Schematic layout of the optics at beamline APE. Bottom panel: the chicanelike steering of the electron beam for the APE undulators EU12.5 (LE) and EU6.0 (HE).
Schematic mechanical layout of the two-branch beamline APE (LE and HE). In both panels (top view and side view), positions of the optical elements are indicated. In panel (a) on the right: the end stations interconnected by several UHV transfer chambers.
Undulator layout. Schematic of the magnetic structure and polarization control of the APPLE-II-type undulator indicating the mechanical movements of gap and phase ( and , respectively) to obtain linear horizontal, linear vertical, and circular polarized radiations.
Thermal analysis result for the photon beam shutter with both undulators in horizontal polarization mode, i.e., at maximum power of radiation. Maximum surface temperature is .
Power density patterns from the two undulators at minimum gap for horizontal , circular , and vertical polarizations. The yellow lines represent the boundaries corresponding to the part of the radiation cone hitting the vacuum chambers.
(Top left) Schematic of the magnetic structure of the quasiperiodic LE undulator EU12.5 with low fringe field termination. (Bottom left) Calculated figure of merit and performances of the LE (12.5) and HE (6.0) undulators as a function of photon energy. In linear mode, the figure of merit (polarization ) coincides with flux . Right: LE undulator settings. (Top panel) Calculated tables indicating (black points) and (white points) values vs phase shift in millimeter for different gap values. When circular mode is obtained. (Bottom panel) Calculated photon energies of fundamental harmonics vs gap and phase shift.
(Top left) Measured field distribution of the quasiperiodic arrangement in circular polarization mode: one notices the four locations of perturbed field due to the missing blocks. (Bottom left) Computed trajectory corresponding to field distribution is along two different axes. Vertical field (horizontal trajectory) shown in black, horizontal field (vertical trajectory) in blue. (Right) Angle integrated spectra of LE (12.5) undulator in linear (top panel) and circular polarization mode (bottom panel) with angular acceptance of . Spectra are computed from ideal (black line) and measured (red line) field.
Details of both mounting and cooling system of the first spherical mirrors HEM1 and LEM1. The mirrors are accommodated in the same UHV vessel. The two beams from HE and LE undulators are separated by 48 mm.
Fermi level from polycrystalline Ag measured at and 16 K. The red line is the best fit obtained, revealing an overall experimental broadening of .
Beam stability test. Series of Fermi level measured from poly-Ag as a function of time and probe. Top: reference vs time measurements obtained via He-discharge lamp , revealing a stability of 1 meV over 24 h. Bottom: same test with SR at . Results indicate a 2 meV stability over 12 h.
Intensity of LE quasiharmonics as measured by a calibrated diode with 2 GeV and slits of . From left to right: lineshapes are presented as a function of gap value and photon energy for three gratings (1200 l/mm, track 1 and 2, and 1600 l/mm).
Contribution of higher orders at LE branch. Extended valence band spectra from Ag(100) at . Counts measured on the maximum of the states are indicated, and the inset shows a zoom into the region of the Fermi level around 20.7 eV of kinetic energy. The region spans over the possible second and third order contribution, showing roughly 1% overall contribution, as indicated by the arrow and number of counts measured at the location of the second order for .
Intensity of HE harmonics as measured by a calibrated diode with 2 GeV and slits of . Grating and polarization are indicated in each panel. Points correspond to measured intensity at fixed gap value with different harmonics (first, second, and third).
3D artistic view of the end stations and preparation chambers.
Fermi surface mapping from Cu. Planar cuts through the Cu Fermi surface in (111) plane (parallel to the sample surface). (left), (right). Red contours: tight binding model calculation.
Example of x-ray based spectroscopy performed at APE-HE. (a) sketch of the picture frame Fe(001) sample. Scanned area is indicated by the red square. (b) XMCD as measured in total electron yield at the edge maximum absorption of Fe. White and dark areas correspond to different Fe domains whose orientation along the (001) direction is indicated by green and red arrows. (c) Spin-polarization maps of the same sample area as measured by Mott detector scattering along the Fe(001) and (010) directions, respectively. Out of plane magnetization is absent, whereas in-plane magnetization well reproduce the XMCD results.
STM topography image with atomic resolution . The sample is a 2 ML Pb thin film epitaxially grown onto a Cu(111) single crystal .
Optical parameters (LE branch). Angle is defined as grazing incidence angle. All the LE-branch optics are not coated.
Optical parameters (HE branch). Angle is defined as grazing incidence angle. All the HE branch optics are platinum coated.
Parameters of LE (12.5) and HE (6.0) undulators. is the number of periods, is the peak on-axis magnetic field, and the energy of the fundamental spectral harmonic at the minimum operational gap.
Grating characteristics. LE gratings are made of pure silicon; HE gratings are platinum coated. Radius of the whole set of gratings is . Slope error and surface roughness are, respectively, and 0.25 nm (rms values).
Article metrics loading...
Full text loading...