SLS D igital B eam P osition M onitoring S ystem

Patrick Pollet, Thomas Schilcher Care-N3-ABE Networking / June 2004

SLS Digital BPM SystemSLSPAUL SCHERRER INSTITUT

SLS Digital Beam Position Monitoring System

• System overview

• System elements

• Run modes

• Problems and solutions?

• Future developements

Care-N3-ABE Networking Workshop

June 2004

Outlines



BPMs in SLS Accelerators

- linac / linac to booster transfer line: 6 BPMs- booster: 54 BPMs- tune BPM in booster: 1 BPM- booster to storage ring transfer line: 3 BPMs- storage ring: 72 BPMs- tune BPM in storage ring: 1 BPM

Total Number of BPMs: 137 BPMs

Strategy

Use one type of BPM electronics for all sections of the machineDigital BPM System with reprogrammable digital down converters



Development Collaboration between

ELETTRA (Trieste, Italy)SLSR. Uršič (Consultant)

Concept • 4 channel system• modular system (VME technology )

- RF front end (down conversion to IF)

- Quad Digital Receiver (digital down conversion to base band)

- Digital Signal Processing (position calculation)• pilot signal in all four channels → calibration of electronics by individual gain settings



Development Milestones

• June 1998: Concept and proposal.• October 1998: Start evaluation of commercials digital receiver

systems and in parallel start developement studies for a custom solution.

• January 1999: Decision for custom developement.• July 1999: First prototype works @ Elettra, proof of

principle.• June 2000: SLS linac & transfer lines commissioning with

DBPM serie 1.0.• August 2000: SLS booster commissionning with DPBM serie 1.1.• December 2000: SLS Storage ring commissionning with DBPM

serie 1.2.

No significant hardware changes made since january 2001 !!!





Hardware modularity

RF Frontend Quad Digital Receiver DSP





Operating modes

• Turn by Turn / pulsed mode / tune mode– Positions of 8192 turns available after trigger event from timing system,

batch processing done by DSP.

• Closed orbit / feedback mode– DDC samples available at DDC output rate, real time position processing

done by DSP.

– Position average and RMS calculation for operators display and archiving.

• Ramp mode (booster mode)– Similar to turn by turn mode, with reduced data rate (higher decimation)

in order to provide beam position through-out the acceleration cycle.



Resolution

Mode DDC Output Rate [kHz]

Passband BW [kHz]

Resolution [m]

Turn-by-turn 1041 416 < 20

Ramp 250ms 32 11 3

Closed orbit / feedback 4 0.2 0.8

gain ranges(80% filling pattern)



Stability

<2 m *)

<2.5 m *)

*) hall temperature (technical gallery) regulated < ±1 ºC (spec)

long term stability measurement in technical gallery(with RF signal generator):



Stability (2): Lab Measurements

• due to hot summer 2003: “relaxed” setting in cooling system • air conditioning system in lab shows a strong 2 ºC swing now• “small” temperature reservoir in lab compared to technical gallery hall

upgrade plans: measure air temperature at BPM crates and correct for systematic temperature effects



Beam Current Dependency

• top-up operation minimal influence of beam current dependency • orbit correction only for Ibeam > 20 mA



Booster Ramp

Booster current: ~0.5 mA Booster current: ~5 A

Intensity

horizontalposition

verticalposition

injection booster extr. injection



Numerical Controlled Oscillator Frequency Tracking

• main RF frequency changes (→ orbit correction)• fixed LO frequencies in RF front ends (DBPM1) • DBPM closed orbit mode → 200 Hz passband bandwidth

track main RF frequency on DBPM by reprogrammingthe digital receivers (automated in EPICS control system)



Local Oscillator Frequency drifts in RF Front Ends

• drift of LO freq. correlated with techn. gallery air temperature• small passband bandwidth of BPM in closed orbit mode require weekly measurements of LO frequencies

DBPM system will profit from plannedcooling system upgrades



Systematic Effects

Sector Layout:

• slow feedback on X-BPM changes reference for fast orbit feedback• photon beam position kept constant with asymmetric bump

observation:• slow drift related to temperature changes of DBPM RF front end• 40-50 min period due to filling pattern dependence of DBPM



Systematic Effects (cont’d)

• implementation of filling pattern feedback compensates 40-50 min period• remaining: temperature dependence of RF front end

upgrade plans: temperature calibration with lookup tables



Conclusion

• DBPM was available on time.

• System fulfills the specifications

• System flexibility contributed to the success of the SLS commissioning

• Excellent orbit reproducibility

• Availability of the DBPM system is vital for the SLS operation

• Systematic effects in the order of the system resolution , mainly due to the analog part of the system (RF – Frontend)

• Still plenty of room for improvements– Higher ADC resolution

– Local oscillator frequency tracking

– Temperature compensation by software



The future …

• VPC Generic PMC carrier Board.

Documents

SLS D igital B eam P osition M onitoring S ystem