1. Closed Orbit Feedback and Tune Measurement: Status of realization at SIS18
P. Forck, P. Kowina, M. Schwickert, R. Singh
for the GSI Beam Diagnostics Group and DELTA (TU-Dortmund)
5th FAIR Machine Advisory Committee Meeting
May 9th/10th 2011

2. Overview Outline Status of Closed Orbit Feedback for SIS18
performed in collaboration with DELTA (TU-Dortmund) & COSY (FZ-Jülich)
Status of Tune Measurement System at SIS18
The BPM signals are digitized by the I-Tech LIBERA Digitalization Units
SIS18 serves as a test installation for FAIR:
Validation the general design consideration
Preparation of final realization for FAIR
Gain of operational experiences

3. Digital BPM Readout: Digitalization and Evaluation
System Description:
Digitalization of BPM signals at LIBERA
with 14 bit and 125 MS/s ADC
Individual bunch position evaluation
with FPGA (presently Virtex-II Pro)
Monitoring: data transfer to PC for
either further down conversion for CO
or bunch by bunch evaluation e.g. tune
Planned Closed Orbit Feedback (COFB):
Digital Down Conversion on LIBERA,
Real-time transfer to concentrator
via Diamond Com. Controller (DCC)
Advantage: Single bunch position
for flexible further processing
For FAIR: Comparable successor system
Scalable software realized at SIS18
Integration & Δ/ delivers bunch position
I-Tech LIBERA Hadron

4. Closed Orbit Feedback at SIS18: Hardware for BPM Data
System Description COFB:
Position data reduction on LIBERA
10 kHz input to ‘BPM Extender’
Input of time-dependent (triplett  duplett)
Orbit Response Matrix from Control System
SVD Algorithm for correction calculation
Digital output to corrector power converter
with  1kHz (to be tested)
Beam
DCC over SFP
Corrector
Hardware:
Design & test
by TU-Dortmund

5. designed by GSI EET Group
Closed Orbit Feedback at SIS18: Hardware for Power Converter
Multi Function Unit
designed by GSI EET Group
System Description PS control:
Multi Function Unit (MFU)
as standard for all PS at FAIR
(10 kHz digital bandwidth, 32 bit DAC)
Input from BPM-Extender via USB
 Quasi real-time communication
for corrector value, bandwidth > 1 kHz
Installation of MFU-control for SIS18
correctors required (foreseen end 2011)
First tests for communication performed
SIS18: 12 BPMs and 12 hor. & vert. correctors
SIS100: 84 BPMs and 84 hor. & vert. correctors

6. Closed Orbit Feedback at SIS18: Status
General: System design according to Synchrotron Light Source standards
Implementation at DELTA (TU-Dortmund): summer 2011
Readout of 54 BPMs and control of 20 hor. & vert. correctors
Reaction bandwidth: 0.3 to 1 kHz (projected)
About 1 year delay due to severe illness of PhD student at TU-Dortmund !
Implementation at SIS18: Foreseen in 2012
12 BPMs and 12 hor.& vert. correctors, projected reaction bandwidth 1 kHz
Ongoing: Input of time-dependent Orbit Response Matrix via Control System
Ongoing: Digital interface to power converter controller MFU
Design for SIS100:
84 BPMs will be installed and 84 correctors  data treatment can be scaled
Constant lattice  time-independent Orbit Response Matrix
Hierarchical scheme for CO stabilization:
1. Magnetic field control by reference dipole  correction of e.g. hysteresis
2. Feed-forward using position data for creation of new set-values
 correction of reproducible errors
3. Real-time feedback  residual, non-reproducible errors on 10 ms time scale

7. Tune Determination at SIS18: Hardware
The beam is excited to betatron oscillation
→ the beam position is measured each revolution (’turn-by-turn’)
→ Fourier Transformation gives the non-integer tune q.
Advantage of digital processing:
Digital bunch identification for turn-by-turn evaluation
Varying revolution frequency: Matched ‘filter’ due to individual bunch integration
 Precise determination of bunch position required for low excitation

8. Maximum Position Variation
Tune Determination at SIS18: Online Display of Results
Tune versus time
horizontal
vertical
Working Diagram
Tune at fixed time
Maximum Position Variation
Qy  0.02
Qx  0.015
2 mm
5 mm
Online display for
tune measurement:
Time resolution for plot:
4096 turns  20 – 4.5 ms
Features:
Minor emittance growth
but good signal-to-noise
Online display
Ready for users
DAQ in FESA
GUI according FAIR spec.
Ongoing:
Improvement of algorithm
Tune variation due to
triplett  duplett lattice
Beam parameter: Ar18+ acc. 11  300 MeV/u within 0.7 s

9. Tune Determination at SIS18: Exploration of Working Range
Condition for ‘Working Range’:
Sufficient signal strength & minor emittance growth
Orbit and tune for 3.5 W exciter power (50mW/Hz)
Turns x 1000
Vertical
Beam parameter: 6·109 Ar18+, 11  300 MeV/u within 0.4 s,
Measurement parameter: Vertical excitation only, 516 turn FFT

10. Tune Determination at SIS18: Exploration of Working Range
Condition for ‘Working Range’:
Sufficient signal strength & minor emittance growth
Result:
Measurement without significant emitance growth
Transverse profile by an Ionization Profile Monitor
Beam parameter: 6·109 Ar18+, 11  300 MeV/u within 0.4 s,
Measurement parameter: Vertical excitation only, 516 turn FFT

11. Conclusion Tune measurement system for SIS18:
‘Oversampling’ of bunches with 125 MSa/s > 20 · frf
One position value per bunch by integration  cuf-off low-frequency noise
Calculation of FFT  flexible time resolution e.g. 512 turns  1 ms
Resolution Δq << 0.01 i.e. better than specified
(spectrum broadening by tune spread contribution, to be investigated)
Working range determined, no significant transverse emittance growth or beam loss
Tests of ‘BBQ’ analog system: at SIS18 low-frequency noise is an issue
Tune measurement: Demonstrated for SIS18, system design suited for SIS100
Tune feedback: Detailed consideration not started (CO stabilization as precaution)
Possible solutions: Hardware comparable to COFB or ‘PLL tune tracking’
Closed Orbit Feedback:
Anticipated bandwidth: 1 kHz
Electronics realization comparable to Synchrotron Light Sources
Collaboration with TU-Dortmund  demonstration expected late 2011
FAIR: Comparable systems will be installed.