Closed Orbit Feedback and Tune Measurement: Status of realization at SIS18

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. 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. Tune at fixed time Maximum Position Variation 5 mm horizontal horizontal vertical vertical 2 mm Tune versus time Working Diagram vertical horizontal Qy  0.02 Qx  0.015 Tune Determination at SIS18: Online Display of Results 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. Turns x 1000 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) Vertical Beam parameter: 6·109Ar18+, 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: 6·109Ar18+, 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.