Systematic X-ray absorption study of hole doping in BSCCO - phases

X-ray absorption spectroscopy (XAS) on the O 1s threshold was applied to Bi-based, single crystalline high temperature superconductors (HTc's), whose hole densities in the CuO2 planes was varied by different methods. XAS gives the intensity of the so-called pre-peak of the O 1s line due to the unoccupied part of the Zhang-Rice (ZR) singlet state. The effects of variation of the number n of CuO2 - planes per unit cell (n = 1,2,3) and the effect of La-substitution for Sr for the n = 1 and n = 2 phase were studied systematically. Furthermore the symmetry of the states could be probed by the polarization of the impinging radiation.Comment: 4 pages, 2 figures, to appear in the proceedings of SCES2001, Ann Arbor, August 6-10, 200

A Canted Double Undulator System with a Wide Energy Range for EMIL

At BESSY II a canted double undulator system for the Energy Materials In situ Laboratory EMIL is under construction. The energy regime is covered with two undulators, an APPLE II undulator for the soft and a cryogenic permanent magnet undulator CPMU 17 for the hard photons. The layout and the performance of the undulators are presented in detail. The minimum of the vertical betatron function is shifted to the center of the CPMU 17. The neighboring quadrupoles and an additional quadrupole between the undulators control the vertical betatron function. Prior to the undulator installation a testing chamber with four movable vertical scrapers has been implemented at the CPMU 17 location. Utilizing the scrapers the new asymmetric lattice optics will be tested and optimize

SHIMMING OF THE DYNAMIC FIELD INTEGRALS OF THE BESSY II U125 HYBRID UNDULATOR

Abstract Within a continuous program the BESSY II undulators are prepared for Topping-Up operation. The U125 planar hybrid undulator has a period length of 125 mm and a pole width of only 60 mm. The horizontal defocusing of the 1.7 GeV e-beam may result in a significant reduction of the horizontal dynamic aperture, reducing the injection efficiency when injecting into the closed gap. The dynamic field integrals are derived from a 2D-Fourier decomposition of the 3D-field. An analytic description of the dynamic field integrals based on the Fourier coefficients is presented. Magic fingers have been installed in order to minimize the dynamic field integrals and to enlarge the good field region of the device

Cryogenic Design of a PrFeB Based Undulator

A PrFeB based cryogenic undulator has been built at Helmholtz Zentrum Berlin HZB in collaboration with the Ludwig Maximilian University München LMU . LMU will operate the undulator at a laser plasma accelerator at the Max Planck Institut für Quantenoptik in Garching. The 20 period device has a period length of 9mm and a fixed gap of 2.5mm. The operation of a small gap device at a high emittance electron beam requires stable magnetic material. A high coercivity is achieved with PrFeB material cooled down to 20 30K. In this paper we present the mechanic, magnetic and cryogenic design and compare predictions with measured dat

Correction of Self Absorption on XAS Measurements in Fluorescence Mode

Self absorption and influence of neighbouring absorption edges make it necessary to correct data of XAS measurements in fluorescence mode. To simulate the fluorescence process and to calculate the absorption coefficients from experimental data, informations about stoichiometric composition and fluorescence yields are needed Some examples show the necessity of conection of fluorescence spectra to get true absorption coefficients and me adrmtage of the meniod hi ZnSe the Se absorption coefficient can be calculated from the Zn L absorption spectrum. In the same system the intensity breakdown of Zn L fluorescence absorption spectra due to Se absorption above the.Se L-edges can be remove

Mini Beta Sections in the Storage Ring BESSY II

At BESSY II photon energies above 2keV can be produced only with a permanent magnet wiggler, with superconducting wavelength shifters and with a superconducting wiggler. The wiggler brilliance suffers from the depth of field effect and the wavelength shifters produce the X rays only from a single pole. For the generation of brilliant radiation above 2keV a small period cryogenic undulator has to be used. This paper discusses the machine requirements for the operation of small gap cryogenic devices at BESSY II. A scheme with two adjacent vertical low beta sections inside of one of the long straight sections is suggested. The straight is divided into two parts by a quadrupole triplet in the center. An optic with an increased vertical beta tune by 0.5 is presently studied. The optics outside of the low beta section and the horizontal tune are kept unchange

Universal Mode Operation of the BESSY II UE112 APPLE Undulator

The UE112 APPLE undulator operated at BESSY II covers the low photon energies down to the visible regime. Below 100eV the state of polarization is significantly modified by the optical components of the beamline. Moving three magnet rows of the APPLE undulator universal mode any state of polarization can be produced by the undulator which permits the compensation of the beamline effects. The dynamic multipoles in the universal mode have to be compensated for a transparent operation. An analytic model of the multipoles has been developed and compared to measurements. A real time compensation scheme is presente

XANES Analysis of L3,2 Edges of Zinc Selenides with Transition Metals

X-ray Absorption Near Edge Structure (XANES) for ternary compounds Zn1-xTMxSe (TM=Cr, Mn, Fe, Co, and Ni) with different concentration x of transition metals (TM) has been studied with the use of synchrotron radiation. XANES measurements were carried out in the fluorescence detection mode using synchrotron radiation from the HE-PGM2 plane grating monochromator at BESSY. The L3.2 edges for Se, Zn and different transition metals (Cr, Mn, Fe, Co, and Ni) in Zn1-xTMxSe compounds have been analyzed. Moreover, the analysis of L3.2 edges for different transition metals in binary TMSe has also been made. The characteristic feature of L3.2 edges for transition metals containing two white lines was observed. The energy positions of these maxima are in good agreement with the theoretical results. The studies of L3.2 edges of Se in ternary compounds in comparison to the same edge of host crystal (ZnSe) allowed us to obtain information about the influence of additional 3d-states of TM on the density of states of ternary compounds