NSLS-II Beam Stability Requirements: Maintaining Experimental Precision

1. NSLS-II User Requirements for Beam Stability Contributors Dario Arena Lonny Berman Larry Carr Ken Evans-Lutterodt John Hill Steve Hulbert Paul Northrup Cecilia Sanchez-Hanke Yuri Shvyd’ko Peter Siddons Nick Simos Lin Yang Zhong Zhong

2. Type of source: 5 m straight section 8 m straight section Bending magnet 1 T three-pole wiggler σx [μm] 38.5 99.5 44.2 (35.4-122) 136 σx' [μrad] 14.2 5.48 63.1 (28.9-101) 14.0 σy [μm] 3.05 5.51 15.7 15.7 σy' [μrad] 3.22 1.78 0.63 0.62 Electron Beam Sizes and Divergences for Selected NSLS-II Sources

3. The Apparent Photon Source Size is Photon Energy Dependent

4. As Is the Apparent Photon Source Angular Divergence

5. Program Vertical Position Stability Requirement (µm) Vertical Angle Stability Requirement (µrad) Horizontal Position Stability Requirement (µm) Horizontal Angle Stability Requirement (µrad) Radiation Source(s) Inelastic x-ray scattering Needs further study Needs further study; 1 instr is sensitive to 40 nrad! Needs further study Needs further study CPMU or SCU Infrared 1 3 2 6 Dipole Macromolecular crystallography 1 1 1 4 CPMU or SCU Nano focusing/probe 10% of beam size 10% of opening angle 10% of beam size 10% of opening angle CPMU or SCU Powder diffraction 10 1 10 --- DW or 3PW Determined Stability Requirements for Various Techniques (Most Stringent for Each, So Far)

6. Program Vertical Position Stability Requirement (µm) Vertical Angle Stability Requirement (µrad) Horizontal Position Stability Requirement (µm) Horizontal Angle Stability Requirement (µrad) Radiation Source(s) Small angle x-ray scattering 20 8 8 3 CPMU or SCU Soft x-ray 10% of beam size 10% of opening angle 10% of beam size 10% of opening angle Undulator or dipole High-energy x-rays 50 10 50 --- SCW X-ray absorption spectroscopy 10% of beam size 1 --- --- DW or 3PW X-ray magnetic circular dichroism Needs further study Needs further study Needs further study Needs further study EPUs X-ray photon correlation spectroscopy Needs further study Needs further study Needs further study Needs further study CPMU or SCU Determined Stability Requirements for Various Techniques (Continued)

7. Some Observed Trends • In the cases studied so far, a stability criterion of 10% of the beam size and 10% of the beam opening angle is sufficient, with the exception of the horizontal position for a few techniques • A common theme which has been expressed is in stability of beam intensity delivered to the experiment, which affects signal-to-noise directly, and this explains why some cases require beam position stability of <10% of the beam size • Many methods will use more than one kind of radiation source, and may have different stability requirements for each one • A “one size fits all” approach may not work for everyone, and tighter stability for a particular experimental program may require local measures

8. Maintaining Experimental Stability When the Beam is Already Stable • Obviously, a “quiet” floor structure and surroundings are helpful • In many cases, though, relative stability of key beamline and experimental station components is all that matters in order to ensure experimental stability • This can usually be achieved through common support of these key components • But this becomes more challenging in cases when key components are distant from each other (e.g. for long beamlines) • Active feedback is often employed to solve this challenge, but extreme care is normally required to implement this

9. We’ll elaborate in greater detail in the focused presentations that will be given in the working group discussions.