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A Prototype Energy Spectrometer for the ILC at End Station A in SLAC F. Gournaris, A. Lyapin*, B. Maiheu+, D. Miller, M. Wing, UC London, UK M. Slater, M. Thomson, D. Ward, University of Cambridge, UK S. Kostromin, N. Morozov, V. Duginov, JINR, Dubna, Russia S. Boogert, G. Boorman, Royal Holloway University of London, UK [email protected] *[email protected] M. Chistiakova, Yu. Kolomensky, M. Sadre-Bazzaz, E. Petigura, Berkeley and LBNL, USA H.-J. Schreiber, M. Viti, DESY, Germany M. Hildreth, University of Notre-Dame, USA C. Adolphsen, R. Arnold, C. Hast, D. McCormick, Z. Szalata, M. Woods, SLAC, USA Abstract The main physics program of the International Linear Collider requires a measurement of the beam energy with a relative precision of the order 10-4 or better. To achieve this goal a magnetic spectrometer using high resolution beam position monitors has been proposed. A prototype spectrometer chicane using 4 dipole magnets is currently under development at the End Station A in SLAC, intending to demonstrate the required stability of this method and investigate possible systematic effects and operational issues. This contribution reports on the successful commissioning of the beam position monitor system and the resolution and stability achieved. Also, the initial results from a run with a full spectrometer chicane are presented. Commissioning of Cavity BPMs The setup used in 2006 included 1 doublet and 2 triplets of Beam Position Monitors (BPM). These were new cavities developed at SLAC for the ILC linac as well as the old SLAC linac BPMs. End Station A facility at SLAC A testbeam experiment T-474 has been set up at Stanford Linear Accelerator Center in the End Station A beamline to demonstrate the performance of the Spectrometer at a 28.5 GeV beam. The studies focused on the stability of various components with an aim of measuring the energy with a precision of 10-4 over a few days. Parameter SLAC ESA ILC-500 10 Hz 5 Hz Energy 28.5 GeV 250 GeV Bunch Charge 2.0 x 1010 2.0 x 1010 Repetition Rate measured over 1 hour Resolution of the BPMs and precision of the position measurement were measured with the 8 BPM setup in 2006, sub-micron resolution was measured for most BPMs and 1µm drifts over 1 hour of operation were observed. BPM Bunch Length 300-500 mm 300 mm Cavity BPMs designed Energy Spread 0.2% 0.1% for the ILC linac Bunches per train 1 (2*) 2820 - (20-400ns*) 337 ns Microbunch spacing Precision of the orbit reconstruction T-474 BPM setup as in 2006 Cavity BPM previously used in the SLAC’s main linac 1,2 3 4 5 9 10 11 All X 1.64 0.49 1.26 0.59 0.28 0.16 0.28 0.43 Y 4.71 0.50 1.12 0.44 0.34 0.20 0.25 0.37 Resolution of individual BPMs in µm Prototype Energy Spectrometer Four dipole magnets were commissioned and installed in the ESA beamline. In the process of commissioning the field was found to be uniform to the level of 10-4 in the region of ±15 mm, the stability of the integral of about 100 ppm, integral field stability 60 ppm per 10C. A high resolution Zygo interferometer system monitors mechanical motion of BPMs at the center of the chicane in the horizontal plane. The setup of 2007 included 4 dipole magnets mapped and commissioned before the installation and monitored in-situ. Additional probes provided a measurement of the ambient magnetic field. BPMs were used to predict the beam orbit in the middle of the chicane which was compared to the actual reading in BPM4. The residual was inversely proportional to the beam energy. Future Plans • Installation of a new BPM prototype in the center of the chicane • Extension and further commissioning of the gain monitoring system • Installation of metrology grid to improve the accuracy of the interferometer system • Data taking in July 2007, planning to run in 2008 In early 2007 the T-474 collaboration was taking data with the full Spectrometer chicane. SLAC linac control system allowes to change the setpoins of the energy feedback in a range of a few hundred MeV. In order to check the spectrometer the energy of the beam was scanned in 50 MeV steps. This scan was clearly tracked by the Spectrometer. In addition, Spectrometer data was compared to the data from the "energy" BPMs located at high dispersion points in the ESA extraction line and a good correlation was observed.