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\begin{document}
\title{Energy Deposition Simulation and Measurements in a LHC Collimator and Beam Loss Monitors}

\author{T. B\"ohlen%\thanks{Till.Tobias.Boehlen@cern.ch}
, B. Dehning\thanks{Bernd.Dehning@cern.ch}
, CERN, Geneva, Switzerland}

\maketitle




\begin{abstract}
The LHC collimators are protected against beam-caused damages by measuring the secondary 
particle showers with beam loss monitors. Downstream of every collimator an ionisation 
chamber and a secondary emission monitor are installed to determine the energy deposition in 
the collimator. The relation between the energy deposition in the beam loss monitor and the 
collimator jaw is based on secondary shower simulations. To verify the FLUKA simulations the 
prototype LHC collimator installed in the SPS was equipped with beam loss monitors. The 
results of the measurements of the direct impact of the 26 GeV proton beam injected in the 
SPS onto the collimator are compared with the predictions of the FLUKA simulations. In 
addition simulation results from parameter scans and for mean and peak energy deposition 
with its dependencies are shown.

\end{abstract}

\section{INTRODUCTION}

TODO: GeneralLHC BLMsystem introduction \cite{bib:BLMsystem}. BLM system serves damage prevention of LHC components; mainly sc magnets.

Second critical beam-line elements are collimators, see \cite{bib:collimationsystem} for a detailed description of the LHC collimation system.
In order to limit losses on sensitive beam-line components, movable LHC collimators are placed in vicinity of the beam (about $6$ to $10\sigma$) to intercept particles from the beam halo.
Collimators of various types, depending on their protective purpose, are placed at crucial positions along the LHC ring and its transfer beam lines to form a sophisticated multi-stage collimation approach.
Losses on these exposed elements are individually surveyed by BLM detectors.
The abundance of collimators (about 80\% for initial Phase I collimation) are placed in the LHC loss-intensive cleaning insertions \cite{bib:collimationsystem}. They contain three types of collimators: primaries (TCP), secondaries (TCSG), and active absorbers (TCLA)%, see Table~\ref{tab:coltypes}
, each monitored by a pair of BLM detectors as shown in Fig.~\ref{fig:LHCBLMsetup}.
% \begin{table}[hbt]
%    \centering
% 
%    {\footnotesize
%    \begin{tabular}{l|cc}
%        \toprule
%        \textbf{Collimator} & \multicolumn{2}{c}{\textbf{Jaw Length \& Material}}  \\ 
%        \midrule
%            Primary	(TCP)        & 60\,cm            & C reinforced graphite \\
%            Secondary	(TCSG)       & 100\,cm           & C reinforced graphite \\
%            Absorber	(TCLA)       & 100\,cm           & W embedded in Cu \\
%            
%        \bottomrule
%    \end{tabular}
%    }
%    \caption{Collimator types in LHC cleaning insertions. Other, similar structured, collimators are placed along the LHC ring.}
%    \label{tab:coltypes}
% \vspace*{-0.3cm}
% \end{table}
\begin{figure}[htb]
   \centering
   \includegraphics*[angle=0,width=65mm]{fig/PSLscheme_v3.eps}
   \caption{Side view of a ``collimator-detector cell'' composed of a collimator, an IC, and a
SEM, as installed in the LHC cleaning insertions. A vertical collimator is shown.}
   \label{fig:LHCBLMsetup}
\vspace*{-0.5cm}
\end{figure}
There are many failure scenarios that can lead to increased beam losses which pose a threat for damage. Depending on the type of failure, the scenario of impact on the collimator can vary considerably.
For the protection of the collimators there is the need to estimate damage limits for the collimators as a function of the BLM detector signals.
This study reports for the collimation cleaning insertions the relation of energy deposition due to impacting beam protons on LHC collimator elements to energy deposition in the BLM detectors which translates to a corresponding BLM signal (energy deposition-to-signal ratio). Depending on the time-scale of beam losses, total energy deposition in the movable collimator elements and maximal energy density in the collimator jaws were chosen for steady-state and transient losses, respectively, as meaningful quantities for damage limits in the collimator components.
The accuracy of predicting BLM detector signals at collimators with Monte Carlo (MC) simulations is investigated by a comparison with measurements in an LHC-like setting mounted in the Super Proton Synchrotron (SPS).
Secondly, dependencies of the energy deposition-to-signal ratio on parameters of the beam impact scenario are investigated. This paper is based on \cite{bib:thesis}, details can be found therein.


