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\documentclass{chowto}

\title{Design of Enge Sieve Slit/Collimator}
\howtotype{reference}
\experiment{HKS}
\author{Liguang Tang and Lulin Yuan}
\category{Enge}

%\maintainer{Name of person maintaining document} % Optional
\date{May 10, 2005}

\begin{document}

\begin{abstract}
This Howto outlines the purpose of the Enge Sieve Slit/Collimator, its 
design parameters.  
\end{abstract}
 
\section {Purpose}
The sieve slit is a collimator plate with array of holes that select events 
with specific angles. With a point target and recognition of the correlations
of the focal plane parameters, these events separated into specific holes are 
used to optimize the angular reconstruction matrices.

On the same plate, an open collimator is made to basically match the Enge 
spectrometer acceptances in order to minimize the particles that may hit
the irons inside the spectrometer.
 
There is also an un-collimated opening on the plate.  This is an option in 
case a study of the blocking effect of the bremsstrahlung and Mollor electrons
is needed using the lower edge.
  

\section {Design}
The electron arm is formed by Splitter dipole which separates the scattered 
electrons from oppositely charged kaons followed Enge spectrometer, the 
plate is behind the Splitter magnet. The location of the plate is 43 cm from downstream side of collimator plate to the effective field boundary of the first pole of Enge Split-Pole spectrometer.
The plate has a thickness of 2.54 cm.

Since the plate is located inside of the overall optics with Splitter field in front 
of it, slight momentum dependence in the events selected from each hole appears.
Thus the optimization procedure and method for the angular matrix are different
from those used for the SOS and HMS spectrometers.  Calibration method and 
procedure will be described in separate Howto.

Since the Enge is tilted up with respect to the virtual target position then shifted 
in Y in order to block the bremsstrahlung and Mollor electrons while remain 
minimum scattering angle, the overall optics has a ``twist''.  This makes the acceptance 
not symmetric.   Thus, the sieve slit hole pattern is not symmetric in X but designed 
basic on central optics and actual twisted acceptance.  There are 6 columns and 
5 raws.  The hole at 3rd column and 3rd raw (counted from -X and -Y side) is on the Enge spectrometer Z-axis.  Similarly, the size of the collimator is also not symmetric in X.

The hole size is 5 mm (0.2 inch) in diameter and is drilled normal to the plate.  Thus this
hole size is to ensure the angular reconstruction accuracy better than 2 mr in $\sigma$ 
under the given focal plate angular measurement accuracy and at same time to obtain 
sufficient event rate. 

\end{document}

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