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DISPLACEMENT MONITORS USING DIODE LASERS



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III 275 DISPLACEMENT MONITORS USING DIODE LASERS Yasunori Takeuchi Timo Korhonen and Yoshisato Funahashi 1 1 Oho Tsukuba Ibaraki 305 Japan ABSTRACT In low emittance high current accelerators the magnet position should be monitored continuously to keep the magnet alignment as precise as several tens of microns Two kinds of monitors are proposed 1 a monitor of the relative displacement between two adjacent magnet support tables and 2 a monitor of the displacement of a wire that is a wire alignment system Both monitors use laser diodes and PSDs Position Sensitive Detectors The first one monitors the relative displacement by measuring the position of the laser spot on the PSD The resolution of the monitoring is expected to be about 1 pm The second one detects the reflected laser light from the wire by two PSDs The position of a thin wire 50 pm in diameter can be monitored with a resolution of about 1 pm 1 INTRODUCTION An Accelerator Test Facility ATF 1 is under construction at KEK as a part of R D efforts for linear colliders It comprises a 1 54 GeV linac and a racetrack shape damping ring The main purpose of the damping ring is to realize a beam with very low emittance the vertical and 8 6 horizontal normalized emittances will be 5 x 1 0 m rad and 3 x 1 0 m rad respectively Precise alignment of magnets is required to achieve such low emittance Simulations have shown that alignment tolerances of magnetic center are 60 pm in horizontal and 50 pm in vertical and the tolerance for rotation around the beam line is 0 2 mrad Real time monitors are important to maintain such precise alignment The FFTB of SLAC and the ESRF have real time monitor systems The FFTB uses a wire alignment system 2 and the ESRF uses the HLS Hydrostatic Leveling System 3 Although both of them are excellent the former is difficult to apply to arc sections and the latter does not give the information on horizontal displacement We propose two kinds of real time monitors Both of them use laser diodes and



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