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Hall C Beam Energy Measurement

\documentclass{chowto}

\title{Hall C Beam Energy Measurement}
\howtotype{user} % ``expert'', ``user'', ``reference''
%\experiment{Name of experiment} % Optional
\author{M. K. Jones}
\category{beamline} % Subject area of this document
%\maintainer{Name of person maintaining document} % Optional
\date{\today} % Can use \today as the argument

\begin{document}

\begin{abstract}
MCC does the beam energy measurement. It is important for the user 
to make an hclog entry as documentation. 

\end{abstract}

\section{MCC energy measurement}
MCC follows a standard \htlink{procedure}{http://opsntsrv.acc.jlab.org/ops_docs/online_document_files/MCC_online_files/HallC_energy_measure_proc.pdf} for doing the Hall C beam energy measurement. The basic
idea is to setup a dispersive tune. Setting up a clean dispersive tune is usually what takes the
most time. Then MCC adjusts the current  of the arc dipole string (MBSY3C) to
center the beam at the end of the arc on IPM3C17H. From the current one can calculate
the beam energy assuming the beam follows the central path. 
By measuring the positions and angles at the entrance and exit of the dipole arc
one can correct for small deviations for the central path. To measure these
positions superharp scans are performed 3C07 and 3C17 positions. 
The beam current for the harp scans is 10~$\mu$A.

\section{Making an hclog entry}

It is important for the user to make an hclog entry. The user should log the following 
information.

\begin{enumerate}
\item The current of the arc dipole string MBSY3C. 
\item The Elog entry number of the {\it Hall C Energy Measurement} screen that MCC should make.
An example is Elog entry \htlink{1134263}{http://opweb.acc.jlab.org/CSUEApps/elog02/elog_item.php?elog_id=1134263}.
 \item The Elog entry number of the {\it Hall C Superharp Analyzer} screen that MCC should make.
An example is Elog entry \htlink{1134260}{http://opweb.acc.jlab.org/CSUEApps/elog02/elog_item.php?elog_id=1134260}.
 \item The uncorrected and corrected beam energies from the {\it Hall C Superharp Analyzer} screen. One
can calculate the uncorrected beam energy using the current of the arc dipole string MBSY3C and the
program {\it magnet} in the directory  { \it Beam\_Energy } in the cdaq account on the cdaql1
machine. An example session is :
\begin{verbatim}
cdaql1.jlab.org> pwd
/net/cdaqfs/hallc/home/cdaq/Beam_Energy
cdaql1.jlab.org> magnet
Include extrapolation uncertainty (<y> or <n>) ? :
y
do you want to do a calculation (<y> or <n>) ? :
y
enter current (amps) : 126.41194
Current: 126.41194 A
Bdl =  756226.317 Gauss.cm
P = (3.02898 +/- 0.00122) GeV/c
do you want to do a calculation (<y> or <n>) ? :
n
\end{verbatim}

\item The values for the epics variables {\it halla\_MeV}  and {\it hallc\_MeV} . These values
have been calibrated to previous energy measurements in Hall A and C and have been accurate in
the past. To get the values do the following on a cdaq computer:
\begin{verbatim}
cdaql1.jlab.org> caget halla_MeV
halla_MeV                     5008.97 
cdaql1.jlab.org> caget hallc_MeV
hallc_MeV                     3028.39 
\end{verbatim}


\end{enumerate}

\end{document}

% Revision history:
% $Log: hallc_beam_energy_meas.tex,v $
% Revision 1.1  2003/04/01 22:17:33  saw
% Hall C Beam Energy Measurement
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