\section{METHODS}

The multi-purpose MC code \textsc{Fluka} \cite{bib:fluka1,bib:fluka2}  was employed (\textsc{Fluka} version 2006.3b) for the modeling of particle showers and energy deposition scoring in the relevant beam line geometries. Simulations were made with the NEW-DEFAULTS physics settings.
Dependence of results on different cut values for production and transport of particles were investigated and chosen to reduce computation time while not influencing the results. Statistical errors were kept about or below 5\%.

\section{ACCURACY OF SIMULATION OF BLM SIGNALS}

Experimental data, acquired in an LHC collimation-like installation in the SPS
ring, is compared to the predictions of detector signals by simulations with \textsc{Fluka}.
This allows to evaluate the overall accuracy of predicting the integrated signal of BLM detectors by simulations with a radiation field similar to the one expected in the LHC collimation area.

\subsection{Experimental Setup}

An LHC prototype secondary graphite collimator (TCSG) is mounted in the SPS Long Straight Section 5. About $1.9\,\hbox{m}$ downstream of this collimator a set of BLM detectors is installed, consisting of two ICs (IC1A, IC1B) and one SEM as shown in Fig.~\ref{fig:SPSBLMsetup}. 
%One IC is mounted in a vertical position with respect to the beam pipe (BLM IC1A), and a second one is mounted parallel to the beam pipe (BLM IC1B). The shorter SEM is installed parallel to the beam pipe at the height of the beam. 
IC1A and the SEM are located in a similar position with respect to the collimator as in the standard LHC collimation installation.

\begin{figure}[htb]
   \centering
   \includegraphics*[angle=-90,width=65mm]{fig/LSS05sketch_v2.eps}
   \caption{Top view of the horizontally mounted secondary collimator (TCSG) in the SPS and the BLM detectors. %The beam impacts on the jaws of a horizontally mounted secondary collimator (TCSG). Two ICs and one SEM detector are mounted downstream of the collimator.
}
   \label{fig:SPSBLMsetup}
\vspace*{-0.5cm}
\end{figure}

\subsection{Measurements}

Three measurement sessions resulted in sets of data allowing to derive BLM signals per proton lost on the collimator. Measurements were conducted at SPS injection energy of $26\,\hbox{GeV}$.
Measurements were taken in two different modes. One with high dose rates at larger impact parameters and a second one with low dose rates at small impact parameters. High dose rates at the collimator caused the ICs to enter in a saturation regime, consequently only data for lower energies could be used for comparison.
%In the first one, referred to as \textit{direct dumping}, the beam was injected with one of the collimator jaws moved partly or completely into the beam. High dose rates at the collimator caused the ICs to enter in a saturation regime, consequently only data for lower energies could be used for comparison.
%In the second one, referred to as \textit{continuous scraping}, both collimators jaws were initially withdrawn from the beam. During the injection plateau, one of the collimator jaws was moved continuously into the beam until the intensity of the circulating beam diminished. This resulted in lower dose rates and small impact parameters on the collimator.
Assuming the collimator to be the limiting aperture on which beam particles are lost, the number of protons lost on the collimator was derived from beam current transformer measurements.
%beam impact scenario
The position of the beam with respect to the collimator jaws was calibrated by moving the collimators into the beam and monitoring the drop in beam current.
The beam width at the collimator was determined with wire scanner measurements of the beam profile. 
%The corresponding beam width at the collimators was calculated by using the Courant-Snyder parameters at the wire scanner and the collimator.
%Courant 

