F2 Beamline

High-Energy Beamline

F2 Station Summary
Monochromator: Cryo-cooled double Laue with sagittal focusing
Energy Range: 38-80 keV
Bandpass: ΔE/E ≈ 0.25%
Source Size: 3.6 mm H × 1.0 mm V
Source-to-Monochromator Distance: 20.75 m
Monochromator-to-Sample Distance: ≈ 6.7 m
Beam Size at Sample: 1.0 mm H × 1.5 mm V (nominal @ 40 keV)
Far-Field Area Detector: GE 2048x2048, 200 µm pixels
Near-Field Area Detector: Retiga 4000DC, LuAG:Ce scintillator; 2x, 5x, 7.5x, 10x Mitutoyo infinity optics
Load Frame: RAMS2, 2 kN tension/compression; Displacement control mode
Data Acquistion: Spec, EPICS, LabVIEW
3 Data Analysis Workstations: 2 Intel E5-2695 CPUs (12 cores each) 256 GB DDR 3 RAM; nVidia Tesla K40 GP-GPU 4.29 Tf, 12 GB GDDR5 Scientific Linux 6.5

The F2 beamline has been extensively upgraded and recommissioned as a dedicated high-energy facility to meet increading demand for high-energy x rays. F2 utilizes a double-bounce Laue monochromator with bent crystals to provide sagittal horizontal focusing and optimize the bandpass, yielding the highest flux of high-energy X-rays obtainable at CHESS. The first monochromator crystal is cryogenically cooled to liquid nitrogen temperatures to accommodate the intense power produced by the CHESS East Wiggler, and all of the monochromator adjustments are motorized to allow fine tuning at cryogenic temperatures during x-ray experiments. As a result, the flux available at F2 is more than an order of magnitude greater than what could previously be achieved at CHESS.

The F2 hutch has been completely reinstrumented for high-energy x-ray experiments. A new large-format GE area detector optimized for high-energy x-rays is mounted on a new remotely-controlled stage providing more than 1 meter of adjustment in sample-detector distance, plus fine adjustments in both transverse directions and pitch, yaw, and roll. The beam stop is also mounted on an independent stage, decoupled from adjustments to detector or sample stages. The new incident flightpath includes a fast x-ray shutter with ~1 ms transit time, and an array of thin metal foils to monitor potential drift in the x-ray energy (which has so far been observed to be well under the ~0.25% bandpass of the monochromator.) The station has been equipped with a new oscilloscope, function and delay generators for general use. A small Huber 4-circle diffractometer is available, as is a general use optical table.

In collaboration with researchers from the Air Force Research Laboratory, a unique 2 kN load frame called RAMS2 has been developed for general use at F2. RAMS2 is designed for in-situ studies of the thermo-mechanical response of structural materials, using a combination of tomography, near-field and far-field diffraction, and digital image correlation measurements. The tomographic rotation axis is built into the load frame itself, using precision air bearings and a unique construction to provide submicron stability in sample manipulation. A custom data acquisition system supports “on-the-fly” scans where a motor moves continuously and a synchronization pulse triggers data to be read from the various subsystems, such as area detectors and hutch sensors. The near-field detector is based designs from APS 1-ID, using a Retiga 4000DC camera with an infinity optical system and Mitutoyo objectives. And the overall “spec” control system software was developed to provide a few simple commands that manage the complex tasks of coordinating the various beamline components, allowing scans to run unattended for many hours. These efforts culminated in June with a collaboration with researchers from DTU for the first grain-mapping experiments to be performed at CHESS, investigating the evolving relationship between microstructure and mechanical response of materials under load.

F2 provides three new dedicated workstations for the computationally intensive analysis of in-situ loading experiments, using the open-source HEXRD and FABLE software packages. These workstations include extensive RAM and dedicated GPUs to speed up certain types of calculations. In collaboration with researchers from AFRL and LLNL, the HEXRD software is currently being developed to add new features and take advantage of GPU resources, with the ultimate goal of performing the majority of the analysis at the beamline.

Work is ongoing to extend the capabilities of the F2 instrumentation and software. The RAMS2 control system is being extended to support a force-control mode and cyclical loading. An in-situ furnace is being developed for RAMS2 to heat samples under load to 1000°C. The general-purpose tomography stages will be upgraded with an air bearing rotation stage to improve precision. We are working on installing the analysis software on the CLASSE computing cluster to make those resources available from offsite, and also making it easy for our users to install the open-source software packages on their own systems.

flux plot
Figure 1: Measured total flux vs energy.