1. AB-RF-FB LLRF Developments at CERN Historic Overview, Highlights, Future Challenges Flemming Pedersen

2. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 2 Outline Overview of RF aspects of current and future CERN Accelerators Evolution of LLRF technologies: Analog, Semi- digital, Master and Slave DDS, All-digital. Coping with beam loading: Direct RF feedback, one-turn delay feedback Developments by accelerator: PSB, PS, AD, LEIR, SPS, LHC. History and challenges ahead What has been left out?

3. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 3 CERN Accelerators 3.5 to 0.1 GeV/c, antiprotons 0.17–1.6, 9.5 MHz 4.2 to 72 MeV/n, ions 0.7-4.7 MHz 72 MeV/n to 5.9 GeV/n, ions 1.4 to 26 GeV, protons 3-10, 13/20, 40, 80 MHz 5.9 to 177 GeV/n, ions 26 to 450 GeV, protons 200, 800 MHz 177 GeV/n to 2.76 TeV/n 450 GeV to 7 TeV, protons 400, [ 200 ] MHz Electrons 3, 30 GHz 50 MeV to 1.4 GeV, protons 0.6–1.7, 1.2 – 3.4, 6 – 17 MHz

4. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 4 Outline Overview of RF aspects of current and future CERN Accelerators Evolution of LLRF technologies: Analog, Semi- digital, Master and Slave DDS, All-digital. Coping with beam loading: Direct RF feedback, one-turn delay feedback Developments by accelerator: PSB, PS, AD, LEIR, SPS, LHC. History and challenges ahead What has been left out?

5. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 5 Evolution of LLRF Technologies 1 Generic, typical analog LLRF (Beam Control) for synchrotron Analog loop signal processing: beam phase, radial and synchro loops Still used in some accelerators at CERN like the SPS Used in PSB, PS, AAC (pre-AD) until 1994 - 1997

6. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 6 Evolution of LLRF Technologies 2 Semi-digital LLRF systems from 1994 in PSB, PS and AD. Initial system in PS for pbar production beam, 1987 Analog superheterodyne RF receivers and phase discriminators Analog loop signal processing: beam phase, radial and synchro loops RF drive signal generated by DDS (Direct Digital Synthesizer) Sum of loop corrections digitized and added digitally to frequency program Digital control of harmonic number, digital frequency corrections Digital frequency program, look up table Later ~1997, RF + 10.7 MHz LO were made with DDS with digital offset

7. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 7 Evolution of LLRF Technologies 3 Master and Slave DDS technology useful for generating several revolution harmonics changing dynamically during cycle (Garoby, 1987, PS -AA) Needed for RF gymnastics: batch compression, bunch splitting, bunch merging PS Upgrade in 1999 PS-AD M-DDS generates high harmonic (h =128), which clocks the S-DDS (Slave DDS) S-DDS frequency word (f SDDS = h = 7 to 21) and phase offset programmed digitally. f out = f MDDS * f SDDS M-DDS clock ‘tagged’ with revolution marker to control relative phase of all S-DDS One S-DDS per cavity allows control of cavity phase according to azimuth and harmonic M-DDSS-DDS Analog feedback loops

8. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 8 Evolution of LLRF Technologies 4 All-digital LLRF Systems Filtering, signal and feedback loop processing are done digitally Mixture of ASICs, FPGA, and DSP signal processing At CERN: LEIR LLRF (Angoletta), LHC LLRF (Baudrenghien), Linac LLRF (Rohlev). Talks Tuesday morning 8:30 – 09:30 FPGA ASIC DSP

9. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 9 Outline Overview of RF aspects of current and future CERN Accelerators Evolution of LLRF technologies: Analog, Semi- digital, Master and Slave DDS, All-digital. Coping with beam loading: Direct RF feedback, one-turn delay feedback Developments by accelerator: PSB, PS, AD, LEIR, SPS, LHC. History and challenges ahead What has been left out?

10. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 10 Coping with Beam Loading 1 Tuning loop keeps cavity in tune for varying frequency (and beam loading). Actuator: Tuner AVC loop keeps cavity voltage to set value. Actuator: RF drive level Beam phase loop (actuator: RF drive phase) damps coherent synchrotron oscillations from 1) injection errors (energy, phase), 2) bending magnet noise, 3) frequency synthesizer phase noise Coarse frequency program derived from magnetic field Loops independent at low intensities

11. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 11 Coping with Beam Loading 2 Linearise propagation of small modulations (phase and amplitude) of main vectors: Cavity voltage to beam current: Beam Dynamics Cavity voltage to generator current: RF feedback loops Total current (sum of generator and beam currents) to cavity voltage: Cavity impedance

12. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 12 Coping with Beam Loading 3 At high intensity, vector geometry and detuned cavity leads to significant cross coupling between loops, which cause instability With no feedback present, the stability of beam cavity interaction can be solved analytically: Robinson criterion

13. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 13 Coping with Beam Loading 4 Most effective cure for beam loading is ‘Direct RF Feedback’ A fast loop (short delay!) is formed around the cavity and its power amplifier with loop gain H The effective Q value of the cavity as seen by the beam and the feedback loops is lowered by a factor (1+H) : Q* =Q/(1+H); R 0 * = R 0 /(1+H) This is achieved without increasing the power lost in R 0 (shunt impedance)

14. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 14 Coping with Beam Loading 5 ‘ Direct RF Feedback’ is very effective in –raising the high current limit of the Robinson criterion –reducing the harmful cross coupling between AVC, tuning and beam phase loops –Reducing growth rates of longitudinal coupled bunch modes driven by the fundamental mode The maximum achievable gain is limited by propagation delay around this loop Recent RF systems designed for high beam loading therefore place power amplifiers in close proximity to the cavity and uses power amplifiers with short delay CERN History: ISR( 1970?), AA(1980), PSB C16 (1982), PSB C08 (1988), PS C10 (1989), PSB C02/C04 (1997), PS C40/C80 (1997), AD (1997), LHC C400 (2005),…

15. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 15 Coping with Beam Loading 6 Further RF cavity impedance reduction near revolution harmonics can be achieved with periodic comb filters and one-turn delays. Not limited by loop delay, beam needs low impedance near revolution harmonics. Comb filter suited for digital implementation. CERN history: SPS (Boussard 1983), PS (Garoby 1990), SPS Upgrade (Baudrenghien 2000), LHC (Baudrenghien 2006) SPS block diagramPS Impedance versus frequency

16. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 16 Outline Overview of RF aspects of current and future CERN Accelerators Evolution of LLRF technologies: Analog, Semi- digital, Master and Slave DDS, All-digital. Coping with beam loading: Direct RF feedback, one-turn delay feedback Developments by accelerator: PSB, PS, AD, LEIR, SPS, LHC. History and challenges ahead What has been left out?

17. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 17 PSB Evolution Highlights 1 RF systems: –C02 (0.6 – 1.7 MHz) - main –C04 (1.2 – 3.4 MHz) - bunching factor, shaping, splitting –C16 (6 – 17 MHz) - controlled emittance blow-up Principal beams: –protons for PS/SPS fixed target –protons for PS/East Hall, –protons for PS/nTOF, –protons for PS/SPS/LHC, –protons for PS/AD –(ions for PS/SPS fixed target) –protons for Isolde

18. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 18 PSB Evolution Highlights 2 C08 Era (3 – 8 MHz, h = 5, 1972 – 1997) –Damping of all coupled bunch modes, dipolar & quadrupolar (1977) –Addition of C16 (h = 10, 1981) with direct RF feedback to improve bunching factor at injection (dual harmonic RF, transverse space charge limit) –Retrofitting direct RF feedback for C08 (1988), cures beam loading instabilities at low voltage (iso-adiabatic capture) –Lead ion acceleration using new modular semi-digital LLRF (DFP, DLP, DAU, DDS) and harmonic number change (1994) C02 Era (0.6 – 1.7 MHz, 1998 - ??) –Deploying new modular semi-digital LLRF (DFP, DLP, DAU, DDS) for all proton and fixed target ion beams. Bunch splitting, controlled blow-up with C16 (1998) –Successful MD test of all-digital FPGA and DSP based digital beam control (CERN/BNL collaboration, 2003 – 2004): digital phase and radial loops, digital radial normalisation, DSP based frequency program

19. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 19 PS Evolution Highlights 1 RF systems: –C10 (2.8 – 10 MHz)- main –C20 (13/20 MHz)- LHC bunch splitting –C40 (40 MHz)- LHC bunch splitting –C80 (80 MHz)- LHC bunch compression –C200 (200 MHz)- blow-up and SPS pre-bunching Principal beams: –protons for SPS fixed target –protons for East Hall –protons for nTOF –protons for SPS/LHC –protons for AD –[ ions for SPS fixed target ] –ions for SPS/LHC, 2006

20. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 20 PS Evolution Highlights 2 Semi-digital LLRF used for (M-DDS & S-DDS configuration) used for antiproton production beam (Garoby 1987) Direct RF feedback on all C10 cavities to ensure beam loading stability for low voltage operation, bunch merging, batch compression (Garoby 1988) One-turn delay added to reduce beam loading transients (Garoby 1991)

21. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 21 PS Evolution Highlights 3 Semi-digital modular LLRF systems gradually replacing old analog systems for many beams 1994 – 1996 (h = 20) New LHC era harmonic numbers from 1998: h = 8, 16, 7, 14, 21, 84 New LHC related RF systems: C40 and C80 (1998), C20 (2004). Upgrade of AD production beam for new harmonic numbers, 61 MHz (h = 128) tagged master clock, new FPGA based S- DDS (called MHS, Garoby et al. 1999). h = 8, 10, 12, 14, 16, 18, 20

22. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 22 PS Evolution Highlights 4 Replacing debunching / rebunching for LHC with successive bunch splittings using new M-DDS / S-DDS hardware (Garoby et al. 2000) New high frequency DDS for M-DDS clock generation (AD 1 GHz chip). Provide alternative bunch spacing for LHC (75 ns in stead of 25 ns) Mode by mode longitudinal feedback installed for few modes for LHC beam

23. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 23 PS Evolution Highlights 5 Being built: Beam control (LLRF) for I-LHC beam (commission 2006). Using M-DDS / S-DDS hardware already used for LHC and AD beams.

24. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 24 LEIR LLRF Project RF systems: –C05 (0.6 – 4.7 MHz)- main (finemet, no tuner) Principal beam: –ions for PS/SPS/LHC All-digital DSP and FPGA LLRF system developed in collaboration with BNL. Large software effort required to provide an acceptable environment for RF experts and operation. Realistic first tests in LEIR: February 2006 See talk by Maria Elena ANGOLETTA Tuesday morning

25. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 25 AD Evolution Highlights RF systems: –C10 (9.5 MHz)- bunch rotation at injection –C2 (0.174, 0.5 – 1.6 MHz)- deceleration, bunching for extraction Principal beam: –cooled antiprotons for AD experimental area (since 2000) Main challenges: –very low intensity N = 2 10 7. Several ultra low noise longitudinal pick-ups built: T noise = 0.3 °K –RF voltage dynamic range for C02: 0.1 Vp to 3 kVp – 90 dB! RF system is using modular semi-digital LLRF (DFP, DLP, DAU, DDS, anno 1994) like PSB and PS DSP based system using commercial DSP board (Pentek) and DDC’s (Digital Down Converter) for beam diagnostics: intensity and longitudinal Schottky.

26. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 26 SPS Evolution Highlights 1 RF systems: –C200 TW (200 MHz)- main, tetrode driven –C800 TW (800 MHz)- Landau damping, klystron driven Principal beams: –protons for fixed target –Protons for CNGS (Cern Neutrinos for Gran Sasso, 2006) –protons for LHC (2008), –ions for LHC (2007)

27. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 27 SPS Evolution Highlights 2 Major effort to reduce phase noise of RF system and phase pick-up for pbar-p collider operation (1980 – 1991): RF lifetime > 120 hours. The worlds first bunched beam hadron collider!! Several very high impedance RF systems (100 MHz SW, 200 MHz SW, 350 MHz S/C, 400 MHz S/C) during LEP era (1989 – 2000), all with direct RF feedback systems. One-turn delay comb filter cavity feedback pioneered by Daniel Boussard in 1983, several up-grades since then Fixed frequency acceleration of lead ions Pb +82, f acc = h acc * f rev, where h acc is continuously swept through non-interg values to keep f acc constant (analog system, 1994 - 2004)

28. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 28 SPS Evolution Highlights 3 Major upgrade of LLRF done to achieve nominal LHC parameters: –High instantaneous beam current in LHC batches, beam gap transients –One-turn delay feedback upgrade, –Feed-forward system to further reduce beam loading transients –Longitudinal coupled bunch system for low order modes for damping of batch by batch injection errors (phase, momentum) –DSP based frequency program used to accelerate with synchro loop reference in stead of radial loop reference (deterministic cycle phase advance). I-LHC beam LLRF being developed –Fixed frequency acceleration, but with synchronized bucket to bucket transfer PS/SPS and SPS/LHC. –Will most likely be a digital system with M-DDS and S-DDS architecture –Analog option also explored

29. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 29 LHC LLRF Project RF systems: –C400 S/C (400 MHz)- main, superconducting, klystron driven –[ C200 SW (200 MHz) ]- more bucket area for injection errors, option Principal beams: –Proton pilot beams (2007) –Colliding protons (2007), –Colliding Pb +82 ions for LHC (2008) Challenges and technology –All-digital cavity feedback system and beam control system based on DSP’s and FPGA’s. See Philippe Baudrenghien’s talk Tuesday morning. –Aggressive cavity feedback to reduce fundamental mode impedance and RF noise generated by klystron –The worlds first bunched beam hadron collider with klystron driven RF and superconding cavities

30. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 30 Outline Overview of RF aspects of current and future CERN Accelerators Evolution of LLRF technologies: Analog, Semi- digital, Master and Slave DDS, All-digital. Coping with beam loading: Direct RF feedback, one-turn delay feedback Developments by accelerator: PSB, PS, AD, LEIR, SPS, LHC. History and challenges ahead What has been left out?

31. AB-RF-FB 10 October 2005LLRF Developments at CERNSlide 31 What has been left out? CTF3 activities Linac 2 and Linac 3 SPL and Linac 4 activities AD stochastic cooling PSB, LEIR, PS, SPS and LHC transverse damper systems LEP LLRF (decommissioned in 2000) My apologies