1. PSB DSP Based Low Level RF Operational Experience. April 2015 M.E. Angoletta, A. Blas, A. Butterworth, A. Findlay, S. Hancock, M. Jaussi, J.Molendijk, J. Sanchez Quesada, J. Simonin. 24/4/2015

2. Introduction The Initial Commissioning First Operational Beams Getting the C16 Blow-up Up Working Status End 2014 Start-up 2015 Longitudinal Beam Status Today What We Are Still Working On Conclusions

3. Initial Commissioning In coordination with OP, we organised a rota to have daily cover by the RF team for 7 days a week during 3 weeks, 9-23 rd June. Aim to commission the low level for each ring to allow the OP crew to continue the machine setting- up. 3 days to get low intensity (165E10) captured, accelerated with h=1 only, phase, radial & synchronisation loops closed for R3. Another 5 days to commission the basics noted above for the other 3 rings. Problems were identified and fixed on one ring while work could continue on other rings.

4. Initial Commissioning The second harmonic was then commissioned with low intensity taking another 7 days, with many issues solved. A further week spent solving the issues identified that were hindering pushing the intensity. After 3 weeks we had medium intensity (~300E10) and could work in single or double harmonic with the phase, radial and synchronisation loops closed, as we had planned. First beam request was an LHCINDIV type which requires h=1 plus C16 to provide the blow up to perform longitudinal shaving delivered 27 th June. LHCINDIV Tomogram 26/6 Phase jump R4

5. First Operational Beams EASTA&B were set up using h=1+2 plus C16 for blow up. The ISOLDE beams were set up using h=1+2 plus C16 for blow up, but the intensity was still very low. The AD user was set up using h=1+2 plus C16 for blow up, intensity was still low, it would take until late July to get the nominal 400E10. TOF was set up using h=1+2 plus C16 for blow up, and the intensity was slowly increasing with 590E10 by late July. By the end of July the intensity for ISOLDE was 600-650E10 per ring (nominal ~850E10 per ring). End of July R2 was the best ring, but with our best efforts (on all systems) we could still only achieve 800E10. Work started on SFTPRO for splitting. TOF 530E10 21/7 AD 4 bunches ejected 18/7 AD synchro 30/7

6. First Operational Beams Throughout August the work continued to achieve lower losses for the high intensity beams, but it was becoming evident that many of the losses were not due to the RF, but perhaps due to other systems such as the orbit or resonance compensation not yet being optimized. Although we had some samplers (with 1ms resolution) we were still lacking the OASIS signals required to debug the system, which left us rather blind unless using specialist tools. The bunch splitting for SFTPRO was set up and worked well by mid-August, but the h=2 synchronisation would require significant work to stabilize. It became obvious that there were some issues with the C16 blow-up that prevented it from working correctly, so investigations started. SFTPRO splitting 27/8 TOF 850E10 15/8

7. First Operational Beams September we achieved decent h=2 synchronisation for SFTPRO and up to 600E10 per ring extracted. The LHC25ns & LHC50ns beams were requested and produced quite easily after all that had been learnt from setting up the other users. SFTPRO split & sync’d 12/9 SFTPRO synchro 24/9 SFTPRO 8 bunches extracted 24/9

8. First Operational Beams The LHCPROBE (a longitudinally shaved beam) setting up started in October, and this was when some bugs in the C16 blow-up were identified and fixed. We now had the experience to be able to check the details of the blow-up processes and would have to work our way through the beams to get it to work as desired. LHCINDIV improved distribution 30/10 No Modulation Modulation LHCPROBE longitudinal shaving 27/10

9. Getting the C16 Blow-up Up Working By November we were in a stable situation and called upon S. Hancock to help us properly set up the C16 for longitudinal blow-up and shaving. Steve had already developed an improved method of longitudinal blow up & shaving for the LHCINDIV and LHCPROBE beams that was commissioned with the new HW, and once the C16 modulation was de-bugged this worked well. (Improved Longitudinal Blow-up and Shaving in the Booster / Hancock, S :CERN-ATS-Note-2013-040 MD. – 2013). With the old LL we did a frequency modulation which was not very efficient and required a long C16 program (~200-300ms) to achieve the desired goal. LHC25ns old blow up 27/8

10. Getting the C16 Blow-up Up Working Blow up for Longitudinal shaving (LHCPROBE & LHCINDIV):  h=1 + C16 only  Calculate h=1 voltage program required early in the cycle to maintain a fixed fs but still accelerate a low intensity beam  Apply a fixed frequency (or multiple of) phase modulation during the fixed fs to the C16 frequency that follows h=1 using a fixed harmonic.  Increasing the amplitude of the C16 voltage blows up the beam and it’s lost from the small bucket.  Apply an RF bottle neck after this to set the longitudinal emittance.

11. Getting the C16 Blow-up Up Working Controlled longitudinal blow-up (most other beams):  Calculate fs function for the cycle according to the voltage functions programmed  Input the fs function to the blow-up HW so that the C16 modulation tracks fs during the cycle.  As this is a resonant process, a much shorter blow-up time of ~50ms should be achievable. LHC25ns improved blow- up 7/10

12. Status End 2104 The Highs The new LL system was successfully commissioned without the need to switch back to the old LL at any point. A MASSIVE amount of work by the whole team got us through the year. All the basics were working acceptably but many details would require further work. The system was fully PPM and integrated into the CERN controls infrastructure, allowing the use of the standard INCA tools for copying, comparing, archiving etc. There was also a significant MD program completed using the clones of the operational beams or dedicated beams. We had learnt how to use & program the 5 new systems in great detail, allowing fast set up for the Finemet MD program. What had been learnt about controlled longitudinal blow-up would be applied to all beams next start-up.

13. Status End 2014 The Lows We had still had a fear of the dark, as the black box was still black, without OASIS signals to light our way. Specialists often required to intervene when RF team rebooted the LL crates, as they didn’t come back up automatically. We didn’t have our final version of the firmware for the HW, so we’d risk more debugging time when this was released. No general training had been done in the operation of the system. The synchronisation process disturbed the beam, often causing oscillations and blow up (after a beautiful acceleration!) The machine would need some re-alinement before we could achieve pre-LS1 performance, this often made setting up nominal performance impossible.

14. Start-up 2015 A simple training course in PSB LL operation was presented as part of the AXEL training program. We swapped to the Highland generator for the extraction reference to replace the old Pentek unit, now fully functional. New cables for the PS trains were tested and connected. We deployed the new firmware for our HW and started de-bugging, but we’d later need to roll back after bugs were identified. We had the essential for operation OASIS signals delivered and these were tested and de-bugged as delivered, lighting the way forward. Sychronisation trains 29/1 The 4 radial loop pick-ups R3

15. Start-up 2015 The improved C16 blow-up was applied and tweaked on the SFTPRO & TOF users. The bugs in the firmware had been identified and tested, once applied to the machine the beam proved they had been fixed. The machine re-alignment was bearing fruit and once the orbits had been corrected the performance improved greatly. TOF 865E10 with improved blow-up 25/2 Controlled longitudinal blow-up SFTPRO, increasing only C16 voltage 20/2

16. Start-up 2015 The improved C16 blow-up was applied and tweaked on the LHC25ns & LHC50ns users. The EAST users were updated to use the improved blow-up. LHC50ns 4 rings superimposed 4/3 LHC25ns phase and radial loop response on OASIS 3/3 LHC50ns phase & radial loops + BCT, plus 4 synchro loops OASIS 4/3

17. Longitudinal Beam Status Today LHCPROBE: improve shot to shot intensity stability LHCINDIV: up to nominal spec. LHC25ns: up to nominal spec. LHC50ns: up to nominal spec. EASTA&B (incl. parasitic TOF): up to nominal spec. TOF: up to nominal spec. AD: setting up in progress BCMS: next beam to be set up ISOGPS & HRS: bunch shape improvement and final push for max. intensity

18. What We Are Still Working On. Synchronisation: Improve frequency steering and phase loops to stop oscillations blowing up beam and have second batch in PSB synchronous with first batch in PS. Requires ~10 working days of specialist time including MDs for tests. Ensure all crates boot correctly after power cycle: This may be unique to R0 (with the additional Finemet HW), as we rarely boot R1-4, but to be confirmed with R1-4. Finish OASIS & system integration: The essential operations signals are already available, but many specialist signals have been requested. A number of knobs and WS were requested to be modified by operations, this work has still to be completed. Achieve nominal longitudinal parameters on the beams not yet fully up to spec.

19. Conclusions. Six months were required to get all the basic operational beams back up to an acceptable level after LS1. Although the LL & beams are in reasonably good shape after re-starting in 2015, there will be further work required by the specialists to finish the job. We have excellent results for many of the operational beams thanks to the fully ppm LL and the application of the improved blow-up. Reproducibility of the beams has been greatly improved, with significantly less day to day adjustment required. We have the whole of the LL system available for adjustment via knobs or RF synoptic, 100s of parameters that were never before visible.

20. Conclusions. We have 10’s of sampler signals and 100’s of OASIS signals available to observe and de-bug the systems. Getting the “virtual” signals into the standard visualization tools such as OASIS takes a huge effort from the RF specialists in time and understanding, as was also noted in LEIR. Working with a single specialist for each part of the system means there are inevitable delays, as they all have many other commitments, patience often required. Disentangling which of the machines systems cause problems for the machine performance is not obvious after a long shut down.

21. Acknowledgments A very promising start thanks to the dedication and hard work of all the people involved.