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Morrison, L. H.

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TUPMN102 Electromagnetic Design of the RF Cavity Beam Position Monitor for the LCLS 1153
  • G. J. Waldschmidt, R. M. Lill, L. H. Morrison
    ANL, Argonne, Illinois
  Funding: Work supported by the U. S. Department of Energy under Contract Nos DE-AC02-06CH11357 and DE-AC03-76SF00515.

A high-resolution X-band cavity beam position monitor (BPM) has been developed for the LCLS in order to achieve micron-level accuracy of the beam position using a dipole mode cavity and a monopole mode reference cavity. The rf properties of the BPM will be discussed in this paper including output power, tuning, and issues of manufacturing. In addition, methods will be presented for improving the isolation of the output ports to differentiate between horizontal/vertical beam motion and to reject extraneous modes from affecting the output signal. The predicted simulation results will be compared to data collected from low-power experimental tests.

FROBC04 Thermomechanical Design of Normal-Conducting Deflecting Cavities at the Advanced Photon Source for Short X-ray Pulse Generation 3827
  • B. Brajuskovic, J. T. Collins, P. K. Den Hartog, L. H. Morrison, G. J. Waldschmidt
    ANL, Argonne, Illinois
  Funding: Work supported by U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357

A normal-conducting deflecting cavity is being designed at the Advanced Photon Source (APS) as a part of the short x-ray pulse project intended to provide users with approximately 2 picosecond x-rays. The system will use two pairs of 3-cell cavities in sectors 6ID and 7ID for the generation of the x-ray pulse in the 7ID beamline. The 3-cell cavities are designed to provide the desired beam deflection while absorbing in excess of 4 kW of power from a pulsed rf system and up to 2.6 kW in the damper system of high-order mode (HOM) and low-order mode (LOM) waveguides. Since the cavity frequency is very sensitive to thermal expansion, the cooling water system is designed so that it is able to control cavity temperature to within 0.1?C. This paper describes the optimization of the thermomechanical design of the cavity based on calculation of thermal stresses and displacement caused by the generated heat loads, and presents the design of a cooling water system required for the proper operation of the cavities.

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FRPMN109 200-mA Studies in the APS Storage Ring 4354
  • K. C. Harkay, Y.-C. Chae, L. Emery, L. H. Morrison, A. Nassiri, G. J. Waldschmidt
    ANL, Argonne, Illinois
  Funding: Work supported by U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

The Advanced Photon Source storage ring is normally operated with 100 mA of beam current. A number of high-current studies were carried out to determine the multibunch instability limits. The longitudinal multibunch instability is dominated by the rf cavity higher-order modes (HOMs), and the coupled-bunch instability (CBI) threshold is bunch-pattern dependent. We can stably store 200 mA with 324 bunches, and the CBI threshold is 245 mA. With 24 bunches, several components are approaching temperature limits above 160 mA, including the HOM dampers. We do not see any CBI at this current. The transverse multibunch instabilities are most likely driven by the resistive wall impedance; there is little evidence that the dipole HOMs contribute. Presently, we rely on the chromaticity to stabilize the transverse multibunch instabilities. When we stored beam up to 245 mA, we used high chromaticity, and the beam was transversely stable. The stabilizing chromaticity was studied as a function of current. We can use these experimental results to predict multibunch instability thresholds for various upgrade options, such as smaller-gap or longer ID chambers and the associated increased impedance.

FRPMN111 Design and Performance of the LCLS Cavity BPM System 4366
  • R. M. Lill, L. H. Morrison, W. E. Norum, N. Sereno, G. J. Waldschmidt, D. R. Walters
    ANL, Argonne, Illinois
  • S. Smith, T. Straumann
    SLAC, Menlo Park, California
  Funding: Work supported by U. S. Department of Energy under Contract Nos. DE-AC02-06CH11357 and DE-AC03-76SF00515

In this paper we present the design of the beam position monitor (BPM) system for the LCLS undulator, which features a high resolution X-band cavity BPM. Each BPM has a TM010 monopole reference cavity and a TM110 dipole cavity designed to operate at a center frequency of 11.384 GHz. The signal processing electronics features a low-noise single-stage three-channel heterodyne receiver that has selectable gain and a phase locking local oscillator. We will discuss the system specifications, design, and prototype test results.