Simulation Studies on the Vertical Emittance Growth at the Existing Atf Extraction Beamline*

Significant beam intensity-dependence of the vertical emittance growth was experimentally observed at the Accelerator Test Facility (ATF) at KEK extraction beamline. This paper presents the simulations of possible vertical emittance growth sources, particularly in the extraction channel, where the magnets are shared by both the ATF extraction beamline and its damping ring. The vertical emittance growth is observed in the simulations by changing the beam orbit in the extraction channel, even with all optics corrections. The possible reasons for the experimentally observed dependence of the vertical emittance growth on the beam intensity are also discussed. An experiment to measure the emittance versus beam orbit at the existing ATF extraction beamline is on-going led by the European colleagues. Presented at 11th European Particle Accelerator Conference, Genoa, Italy, June 23–June 28, 2008. SIMULATION STUDIES ON THE VERTICAL EMITTANCE GROWTH AT THE EXISTING ATF EXTRACTION BEAMLINE F. Zhou, J. Amann, S. Seletskiy, A. Seryi, C. M. Spencer, M. D. Woodley SLAC, Menlo Park, CA 94025, USA Abstract Significant beam intensity-dependence of the vertical emittance growth was experimentally observed at the Accelerator Test Facility (ATF) at KEK extraction beamline. This paper presents the simulations of possible vertical emittance growth sources, particularly in the extraction channel, where the magnets are shared by both the ATF extraction beamline and its damping ring. The vertical emittance growth is observed in the simulations by changing the beam orbit in the extraction channel, even with all optics corrections. The possible reasons for the experimentally observed dependence of the vertical emittance growth on the beam intensity are also discussed. An experiment to measure the emittance versus beam orbit at the existing ATF extraction beamline is ongoing led by the European colleagues.Significant beam intensity-dependence of the vertical emittance growth was experimentally observed at the Accelerator Test Facility (ATF) at KEK extraction beamline. This paper presents the simulations of possible vertical emittance growth sources, particularly in the extraction channel, where the magnets are shared by both the ATF extraction beamline and its damping ring. The vertical emittance growth is observed in the simulations by changing the beam orbit in the extraction channel, even with all optics corrections. The possible reasons for the experimentally observed dependence of the vertical emittance growth on the beam intensity are also discussed. An experiment to measure the emittance versus beam orbit at the existing ATF extraction beamline is ongoing led by the European colleagues. MULTIPOLE FIELD ANALYSIS A small vertical emittance was experimentally achieved in the ATF/KEK damping ring [1]. However, significant dependence of the vertical emittance growth on the beam intensity was observed [2-3] at the ATF extraction beamline when the beam was extracted from the damping ring. Magnets in the extraction channel, such as QM7R and BS1X [4], shared by both the extraction beamline and the damping ring, are probably one of major nonlinear magnetic field sources that create the emittance growth. The extracted beam has a nominal horizontal deviation from the magnet centers, 0.022 m for QM7R and 0.0855 m for BS1X, and the magnetic fields of both magnets are modeled with the 2-D Poisson program [5]. Fig. 1 shows the 1/8 of QM7R and the locations of both extracted and stored beams. The magnetic field multipoles are decomposed with respect to the nominal position of the extracted-beam (0.022 m of horizontal offset from the magnet center for QM7R) using the following equation: