Changeset 605 in ETALON


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May 7, 2016, 5:40:37 PM (8 years ago)
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delerue
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papers/2016_IPAC
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  • papers/2016_IPAC/MOPMB002_SPESO/MOPMB002.tex

    r598 r605  
    8787\subsection{SOLEIL's LINAC}
    8888
    89  The SOLEIL Linac, Helios~\cite{HELIOS}, is made of a 50~kV thermioninc gun followed by a pre-bunched and two LIL cavities~\cite{LIL-Cavity}. It accelerates the electrons up to an energy of 110~MeV.
     89 The SOLEIL Linac, Helios~\cite{HELIOS}, is made of a 50~kV thermioinc gun followed by a pre-bunched and two LIL cavities~\cite{LIL-Cavity}. It accelerates the electrons up to an energy of 110~MeV.
    9090
    9191The Linac can produce single bunches or trains. In users operation, several filling patterns in the ring can be
    … …  
    119119\subsection{SPESO}
    120120
    121 SPESO is installed at the end of the linac. It consists of a vacuum chamber with an insertion system that allows to insert close to the beam axis. The vacuum chamber has a large crystalline quartz window (sealed with indium) to let the radiation exit toward the detectors.
    122 The distance of minimal approach of the grating to the beam has been calculated so that  even when the grating is inserted the beam is not affected and therefore the experiment can be run parasitically. The grating currently installed has a pitch of \SI{10}{mm} and a blaze angle of 30$^{\circ}$.
    123 
    124 The experiment is mounted on an optical breadboard. The breadboard is mounted on 3 linear translator allowing rotation along 3 orthogonal axis X, S and Z (S being parallel to the linac direction and Z being the vertical axis).
    125 On the breadboard two sets of two rotary stage allow to control the direction of the detectors. A photo of the experimental apparatus can be seen on figure~\ref{fig:SPESO_linac}.
     121SPESO is installed at the end of the linac. It consists of a vacuum chamber with an insertion system that allows to insert a grating close to the beam axis. The vacuum chamber has a large crystalline quartz window (sealed with indium) to let the radiation exit toward the detectors.
     122The distance of minimal approach of the grating to the beam has been calculated so that  even when the grating is inserted, the beam is not affected and therefore the experiment can be run parasitically. The grating currently installed has a pitch of \SI{10}{mm} and a blaze angle of 30$^{\circ}$.
     123
     124The experiment is mounted on an optical breadboard. The breadboard is mounted on 3 linear translators allowing rotation along 3 orthogonal axis X, S and Z (S being parallel to the linac direction and Z being the vertical axis).
     125On the breadboard two sets of two rotary stages allow to control the direction of the detectors. A photo of the experimental apparatus can be seen on figure~\ref{fig:SPESO_linac}.
    126126
    127127\begin{figure}[htbp]
    … …  
    149149\section{Operations}
    150150
    151 During normal beam operations the experiment is running autonomously: each time there is a linac trigger the data from the oscilloscope are recorded. Every 30 minutes the detectors are moved to a different location. In each 30 minutes cycle the grating is inserted for about 25~minutes and retracted for 5 minutes to allow measurement of the background (see figure~\ref{fig:data_trend_30_minutes}). The data are then analysed by a script that runs every hours for data quality check (for security reasons this scripts has only access to detector signal level but not access to the machine data). On figure~\ref{fig:data_trend} one can see the trend of data recorded over a day while the detectors where moving along the S-direction. A more advanced analysis is done off-line to extract physical information from the data after merging the detector data with the machine data.
     151During normal beam operations the experiment is running autonomously: each time there is a linac trigger the data from the oscilloscope are recorded. Every 30 minutes the detectors are moved to a different location. In each 30 minutes cycle the grating is inserted for about 25~minutes and retracted for 5 minutes to allow measurement of the background (see figure~\ref{fig:data_trend_30_minutes}). The data are then analysed by a script that runs every hours for data quality check (for security reasons this scripts has only access to detector signal level but not access to the machine data). On figure~\ref{fig:data_trend} one can see the trend of data recorded over a day while the detectors where moving along the S-direction. A more advanced analysis is done off-line to extract physical information from the data, after merging the detector data with the machine data.
