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\documentclass{chowto}

\title{Enge Magnet}
\howtotype{expert}
\experiment{HKS}
\author{Liguang Tang}
\category{magnet}
%\maintainer{Name of person maintaining document} % Optional
\date{March 18, 2005}

\begin{document}

\begin{abstract}
This Howto outlines the purpose of the Enge magnet and its operation and 
monitor.
\end{abstract}
 
\section {Purpose and Optics}

The Enge Split-Pole magnet is used behind and combined with the Splitter magnet
as the electron spectrometer which analyzes the electron's momentum and scattering
angle.  The momentum and angular reconstructions are done using the measured 
focal plane parameters, reconstruction matrices, and defined target point target 
X position. 

The central momentum is $316$ MeV/c with a bite of about $\pm30\%$.  The solid angle 
acceptance is about 9 msr in average.  Due to the non-negligible momentum 
dispersion from the front Splitter magnet and extremely small scattering angle, the 
total virtual photon flux is obtained by more precise integrals over momentum bite 
and angle rather than simply using this average acceptance.

At a location between the Splitter and Enge Split-Pole, the Enge magnet is tilted 
by rotate about X-axis and followed by a shift along Y-axis.  This arrangement
effects as rotating at the virtual target position then shifting this point off the Splitter
middle plane.  By doing this, the spectrometer remains detecting small forward angle 
scattered electrons but just avoid the high rate bramstrahlung and Moller electrons.
Such tilt does not effect the resolution but symmetry in acceptance.

\section {Setting the magnet}

Since this magnet is not directly effect the beam, thus it will be controlled and operated 
by Hall C experimentalists.  However, due to fringe field does have slight effect to beam
and other magnets nearby, such as Splitter and HKS Q1, it is preferred to turn off the 
beam during the process of setting up the magnet.   Since this magnet is sharing the 
same power supply with Moller magnet, existing control will be used in setting up the 
magnet by referring to steps of ``Getting started'' and ``Setting the magnets'' in ``How to 
set the SOS magnets'' in Hall C online Howto document.  Since no polarity change in
operating this magnet for hypernuclear experiment, step of ``Degaussing'' is not Needed.

\section {Monitor}

The field is monitored directly by a hall probe.  The stability should be controlled within
an error of $\pm 10^{-4}$ or $\pm 1.5$ gauss.

\end{document}

% Revision History:
% $Log: Enge-magnet.tex,v $
% Revision 1.1.2.1  2005/05/12 14:22:53  saw
% Initial version
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