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\begin{document}
\title{Beam Delivery Systems at 500 GeV}
 
%\author{{\bf D.~Angal-Kalinin}, G.~Burt, B.~Dalena, L.~Deacon, ,J.L.~Fernandez Hernando, F.~Jackson, J.~Resta L\'opez, D.~Schulte, {\bf A.~Seryi}, {\bf R.~Tom\'as}}

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\subsection{Beam Delivery Systems at 500 GeV}\label{BDS500}


\subsubsection{Overview}\label{BDS500:Overview}
The design of the CLIC BDS at 500~GeV follows the same philosophy and criteria
as for the nominal design at 3~TeV, see~\ref{BDS}.
Therefore both designs consist of the same sections and fullfil the same
functions. The constrains applied to 500~GeV design follow:
\begin{itemize}
\item[1.] The IP must be at the same location at 500~GeV and at 3~TeV. The crossing angle
      can vary slightly. 
\item[2.] The linac location and orientation must remain unchanged at both energies.  
\item[3.] The two BDS designs must fit in the same tunnel of 5.3~m diameter.
\item[4.] The BDS at 500~GeV can be shorter to reduce the cost of the first stage.
\end{itemize}




\subsubsection{Beam parameters}\label{BDS500:parameters}
Table~\ref{BDS:parameters:table} shows the key BDS parameters. The IP beam parameters are shown
at 0.5~TeV CM.

\begin{table}
\caption{Key parameters of the BDS at 500~GeV CM. Effective values are given for the IP parameters.}\label{BDS:parameters:table}
\begin{center}
\begin{tabular}{|l|c|c|}\hline
Parameter & Units & Value \\\hline\hline
Length (linac exit to IP distance)/side & m   & 1750 \\\hline
%Length of main (tune-up) extraction line& m   & 300 (467) \\\hline
Maximum Energy/beam     & TeV & 0.25 \\\hline
Distance from IP to first quad, L* & m & 4.3 \\\hline
Crossing angle at the IP &mrad& 18.6   \\\hline
Nominal core beam size at IP, $\sigma^*$, x/y & nm & 202/2.3  \\\hline
Nominal beam divergence at IP, $\theta^*$, x/y& $\mu$rad & 25/23  \\\hline
Nominal beta-function at IP, $\beta^*$, x/y & mm & 8/0.1  \\\hline
Nominal bunch length, $\sigma_z$ & $\mu$m & 72  \\\hline
Nominal disruption parameters, D, x/y &&   0.1/12   \\\hline
Nominal bunch population, N & & $6.8\times10^{9}$   \\\hline
Beam power in each beam &MW& 4.9  \\\hline
Preferred entrance train to train jitter & $\sigma$ & < 0.2  \\\hline
Preferred entrance bunch to bunch jitter & $\sigma$& < ?  \\\hline
Typical nominal collimation aperture, x/y & $\sigma_x/\sigma_y$& 10/55  \\\hline
Vacuum pressure level, near/far from IP &nTorr& 100/10  \\\hline
\end{tabular}
\end{center}
\end{table}




\subsubsection{Systems}\label{BDS:Systems}
The diagnostics and collimation sections of the 500~GeV BDS have been scaled down 
from the 3~TeV design. Since the emittance is larger the lower energy beta functions
can be lower and still meet the 1~$\mu$m beam size at the laser wire and guarantee survivability
of the first collimator.
The bending angles at 500~GeV need to be larger in order to increase dispersion
and better cancel the chromatic aberrations. 
The final layout is obtained by slightly varying the IP crossing angle and the collimation
bending angles until the above constrains are satisfied. The resulting optics and layout are displayed
in~Fig.~\ref{500GeVlayout}. The maximum deviation between the 500~GeV and the 3~TeV
layout is 40~cm. This is consistent with a common tunnel of 5.3~m diameter.
The IP crossing angle is 18.6~mrad instead of the 20~mrad at 3~TeV. This variation
is considered affordable to the detector and the post-collision line, see~\ref{Detector500GeV} and ~\ref{PostCollisionLine}, respectively.


%The main subsystems of the beam delivery starting from the exit of the main linacs are
%the diagnostics region, the energy and betatron
%collimation and the final focus. The layout of the
%beam delivery system is shown in Figure~\ref{500GeVlayout}.


\begin{figure}\vspace{-0.cm}
\begin{center}
\includegraphics[width=10.4cm, angle=-90]{layout500GandOpt.eps}
\end{center}\vspace{-0.cm}
\caption{CLIC 500~GeV optics (top) and layout (bottom). Dipoles, quadrupoles and collimators are shown in blue, red and black, respectively on the layout plot.}\label{500GeVlayout}
\end{figure}



%There is a single collision point with a 18.6 mrad crossing angle. 
%The 20 mrad geometry provides space for separate extraction lines and
%requires crab cavities to rotate the bunches horizontally for head-on collisions. There are
%two detectors in a common IR hall which alternately occupy the single collision point, in a
%so-called "push-pull" configuration. 


%\subsubsubsection{Final Focus}\label{BDS500:FFS}


%\subsubsubsection{Tune-up extraction lines \& dumps}\label{BDS500:tune-up}
%During the commissioning of the main linacs 
%beams are not desired in the collimation, final focus, or IR areas.
%An extraction line right before the energy collimation guides the
%beam to a full-beam power water-filled dump.




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\bibitem{bib:voss2005} ex
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\end{document}
