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\documentclass{chowto}

\title{Operation and Tracking of HKS Drift Chamber}
\howtotype{user}
\experiment{HKS} % Optional
\author{Lulin Yuan and Liguang Tang}
\category{hks}

%\maintainer{Name of person maintaining document} % Optional
\date{March 25, 2005}

\begin{document}

\begin{abstract}
This document describes the operational parameters,commissioning procedure and tracking method for
HKS drift chamber. 
\end{abstract}
 
\section {Purpose}

The HKS drift chambers were built at Jefferson Lab by Hampton
University group. The two chambers (DC1 and DC2) are mounted directly on the
HKS dipole magnet and are the first detetors after dipole exit. They
measure particle trajectory at HKS spectrometer focal plane. This
combined with spectrometer optics can be used to reconstruct particle
momentum and angles at target.    

\section {Operational Parameters}

\begin{table}[!hbt]
\caption{Geometrical parameters}
\begin{center}
\begin{tabular}{ll} \hline
Dimension (L$\times$W$\times$T)       & 59.25"$\times$22.75"$\times$3"\\
Active Region           & 48.2"$\times$12"\\      
Wire plane configuration& U,U',X,X',V,V'\\ \hline
\end{tabular}
\end{center}
\end{table}

\begin{table}[!hbt]
\caption{Operational parameters}
\begin{center}
\begin{tabular}{ll} \hline
Operation HV   & 1970 V \\ 
Threshold      & 3.0 V  \\
Gas content    & Argon/Ethane 50:50 mixture \\
Gas pressure:  & $\sim16$ psi \\ \hline
\end{tabular}
\end{center}
\end{table}

The cathode foil planes and field wires are applied the same HVs. Each chamber has 4 HV input connectors, two for foil planes and two
for field wires. The signals from sense wires goes into Nanometrics
N277 cards for preamplifying and discriminating. There are 20
preamplifier cards for each chamber, 10 on one side and 10 on the
other side of the chamber.  These Nanometrics cards need both +5 and
-5 power input. The voltages are supplied by two Acopian power
supplies, for +5 V and -5 V respectively.

The working gas inside the chambers is Argon and Ethane 50:50
mixture. It also contains a small amount of (about 1\%) alcohol vapor
to prevent aging of the wire chamber. The gas is mixed in the outside
gas shed. For detail information about Hall C gas system, Please
refer to Hall C How-To: Drift Chamber Gas System.

\section {Commissioning Procedure}

Following is the list of major steps to bring the chamber into working
condition:
\begin {enumerate}

\item Check gas system for correct setting of pressure and flow
rate. Flush working gas into the chamber for at least several days to
drive out air and moisture.

\item Apply HV up to setting point (currently 1970 V). Monitor leakage
current at the same time.

\item Turn on threshold voltage and LV power for the preamp cards. The
threshold voltage supply will be located inside the eletronic room of
the counting house. 

\item Taking some data to check the tracking efficiency and wire map,
drift time and tracking residue histograms. Ajusting the drift
velocity and plane position offset parameters if necessary. Refer to
section \ref{sec:tp}:Traking Parameters.   

\end{enumerate}
    
 
\section{Wire Layout and Coordinates System}

The wire planes measure positions in three directions X,U and V. These
coordinates are then transformed into focal plane coordinates X,Y and Z.

\begin{figure}[!h]
\centering \includegraphics[width=10cm]{hdchowto-wirecoord.eps}
\caption{ HKS DC wire layout and coordinate system}
\end{figure}

\section{Tracking Parameters}
\label {sec:tp}
The parameter set for HKS DC tracking comprises geometrical constants,
tracking criterion and other wire chamber constants. They are needed
in the tracking routine to convert raw wire hit into coordinates and
fitting the tracks. 

Each wire plane of the chamber is described by the following
constants:

\begin{enumerate}
\item Plane number: From 1 to 12.

