SRC Users' Meeting - Synchrotron Radiation Center - University of ...

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ACCELERATOR DEVELOPMENTS Ken Jacobs Synchrotron Radiation Center, University of Wisconsin - Madison 3731 Schneider Drive, Stoughton, WI 53589-3097 Work has continued on a variety of accelerator developments at the SRC over the past year. The low emittance operating mode “LF15” is now routinely run for all 800 MeV beams. This gives a factor of three reduction in horizontal beam size, with unchanged vertical beam size and beam lifetime. The exception to routine LF15 running is when vacuum work is done in the ring, after which Base Lattice is run for the first few weeks. LF15 cannot be run at 1 GeV due to power supply, cabling, and magnet limitations. For reduced emittance at 1 GeV, an alternate lattice with emittance between LF15 and Base Lattice has been designed. Operation will require upgraded cables on some of the quadrupoles, and this is presently being pursued. However, LF15 can be run at 950 MeV, requiring only the cable upgrades. Tests of 950 MeV LF15 have been encouraging. We are also investigating other low emittance 950 MeV lattices. We continued to make improvements made in beam stability. An additional feedback loop was installed in the main RF system to reduce coherent synchrotron oscillations of the beam. This, combined with a general reduction of 60 Hz harmonics on the beam, has reduced noise levels on the infrared beamlines so that they can now be used when running low emittance beam. Undulator compensation has progressed to the point that U1 and U3 can now be scanned over their full ranges in LF15. Compensation work is continuing with U2, and in Base Lattice. In an effort to improve beam lifetime, we are continuing studies to more fully understand beam loss mechanisms. To increase lifetime, it may be necessary to open up some limiting apertures in the ring. Other projects completed over the past year include upgrading the accelerator control system CPUs, coating the injection kicker ceramics to reduce wakefields and radiated RF, and installation of a modern scripting language on the control system. Scripts are used to simplify accelerator operations, implement control algorithms to improve beam stability, and perform experiments during accelerator development periods.
INTERACTIONS IN THE PHOTOEMISSION PROCESS OF MATERIALS WITH LOW CONDUCTIVITY Christian R. Ast Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany Scattering of the photoelectron is an omnipresent phenomenon in photoemission spectra. In most cases inelastic scattering manifests itself in either discrete loss structures, a featureless background or an asymmetric line shape. Two examples are presented in which increased interactions of the photoelectron with its surroundings lead to additional emission features in the photoemission spectra of the semimetal bismuth. Scattering events can be seen in core level spectra as structured loss features from interband transitions. In valence band spectra, scattering processes can contribute additional structures from secondary cone emission. Spectra of the Bi 5d core level show an additional peak split off in energy between 160 and 260meV, which can be related to momentum dependent energy losses suffered by the photoelectron from interband transitions. Similar phenomena have been observed in the 4d core levels of Sb, which leads to the conclusion that loss features are enhanced in materials with low conductivity and low charge carrier concentration. Valence band spectra of Bi(111) at normal emission as a function of photon energy show multiple emission features from the same initial state band. These emission features can be attributed to primary and secondary cone emission. To be observed in the normal emission spectra photoelectrons from secondary cone emission have to be scattered back into the normal emission direction. Accounting for the secondary cone emission in the analysis of the final state dispersion, it is than possible to experimentally determine the deviations of the final states from the free electron band structure. With these experimentally determined final state bands on hand, it is than possible to extract the initial state band structure E i (k).
Page 2 and 3: Welcome to the 36 th SRC Users’ M
Page 4 and 5: 12:20 - 1:10 Lunch 1:10 -1:45 Poste
Page 6 and 7: Administration Executive Director D
Page 8 and 9: STATUS OF THE SRC BEAMLINES AND INS
Page 12 and 13: HIGH ENERGY RESEARCH POSSIBILITIES
Page 14 and 15: ATOMICALLY UNIFORM THIN FILMS ON SI
Page 16 and 17: calculated binding energies of the
Page 18 and 19: MANY-ELECTRON EFFECTS ON THE XE 5S
Page 20 and 21: PHOTOELECTRON SPECTROMETRY OF ATOMI
Page 22 and 23: PHOTOEMISSION STUDY OF USb AND UTe
Page 24 and 25: CANADIAN SYNCHROTRON RADIATION FACI
Page 26 and 27: SELF-ASSEMBLY OF BLOCK COPOLYMERS O
Page 28 and 29: A B S T R A C T S
Page 30 and 31: Photoemission spectra, a.u. -0.3 -0
Page 32 and 33: THE INITIAL AND FINAL STATE BANDS I
Page 34 and 35: TRANSITION LAYERS AT BURIED FERROMA
Page 36 and 37: LOW-DIMENSIONAL ELECTRONS AT SILICO
Page 38 and 39: SUBCELLULAR DISTRIBUTION OF MOTEXAF
Page 40 and 41: LINEAR POLARIZATION MEASUREMENTS OF
Page 42 and 43: Fig.1: Photoemission spectra of opt
Page 44 and 45: The sample manipulator has a cool d
Page 46 and 47: Cr and Fe but for these U systems t
Page 48 and 49: [4] G. -H. Gweon, J. W. Allen, and
Page 50 and 51: References [1] S. Cho, Y. Kim, A. D
Page 52 and 53: [3] D. L. Mills, Physical Review B
Page 54 and 55: CHARACTERIZATION OF SULPHATE INTERA
Page 56 and 57: in the data acquisition chamber. Th
Page 58 and 59: spatially resolved chemistry of the
Page 60 and 61:
THE RELATIONSHIP BETWEEN PHOSPHATE
Page 62 and 63:
PHOTOEMISSION STUDIES OF QUANTUM WE
Page 64 and 65:
Ag surface state such that it moves
Page 66 and 67:
HIGH-RESOLUTION STUDY OF THE LITHIU
Page 68 and 69:
RELATIVE PARTIAL CROSS SECTIONS AND
Page 70 and 71:
Christian Ast Max-Planck Institute
Page 72 and 73:
David L. Huber Physical Sciences La
Page 74 and 75:
Tom Miller University of Illinois a
Page 76 and 77:
Eric Wiedemann University of Wiscon
Page 78 and 79:
Pete Hagen Phone: (608) 877-2154 Em
Page 80:
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