Changeset 753 in ETALON for papers/2016_HDR_ND/Compton/thomx.tex

Timestamp:

Dec 4, 2017, 12:10:19 AM (7 years ago)

Author:

delerue

Message:

HDR finished

File:

• papers/2016_HDR_ND/Compton/thomx.tex (modified) (4 diffs)

papers/2016_HDR_ND/Compton/thomx.tex

@@ -5 +5 @@
  \label{chap:thomx}
 
-The expertise available at LAL in Fabry-Perot cavity makes it an ideal place for the development of a Compact Light Source based on Compton Scattering. This project is called ThomX and it has been described extensively in~\cite{ThomX_TDR}. When I joined the project it was already under way. My contributions to this project are the optical diagnostics which are documented in~\cite{ThomX_TDR}, the synchronisation which will be discussed in section~\ref{sec:thomx_synchro} and the guidance of a graduate student to study the beam dynamics in the ThomX ring.
+The expertise available at LAL in Fabry-Perot cavities makes it an ideal place for the development of a Compact Light Source based on Compton Scattering. This project is called ThomX and it has been described extensively in~\cite{ThomX_TDR}. When I joined the project it was already under way. My contributions to this project are the optical diagnostics which are documented in~\cite{ThomX_TDR}, the synchronisation which will be discussed in section~\ref{sec:thomx_synchro} and studies of the beam dynamics in the ThomX ring, including the guidance of a graduate student on that subject~\cite{drebot:tel-00920424}. I will also be in charge of the commissioning of the ThomX ring.
 
 \section{Beam dynamics at ThomX}
 
-The ThomX ring will have a circumference of about \SI{16.8}{m}~\cite{ThomX_TDR} and a beam energy of \SI{50}{MeV}.  A fresh beam will be injected every \SI{20}{ms} whereas the damping time will be of \SIrange{0.5}{1}{s}. This will put the machine in a  transitory regime that has not been explored so far. It is therefore important to understand beforehand how each effect in the ring will affect the beam, what will be the competition between these effects and how to optimise the various parameters to maximise the X-ray production.
+The ThomX ring will have a circumference of about \SI{16.8}{m}~\cite{ThomX_TDR} and a beam energy of \SI{50}{MeV}.  A fresh beam will be injected every \SI{20}{ms} whereas the damping time will be of the order of  \SIrange{0.5}{1}{s}. This will put the machine in a  transitory regime that has not been explored so far. It is therefore important to understand beforehand how each effect in the ring will affect the beam, what will be the competition between these effects and how to optimise the various parameters to maximise the X-ray production.
 
-It is this work that I have done with a graduate student, Illya Drebot and it is extensively documented in his thesis~\cite{drebot:tel-00920424} as well as in~\cite{Delerue:2014oca}. It is briefly summarized here.
+
+This work has been done with a graduate student, Illya Drebot, and it is extensively documented in his thesis~\cite{drebot:tel-00920424} as well as in~\cite{Delerue:2014oca}. It is briefly summarized here.
 
 One of the key findings is that Compton scattering is not, by far, a dominant effect in the disruption of the beam. Simulations with and without Compton scattering yield very similar results (however our implementation of Compton scattering based on CAIN~\cite{cain} make simulations with Compton scattering much slower~\cite{drebot:tel-00920424}).
 
-When it is injected in the ring the bunch is not matched to the ThomX ring, in particular it is much smaller (longitudinally) than  the RF bucket. The first few thousand turns will therefore see the bunch expand under the effect of Coherent Synchrotron Radiation (CSR) until it has expanded and CSR is therefore much weaker. This is illustrated on figure~\ref{fig:tx_evolution}.
+When it is injected in the ring the bunch is not matched to the ThomX ring, in particular it is much smaller (longitudinally) than  the RF bucket. The first few thousand turns will therefore see the bunch expand to fill its bucket and this effect is amplified under the effect of Coherent Synchrotron Radiation (CSR). One the bunch has expanded and fillets bucket CSR becomes much weaker. This is illustrated on figure~\ref{fig:tx_evolution}.
 
