National Synchrotron Light Source II To Have X-Rays a Billion Times Brighter Than a Doctor’s Office – CHX beamline will use vacuum chambers for scientific research

Posted on: April 29, 2019

The National Synchrotron Light Source II is nearing completion at Brookhaven National Labs. Initial beamlines are expected to provide a significant capacity early in NSLS-II operations to allow the exploration of the unique scientific opportunities offered by the new facility, as well as support the wide-ranging research programs of the user community served by the original National Synchrotron Light Source. When fully built out, the NSLS-II will accommodate about 60-70 beamlines using 27 straight sections for insertion-device sources, 30 bending-magnet or three-pole-wiggler sources and multiple branches (NSLS-II beam lines: http://www.bnl.gov/ps/nsls2/beamlines/).

Coherent Hard X-Ray Scattering (CHX)

Scientific Scope

The Coherent Hard X-ray Scattering (CHX) beamline is an undulator beamline at sector 11-ID that is dedicated to studies of nanometer-scale dynamics in materials using x-ray photon correlation spectroscopy (XPCS) with world-leading hard x-ray coherent flux and a detection system for fast dynamics into the sub-millisecond regime.

Small Vacuum
Small Vacuum
(Small vacuum chamber made by Applied Vacuum Technology (AVT) for hard x-ray attenuator assembly.)

XPCS is based on measuring time correlation functions of the speckle fluctuations that occur when a coherent x-ray beam is scattered from a disordered sample. It can be used to measure equilibrium dynamics via the “usual” single- speckle intensity-intensity autocorrelation functions g(2) (q, t). When combined with 2D area detectors and a multispeckle detection technique, it can also be used to measure non-stationary, non-equilibrium dynamics via two-time correlation functions g(2) (q, t1, t2). Higher-order correlation functions g(n) (q, t) can be used to characterize heterogeneities in the dynamical properties. The key quantity that enables XPCS experiments is the source brightness. This determines the flux of coherent x-ray photons and ultimately the signal-to-noise ratio (SNR) of the measured correlation functions. With the unprecedented brilliance of the NSLS-II storage ring exceeding 1021 ph/s/mrad2/mm2/0.1% bandwidth at 8 keV, the CHX beamline will allow studies of dynamics on time scales that can be 100 times faster and on shorter length scales than currently achievable.

Small Vacuum chamber
(AVT vacuum chamber with o-ring sealed panels for X-ray Photon Correlation Spectroscopy (XPCS) experiments.)
AVT Detector
(AVT detector chamber for the CHX Small Angle X-ray Scattering instrument, hosting beam stop and detector positioning systems and a DECTRIS 4M Eiger detector.)

The design of the CHX instrument is simple and robust and puts an emphasis on three key elements: (1) coherence (brilliance) preservation by carefully designing and engineering key optical elements, reducing the number of windows, mirrors, etc. to an absolute minimum, (2) maximizing the useful signal by using the entire available coherent flux via focusing optics, and (3) maximizing the mechanical stability of the instrument.

“The CHX beamline will be one of seven slated to do early science at NSLS-II when it comes online in 2015. For staff and visiting scientists, it will be a tool to do a wide range of science, such as study materials for energy storage, or imaging biological samples to understand drug delivery processes.

… Lutz Wiegart is responsible for developing the endstation instrumentation at CHX and its technical implementation in preparation for the start of the scientific research program…

… When assembled, the beamline will act as a high-speed camera with an extremely fast shutter, capable of taking “nanoscale movies” of motion within materials or biological samples… NSLS-II will be one of the brightest light sources in the world with x-rays a billion times brighter than those at a doctor’s office.

Seeing the infinitesimal structures of materials requires x-rays exiting a sample at large angles, while measuring the dynamics of material – how matter moves within a sample on the mesoscale – requires detection of x-rays scattered by a small angle. The combination of a high stability multi-circle diffractometer and a 15-meter long small-angle x-ray scattering (SAXS) table at CHX will allow for both of these types of measurements to be performed on the same sample at the same beamline. Doing both with the same setup reduces error and provides “purer data,” Wiegart said.

References:
http://www.bnl.gov/ps/nsls2/beamlines/
http://www.bnl.gov/ps/nsls2/beamlines/CHX.php
http://www.bnl.gov/newsroom/news.php?a=24440
Lutz Wiegart – responsible for developing the endstation instrumentation at CHX