    152152
    153153
    … …  
    182182   \includegraphics*[width=\linewidth]{MOPMB002f5a.png}
    183183   \includegraphics*[width=\linewidth]{MOPMB002f5b.png}
    184    \caption{Example of raw signal collected with the the two detectors while the detectors were moving vertically. The red line correspond to the grating in the inserted position and the blue line to the grating in the retracted position (background). The upper plot correspond to the data recorded with the Ka-band detector and the lower plot to those recoded with the Q-band detector. }
     184   \caption{Example of raw signal collected with the the two detectors while the detectors were moving vertically. The red line corresponds to the grating in the inserted position and the blue line to the grating in the retracted position (background). The upper plot corresponds to the data recorded with the Ka-band detector and the lower plot to those recorded with the Q-band detector. }
    185185   \label{fig:raw_data_Tz}
    186186%   \vspace*{-\baselineskip}
    187187\end{figure}
    188188
    189 Using the data collected so far it is possible to reconstruct the radiation profile emitted in several angle. The power measured from the Gunn diodes has to be corrected to take into account the diode efficiency and to give the radiation intensity. The transmission efficiency of the window's crystalline quartz is also taken into account. The data distribution obtained after all these corrections is shown on figure~\ref{fig:signal}. As the gun diode sensitivity is certified by the supplier only on a narrow range but our measurements clearly show that it is sensitive over a much wider range we separate the data for each detector in two sets. The figure also show the expected signal for 4 different pulse length (corrected for near-field effect) using the model described in~\cite{Doucas_Theory_1998}.
     189Using the data collected so far it is possible to reconstruct the radiation profile emitted in several angles. The power measured from the Schottky diodes has to be corrected to take into account the diode efficiency and to give the radiation intensity. The transmission efficiency of the window's crystalline quartz is also taken into account. The data distribution obtained after all these corrections is shown on figure~\ref{fig:signal}. As the Schottky diodes sensitivity is certified by the supplier only on a narrow range (but our measurements clearly show that it is sensitive over a much wider range we separate the data for each detector in two sets. The figure also shows the expected signal for 4 different pulse lengths (corrected for near-field effect) using the model described in~\cite{Doucas_Theory_1998}.
    190190
    191191
    … …  
    200200
    201201
    202 From these data it is possible to follow the method described in~\cite{reco_paper} to extract the form factor of the bunch and the recover its profile. The recovered profile is shown on figure~\ref{fig:recovered_profile}. From this profile we get a measured bunch length of about \SI{14.2}{ps} FWHM in high charge LPM mode.
     202From these data it is possible to follow the method described in~\cite{reco_paper} to extract the form factor of the bunch and to recover its profile. The recovered profile is shown on figure~\ref{fig:recovered_profile}. From this profile we get a measured bunch length of about \SI{14.2}{ps} FWHM in high charge LPM mode.
    203203
    204204
    … …  
    253253 % I.~Konoplev, M.~Labat, C.~Perry, A.~Reichold, S.~Stevenson, and M.~Vieille
    254254 % Grosjean.
    255 \newblock Longitudinal profile monitors using coherent smith--purcell
    256   radiation.
     255\newblock Longitudinal profile monitors using Coherent Smith--Purcell
     256  Radiation.
    257257\newblock {\em NIM A}, 740(0):212
    258258  -- 215, 2014.
    … …  
    282282
    283283\bibitem{LIL-Cavity}
    284 R.~Belbeoch et~al. R. Belbeoch et al. R. Belbeoch~et al.
     284R.~Belbeoch et~al.
    285285\newblock Rapport d'etudes sur le projet des linacs injecteur de lep (lil).
    286286\newblock Lal/pi/82-01/t, LAL, 1982.
    … …  
    290290\newblock {Study of Phase Reconstruction Techniques applied to Smith-Purcell
    291291  Radiation Measurements}.
    292 \newblock {\em ArXiV}, 2015.
     292\newblock {\em ArXiV}, 1512.01282.
    293293
    294294\end{thebibliography}

  • papers/2016_IPAC/WEPMY003_Plasma_acceleration/WEPMY003.aux

    r598 r605  
    3333\bibcite{WAKE}{9}
    3434\bibcite{astra}{10}
    35 \@writefile{lof}{\contentsline {figure}{\numberline {5}{\ignorespaces Propagation of the the electrons (in black) and the laser (in blue) at different $z$ positions in the plasma. The horizontal axis is the comoving frame (that is the distance of the electrons behind the laser pulse). For the electrons the vertical axis is their energy expressed by their Lorentz factor. For the laser it is the longitudinal accelerating field compared to the maximum field $E_0 = mc \omega _p / e = \SI {608}{MV/cm}$. \relax }}{3}}
     35\@writefile{lof}{\contentsline {figure}{\numberline {5}{\ignorespaces Lorentz factor of the electrons (black and left vertical axis) and longitudinal accelerating field divided by $E_0 = mc \omega _p / e = \SI {608}{MV/cm}$ ( blue and right vertical axis), versus the distance behind the laser pulse at different z positions in the plasma. \relax }}{3}}
    3636\newlabel{fig:simulations}{{5}{3}}
    3737\@writefile{lof}{\contentsline {figure}{\numberline {6}{\ignorespaces Energy distribution at the end of the acceleration process.\relax }}{3}}

  • papers/2016_IPAC/WEPMY003_Plasma_acceleration/WEPMY003.tex

    r598 r605  
    9191 \item{Maximum Accelerating field} $E_0 = \frac{2 \pi m_e c^2}{e \lambda_p} $ hence  \\ $$E_0 [GV / m]= 96.2 \sqrt{n_e [\SI{e18}{cm^{-3}}]}$$.
