Nt1310 Unit 9 Lab Report

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\subsection{Test results}
\label{sec:Test results}

An optimized gas mixture of C$_2$H$_2$F$_4$/iso-C$_{4}$H$_{10}$/SF$_{6}$ = 95/4.5/0.5 was flown through the RPCs with a total flow rate of 10
SCCM and operated in the avalanche mode. The schematic of the gas flow system for two RPCs is shown in figure~\ref{fig:5_Gas_flow_system}. The following characterization studies were conducted on the RPCs at $\sim$45\% relative humidity (RH) and 20 $^{\circ}$C temperature. These are the optimized ambient RH and temperature conditions for operating the INO-ICAL RPCs.

\subsubsection{Voltage-current characteristics}
\label{sec:Voltage-current characteristics}

The simple electrical equivalent circuit representation of a single gap RPC is shown in figure~\ref{fig:5_Equivalent_circuit_RPC}.
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From equation~\ref{eq:Electric_field_displacement}, it indicates that the RPCs made out of electrodes with larger relative permittivity (section~\ref{sec:Relative permittivity}) can be operated at lower bias voltages. The experimental arrangement and electronic circuit for measuring the efficiencies of RPCs is shown in figure
\ref{fig:5_Schematic_experimental_setup}. The oscilloscope trace of pulses produced from the RPCs and the telescope trigger pulse are shown in figure~\ref{fig:5_Oscilloscope_pulses}. The efficiency measurements on RPCs were performed using C.A.E.N Mod. V830 Scaler. The telescope trigger pulse was recorded as 3-fold pulse. The efficiency is defined as the ratio of the number of coincident pulses of RPC strip with that telescope trigger (i.e., 4-fold pulses) to the number of trigger pulses (3-fold pulses). This definition is written as:

\begin{equation}
{\text{Efficiency}} = {\frac{4\text{-}{\text{fold}} \ (4\text{F}) \ \text{rate}}{3\text{-}\text{fold} \ (3\text{F}) \ \text{rate}}} \times
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The measured efficiency of RPCs as a function of applied high voltage are shown in figure~\ref{fig:5_Efficiencies_of_RPCs}. The four
RPCs showed greater than 95\% efficiency on the plateau. It is observed that the knee of efficiency plateau of A-RPCs starts at 10.8 kV, whereas that of S-RPCs starts at 12.0 kV. Therefore, A-RPCs can be operated at 1.2 kV lower bias voltage in comparison to S-RPCs. These results are in consistent with equation~\ref{eq:Electric_field_displacement}.

\begin{figure}[ht] \centering