% 
% The study includes an estimation of deviations of the BLM signals due to simplifications and misalignment of
% the geometry in the simulation, different physics parameters of the simulation, calibration of
% the signal of the BLM detectors, and uncertainties for the beam impact scenario. It enables
% to assess the accuracy of threshold predictions for the BLM detectors in the LHC collimation
% setup.
%  This method allowed to direct the beam on the
% collimator with different mean impact parameters, depending on the position of the collimator
% jaw with respect to the beam.



\subsection{Simulations}

The SPS section containing the collimator and the BLM detectors was modeled with a special focus on the collimator the beam line and the BLM detectors.
Materials and material properties of the collimator and the BLM detectors were carefully chosen and are in
agreement with the design specifications. Instrumentation and supports in vicinity were included making some simplifications in geometry and assuming standard materials.
The influence of simplifications, such as for the collimator support, and uncertainites of the geometry on the results was assessed by variation studies and found to be below 15\%.%, for details cf. \cite{bib:thesis}.


\subsection{Results and Discussion}

The responses of the BLM detectors, measured as signal per proton lost on collimator, were compared with simulations. Simulations could reproduce IC measurements within $\pm21\%$. For SEM simulations the agreement was worse and maximal deviation was found to be $+73\%$ and $-30\%$.
Deviations between measurements and simulations are attributed to several sources. These include
uncertainties of parameters of the experimental setup for reproduction by simulation, i.e., the precise impact scenario on the collimator (impact parameter distribution), the surface structure of the collimator, and the beam-jaw angle, space-charge effects for the IC, and the calibration uncertainty of the IC and SEM. Additionally, the fraction of returning protons which are not removed from the beam after an initial impact on the collimator was only estimated roughly.

\section{LHC SETUP}

\subsection{Simulations}
\textsc{Fluka} simulations of a ``collimator-detector cell'' as shown in Fig.~\ref{fig:LHCBLMsetup} were employed to calculate the ratios of BLM-signal to energy deposition in the collimator and BLM-signal per proton on collimator $N_{poc}$, called normalized BLM signal, dependent on different beam impact scenarios.
Implementation of geometry and materials was done similarly as described in the previous section% and is alike the one described in \cite{bib:mag06}
. Simulations for all collimator types (i.e., TCP, TCSG, and TCLA) were done at LHC injection and top energy, $450$ and $7000\,$GeV, respectively.

\subsection{Results}

Relative particle fluence spectra through the BLM detector volumes differential in energy were found to be alike at 26, 450, and 7000\,GeV. Thus, simulation of BLM detector responses are expected to have a similar level of accuracy as in the previous section, given that the simulation of secondary shower propagation through the components is of the same precision for all relevant energies.

