# Presentation: 214068

## User requirements

- _Session chair_
- K.Evans-Lutterodt
- _Speakers:_
- Jorg Maser
- N. Simos
- D.Arena
- P.Northrup
- C. Sanchez-Hanke

## There needs to be a holistic approach to design that considers the source, beamline, endstation and beamline floor in an even handed way. (MASER)

- Typical parameters of an NSLSII Nanofocusing Beamline (5 m straight)
- Source distance: 				50 m
- Source size dv(FWHM)			3.8 um
- Lateral coherence length at position of focusing optics (sv=/):
- 							520 um, E = 10 keV
- Focal length:				4.2 mm, E = 10 keV
- Depth of focus:				DOF = 20 nm

- KEY POINT: focal length f ~ 1<f<5mm , so it will not be too difficult to keep optic and sample on a short mechanical path

## Stability of electron beam is crucial

- Position of electron beam translates directly into stability of image.
- Typical tolerance is 10%.
- If e-beam size is 3 microns,
- =>Positional tolerance is 0.3 microns.
- Angular stability?

- 

- L=undulatar length

- Assume beam position monitors placed at two ends of undulator
- Angular uncertainty ~ (0.3 microns/ 3 meter) ~ 1e-7 radians

- KEY POINT: Positional tolerance 0.1, =0.3microns, Angular = 0.1 micro-radians

## KEY POINT: The 0.1 gives 1% changes in intensity, and contributes negligibly to size 

**B: Intensity**

- If sigma stability is 10%, then stability adds negligibly to size

- If you are measuring fluorescence intensity, and we assume a gaussian profile
- And we want to keep signal intensities within 1%:

- A: Size

- 1% criterion

- 5% criterian

- 0.1% criterion

**Effects of stability on beam size and measured intensity**

## KEY POINT: Astigmatic Beamline design has:

- Nonsymmetric source size
- Astigmatic beamline design required
- Spatial filter  remove source/BL optics motion effects
- High position accuracy requirements for beam defining aperture

- Vertical stability is due to electron beam position (ring responsibility)
- Horizontal stability is due to BDA (Beam defining Aperture) (beamline responsibility).

- Beamline design (Maser)

## Some issues

- Need X-ray beam position monitors downstream of monochromator and other mirrors, but before high resolution focusing element.
- Needed: A way to measure the flux exiting the lens. Tough to do because the focal length is so short. If this cannot be done the stability requirement goes from 0.1 to 0.01, a much more difficult target for the ring. For soft x-rays which have focal lengths of order < 1mm, this is as yet an unsolved problem.
- Positioning is going to be difficult. Temperature control will be required. Invar expansion coefficient is 160nm/K, and that is one of the better cases.
- Keep sound vibrations away from sample, by enclosing, perhaps vacuum.
- Unresolved issue:  will a helium environment or vacuum be more thermally stable

## Some points derived from Simos’ talk

- Every endstation/beamline has a response function to the vibration  spectrum present. The vibration spectrum at the hutch location should be measured, and the mechanical design of the endstation should be designed to minimize its response, by shifting endstations resonances to minima in vibration spectrum.
- Be careful. You can make a “quiet” environment “noisy” by inattention to details.
- Should we have vibration “police”? We will definitely need continuous monitoring and sensors permanently located on the floor.
- The positions and design of the utility building should continue to receive the level attention it is receiving, and should be optimally placed to minimize effect on ring.
- Is there a way to design slabs for the beamlines that will give maximum ridgidity but still minimize the effect of noise from other beamlines?

- KEY POINT: Use Simos simulation program to get insight

## The other techniques are mostly satisfied with the 0.1, 0.1’ 

- Soft X-ray (Arena): 1 change in beam position changes energy response negligibly.
- EXAFS (Northrup) : Energy resolution required needs angular stability of 1 microrad which is fine. Toughest issues will be heat load issues on beamline optics.
- Polarization (Sanchez-Hanke): More analysis required. Complicated.
- XPCS: Very tolerant to positional and angular. May have to be revised.

## Summary

- Most techniques are mostly satisfied with the 0.1, 0.1’ stability.
- However, if a intensity monitor downstream of the focusing optic cannot be developed, the stability requirement may have to be tightened to 0.04.
- Unresolved: How to take account of changes due to top-up injection