Difference between revisions of "Sadiq Proposal Defense"
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Revision as of 10:23, 17 June 2012
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\author{Sadiq Setiniyaz (Shadike Saitiniyazi)\thanks{Email: sadik82@gmail.com}} %{address={Department of Physics, Idaho State University}} \title{PROPOSAL FOR POSITRON PRODUCTION EFFICIENCY STUDY USING HIGH REPETITION RATE LINAC AT IAC}
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\abstract{ \indent
I propose to measure the positron production efficiency for a positron source that uses a quadrupole triplet system to collect positrons from a tungsten target that are produced when the target is impinged by electrons from the High Repetition Rate Linac (HRRL) at Idaho State University's (ISU) Idaho Accelerator Center (IAC). Positrons were observed in May of 2008 at the IAC without the use of a quadrupole triplet collection system. Positrons escaping from the downstream side of the tungsten target have a wide momentum spread of 0 to 2 MeV when using a 10 MeV electron beam and a large divergence of $\pi$ rad. A quad triplet collection system can focus the positron beam and as a result increase our positron collection efficiency. I will install the collection system and associated beam line components to measure the positron production efficiency using the HRRL.}
\section{Introduction} \indent
I propose to measure the positron production efficiency for a positron source that uses a quadrupole triplet system to collect positrons from a tungsten target that are produced when the target is impinged by electrons from the HRRL. A polarized Positron source, as a new probe to explore nuclear and particle physics at Jefferson Lab, is being studied at the Continuous Electron Beam Accelerator Facility (CEBAF). While their main mission is to measure and increase polarization, ISU's, goal is to max positron production efficiency. On the other hand, positron beamline at ISU is also potential tool for more nuclear physics studies. I have 4 NaI detectors to use for positron detection, and I have measured the emittance of the electron beam for beamlien optimization. I will install the collection system and associated beam line components to measure the positron production efficiency using the HRRL.
\section{Previous Measurements} \indent
Earlier measurements were conducted at ISU's IAC, May of 2008. The setup is shown in Fig.~\ref{fig:2008-pos-beamline} and the beamline elements are described in Table~\ref{tab:2008-pos-beamline-elements}. The accelerator was operated at a 300~Hz repetition rate, and 10~MeV energy. The electron was bent by the first dipole, and sent to a 2~mm thick tungsten target. Positrons produced were focused using two quadrupoles and bent 45 degree by the second dipole which was set for 3~MeV positrons. Positrons were transported to the end of the linac where they were annihilated in the Ta target. 511~keV photons were observed in both HpGe and NaI detectors. In Fig.~\ref{fig:2008-spectrum}, the spectrum was taken over 600 seconds.
\begin{figure}[htbp]
\centering
\includegraphics[width=80mm]{2008_positron_measurement_at_IAC.eps}
\caption{The HRRL beamline configured for positron production at IAC in 2008. }
\label{fig:2008-pos-beamline}
\end{figure}
\begin{table}[htbp] \caption{Beamline elements for positron production at IAC in 2008.}
\begin{tabular}{ll} \hline
\textbf{Item} & {$\textbf {Description}$} \\
\hline
Tantalum foil & 6 mm thick 20 mm x 20 mm area \\
Tungsten foil & 2 mm thick 20 mm x 20 mm area \\
Phosphorus flag & 1 mil aluminum backing \\
HpGe detector & 81.3mm Diameter, 55.5mm Length \\
%NaI detector &
\hline \end{tabular} \label{tab:2008-pos-beamline-elements} \end{table}
\begin{figure}[htbp] \centering
\includegraphics*[scale=0.45]{2008_Run60_HpGe-NaI}
\caption{Spectrum from HpGe Detector and NaI detecotrs.} \label{fig:2008-spectrum} \end{figure}
%\begin{figure}[htbp] %\centering % \includegraphics[scale=0.45]{2008_PositronYield_SweeperMagnet_run60-61} %\caption{Spectrum.} %\label{fig:2008-spectrum-zoom} %\end{figure}
\section{Proposed Beamline}
\indent
I propose a measurement of the positron production efficiency using the HRRL. The HRRL can provide electron beams with energies between 3~MeV and 16~MeV, and a maximum repetition rate of 1~kHz. The HRRL beamline had recently been reconfigured to generate and collect positrons, while still can provide electron beam with improved quality. More details about the HRRL are shown in Table~\ref{tab:hrrl}.