Collimator jaws are installed with different tilt angles. Variations of these angles with respect to a collimator with horizontal jaws resulted in signal changes of maximum $-36\%$ and $-19\%$ for IC and SEM detector, respectively. Following simulations were done for collimators with horizontal jaws.
Typical misalignment of BLM detectors is within $\pm 3\,$cm (transversal), and $\pm 5\,$cm (longitudinal). BLM detectors are most sensitive to a displacement in height. Maximum changes for both LHC injection and top energy are 21\%.
Impact of omitting the collimator support in the simulation were assessed by introducing a simplified model and yielded changes of maximum 16\%.\footnote{Differences to values presented in \cite{bib:BLMthreshold}, are a consequence of reanalysing variations with more realistically chosen parameters.}
\begin{figure}[t]
    \centering
    \begin{tabular}{c}
    \includegraphics*[angle=0,width=65mm]{fig/impscan-color.eps}\\
    \includegraphics*[angle=0,width=65mm]{fig/impscanED-color.eps}\\
    \end{tabular}
%width=145mm
    \caption{Top: normalized BLM signal versus impact parameter is shown for a horizontal TCP collimator. Bottom: BLM signal-to-energy deposition ratio versus impact parameter for a horizontal
 TCP collimator. Isolated points are calculated reducing carbon density in a $1\,\mu$m surface layer of the collimator jaws %(they fall together with the other points for the graph on the bottom)
.}
    \label{fig:PSLimpact}
\vspace*{-0.5cm}
\end{figure}
The response of the BLM detectors for different impact parameters was simulated. Fig.~\ref{fig:PSLimpact}
shows the normalized BLM signal and the signal-to-energy deposition ratio versus impact parameter of a pencil beam. The carbon density in a $1\,\mu$m surface layer of the collimator jaws was set to one-half of the regular density to assess effects of the surface roughness of the jaws. The signal-to-energy deposition ratio was found to be virtually constant for graphite-jaw collimators (TCP, TCSG). For the TCLA collimator an increase for smaller impact parameter of about 50\% was found for the relevant range.
\begin{figure}[t]
   \centering
   \begin{tabular}{c}
    \includegraphics*[angle=0,width=65mm]{fig/anglescan-color.eps}\\
    \includegraphics*[angle=0,width=65mm]{fig/anglescanED-color.eps}\\
   \end{tabular}
 \caption{Top: normalized BLM signal is plotted for a TCP collimator versus beam-jaw angle between $\pm 300\,\mu$rad.
 Bottom: ratio of BLM signal to total energy deposition in the jaws is plotted for a TCP collimator versus
 beam-jaw angle.}
   \label{fig:PSLangle}
\vspace*{-0.5cm}
\end{figure}
Fig.~\ref{fig:PSLangle} shows the BLM-signal ratios versus beam-jaw angle
for a TCP collimator. A pencil beam with an impact parameter of 2\,$\mu$m was used. Beam-jaw
angles were varied between $\pm$300\,$\mu$rad. The normalized signal was found to vary about 2 to 3 orders of magnitude for both LHC injection and top energy. The ratio of BLM signal to total energy deposition in the jaws is nearly constant for negative angles and rises by a factor of about 2.5 and 4.0 for ICs and SEMs, respectively.
% This rise in signal ratio is due to two effects. Firstly, showers evolve only in the jaw-end
% of the collimator, thus there is no energy deposition in the upstream part of the collimator
% jaw. Secondly, the showers created in the jaw-end can propagate freely in direction of the
% detectors, unshielded by further jaw material.
Not only protons, also mixed particle showers generated at collimators upstream impinge on the collimators.
An exemplary simulation of second and third order halos impinging TCP collimators resulted in ratios of BLM signal to energy deposition which were lower by a factor of up to 4 compared to ratio for impinging protons. Energy deposition in the collimators is mostly due to higher order halos.
An assessment of the ratio of BLM signal to peak energy deposition in the collimator jaws was done assuming  impact parameter distributions for typical failure cases having the form of a Gaussian tail, see \ref{bib:alo06,bib:alo08}. For graphite collimators a maximum variation by a factor of about 10 was found. For TCLA collimators the signal variation was much higher due to unrealistically large variations of impact distributions assumed for those collimators.


% 
% \begin{figure}[htb]
%     \centering
%     \includegraphics*[angle=0,width=65mm]{fig/PSLImpDist-color.eps}
%     \caption{BLM signal-to-peak energy deposition ratio as a function of the mean impact parameter for a
%  horizontal TCP collimator.}
%     \label{fig:PSLdensity}
% \end{figure}




% 6.6, fig/impscan-color.eps
% Fig. 6.6.: Normalized BLM signal versus impact parameter is shown for a horizontal TCP collimator.
% The isolated points are calculated reducing carbon density in a 1 μm surface layer of the collimator
% jaws to 1/2 of the regular density to cope for the surface roughness of the jaws.
% 6.7, fig/impscanED-color.eps
% Fig. 6.7.: BLM signal-to-energy deposition ratio as a function of the impact parameter for a horizontal
% TCP (a) and a TCSG (b) collimator. The isolated points of the graph of the TCP collimator are
% calculated reducing carbon density in a 1 μm surface layer of the collimator jaws to 1/2 of the regular
% density to cope for the surface roughness of the jaws (the points are not clearly distinguishable as
% they fall together with the other ones).