    9292 \item{Longitudinal accelerating field} \\ $$E_{0z} = \frac{\eta}{4}  a_0^2 \cos(k_p d_l) \exp(- \frac{2 \rho^2}{w_z^2}) \times E_0$$.
    93 \item{Radial accelerating field}\\ $E_0r = \frac{\rho}{k_p w_z^2} \eta  a_0^2 \sin(k_p d_l) \exp(- \frac{2 \rho^2}{w_z^2}) \times E_0$
     93\item{Radial accelerating field}\\ $E_{0r} = \frac{\rho}{k_p w_z^2} \eta  a_0^2 \sin(k_p d_l) \exp(- \frac{2 \rho^2}{w_z^2}) \times E_0$
    9494\end{itemize}
    95 with $m_e$ the electron mass, $e$ the electron charge, $\lambda$ the laser wavelength (\SI{0.8}{\micro \meter}), $n_e$ the plasma density, $n_c = \frac{1.11 10^{21}}{\lambda^2 [ \si{um^2]}} \si{cm^{-3}}$, $\lambda_p$ the plasma wavelength ($\lambda_p = \lambda \times \sqrt{\frac{n_c}{n_e}}$) , $k_p$ the plasma wave number,  $\eta$ the laser-plasma coupling $a_0$ the plasma relativistic limit, $d_l$ the laser distance behind the pulse, $\rho$ the radial distance and $w_z$ the laser waist radius at position $z$ (and $w_0$ at $z=0$, the focal point).
    96 
    97 Therefore a pressure of \SI{4e17}{cm^{-3}} will give a maximum longitudinal accelerating field of more than \SI{10}{GV/m}. This corresponds to a plasma wavelength of about \SI{50}{\micro m} (that is about \SI{180}{fs}). It is important to note also the the radial accelerating field can take either positive or a negative value, that is, it can be either focussing or defocussing.
     95with $m_e$ the electron mass, $e$ the electron charge, $\lambda$ the laser wavelength (\SI{0.8}{\micro \meter}), $n_e$ the plasma density, $\lambda_p$ the plasma wavelength ($\lambda_p = \lambda \times \sqrt{\frac{n_c}{n_e}}$) , $k_p$ the plasma wave number,  $\eta$ the laser-plasma coupling $a_0$ the plasma relativistic limit, $d_l$ the laser distance behind the pulse, $\rho$ the radial distance and $w_z$ the laser waist radius at position $z$ (and $w_0$ at $z=0$, the focal point).
     96
     97Therefore a pressure of \SI{4e17}{cm^{-3}} will give a maximum longitudinal accelerating field of more than \SI{10}{GV/m}. This corresponds to a plasma wavelength of about \SI{50}{\micro m} (that is about \SI{180}{fs}). It is important to note also that the radial accelerating field can take either positive or a negative value, that is, it can be either focussing or defocussing.
    9898
    9999With a \SI{2}{Joules} laser focused on a \SI{55}{\micro \meter} waist we get a Rayleigh length of about 1cm. This will give a sufficient length to compress and accelerate the electrons. These electrons must also be focussed in a comparable volume.
    … …  
    102102\subsection{Proposed experiment}
    103103
    104 The proposed experiment will be performed within the ESCULAP  ({\em ElectronS CoUrts et LAsers Plasmas}) installation at LAL, by combining the LASERIX laser~\cite{Ple:07,Zimmer:10,Delmas:14}  with the PHIL photoinjector~\cite{1748-0221-8-01-T01001,Vinatier2015222}. PHIL is a conventional  \SI{5}{MeV} Photoinjector that is currently being upgraded to \SI{10}{MeV}. A layout of PHIL is shown on figure~\ref{PHIL}. Laserix is a 50 TW, 50~fs high-power Ti:Sa laser. As part of ESCULAP a small leak from Laserix will be directed on the PHIL photocathode to produce short electron pulses. Laser-driven plasma acceleration experiment will be performed by injecting simulaneously the high energy laser beam with the PHIL generated relativistic electron beam.