\begin{table}[hbt]
\centering
\caption{Operational Parameters of The HRRL Linac.}
\begin{tabular}{lccc}
\toprule
Parameter & Unit & Value \\
\midrule
maximum electron beam energy $E$ & MeV & 16 \\
\midrule
electron beam peak current $I_{\textnormal{peak}}$ & mA & 80 \\
\midrule
macro-pulse repetition rate & Hz & 1000 \\
\midrule
macro-pulse pulse length (FWHM) & ns & 250 \\
\midrule
rms energy spread & \% & 4.23 \\
\bottomrule
\end{tabular} \label{tab:hrrl} \end{table}
The new beamline was first designed by Dr. G. Stancari, it uses quadrupole triplet system to collect positrons~\cite{stancari}. The design was further optimized by Dr. Y Kim, and J.Ellis. The final design of the beamline is shown in Fig.~\ref{fig:HRRL-e+-line}. The HRRL accelerator room is divided into two parts by an L-shaped cement wall. The accelerator cell houses the cavity and other elements needed to transport electrons to an experimental cell. The experimental cell is located in an adjacent room to the accelerator cell. The HRRL beamline was reconfigured into an achromat by moving the accelerator cavity to accommodate two dipoles and a system of quadrupole magnets optimized for collecting positrons.
In the new beamline, shown in Fig.~\ref{fig:HRRL-e+-line}, the electron beam from the cavity passes first through a quadruple triplet magnets that will be used to focus the electron beam onto the positron target. Positrons produced from the positron target will be collected by the second quadruple triplet that will be optimized to collect positrons. The first dipole magnet bends the positrons/electrons, depending on the magnet polarity, by 45 degrees towards the second dipole magnet. The second dipole will bend the beam another 45 degrees, thus completes a 90 degree bend. A third quadruple triplet will focus the e-/e+ beam, as users desire. All beam elements are described in Table~\ref{tab:new-hrrl-line-elements}.
%\begin{figure*}[htbp] \begin{sidewaysfigure*}[htbp]
\centering %\includegraphics[scale=0.28]{HRRL_Pos_and_Ele_Go} \includegraphics[scale=0.35]{HRRL_Pos_and_Ele_Go.eps} \caption{The new HRRL beamline cofiguration for positron generation.} \label{fig:HRRL-e+-line} \end{sidewaysfigure*}
%\end{figure*}
\begin{table}[hbt]
\centering
\caption{The new HRRL positron beamline elements.}
\begin{tabular}{lccc}
\toprule
Item & Description \\
\midrule
T1 & Positron target \\
\midrule
T2 & Annihilation target \\
\midrule
EnS & Energy Slit \\
\midrule
FC1, FC2& Faraday Cups \\
\midrule
Q1,...Q10 & Quadrupoles \\
\midrule
D1, D2 & Dipoles \\
\midrule
NaI & NaI Detecotrs \\
\midrule
OTR & Optical Transition Radiaiton screen\\
\midrule
YAG & Yttrium Aluminium Garnet screen\\
\bottomrule
\end{tabular} \label{tab:new-hrrl-line-elements} \end{table}
%00000000000000000000000000000000000000000000000000000000000 \section{Preparation for the Positron \\ Production Experiment} \subsection{HRRL Emittance measurements} \indent
Emittance, a key parameter in accelerator physics, is used to quantify the quality of an electron beam produced by an accelerator. The beam size and divergence at any point in the beamline can he obtained using emittance and Twiss parameters by simulation. This will allow user to have better control over the beam. The energy spread was also measured by scanning the beam with a dipole.
An Optical Transition Radiation (OTR) based viewer was installed to allow measurements at the high electron currents available using the HRRL. The visible light from the OTR based viewer is produced when a relativistic electron beam crosses the boundary of two mediums with different dielectric constants. Visible radiation is emitted at an angle of 90${^\circ}$ with respect to the incident beam direction~\cite{OTR} when the electron beam intersects the OTR target at a 45${^\circ}$ angle. These emitted photons are observed using a digital camera and can be used to measure the shape and intensity of the electron beam based on the OTR distribution.
The projected emittance of the HRRL was measured to be less than 0.4~$\mu$m as measured by the OTR based tool at an energy of 15~MeV. The details on this emittance measurement with quadrupole scanning method were described in the IPAC12 proceeding~\cite{setiniyaz-q-scan}. Results are summarized in table~\ref{results}.
