# Presentation: 419786

## SPEAR 3 Beam Stability and Stabilization

***R. Hettel***
***NSLS-II Stability Workshop***
***April 18-20, 2007***

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## Acknowledgments

- Primary developers:
- 	T. Straumann:  real-time processing, system architecture and communication
- 	A. Terebilo:  accelerator physics, system operation development
- 	J. Sebek:  turn-turn BPM processing
- 	D. Martin:  BPM systems
- 	F. Rafael, G. Leyh:  corrector power supply development
-  Main contributors:
- 	S. Allison
- 	J. Corbett
- 	R. Hettel
- 	E. Medvedko
- 	G. Portmann
- 	T. Rabedeau
- 	J. Safranek
- 	C. Wermelskirchen
- 	E. Daly, N. Kurita, J Langton, A. Ringwall, J. Tanabe (SPEAR 3 mech des)
-  	EDM electrical support group

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## Stability Requirements

- Stability requirements for small beams may be relaxed if beam size at experiment is limited by beam line optics (e.g. mirror slope error, point-spread function, etc.)
- Stability requirements depend on time interval

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## Stability Time Scales

**	****	**Orbit disturbances blow up effective beam **** and  ****, reduce intensity at 	experiment, but do not add noise
-     	For / = cm/o < ~10%:  	******y****cm****(rms) < ~0.3 ********y****	********y********cm****(rms) < ~0.3 ********y'**
**	****	****	****Note:  can have frequency aliasing if don't obey Nyquist....**
** ****Disturbance periods**** ******** experiment integration time:**
- 		Orbit disturbances add noise to experiment
-  	   	For / = ~2** **cm/o <~10%: 	******y****cm****(rms) < 0.05 ********y ****     ****	********y********cm****(rms) < 0.05 ********y' **
** ****Disturbance periods >> experiment time ****(day(s) or more):**
- 		Realigning experiment apparatus is a possibility
** ****Sudden beam jumps or spikes can be bad even if rms remains low**
- 		Peak amplitudes can be **> x5** rms level
** ****Most demanding stability requirements:**** **
- 	 Orbit disturbance frequencies approximately bounded at high end by data
- 	 sampling rate and a low end by data integration and scan times
- 				****** ****noise not filtered out**

***Stability Time Scales***

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## SPEAR 3 Mechanical Design

- Short stiff girders and magnet supports (>20 Hz)
- Chamber constrained vertically and horizontally at BPMs
- Invar supports for key BPMs (~3 m/oC)
- 18”-24” concrete floor
- Tunnel temp stable to ± ~1oC/day

***SPEAR 3 Mechanical Design***

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## SPEAR 3 Electrical Design – Power Supplies

- Dipole:
- stability:  50ppm (or better);  3 ppm/OC diurnal
- ripple:  0.2% pk-pk of full output voltage ripple (DC-1 MHz)
- chopper freq:  20 kHz
- Quadrupole and Sextupole:
- stability:  100 ppm;  6 ppm/OC diurnal
- ripple:  0.2% pk-pk of full output voltage ripple (DC-1 MHz)
- chopper freq:  40 kHz
- Correctors:
- stability: 500ppm;  30ppm/OC diurnal
- noise:  17 ENOB,  0.001 Hz – 4 kHz
- chopper freq:  40-60 kHz
- DAC resolution/update rate:  24-bit (>18 bit for ± 1 mrad corrector) / 4 kHz
- bandwidth:  ~1 kHz
- RF HVPS (90 kV)
- stability:  < 0.1% FS
- ripple:  < 1% pk-pk (<0.2% rms) above 60 kV
**Power supply stability requirements depend on ring design**

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## SPEAR 3 BPMs and Processors

- Echotek Digital Receivers
- parallel I/Q processing of down-converted button signals (8 chan/module = 2 BPMs)
- IF = 16.65 MHz (13 frev)
- sample freq = 64.02 MHz (50 frev)
- provision for simultaneous processing of test tone calibration signal
- ~0.3-mm res for injected beam (0.03 mA)
- 2-μm turn-turn resolution at >~10 mA
- nanometer resolution in 100 Hz BW

**BPM processor temperature regulated to < ****± 0.4****o****C pk**

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## SPEAR 3 BPM Processing and Fast Orbit Feedback

- Note:
- SPEAR 3 was commissioned and operated until recently using slow orbit feedback running on MATLAB
- (Corbett, Portmann)

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## SPEAR 3 Fast Orbit Feedback

**Dynamic orbit correction**

**· ****4 kHz update****	****	**** ****· ****latency (pipeline delay + deadtime) = 0.7-1 ms**
**·**** RTEMS realtime OS****	**** ****·**** EPICS control and monitoring****	**** **

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## SPEAR 3 Orbit Motion

**Distributed weak perturbations:**
- Uncorrelated small (~1μm) vibrations of individual magnets and supports cause orbit motion is concentrated in the modes with large singular values and frequency range 1-200Hz.

