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Revision: 1.1, Wed Nov 26 19:06:36 2003 UTC (20 years, 9 months ago) by saw Branch: MAIN CVS Tags: mar2005, HEAD Branch point for: hks05 Initial checkin from Chen Yan |
\documentclass{chowto} \title{Beam Kicker System for Hall C Moeller Polarimeter} \howtotype{user} % ``expert'', ``user'', ``reference'' \category{beamline} %\maintainer{} % Optional \author{Chen Yan} \date{November 26, 2003} \begin{document} \begin{abstract} The kicker system of Hall C Moeller polarimeter uses a fast intermmitant beam kick technique to control exposure time and cooling time of the iron wire target in order to operate polarimeter at higher beam current, also to achieve on-line Moeller measurement. \end{abstract} \section{Introduction} The first Hall C kicker system was installed in October 2003. The kicker magnet, located at the begining of Hall C arc, will bend beam vertically across an iron wire target. The beam sweeps the iron wire within in 1 $\mu$s. The kick frequency can be continuously adjusted from 10 kHz down to 1/10 Hz. The beam heating effect on the target can be precisely restricted by proprely adjusting time interval of trigger signals. A 20 $\mu$s gate signal simultaneously generated from the kick pulse can be used to alternate data aquisistion of G0 experiment and Moeller measurement in a time-share mode. The estimated maximum beam current is 20 to 40 $\mu$A. \section{Kicker Magnet} The kicker magnet is located at station $\#$ 4070 - right after Hall C superharp IHA3C07A. The location is very close to the beginning of Hall C arc achromat transport line, where double focusing is achieved. For preliminary test, one Hall C fast raster magnet is temporarily installed as kicker magnet. The magnet inductance is 88 $\mu$H, which determines the shortest time for a single traversal (10 $\mu$s). The distance from kicker magnet to Moeller target is about 44 m. If the optical transportation in vertical direction can be simplified as free drift, the corresponding bending angle for 1 mm displacement on Moeller target is about 0.02 mr. The field integral value of the fast raster magnet is 80 Gauss cm per Ampere. The magnet is positioned in vertical direction. If one faces the magnet in front of the girder 3C07, the winding direction is anticlockwise. Excited by a positive current pulse, the magnet generates a pulse field along the normal of magnet plane. By applying left-hand role, electron beam will be moved up. \section{Kicker Driver Electronics} A diagonal half of H-bridge is configurated as the main component of kicker driver. When a trigger pulse comes, a 10 $\mu$ width gate is generated from controller and the half bridge becomes conductive. The magnet is then connected to HV power supply. The magnet current rises with a time constant $\tau$ = L/R $\sim$ 7.33 ms. As the gate width is much shorter than $\tau$, the current is rising in approximately linear mode (linearity is better than 98\%). Magnet current starts to drop down from its peak value as the fall edge of gate pulse arrives. The ramping up and ramping down process is complete in 20 $\mu$s for each trigger signal. The 20 $\mu$s TTL signal is sent to data aquisition electronics of both Moeller and Hall C as strobe of data stream. \section{System Configuration} The first kicker system is manually controlled. The basic functions of such a system fulfills operation requirement of system commissioning. \begin{itemize} \item{Magnet - on the first hall C superharp granite table 3C07 at station $\#$ 4070} \item{Power driver - inside the lead shielding by the 3C07. Two signals are generated from the power module: the kicker current analog signal from Pearson current probe and the synchronized 20 $\mu$s gate signal for alternatively strobe data aquisition systems of Moeller measurement and experiments.} \item{Manual Controller - in the rack CH03B14 in Hall C counting house, left potentiometer is used to adjust voltage of HV unit. Left LCD window displays voltage value, the right LCD window shows the load current of HV unit. The POWER ON switch also controls the remote AC power relay unit of the power module. On the rear panel, a LEM socket gives a 5 V level output indicating kicker system "ON" for MCC.} \item{Kick Frequency Generator - WAVETEK function generator model 29 on CH03B14 rack, generates TTL level trigger frequency.} \item{Kick Waveform Monitor - Tektronix TSD 211 storage oscilloscope in rack CH03B13 in Hall C counting house displays the single kick current waveform synchronized by the full gate signal. On the scrteen, readout of kick amplitude and frequency is automatically displayed.} \end{itemize} \section{System Calibration and Conversion Formula} \subsection{Determination of kick amplitude from HV setting} \begin{itemize} \item{The scale of Pearson current probe output is 1 volt per 10 A} \item{The kick amplitude is determined by HV setting voltage. Current amplitude is read out from Pearson current probe. The magnet current to HV voltage setting conversion factor is $\Delta I/ \Delta V = 0.121 {\rm A/V}$} \item{From Jeff Karn's DC mapping data, the field interal of the kicker magnet (i.e. FR magnet) is 80 Gauss cm per Ampere} \item{From bending power formula, \[ \int Bdl [{\rm kG m}] = 33.356 p [{\rm GeV}/c] \theta [{\rm rad}] \]} \item{Convert field integral to magnet current (Pearson probe output in volt), we have: \[ V[{\rm volt}] = 7.7 \times \Delta h [{\rm mm}] \times p[{\rm Gev}/c] \]} here, $\Delta$h is the vertical kick amplitude on Moeller target in mm and V is HV voltage in volt. \end{itemize} \subsection{Kick frequency calculation} Based on the target thermo-equilibrium, the kick operational frequency can be simply estimated. The major constraint is the temperature rise of the iron wire target. Here we assume: \begin{itemize} \item{The iron wire target is 1 cm in length, 25 $\mu$m in diameter} \item{Kick ramp is 10 $\mu$s, beam exposure time is 2 $\mu$s for two traversals in a single kick.} \item{Allowable temperature gradient is 200 $^{o}$C/cm along the wire target} \item{Beam deposit power on the wire can be expressed as: \[ P_{\rm beam}[{\rm W}] = I_{{\rm beam}}[\mu A] \times \Delta E[{\rm MeV}], \] $I_{\rm beam}$ is the effective beam current = \[ I_{0} \times d_{\rm wire}/d_{\rm beam} \] } \item{The cooling power through heat transfer from wire target to the frame: \[ P_{cool} [W] = - k[{\rm W}/({\rm cm} {}^{\circ}{\rm C}] \times A[{\rm cm}^{2}] \times dT/dx[{}^{\circ}{\rm C/cm}], \] here, $k$ is thermo-conductivity of pure iron. A is double wire cross section (for two ends).} \end{itemize} By applying \[ t_{exp} \times P_{beam} = t_{\rm cool} \times P_{\rm cool}, \] the estimated value of kick ferequency can be found as \[ I_{beam} [\mu {\rm A}] \times f_{\rm kick} [{\rm Hz}] = 2000. \] \section{Supplementary Kick Diagnostic Device} Downstream 14 feet from Moeller target, a Russian FEU115M timing PMT was installed on the straight section of Moeller triple pipe with very forward angle. The PMT will pickup radiations generated when beam across the target. We expect the signals are bright enough for observation on the scope when the kicker gate output signal is applied as the trigger. This device is used for verification of kicker function. The LeCroy HV4032A high voltage unit is located in CH03B14 rack. To set high voltage for the pickup PMT, turn the power key at first, then push HV ON switch. Left window displays the channel and right window for HV. Push CH together with UP or DOWN arrow to set the right channel number. Push HV to set the desired high voltage value. The HV channel for this PMT is 5. Normally applied HV is 2000 V. \end{document} % Revision history: % $Log: moeller_kicker.tex,v $ % Revision 1.1 2003/11/26 19:06:36 saw % Initial checkin from Chen Yan %
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