Mary Severson

A plane grating monochromator for the new undulator at Aladdin: 8–240 eV

Abstract A comparative study on the expected performance of two monochromator designs for the new undulator beamline at the Aladdin storage ring is reported. The undulator, a 3.5 m device, will cover the energy range 8–240 eV in the first and third harmonic. The flux and resolution of a stigmatic plane grating monochromator (PGM) equipped with an entrance slit and of a spherical grating monochromator (SGM) with a movable exit slit were calculated analytically and by means of ray-tracings. The PGM design, tuned to a resolving power of 10 4 , can deliver more than 10 12 photons/s at the sample position in the photon energy range 20–170 eV. The illuminated spot size at the sample position will be less than 500 μm (horizontal) by 50 μm (vertical). This performance is not achieved with the SGM design.

Precision motion and position control for the Plane Grating Monochromator at SRC

A nearly stigmatic Plane Grating Monochromator (PGM) under commissioning for the new undulator beamline at the Synchrotron Radiation Center will provide a resolving power > 10000 as it scans from 8 to 240 eV. Scanning requires the precise, simultaneous rotation of a plane mirror and a combined rotation-translation of a plane grating in close proximity to one another inside a UHV chamber. The required scanning motions are significant due to the large energy range covered by a single grating. The mirror and grating rotate nearly 23 and 33 degrees respectively and the grating translates approximately 200 mm. Sub-arcsec angular resolution allows several steps to be taken across the monochromators energy resolution. Both rotations utilize a combination stepping motor-piezoelectric actuator scan drive that is controlled with a feedback loop using a laser interferometer to measure the in-situ rotation of the optics. The grating mechanism is supported via bellows to an external stepping motor driven stage that travels directly on an inspection grade granite block. The stage position is controlled with a feedback loop using a precision linear encoder. A positional accuracy and vertical stability of a few micrometers is achieved on the grating translation which prevents the image from shifting at the exit slit and introducing energy calibration errors.

Vacuum ultraviolet high‐resolution and high‐flux beamline for the Aladdin storage ring

A new vacuum ultraviolet beamline for Aladdin based on an electromagnetic undulator and a 4 m normal incidence monochromator is described. The combination of the undulator, new optics, and an improved version of the currently operational monochromator is expected to deliver more than 3×1011 photons/s at a resolving power of 3×104 in the photon energy range 6–30 eV. At a lower resolving power of 104, more than 1011 photons/s will be available between 30 and 40 eV. Expecting a very high demand for the new beamline, two branches are planned to allow for time sharing.

Undulator 4 meter NIM at SRC

A new 4 meter normal incidence monochromator (NIM) has recently been commissioned at the Synchrotron Radiation Center (SRC). The beamline utilizes two indexing spherical gratings to cover the energy range of 6–50 eV. A resolution of 0.35 meV at 15.765eV has been measured, which agrees well with the theoretical value. The source for the beamline is a 3.5 m long, 10.9 cm period electromagnetic undulator. The device can be scanned through the full energy range at any time with beamline based controls.

System for monitoring position of the photon beam in the new undulator beamline at SRC

A system of beam position monitors was developed for the plane grating monochromator (PGM) undulator beamline at the Synchrotron Radiation Center (SRC). Two monitors are located in the upstream section of the beamline providing the capability of measuring the transverse angular and spatial motion of the photon beam. The jaws of the entrance slit of the monochromator may also be used as monitors to detect changes in the vertical position of the source. Overall, the system allows measurements of the photon beam position and angle to be done with ∼10 μm and ∼3 μrad accuracy, respectively. The aperture of the monitors can be changed in both the vertical and horizontal direction. Thus, the beam motion can be measured with the highest possible resolution for any value of the undulator deflection parameter K. In addition, the design of the monitors provides the capability of mapping the angular power distribution of the photon beam. The first monitor was installed and successfully tested. The design of the syste...