 
-\begin{figure*}[htbp]
+\begin{figure}[htbp]
     \centering
     \hspace*{-10mm}\begin{tabular}{ccc}
@@ -28 +29 @@
     \includegraphics*[width=50mm]{Compton/WEPRO001f8.png} 
    \end{tabular}
-    \caption{Figure taken from~\cite{Delerue:2014oca}. Evolution of the bunch in the longitudinal phase space (energy spread versus longitudinal position) as function of turn number (indicated above each image) after its injection in the ThomX ring.  The color of the dots indicate the particles intensity at that location red being more intense than green and green more intense than blue. }
+    \caption{Figure taken from~\cite{Delerue:2014oca}. Evolution of the bunch in the longitudinal phase space (energy spread versus longitudinal position) as function of turn number (indicated above each image) after its injection in the ThomX ring.  The color of the dots indicate the particles intensity at that location red being the most intense and green more intense than blue. }
     \label{fig:tx_evolution}
-\end{figure*}
+\end{figure}
 
  In some cases the CSR forces will be so disruptive that the bunch will break into two parts as shown on figure~\ref{fig:tx_CSR_split}. As CSR depends on the charge, this beam break up effect is more intense at high charge. There is therefore a charge optimum around \SI{0.9}{nC} as shown on figure~\ref{fig:tx_sum-flux}. These findings are summarized in figure~\ref{fig:tx_compare_effects} where each effect has been turned on and off alternatively to see how they contribute to the reduction of the total X-ray flux. 
@@ -38 +39 @@
     \centering
     \includegraphics[width=90mm]{Compton/WEPRO001f9.eps}
-    \caption{Figure taken from~\cite{Delerue:2014oca}. Longitudinal phase space of the bunch (energy spread versus longitudinal position), at injection (top), after 10~000~turns (middle) and after 70~000~turns (bottom) in two cases with the same beam parameters (but different initial random distributions of the macro particles). On the left  the bunch is relatively stable and only 2\% of the macro particles are lost whereas on the right the bunch is unstable and it is split in less than 10~000~turns, leading to the loss of 44\% of the charge. The color of the dots indicate the particles intensity at that location red being more intense than green and green more intense than blue.}
+    \caption{Figure taken from~\cite{Delerue:2014oca}. Longitudinal phase space of the bunch (energy spread versus longitudinal position), at injection (top), after 10~000~turns (middle) and after 70~000~turns (bottom) in two cases with the same beam parameters (but different initial random distributions of the macro particles). On the left  the bunch is relatively stable and only 2\% of the macro particles are lost whereas on the right the bunch is unstable and it is split in less than 10~000~turns, leading to the loss of 44\% of the charge. The color of the dots indicate the particles intensity at that location red being the most intense and green more intense than blue.}
     \label{fig:tx_CSR_split}
 \end{figure}
@@ -50 +51 @@
 
 
-Figure~\ref{fig:tx_compare_effects} also shows that some mitigation can be achieved by injecting the beam with a slight energy offset and by having a turn by turn feedback on the RF cavity phase (this is described in more details in~\cite{drebot:tel-00920424}. Further mitigation strategy should be considered such as injecting a longer bunch in the ring, increasing even further its energy spread or anticipating first order phase corrections (instead of relying on phase feedback only). Unfortunately such studies were not possible over the duration of Illya's thesis and have not been taken up after.
+Figure~\ref{fig:tx_compare_effects} also shows that some mitigation can be achieved by injecting the beam with a slight energy offset and by having a turn by turn feedback on the RF cavity phase (this is described in more details in~\cite{drebot:tel-00920424}). Further mitigation strategy should be considered such as injecting a longer bunch in the ring, increasing even further its energy spread or anticipating first order phase corrections (instead of relying on phase feedback only). Unfortunately such studies were not possible over the duration of Illya's thesis but should be investigated soon.
 
 \begin{figure}[htbp]