% 6.8, 
% Fig. 6.8.: BLM signal-to-energy deposition ratio as a function of the impact parameter for a horizontal
% TCLA collimator.
% 6.9, 	\includegraphics[angle=0,width=0.50\textwidth]{fig/anglescan-color.eps}&
%	\includegraphics[angle=0,width=0.50\textwidth]{fig/anglescanED-color.eps}\\

% Fig. 6.9.: a) Normalized BLM signal is plotted for a TCP collimator versus beam-jaw angle between
% ±300 μrad.
% b) Ratio of BLM signal to total energy deposition in the jaws is plotted for a TCP collimator versus
% beam-jaw angle.

% 6.10 	\includegraphics[angle=0,width=0.50\textwidth]{fig/PSLImpDistED-color.eps}&
%	\includegraphics[angle=0,width=0.50\textwidth]{fig/PSLImpDist-color.eps}\\
% Fig. 6.10.: a) Peak energy deposition per proton on collimator Npoc as a function of the mean impact
% parameter is shown for a horizontal TCP and a horizontal TCSG collimator.
% b) BLM signal-to-peak energy deposition ratio as a function of the mean impact parameter for a
% horizontal TCP collimator.


\section{CONCLUSIONS}

Measured BLM signals were compared in an LHC-like setup to simulations. Larger deviations were found for SEM detectors. The comparison should be repeated for the LHC setup.
In order to interpret BLM detector signals for the protection of the collimators, a relation between energy deposition in the collimator due to impacting beam particles and signals of the BLM detectors were studied by simulations.
The variation of the impact parameter and the beam-jaw angle for beam protons show that the ratio of BLM signal to energy deposition in the collimator jaws can be safely assessed for protons by using the lowest calculated ratios. Ratios of BLM signal to energy deposition in the collimator jaws from mixed particle spectra were found to be lower. They should be investigated systematically to allow for a safe assessment.
Peak energy densities in collimator jaws were investigated for beam impact distributions of
typical failure cases. The ratios of BLM signal to peak energy density decrease for TCPs
and TCSGs for smaller mean impact parameters by a factor of maximum 10.

% Uncertainties of BLM signals at LHC collimators have been investigated by comparing measured
% BLM signals with simulations and by simulating different impact scenarios and BLM
% misalignment. These uncertainties should be considered to assess BLM thresholds at LHC
% collimators conservatively.

% 
% Collimation mayor design issue of LHC -- luminosity limiting factor. As a consequence, assure operational LHC
% 
% Further detailed studies of BLM signal dependencies are needed to allow for a more precise and reliable adjustment of threshold values with higher restrains on safety margins for later phases of the LHC operation. This includes specificially studies for cross-talks ion-beams.






\section{ACKNOWLEDGEMENTS}

We acknowledge the \textsc{Fluka} team, specifically P. Sala for providing detailed models of the IC and the collimators and M. Brugger for advice. We thank the LHC collimation team for support during the measurements and useful discussions, specifically S. Redaelli, Th. Weber, and R. Assmann.




% figures:

% fig/roughflat.eps
% Fig. 1.6.: The surface of a collimator is not perfectly plane. It has a microscopic structure, referred
% to as roughness, and an overall bend, referred to as flatness.

% 5.1, ok

% 5.7 \includegraphics[width=0.50\textwidth]{fig/varbeamsize.eps}&
%      \includegraphics[width=0.50\textwidth]{fig/penimpact26GeV.eps}\\
% , 5.19, BLM rate measurements -> bad resolution
% , 5.11,measured beam profile -> bad resolution 

% 5.12 \includegraphics[width=0.70\textwidth]{fig/phasespacesheme.eps}
% Fig. 5.12.: a) Single-side cut in normalized phase space at n¾, taken from [Bur04].
% b) Round cut in normalized phase space after many passages of not-scattered beam particles at a
% restrictive aperture, taken from [Bur04].

