# Presentation: 297143

**Beam Stability Overview**
- NSLS-II CFAC Meeting
- May 8, 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

## 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**

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

- Revisit the project design parameters regarding the infield service
- buildings. From vibration prospective, 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
- equipments 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

##   Tolerances on Magnets’ Motion

| Tolerance Limits | ΔX RMS Quads | ΔY RMS Quads |
| --- | --- | --- |
| Random  magnet motion | < 0.15 μm | < 0.025 μm |
| Random girder motion | <0.6 μm | < 0.07 μm |

-   Tolerances on Magnets’ Motion

-   ΔX Tolerance limits are easily achievable.
-   ΔY Tolerance limits:
- Thermal: relative thermal displacement between magnets on the same girder:  < 0.025 μm. (*RMS thermal displacement of girders over a pentant (6 cells) < 0.1 **μm*)
- Vibration: no magnification of ambient floor motion up to 50 Hz.
-   *Below 4 Hz girder motions are highly correlated*
*  **Above 50 Hz the rms floor motion is < 0.001 **μ**m*

##                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

## Support of Beam Position Monitors

- BPMs on the vacuum chambers need to be located near the fixed or flexible supports.
- Thermally insulated, sand-filled steel stands will meet the mechanical stability requirements for the special BPMs.

- Review Committee:  Temperature of insulated supports can change significantly
- over long shutdowns.  Must include method to quickly bring supports to proper
- temperature at beginning of new run.

## 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