source: ETALON/papers/2016_HDR_ND/Advanced_diags/smithpurcell.tex @ 640

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\chapter{Bunch length measurement}

\section{Bunch length measurement techniques}

The length of a particle bunch is rather difficult to measure at lepton accelerators where this length is typically much shorter than what can be measured by fast detectors. It is therefore necessary to convert the bunch length into another quantity that can be measured. Coherence is both a motivation and a tool to measure such length. Coherent collective effects such as coherent synchrotron radiation can significantly disrupt a beam. Their dependance on the beam current and not the beam charge means that to control them it is necessary to measure the bunch length instead of simply the bunch charge. As a counterpart, coherent radiation is one of the means of measuring a bunch length.

In plasma acceleration with external injection (such as FACET's  E-200~\cite{e200_litos}, AWAKE~\cite{awake} or ESCULAP~\cite{Delerue:2016tcy}) this bunch length measurement is important to estimate which fraction of the bunch will fit in the acceleration buckets created in the plasma. As with the transverse measurements, at a plasma accelerator it is necessary to make the measurement in a single shot for it to be meaningful.

When the resolution is sufficient the bunch length measurement can become a bunch profile measurement as is the case with the methods based on coherent radiation methods.

I have worked on this technique for several years.


\subsection{Techniques based on longitudinal to transverse exchange}




- streak



- 3 phases

\subsection{Measures based on transition radiation}

EOptique
CTR

\subsection{Measures based on Coherent Smith-Purcell Radiation}

CSPR 

Resolution max.

\subsection{Single shot Bunch length measurement}

\section{Experimental study of Coherent Smith-Purcell radiation}
\subsection{Smith-Purcell radiation measurement at FACET}
\subsection{Smith-Purcell radiation measurement at SOLEIL}
\subsection{Smith-Purcell radiation measurement at CLIO}
\subsection{Outlook: Application to laser-driven plasma accelerators}
beam grating sep.
stability



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