% 6.6, fig/impscan-color.eps
% Fig. 6.6.: Normalized BLM signal versus impact parameter is shown for a horizontal TCP collimator.
% The isolated points are calculated reducing carbon density in a 1 μm surface layer of the collimator
% jaws to 1/2 of the regular density to cope for the surface roughness of the jaws.
% 6.7, fig/impscanED-color.eps
% Fig. 6.7.: BLM signal-to-energy deposition ratio as a function of the impact parameter for a horizontal
% TCP (a) and a TCSG (b) collimator. The isolated points of the graph of the TCP collimator are
% calculated reducing carbon density in a 1 μm surface layer of the collimator jaws to 1/2 of the regular
% density to cope for the surface roughness of the jaws (the points are not clearly distinguishable as
% they fall together with the other ones).

% 6.8, 
% Fig. 6.8.: BLM signal-to-energy deposition ratio as a function of the impact parameter for a horizontal
% TCLA collimator.
% 6.9, 	\includegraphics[angle=0,width=0.50\textwidth]{fig/anglescan-color.eps}&
%	\includegraphics[angle=0,width=0.50\textwidth]{fig/anglescanED-color.eps}\\

% Fig. 6.9.: a) Normalized BLM signal is plotted for a TCP collimator versus beam-jaw angle between
% ±300 μrad.
% b) Ratio of BLM signal to total energy deposition in the jaws is plotted for a TCP collimator versus
% beam-jaw angle.

% 6.10 	\includegraphics[angle=0,width=0.50\textwidth]{fig/PSLImpDistED-color.eps}&
%	\includegraphics[angle=0,width=0.50\textwidth]{fig/PSLImpDist-color.eps}\\
% Fig. 6.10.: a) Peak energy deposition per proton on collimator Npoc as a function of the mean impact
% parameter is shown for a horizontal TCP and a horizontal TCSG collimator.
% b) BLM signal-to-peak energy deposition ratio as a function of the mean impact parameter for a
% horizontal TCP collimator.


%Fig. 5.21.: Misalignment of the beam-jaw angle is depicted schematically. Beam-jaw misalignment
% shortens the effective length of the collimator for impinging beam protons. For a positive misalignment
% beam particles hit the jaw later and less showers evolve in the jaw material.
%fig/beamjawangle_v4.eps

% Fig. 6.1.: Schematic side view of a “collimator-detector cell” composed of a collimator, an IC, and a
% SEM, as installed in the LHC cleaning insertions IR3 and IR7. A vertical collimator with red jaws at
% 90± is shown.
%fig/PSLscheme_v3.eps


\begin{thebibliography}{9}   % Use for  1-9  references
%\begin{thebibliography}{99} % Use for 10-99 references

\bibitem{bib:BLMsystem} add reference to BLM system

\bibitem{bib:collimationsystem} add reference to collimation system

\bibitem{bib:thesis} T. B\"ohlen, ``Beam Loss Patterns at the LHC Collimators: Measurements and Simulations'', CERN-THESIS-2008-092 (2008)

\bibitem{bib:fluka1} A. Fass\`o, A. Ferrari, J. Ranft, P.R. Sala, ``FLUKA: a multiparticle
transport code'', CERN-2005-10, INFN/TC 05/11,
SLAC-R-773 (2005)
\bibitem{bib:fluka2} A. Fass\`o, A. Ferrari, J. Ranft, P.R. Sala, ``The physics models
of FLUKA: status and recent developments'', Computing
in High Energy and Nuclear Physics 2003 Conference
(CHEP2003), USA (2003)