Mechanical design of a plane grating monochromator for the new undulator at Aladdin

A nearly stigmatic plane grating monochromator under construction for the new undulator beamline at Aladdin will provide a resolving power ≳10000 as it scans from 8 to 240 eV with a single grating. Scanning requires the precise, simultaneous movements of both a plane mirror and a plane grating in close proximity to one another inside a UHV chamber. The mirror, which absorbs up to 16.5 watts, is internally water cooled to minimize thermally induced slope errors. The radiatively cooled grating absorbs less than a watt. Careful examination of the focusing requirements revealed that the monochromator could be scanned either in the conventional mode of rotating‐translating the mirror and rotating the grating or in a modified mode of rotating the mirror and rotating‐translating the grating. The latter mode was chosen for simplicity of design. The mirror and grating rotate nearly 30 and 40 degrees, respectively, with subarcsec resolution. Both utilize a stepping‐motor lead‐screw piezoelectric actuator scan drive...

Current status of the Synchrotron Radiation Center

The Synchrotron Radiation Center operates the Aladdin electron storage ring at energies of 800 meV or 1 GeV in support of a broad range of national and international research programs with a major focus on the study of valence electrons, spectromicroscopy, and nanolithography. Upgrades to the storage ring have improved the stability of the source, and experiments with low emittance lattice configurations show the feasibility of increased brightness for new or enhanced research. Three recently installed undulators, two pure permanent magnet devices and an electromagnetic device, and the associated instrumentation offer experimentalists high flux combined with high resolution. The status of the existing instrumentation, recent scientific results, and an overview of plans for new undulator-based instruments to cover the photon energy range from 7.8 to 400+ eV will be presented.

First Results from the New Varied Line Spacing Plane Grating Monochromator at SRC

A varied line spacing plane grating monochromator (VLS‐PGM) has recently been installed and commissioned on an existing insertion device at the Synchrotron Radiation Center (SRC). The beamline covers the energy range from 70 to 2000 eV and consists of an ellipsoidal mirror, three varied line spacing gratings, an exit slit, and an ellipsoidal refocusing mirror. The beamline is optimized for X‐ray PhotoElectron Emission spectroMicroscopy (X‐PEEM) experiments by providing high flux density at the sample with moderate energy resolution. The insertion device functions as an undulator up to about 420 eV and as a wiggler at higher energies. Wiggler mode is obtained by positioning the undulator at maximum k, using a large horizontal aperture at the front of the beamline, and tapering the undulator by increasing the upstream gap 100 microns. Experimental results show the beamline is performing very well, with resolution and flux measurements in close agreement with theory.

Beam Stability: Raytracing Requirements and Implementations

Stability to‐the‐user fundamentally starts with present needs and future goals from the user community conveyed to facility staff in terms of user observables into the sample chamber. These are then projected onto the requirements for both the beamlines and the sources. In turn, specifications unfold for performance of subsystems, individual components, and facility services. Altogether, this process involves users, and facility staff from beamlines, operations, engineering, controls, and machine physics.This paper focuses on the transformation of user‐to‐source requirements, which is a small, but critical, part of the general subject. This translation has been expedited by semi‐automated use, via scripting, of the SHADOW raytracing software. The dependence of each user observable on each source parameter is functionally determined, and inverted, for variable values of the user observables. In this way, source stability requirements can be readily determined for the needs of a given experiment on a given ...

Ray tracing: Experience at SRC (invited)

SHADOW [B. Lai and F. Cerrina, Nucl. Instrum. Methods A 246, 337 (1986)] is the primary ray‐tracing program used at SRC. Ray tracing provides a tremendous amount of information regarding beamline layout, mirror sizes, resolution, alignment tolerances, and beam size at various locations. It also provides a way to check the beamline design for errors. Two recent designs have been ray traced extensively: an undulator‐based, 4‐meter, normal‐incidence monochromator (NIM) [R. Reininger, M.C. Severson, R.W.C. Hansen, W.R. Winter, M.A. Green, and W.S. Trzeciak, Rev. Sci. Instrum. 66, 2194 (1995)] and an undulator‐based, plane‐grating monochromator (PGM) [R. Reininger, S.L. Crossley, M.A. Lagergren, M.C. Severson, and R.W.C. Hansen, Nucl. Instrum. Methods A 347, 304 (1994)].