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\documentclass{chowto}

%% optional packages, in case you want AMS math macros and AMS symbols 
\usepackage{amsmath,amssymb}   

\title{Splitter Magnet}
\howtotype{expert} % ``expert'', ``user'', ``reference''
\experiment{HKS} % Optional
\author{Liguang Tang and Lulin Yuan}
\category{magnet} % Subject area of this document


%\maintainer{Name of person maintaining document} % Optional
\date{\today} % Can use \today as the argument

\begin{document}

\begin{abstract}
This Howto outlines the purpose of the Splitter magnet and its operation and 
monitor.
\end{abstract}
 
\section {Purpose}
The Splitter magnet will handle beam electrons, scattered electrons
and positively charged kaons at the same time.  It separates the
scattered electrons and kaons at small forward angles to much larger
separation angles before entering the Enge and HKS spectrometers,
respectively.  Therefore, it contributes to the overall optics for
both the Enge and HKS spectrometers.  It will also bend the electron
beam about 8.15 degrees and reorient aiming back to Hall C dump by
later two dipoles, DZ and EZ magnets.

Although using such a common Splitter magnet reduces kinematics
flexibility, it greatly optimizes the usage of large high precision
spectrometers at large physical angles to detect extremely forward
scattered particles with opposite charges under very limited space.

\section {Control and setting of the Splitter magnet}
Since this magnet will effect the exit beam trajectory toward the beam
dump, this magnet can only be operated by MCC.

%To determine the setting point of Splitter power sypply current, the
%Splitter B-I curve was measured up to 780 A in Test Lab before the
%experiment. The reading from fixed Hall Probe was compared with NMR
%measurement. The B-I curves was then fitted by 6-order
%polynomials. From the fitting, the current setting point corresponding
%to 1.546 Tesla is 842.83 A.

The nominal field setting for the Splitter is 1.546 Tesla.  The corresponding power supply current setpoint is 842.83 A. The
Splitter field is monitored by a fixed Hall probe glued to the wall of
target vacuum chamber. 
%The probe should have a reading of 1.54593
%Tesla at this point. The difference is due to the magnetic boundary
%condition near the wall of stainless steel vacuum chamber. 
Between the
field range of 1.4 Tesla and 1.65 Tesla, the Splitter B (in Tesla)-I
(in Ampere) curve can be
expressed as a 6-order polynomial:
\begin {multline}
 B=
2.33427E-18\times I^6-6.12490E-15\times I^5+5.66717E-12\times
I^4-2.56364E-9\times I^3\\
+5.76159E-7\times I^2+1.87247E-3\times I+1.89685E-3 \notag
\end{multline}    

Before setting the splitter, the magnet must be degaussed. The degauss
procedure is ramping up and down the magnet in two full cycles:
0A-1000A-0A-1000A-0A, THe ramping speed is 100A/min with 2 minute
staying time at each minimum and maximum current. After that, the
ramping up speed
to the desired field value is 25A/min. 

To set the magnet %(setting value will be given after calibration is done),

\begin{enumerate}
\item Beam must be off during setting or any field change (even it may
be small).
\item Call MCC to request on and setting up the Splitter magnet.
\item MCC will confirm the setting value in terms of current.
\item MCC will set the magnet following the specified ramping procedure.
\item MCC will call back to confirm the field reading by hall probe monitored 
by Hall C.
\item Small current correction (directly increase or decrease) can be
      done if the.  field is not set to the desired value within an
      accuracy of $10^{-4}$.
\end {enumerate}

\section {Monitoring the Splitter field}
The field of Splitter magnet must stable through out the entire
experiment.  Thus, the hall probe reading is under constant monitoring
as well as writing the value to each data run.  If the value of the
field tends to drift over an accuracy of $10^{-4}$ or $\pm1.5$ Gauss,
current correction should be requested to MCC following the Control
and setting procedure.


%\begin{figure}
%\begin{center}
%\includegraphics[width=10cm] {bisp_fhp.eps}
%\end{center}
%\caption{B-I curve of splitter measured by fixed Hall Probe with fitting.}
%\label{fig:bisp_fhp}
%\end{figure}
%
%\begin{figure}
%\begin{center}
%\includegraphics[width=10cm] {bisp_nmr.eps}
%\end{center}
%\caption{B-I curve of splitter measured by NMR with fitting.}
%\label{fig:bisp_nmr}
%\end{figure}

\end{document}

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