\bibitem{bib:BLMthreshold} E.B. Holzer, \textit{et al.}, ``GENERATION OF 1.5 MILLION BEAM LOSS THRESHOLD VALUES'', LHC Project Report 1158 (2008)

\bibitem{bib:alo06} A. G\'omez Alonso, ``Impact distribution of the beam losses at the LHC collimator in case of magnet failures'', CERN-LHC-Proj.-Note-410, \textit{2006}
	
\bibitem{bib:alo09} A. G\'omez Alonso, Private communications, Dissertation in prep., CERN, \textit{2009}
% 
% \bibitem{accelconf-ref}
% C. Petit-Jean-Genaz and J. Poole, ``JACoW, A service to the Accelerator Community'',
% EPAC'04, Lucerne, July 2004, THZCH03,  p.~249, \texttt{http://www.JACoW.org}.
% 
% \bibitem{jacow-help} A. Name and D. Person, Phys. Rev. Lett. 25 (1997) 56.
% 
% \bibitem{exampl-ref}
% A.N. Other, ``A Very Interesting Paper'', EPAC'96, Sitges, June 1996, MOPCH31, p. 7984 (1996),
% \texttt{http://www.JACoW.org}.


\end{thebibliography}

\end{document}





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% 
% 
% \subsection{Section Headings}
% 
% Section headings should not be numbered. They should
% use  12\,pt  bold  uppercase  letters  and  be  centred  in  the
% column. All section headings should appear directly above
% the text---there should never be a column break between a heading and the
% following paragraph.
% 
% \subsection{Subsection Headings}
% 
% Subsection  headings  should  not  be  numbered.  They
% should use 12\,pt italic letters and be left aligned in the
% column. Subsection headings should appear
% directly above the text---there should never be a column break between a
% heading and the following paragraph.
% 
% \subsection{Paragraph Text}
% 
% Paragraphs should use 10\,pt font and be justified (touch each side) in
% the column. The beginning of each paragraph should be indented
% approximately 3\,mm (0.13\,in). The last line of a paragraph should not be
% printed by itself at the beginning of a column nor should the first line of
% a paragraph be printed by itself at the end of a column.
% 
% \subsection{Figures, Tables and Equations}
% 
% Place figures and tables as close to the place of their mention as
% possible. Lettering in figures and tables should be large enough to
% reproduce clearly. Use of non-approved fonts in figures often leads to
% problems when the files are processed. Please use the approved fonts
% whenever possible. \LaTeX\ users---please be sure to use non bitmapped
% versions of Computer Modern fonts in equations (type 1 PostScript fonts are
% required and their use is described in the JACoW help pages~\cite{jacow-help}).
% 
% All figures and tables must be given sequential numbers (1, 2, 3, etc.) and
% have a captions (10\,pt font) placed below the figure or above the table being described.
% Captions that are one line should be centred in the column, while captions
% that span more than one line should be justified. This template uses the 'booktabs' 
% package to format the tables.
% 
% 
% If a displayed equation needs a number, place it flush with the right
% margin of the column (see Eq.~\ref{eq:units}). Units should be written
% using the roman font, not the italic font.
% 
% \begin{equation}\label{eq:units}
%     C_B={q^3\over 3\epsilon_{0} mc}=3.54\,\hbox{$\mu$eV/T}
% \end{equation}
% 
% \subsection{References}
% 
% All bibliographical and web references should be numbered and listed at the
% end of the paper in a section called ``References''. When referring to a
% reference in the text, place the corresponding reference number in square
% brackets~\cite{exampl-ref}. A URL may be added as part of a reference, but 
% its hyperlink should NOT be added.
% 
% \subsection{Footnotes}
% 
% Footnotes on the title and author lines may be used for acknowledgements,
% affiliations and e-mail addresses. A nonnumeric sequence of characters (*,
% \dag, \ddag, \S) should be used. All other notes should be included in the
% references section and use the normal numeric sequencing.
% 
% Word users--do not use Word's footnote feature (\textbf{Insert, Footnote}) to insert
% footnotes as this will create formatting problems. Instead, insert footnotes
% manually in a text box at the bottom of the first column. Footnotes should only
% appear at the bottom of the first column on the first page.
% 
% \subsection{Acronyms}
% 
% Acronyms should be defined the first time they appear.
% 
% \section{STYLES}
% 
% Table~\ref{style-tab} summarises the fonts and spacings used in the styles of
% a JACoW template (these are implemented in the \LaTeX\ class file).
% % 
% \begin{table}
%     \caption{Summary of Styles}
%     \label{style-tab}
%     \begin{tabular}{llcc}
%         \toprule
%         \textbf{Style} & \textbf{Font}               & \textbf{Space}  & \textbf{Space} \\
%                        &                             & \textbf{Before} & \textbf{After} \\ 
%         \midrule
%          Title         & 14\,pt                      & 0\,pt           & 3\,pt  \\
%                        & Upper case except for       &                 &      \\
%                        & required lower case letters &                 &      \\   %corrected 080515 vrws requred 
%                        & Bold                        &                 &      \\ 
%          \midrule
%           Author list  & 12\,pt                      & 9\,pt           & 12\,pt \\
%                        & Upper and Lower case        &                 &      \\ 
%          \midrule
%          Section       & 12\,pt                      & 9\,pt           & 3\,pt  \\
%          heading       & Uppercase                   &                 &      \\
%                        & bold                        &                 &      \\ 
%         \midrule
%          Subsection    & 12\,pt                      & 6\,pt           & 3\,pt  \\
%          heading       & Initial Caps                &                 &      \\
%                        & Italic                      &                 &      \\ 
%         \midrule
%          Figure        & 10\,pt                      & 3\,pt           & 6\,pt  \\
%          Captions      &                             &                 &      \\
%         \midrule
%          Table         & 10\,pt                      & 3\,pt           & 3\,pt  \\
%          Captions      &                             &                 &      \\
%         \midrule
%          Equations     & 10\,pt base font            & 12\,pt          & 12\,pt \\
%         \midrule
%          References    & 10\,pt, justified with      & 0\,pt           & 0\,pt  \\
%                        & 7\,mm hanging indent          &                 &      \\
%         \bottomrule
%     \end{tabular}
% \end{table}