\begin{table}[hbt]
\centering
\caption{Emittance Measurement Results.}
\begin{tabular}{lcc}
\toprule
{Parameter} & {Unit} & {Value} \\
\midrule
projected emittance $\epsilon_x$ & $\mu$m & $0.37 \pm 0.02$ \\
projected emittance $\epsilon_y$ & $\mu$m & $0.30 \pm 0.04$ \\
% normalized \footnote{normalization procedure assumes appropriate beam chromaticity.} emittance $\epsilon_{n,x}$ & $\mu$m & $10.10 \pm 0.51$ \\ %normalized emittance $\epsilon_{n,y}$ & $\mu$m & $8.06 \pm 1.1$ \\
$\beta_x$-function & m & $1.40 \pm 0.06$ \\
$\beta_y$-function & m & $1.17 \pm 0.13$ \\
$\alpha_x$-function & rad & $0.97 \pm 0.06$ \\ $\alpha_y$-function & rad & $0.24 \pm 0.07$ \\ micro-pulse charge & pC & 11 \\ micro-pulse length & ps & 35 \\ energy of the beam $E$ & MeV & 15 $\pm$ 1.6 \\ relative energy spread $\Delta E/E$ & \% & 10.4 \\
\bottomrule
\end{tabular}
\label{results}
\end{table}
\subsection{Positron Detection using NaI crystals} \indent
For detecting positrons, an annihilation target will be placed at the end of 90 degree beamline. I want to use NaI detectors to detect 511 keV photons. I acquired some NaI crystals from Idaho Accelerator Center (IAC). Since their own bases were not working properly, I built new PMT bases. I modified the design of model PA-14 from Saint-Gobain Crystals \& Detectors Ltd. Now these detectors are tested, calibrated, and ready to be used for the measurement. Fig.~\ref{fig:IAC-dets} shows the crystals and the bases I built. Fig.~\ref{fig:IAC-dets-Co60-Na22-spec} shows the spectrum taken by the detector. %I expect by doing coincidence, the resolution of 511~keV peak in the spectrum will be improved.
\begin{figure}[htbp] \centering \includegraphics[scale=0.08]{IAC_NaI_Detectors} \caption{The NaI detector and base built.} \label{fig:IAC-dets} \end{figure}
\begin{figure}[htbp] \centering \includegraphics[scale=0.18]{Na22_Co60Spectrum_by_IAC_Detectors} \caption{Detector 3 calibrated Spectrum.} \label{fig:IAC-dets-Co60-Na22-spec} \end{figure}
\subsection{Positron Target Installation} \indent
A step motor is ready to be installed once the vacuum chamber is ready. The step motor, shown in the Fig.~\ref{fig:step-motor}, will hold 8 tungsten targets.
\begin{figure}[htbp] \centering \includegraphics[scale=0.08]{setep_motor} \caption{Step motor for holding W targets.} \label{fig:step-motor} \end{figure}
\section{Future Plan} \indent
We want to produce positrons using the HRRL beam line. We can improve positron collection efficiency by applying following methods:
1. By using a quadrupole triplet before tungsten a target, we will have control over the beam size and divergence at the target.
2. Cryogenically cooled converter will be installed, and these targets will be able to take on more beam power and increase positron yield.
3. Positrons will be collected by the quadrupole triplet system, which will improve collection efficiency.
4. Simulations will optimize beam elements for positron collection.
%\bibliographystyle{unsrt} % Order by citation %\bibliography{report}
\begin{thebibliography}{9} %{stancari} %@techreport{stancari, % title =Template:Stancari's proposal-------, % month ={Nov.}, % year = {2005}, % author ={J. Stancari}, % address ={Frascati, Italy}, % number ={}, % institution ={DAFNE Technical Note} \bibitem{stancari}
G. Stancari and T. Forest "Design of a new beamline for electrons, positrons and photons at the HRRL lab", Pocatello, ID, USA (2009).
%@techreport{OTR,
% title =Template:Optical Transition Radiation,
% month ={},
% year = {1992},
% author ={B. Gitter},
% address ={Los Angeles, CA 90024},
% institution ={Particle Beam Physics Lab, Center for Advanced Accelerators, UCLA Department of Physics}
%}
\bibitem{OTR} B. Gitter, Tech. Rep., Los Angeles, USA (1992).
%\bibitem{setiniyaz-q-scan} %@InProceedings{setiniyaz-q-scan, % author = {S. Setiniyaz, K. Chouffani, T. Forest, and Y. Kim}, % title = {TRANSVERSE BEAM EMITTANCE MEASUREMENTS OF A 16 MeV LINAC AT THE IDAHO ACCELERATOR CENTER}, % booktitle = {IPAC2012},%pages = {151--158}, % year = 2012, % address = {New Orleans, USA} %} \bibitem{setiniyaz-q-scan} S. Setiniyaz, K. Chouffani, T. Forest, and Y. Kim, in $Proc$. $IPAC2012$, New Orleans, USA.
%\bibitem{emit-mat} %C.F. Eckman $et$ $al$., in $Proc$. $IPAC2012$, New Orleans, USA.
\end{thebibliography}
\end{document}