# Presentation: 007035

**Stability Issues**
- NSLS-II EFAC Meeting
- May 10, 2007
- S. Krinsky

## Stability Task Force  /  Workshop April 18-20

**Visiting Committee**
- M. Boge		PSI
- J. Byrd		LBL
- J.R. Chen		Taiwan
- Y. Dabin		ESRF
- R. Hettel (Chair)	SLAC
- J. Jacob		ESRF
- J. Maser		APS
- R. Mueller	BESSY-II
- D. Shu		APS
- J. Sidarous	APS
- O. Singh		APS
- C. Steier		LBL

- http://www.bnl.gov/nsls2/workshops/Stability_Wshop_4-18-07.asp

## Electron Beam Sizes and Divergences for Selected NSLS-II Sources

## User Requirements

-   In most 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
- Review CommitteeBeam size stability also critical
-   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
- A “one size fits all” approach may not work for everyone, and tighter stability for a particular experimental program may require local measures

## Review Committee: Comments on Stability Solutions

- May need mechanical motion/position survey sensors at critical points from source to experiment and in accelerator; ability to include sensors in feedback
- Need to mechanically model critical beam line set-ups (supports, modes, etc)
- Find a way to monitor I0 just upstream of sample for all critical systems – normalization on sample-by-sample – but there are limits to quality of I0 detector
- Recommend phase space acceptance analysis projected to source phase space
- Use “telescope technology” to maintain relative stability of components (e.g. D. Shu)
- Need instrumentation infrastructure to verify accelerator vs. beam line stability issues and to help achieve stability goals
- Committee strongly supports beam designer’s goal to consider source and beam line stability “holistically”

## Stability Dependent on Conventional Facilities

- Stability goals driven by conventional facility design
- Stability of storage ring tunnel floor
- Vibration < 25 nm PSD from 4-50hz
- Stability of experimental floor
- Vibration level of < 25 nm PSD from 4-50hz for general floor area
- Vibration level for 1 nm resolution beam lines requires further definition but appears achievable with proper correlation
- Thermal stability of storage ring tunnel environment
- +/- 0.1o C  for 1 hour time constant
- Thermal stability of experimental floor
- +/- 0.5o C  for 1 hour time constant
- Review Committee:  Accelerator group must confirm that there is no significant thermal
- load variation during operation

## RMS (2 – 50 Hz): ~ 20 nm

## Ring Building Section

- Ratchet or
- Shield Wall

- Electrical Mezzanine

- Bldg structure Isolated from tunnel and experimental Floor

- Earth Shield Berm

- Experimental Floor

- Access Corridor

- Tunnel Floor

- “Monolithic Joint”

- Isolation Joint

- Isolation Joint or Void Space

- Tunnel Roof

- Isolated Pier for Column

- Isolated Grade Beam

## Tunnel Design - Ring Building Section

**Non-vibrating Equipment**

**Non-vibrating Equipment**

- Need to assure that vibration mitigation measures are carried out at Ring building interfaces with other structures and where systems enter building or tunnel

**Section at Lab Office Building and Service Building**

**Rotating Machinery**

**Rotating Machinery**

**Distance determined by modeling & empirical analysis**

## equipment as far away from SR as practically feasible. 

- Revisit the project design parameters regarding the infield service
- buildings. From vibration perspective, it may be better to locate
- them in the outfield (maybe incorporated into LOBs)   A discussion
- took place, and CFG will pursue that approach from cost/benefit
- approach.  In either case, even with the analysis resulting in
- acceptable outcome, an attempt should be made to locate rotating
- equipment as far away from SR as practically feasible.

## Mode Shapes of the Girder-Magnets Assembly

- Review Committee: Resonant frequencies often found to be 1.5-2 times
- lower than calculation.  Must prototype magnet-girder assembly

##                Location of BPMs and Correctors

- BPMs mounted on vacuum chambers: ± 0.2 μm (vertical)
- User BPMs (upstream and downstream of IDs) : ± 0.1 μm (vertical)
- X-BPMs: ± *0.1 **μ**m (vertical)*

- There are also fast correctors in straights at both ends of ID

- Review Committee:  Include feed-forward on
- skew quads to correct for ID changes

## Orbit Feedback

-  Orbit motion can be reduced by feedback which centers the beam in
- RF beam position monitors (BPMs) situated around the ring.
-  Essential that motion of the BPMs be less than the tolerance to which
- we wish to hold electron beam stable.
-  It is also necessary for the power supplies of the correction dipoles to
- have high resolution and low noise (~1ppm).
-  Bandwidth of the feedback system will be ~100 Hz.
-  X-ray BPMs on the user beamlines can be used to supplement the RF BPMS
- located around the storage ring

## Processing Units

- Utilized at Elettra, NSSRC, Diamond, Soleil, PLS
- Fast acquisition 10 kHz sampling rate, 2 kHz BW
- Slow acquisition: 10 Hz sampling rate, ~4 Hz BW
- 32 bit data
- RMS uncertainty (for 10 mm scale in 1 kHz BW) -90.5dB →0.3μm @ Pin = -20 dBm
- 8-hour stability (ΔT=±1°C) -80dB→1μm
- Temperature drift (T=10–35°C) -94dB/°C → 0.2μm/°C
- MTBF ≥ 100,000 hours
- For 270 units failure rate will be one unit in 17 days

- Review committee:  NSLS-II needs about factor of 2
- better performance than available today
-       noise, stability <0.15micron
- Technology improving, in a few years will be achievable

## Photon Beam Position Monitors

- Will provide information on photon beam position and angle (to account for errors in the wiggler field)
- Use of photon BPMs will allow sub-microradian pointing stability
- Contamination with dipole radiation can be of less concern due to reduced magnetic field in the bending magnet
- Can be used for orbit feedback and/or control of users optics
- 2D translation stages will precisely locate the photon BPM
- Should withstand high power density

- Review Committee:
- X-ray BPMs will be essential for NSLS-II
- Give serious consideration to Decker distortion
- Hold Workshop on X-Ray BPM Development

## Conclusion

- Maintaining orbit motion below 10% of source size
- and divergence is believed to be achievable and
- satisfies most user requirements