% 
% \section{PAGE NUMBERS}
% 
% \textbf{DO NOT have any page numbers}. The editorial staff will add them
% when they produce the final proceedings.
% 
% \section{TEMPLATES}
% 
% Templates and examples can be retrieved through Web browsers like Firefox, Netscape
% and Internet Explorer by loading to disk. See your local documentation for
% details of how to do this.
% 
% Template documents for the recommended word processing software are
% available from the JACoW Website and exist for
% \LaTeX, Microsoft Word (Mac and PC) and OpenOffice for US letter and A4 paper sizes.
% 
% Authors are required to use templates for the correct paper size and advised to use the template corresponding
% to the correct version of  Word.
% Do not transport Microsoft Word documents across platforms, e.g.
% Mac~$\leftrightarrow$~PC.
% 
% Please see the help files for instructions  on  how to
% install templates in your Microsoft templates folder.
% 
% \section{CHECKLIST FOR ELECTRONIC PUBLICATION}
% 
% \begin{Itemize}
%     \item  Use only Times (bold or italic) and Symbol fonts for
%            text---10\,pt minimum except References which can be 9\,pt or 10\,pt.
%     \item  Figure labelling should be in Times (bold or italic) and
%            Symbol fonts whenever possible---6\,pt minimum.
%     \item  Check that the PostScript file prints correctly.
%     \item  Check that there are no page numbers.
%     \item  Check that the margins are correct on the printed version. There
%            may be differences of $\pm$1\,mm on the margins from one printer to
%            another.
%     \item  \LaTeX\ users can check their margins by invoking the
%            \texttt{boxit} option.
% \end{Itemize}