLAS requirement)
										\end{itemize}
									\end{column}
								\end{columns}
							\end{minipage}
						}
					\end{block}
					\vfill
					\begin{block}{sMDT Chamber Construction}
						\small{
							\begin{minipage}{0.96\linewidth}
								\begin{columns}[T]
									\begin{column}{0.32\textwidth}
										\vspace{0.5cm}
										\begin{itemize}
											\item Semi-automated drift-tube production and chamber assembly take place in a air-conditioned clean room
											\item Automated testing of tube leakage rate, leakage current and wire tension
										\end{itemize}
									\end{column}
									\begin{column}{0.32\textwidth}
										\centering
										\includegraphics[width=0.9\textwidth]{BMG}\\
										\vspace{0.5cm}
										\tiny{Tube positioning using precisely machined jigs}
									\end{column}
									\begin{column}{0.32\textwidth}
										\centering
										\vspace{0.2cm}
										\includegraphics[width=0.9\textwidth]{clean-room2}\\
										\tiny{Chamber assembly in a clean room}
									\end{column}
								\end{columns}
								\vspace{0.3cm}
								\begin{itemize}
									\item Chamber assembly is conducted within one working day.
									\item Measurement of wire positioning with few $\mu$m accuracy 
									\item 2 sMDT chambers already installed in the ATLAS detector
									\item Additional 12 (16) sMDT chambers under construction until 2016 (2018) 
								\end{itemize}
							\end{minipage}
						}
					\end{block}
					\vspace{4.5cm}
					\vfill
				}
				\vfill
			\end{column}
			\hfill
			\begin{column}{0.49\textwidth}
				\parbox[t][\columnheight]{\textwidth}{%
					\begin{block}{Limitation of Present sMDT Read-Out Electronics}
						\small{
							\begin{minipage}{0.96\linewidth}
								\vspace{0.5cm}
								\begin{columns}
									\begin{column}{0.48\textwidth}
										\begin{itemize}
											\item Bipolar shaping used to guarantee baseline stability at high rates
											\item Disadvantage: long overshoot at the end of each signal
											\item[$\Rightarrow$] Effectively higher threshold and increased dead time for subsequent hits
										\end{itemize}
									\end{column}
									\begin{column}{0.48\textwidth}
										\textbf{Signal Pile-Up of Closely Spaced Hits}\\
										\vspace{0.5cm}
										\includegraphics[width=1.0\textwidth]{pile_up}\\
										\begin{tikzpicture}[overlay]
											\node[text width=15cm, color=red] at (20,6.5) {Muon};
											\node[text width=25cm, color=blue] at (14,2.8) {$\gamma$-background};
										\end{tikzpicture}
									\end{column}
								\end{columns}
										\begin{itemize}
											\item Want to operate with short dead time to maintain high efficiency at high rates\\ $\Rightarrow$ strong influence of undershoot
										\end{itemize}
							\end{minipage}
						}
				\end{block}
				\vfill
				\begin{block}{Improvement: Shaping Circuit With Baseline Restoration}
					\small{
						\begin{minipage}{0.96\linewidth}
							\begin{columns}
								\begin{column}{0.35\textwidth}
									\begin{itemize}
										\item High bandwidth (700 MHz) transimpedance amplifier (PreAmp)
										\item Discrete bipolar shaping circuit (2 filter stages) with baseline restoration (BLR)
									\end{itemize}
								\end{column}
								\begin{column}{0.63\textwidth}
									\centering
									\includegraphics[width=1.03\textwidth]{ASBC}\\
									\tiny{Photograph of preamplifier (PreAmp) and shaping circuit (Filter 1-2, BLR) with comparator}
								\end{column}
							\end{columns}
							\vspace{0.5cm}
							\textbf{Principle of baseline restorer \cite{Robinson}}
							\begin{columns}
								\begin{column}{0.1\textwidth}
								\end{column}
								\begin{column}{0.23\textwidth}
									\includegraphics[width=1.0\textwidth]{blr_diode}
								\end{column}
								\begin{column}{0.63\textwidth}
									\begin{itemize}
										\item Diode slightly conducting at working point ($I_{Base}$)
										\item Diode is non-conducting for positive signal polarity
										$\Rightarrow$ signal stays unchanged
										\item Diode is conducting for negative polarity $\Rightarrow$ signal is pulled to baseline $\Rightarrow$ \textbf{Undershoot eliminated}
									\end{itemize}
								\end{column}
							\end{columns}
						\end{minipage}
					}
				\end{block}
			\vfill
			\begin{block}{Bipolar Shaped Pulse with Baseline Restoration}
				\small{
					\begin{minipage}{0.96\linewidth}
						\begin{columns}
							\begin{column}{0.65\textwidth}
								\includegraphics[width=1.00\textwidth]{muon_elec_shaped_blr}
							\end{column}
							\begin{column}{0.33\textwidth}
								\begin{itemize}
									\item Due to the discrete circuit, the amplified signal before and after the signal shaping can be measured in parallel
									\item Baseline restoration leads to a clear suppression of the bipolar undershoot
									\item The diode used in the baseline restorer causes a slightly smaller pulse amplitude compared to shaping without baseline restoration
								\end{itemize}
							\end{column}
						\end{columns}
					\end{minipage}
					}
				\end{block}
				\vfill
				\begin{block}{sMDT Performance Test at the CERN Gamma Irradiation Facility}
					\small{
						\begin{minipage}{0.96\linewidth}
							\begin{columns}
								\begin{column}{0.47\textwidth}
									\includegraphics[width=0.9\textwidth]{resolution_vs_rate_smdt_mdt-7}
								\end{column}
								\begin{column}{0.47\textwidth}
									\includegraphics[width=0.9\textwidth]{efficiency_vs_rate_smdt_mdt-7}
								\end{column}
							\end{columns}
							\begin{itemize}
								\item Measurements show huge improvement in terms of rate capability for sMDT compared to MDT drift tubes in both spatial resolution and muon efficiency
								\item Baseline restoration suppresses the pile-up effects and, therefore, avoids resolution and efficiency degradation at high counting rates
							\end{itemize}
						\end{minipage}
					}
				\end{block}
				\vfill
				\begin{block}{Bibliography}
					\small{
						\begin{minipage}{0.96\linewidth}
							\begin{thebibliography}{9}
								\bibitem{smdt} B. Bittner et al., \emph{Performance of Drift-Tube Detectors at High Counting Rates for High-Luminosity LHC Upgrades}, Nucl. Instr. and Meth. A732 (2013) 250-254.
 								\bibitem{Robinson} L. B. Robinson, \emph{Reduction of Baseline Shift in Pulse-Amplitude Measurements}, Rev. Sci. Instrum. 32 (1961) 1057.
							\end{thebibliography}
						\end{minipage}
						}
					\end{block}
					\vspace{4.5cm}
				}
			\end{column}
		\end{columns}
	\end{frame}
\end{document}

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