     104The proposed experiment will be performed within the ESCULAP  ({\em ElectronS CoUrts et LAsers Plasmas}) installation at LAL, by combining the LASERIX laser~\cite{Ple:07,Zimmer:10,Delmas:14}  with the PHIL photoinjector~\cite{1748-0221-8-01-T01001,Vinatier2015222}. PHIL is a conventional  \SI{5}{MeV} Photoinjector that is currently being upgraded to \SI{10}{MeV}. A layout of PHIL is shown on figure~\ref{PHIL}. Laserix is a 50 TW, 50~fs high-power Ti:Sa laser. As part of ESCULAP a small leak from Laserix will be directed on the PHIL photocathode to produce short electron pulses. Laser-driven plasma acceleration experiment will be performed by injecting simulaneously the high energy laser beam with the PHIL generated relativistic electron beam into a few cm gas cell.
    105105
    106106
    107107\begin{figure}[bthp]
    108108    \centering
    109     \includegraphics*[width=\linewidth]{PHIL.png}
     109    \includegraphics*[width=\linewidth]{WEPMY003f1.png}
    110110     \caption{The PHIL beam line. The electrons are produced on the left of the image and travel toward the right. A spectrometer magnet can be seen in the middle of the beam line.}
    111111    \label{PHIL}
    … …  
    115115\begin{figure}[htbp]
    116116 \centering
    117   \includegraphics*[width=\linewidth]{scheme_Laserix_LAL.png}\\
     117  \includegraphics*[width=\linewidth]{WEPMY003f2.png}\\
    118118  \caption{Scheme of the current LASERIX installation at LAL showing the new high intensity laser beamlines for emerging applications.}
    119119   \label{fig:scheme_laserix_lal}
    … …  
    122122\begin{figure}[htbp]
    123123  \centering
    124   \includegraphics[width=0.9\linewidth]{PHIL_and_Laserix.png}
     124  \includegraphics[width=0.9\linewidth]{WEPMY003f3.png}
    125125  \caption{The PHIL and Laserix facilities. A small leak from Laserix will be sent on the PHIL photocathode and the reminder will be sent in the plasma chamber.}
    126126  \label{PHIL_and_Laserix}
    … …  
    133133\begin{figure}[htbp]
    134134  \centering
    135   \includegraphics[width=0.9\linewidth]{plasma_density.png}
     135  \includegraphics[width=0.9\linewidth]{WEPMY003f4.png}
    136136  \caption{Density profile along the plasma axis. The maximum density, $n_{e0}$ is \SI{4e17}{cm^{-3}}.}
    137137  \label{fig:plasma_density}
    … …  
    140140The simultations were done using an adapted version of the numerical code WAKE-EP~\cite{WAKE}.
    141141
    142 The aim of this special density profile is to keep achieve a compression of the electron bunch before its acceleration. The first part of the density profile (decreasing pressure gradient) will keep all the electron together in the focussing  phase of the plasma wake. As the electrons have a relatively low $\gamma$ the difference in accelerating gradient experienced between the head and the tail of the bunch will compress them all together. Once this is achieved the second part of the density profile (increasing pressure gradient) will keep the bunch together at the back of the wave to accelerate them with the highest field.
     142The aim of this special density profile is to achieve a radial and longitudinal compression of the electron bunch before its acceleration. The first part of the density profile (decreasing pressure gradient) will keep all the electron together in the focussing  phase of the plasma wake. As the electrons have a relatively low $\gamma$ the difference in accelerating gradient experienced between the head and the tail of the bunch will compress them all together. Once this is achieved the second part of the density profile (increasing pressure gradient) will keep the bunch together at the back of the wave to accelerate them with the highest field.