***SPEAR 3 Orbit Motion***

**Localized strong perturbations:**
- Gap or phase changes in undulators occur on a ~1s time scale. **Local feed-forward correction was implemented using ID trim coils,  adjacent quads (tune) and skew quads (coupling).** Cause global orbit distortions of a few m rms without FOFB.
- Vehicle traffic on the overpass bridge causes slow (~1s) motion of the floor and microns of orbit instability.
- RF power supply ripple inducing synchrotron oscillations

- FOFB correction of ID gap changes and bridge traffic effects. Based on 2 hours of averaged (0.5s)

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## SPEAR 3 Phase Oscillations and RF HVPS Ripple

- Phase oscillations measured with turn-turn BPM:
- 3.6 mrad rms = ~1.2 ps rms
- bunch length = 17 ps rms
- Working to implement mode-0 feedback

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## SPEAR 3 Fast Orbit Feedback – Bandwidth

- Fast orbit feedback in operation since June, 2006. Integrator loop gains set conservatively for start of operations. Studies ongoing to find optimal tuning.

***SPEAR 3 Fast Orbit Feedback – Bandwidth***

**Limiting factors:**
- Corrector field penetration in vac chamber
- 	(copper with CuNi inlays for bandwidth to ~200 Hz)
- Time delay - 3 clock cycles

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## SPEAR 3 Fast Orbit Feedback - Eigenmodes

***SPEAR 3 Fast Orbit Feedback - Eigenmodes***

- Uncorrected orbit error from ‘real’ sources
- ‘Spilling’ from other modes accumulating in corrector magnets

**Eigenmode spectrum**

- Ignoring even a single eigenmode results in gradual buildup of error:

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## SPEAR 3 Fast Orbit Feedback – Eigenmodes – cont.

- When modal Ki and Kp gains are tuned to reduce motion seen by in-loop electron BPMs, out-of-loop photon BPMs suffer

***SPEAR 3 Fast Orbit Feedback – Eigenmodes – cont.***

- Feedback gain/BW is reduced for higher eigenmodes to reduce orbit noise but to still allow modal “mop-up”

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## SPEAR 3 Photon Monitor Feedback

- “Beam Line Dynamic Steering” (BLDS) has been introduced:
- Response of photon BPMs to a local angle bump in 2  electron BPMs is measured offline
- Photon BPM data averaged for 1 min for each beamline
- Once a minute apply calculated correction to the electron BPM FOFB target.
- BLDS is not perfect:  1 degree of freedom does not exactly correct source motion; combination of position and angle could be tuned to maximize performance
- FOFB architecture allows to bring in pBPM data at
- 	4 kHz rate and response matrix can be extended to include pBPMs
- Practical issue for including pBPMs in response matrix:  need to reconfigure matrix (add/remove rows) on the fly when beam lines open and close

***SPEAR 3 Photon Monitor Feedback***

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## Beam Line Mirror FeedbackT. Rabedeau, SSRL

- error signal obtained from position sensitive detector near beam focus
- error signal used to control piezo high voltage
- piezo provides mirror fine pitch control with typical full range of motion +/- 30 rad or  +/- 0.6mm or more focus motion.

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## SPEAR 3 Fast Orbit Feedback – Operator Interface 

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## RF Frequency Feedback

***RF Frequency Feedback***

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## SPEAR Floor Motion 

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007

## SPEAR 3 Orbit Stability and Feedback – Future Development 

- Plan to characterize diurnal instability of floor, ring and beam line components using high resolution sensors (HLS, etc).  This information might be included in feedback/feedforward
- Studying to potential improvement gained by adding a roof over SPEAR (and possibly subsequent air conditioning)
- Beam line dynamic steering to be integrated into FOFB
- Better photon monitors are being developed
- More parallel BPM processors will be added (will pay attention to new SLS/DESY design)
- Plan to continue developing feedback to incorporate ring and beam line sensors and actuators

- R. Hettel            SPEAR 3 Orbit Stability and Stabilization            NSLS-II Stability Workshop           April 18-20, 2007