\item \verb+hdc_zpos+: The coordinate in the particle traveling direction.  

\item \verb+hdc_beta+, \verb+hdc_gamma+ and  \verb+hdc_alpha+: These are the three rotation
   angles of wire plane about the Y axis, X axis and Z axis.
   
\item \verb+hdc_nrwire+: number of wires in plane.

\item \verb+hdc_central_wire+: The fictitious wire number of the middle wire. It
   is used in calculation of the wire center position:
\begin {verbatim}
" hdc_wire_center(goodhit) = hdc_pitch(plane)
     &                  * ( (hdc_nrwire(plane) + (1 - wire))
     &                  - hdc_central_wire(plane) ) - hdc_center(plane)"
\end{verbatim}

\item \verb+hdc_wire_counting+: A flag that indicates whether wire is counted
   along positive (-1) or negative (+1) x direction. For HKS DC, all
   wires are counted from the positive X side. So it is +1 for all the
   planes. 

\item \verb+hdc_center+: offsets of the planes along local coordinates.

\item \verb+hdc_length_x+ and \verb+hdc_length_y+: The dimensions of the DC active area
   in x and y directions. 

\item \verb+sigma+: the Gaussian width of the tracking fitting
residues
\end{enumerate}
Currently, the parameter values used in the tracking are:

\begin{table}[!h]
\caption{Tracking parameters}
\begin{center}
\begin{tabular}{lllrrrr} \hline
 Plane & No &\multicolumn{1}{c}{Zpos} &\multicolumn{1}{c}{$\alpha$}  & nrwire &  Central&    sigma \\     
       &    &\multicolumn{1}{c}{(cm)}& \multicolumn{1}{c}{(degree)}&
       &\multicolumn{1}{c}{Wire}&\multicolumn{1}{c}{(cm)} \\ \hline 
 1u1 &   1 & -1.905 & 30     &    87	&     43.75&	0.02\\	
 1u2 &   2 & -1.270 &    30  &   87	&     44.25&	0.02\\
 1x1 &   3 & -0.635 &    90  &  122     &     61.75&	0.02\\
 1x2 &   4 & +0.3175&    90  &  122	&     61.25&	0.02\\
 1v1&	5 & +0.9525 &  150      &  87	&     43.75&	0.02\\
 1v2&   6 & +1.5875 &  150      &  87	&     44.25&	0.02\\ \hline
%\multicolumn{7}{l}{$\beta$, $\gamma$ angles are 0 degree for all planes}\\
%\multicolumn{7}{l}{hdc\_center are 0}\\ \hline
\end{tabular}
\end{center}
\end{table}
The $\beta$, $\gamma$ angles are 0 degree for all planes.
\verb+hdc_center+ are 0 now.
The wire plane Z positions  in the table are relative positions
within one chamber. Assuming a 1 meter seperation between the 2 chambers
after they are mounted on the spectrometer, the actual Z positions for
DC1 wire planes will be $Zpos-48.095$ cm from the HKS reconstruction
plane, for DC2, it will be $Zpos+51.905$ cm.

An important tracking criterion constant is \verb+space_point_criterion+, the
minimum squared distance to combine two hit pairs into one space
point. \verb+hpace_point_criterion+ is 1.2 cm currently.

These tracking parameters are set in files according to standard Hall C CTP file
structure.

\begin{figure} [!h]
\centering \includegraphics [width=14cm]{hdchowto-dcparamstruc.epsi}
\caption{File structure of DC tracking parameters}
\end{figure}

\section {Flowchart of DC tracking code}
%
Following is the flowchart of chamber tracking code: 
\begin{figure} [!hbt]
\centering \includegraphics[width=14cm]{hdchowto-dctrackingflowchart.epsi}
\caption{Flowchart of DC tracking code}
\end{figure}

\end{document}

% Revision history:
% $Log: hdchowto.tex,v $
% Revision 1.1.2.1  2005/05/13 13:42:07  saw
% Initial version
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