    143143
    144144
    145145\begin{figure*}[tbp]
    146146  \centering
    147   \vspace{-1.9cm}
     147  \vspace{-1cm}
    148148  \begin{tabular}{cccc}
    149   (a) &  \includegraphics[width=0.45\linewidth]{electrons_z_m4cm.png} &
    150  (b) &  \includegraphics[width=0.45\linewidth]{electrons_z_m35cm.png} \\
    151  (c) & \includegraphics[width=0.45\linewidth]{electrons_z_m2cm.png} &
     149  (a) &  \includegraphics[width=0.4\linewidth]{WEPMY003f5a.png} &
     150 (b) &  \includegraphics[width=0.4\linewidth]{WEPMY003f5b.png} \\
     151 (c) & \includegraphics[width=0.4\linewidth]{WEPMY003f5c.png} &
    152152%  \includegraphics[width=0.45\linewidth]{electrons_z_0cm.png} \\
    153  (d) &  \includegraphics[width=0.45\linewidth]{electrons_z_3cm.png} \\
     153 (d) &  \includegraphics[width=0.4\linewidth]{WEPMY003f5d.png} \\
    154154  \end{tabular}
    155   \caption{Propagation of the the electrons (in black) and the laser (in blue) at different $z$ positions in the plasma. The horizontal axis is the comoving frame (that is the distance of the electrons behind the laser pulse). For the electrons the vertical axis is their energy expressed by their Lorentz factor. For the laser it is the longitudinal accelerating field compared to the maximum field $E_0 = mc \omega_p / e = \SI{608}{MV/cm}$. }
     155  \caption{Lorentz factor of the electrons (black and left vertical axis) and longitudinal accelerating field divided by $E_0 = mc \omega_p / e = \SI{608}{MV/cm}$ ( blue and right vertical axis), versus the distance behind the laser pulse at different z positions in the plasma. }
    156156  \label{fig:simulations}
    157157\end{figure*}
    … …  
    161161  \centering
    162162  \vspace*{-1cm}
    163   \includegraphics[width=0.95\linewidth]{energy_distribution.png}
     163  \includegraphics[width=0.95\linewidth]{WEPMY003f6.png}
    164164%  \includegraphics[width=0.9\linewidth]{energy_distribution_vs_theta.png}
    165165  \caption{Energy distribution at the end of the acceleration process.}
    166   \vspace*{-0.5 cm}
     166  \vspace*{-0.6 cm}
    167167  \label{fig:energy_dist}
    168168  \end{figure}
    … …  
    170170
    171171
    172 On figure~\ref{fig:simulations} (a) one can see the distribution of the electrons (in black) and of the laser wake (in blue) at $z=\SI{-4}{cm}$, the entrance of the plasma cell. We can see that at injection the electron bunch (coming from a conventional accelerator simulated using ASTRA~\cite{astra}) have a large time spread and a small energy spread. As they progress through the decreasing gradient ramp the trailing electrons will experience a higher accelerating field than the electrons  at the front as at these energy they are barely relativistic this difference will result in these electrons almost catching up with the leading one and the beam will get compressed in time. This is illustrated by figure~\ref{fig:simulations} (b) and figure~\ref{fig:simulations} (c). On figure~\ref{fig:simulations} (b) one can see that the distance between the leading and trailing electrons has significantly reduced and the trailing electrons have now more energy than the leading ones. On figure~\ref{fig:simulations} (c) the trailing electrons are even overtaking the leading ones and the bunch is compressed in only a few micrometers. It is important to note that this compression completely erases the initial energy spread of the bunch and its time spread (with one quarter of plasma wavelength). Once this process is over, after  $z=\SI{-2}{cm}$,  the increase in plasma density will significantly accelerate the electrons. On figure~\ref{fig:simulations} (d) one can see that the electrons reach a Lorentz factor $\gamma$ of about 500 with slightly more than 15\% energy spread (figure~\ref{fig:energy_dist}).
     172On figure~\ref{fig:simulations} (a) one can see the distribution of the electrons (in black) and of the laser wake (in blue) at $z=\SI{-4}{cm}$, the entrance of the plasma cell. We can see that at injection the electron bunch (coming from a conventional accelerator simulated using ASTRA~\cite{astra}) have a large time spread and a small energy spread. As they progress through the decreasing gradient ramp the trailing electrons will experience a higher accelerating field than the electrons  at the front. As at these energy they are barely relativistic this difference will result in these electrons almost catching up with the leading one and the beam will get compressed in time. This is illustrated by figure~\ref{fig:simulations} (b-c). On figure~\ref{fig:simulations} (b) one can see that the distance between the leading and trailing electrons has significantly reduced and the trailing electrons have now more energy than the leading ones. On figure~\ref{fig:simulations} (c) the trailing electrons are even overtaking the leading ones and the bunch is compressed in only a few micrometers. It is important to note that this compression completely erases the initial energy spread of the bunch and its time spread. Once this process is over, after  $z=\SI{-2}{cm}$,  the increase in plasma density and in laser intensity will significantly accelerate the electrons. On figure~\ref{fig:simulations} (d) one can see that at the end of the accelerating process the electrons reach a Lorentz factor $\gamma$ of about 500 with slightly more than 15\% energy spread (figure~\ref{fig:energy_dist}).
    173173
    174174
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