1. I could be brief… LHC OP days 2012 …… WHAT YOU GET ….. ORBIT / TUNE MEASUREMENT AND FEEDBACK M. ANDERSEN, C. BOCCARD, S. BOZYIGIT, E. CALVO, M. FAVIER, J. FULLERTON. GASIOR, S. JACKSON, L. JENSEN, R. JONES, T. LEFEVRE, A. MARGIOLAKIS, A. NOSYCH, J.J. SAVIOZ, R. STEINHAGEN, M. WENDT And colleagues from BE-OP-LHC, BE-ABP, BE-RF, EN-MME, EN-STI

2. I could be brief… Beam Position Monitor Orbit stability and temperature drift Update on BPM non-linearity correction Higher resolution orbit measurement with DOROS Status of Orbit feedback Status Interlock BPMs Tune and Tune Feedback Upgrades and Develoment of Gated BBQ Tune feedback at 7TeV Schottky monitors after LS1 Detection and Measurement of Transverse Instabilities Time domain vs Frequency domain measurements Possible plan for LS1 OUTLINE Concentrating on plans for LS1

3. I could be brief… BPM - WBTN o Orbit resolution measured ~few μm (during MDs) o Main limitation from long term drift in position due to temperature variation in VME integrator mezzanine o Standard BPM calibration added to sequencer mitigates part of the problem – not enough !! VME based Digital Acquisition Board and WBTN Mezzanine Cards from 2010

4. I could be brief… BPM – Temperature issue Racks to be installed during LS1 Thermalized Racks consist of: Heat exchanger (bottom) Air flow isolating walls High constant speed fan (top) PID controlled water valve Tests performed in SUX1 for one year 1 bin ~ 30um

5. I could be brief… BPM – non-linearity corrections BPMD mapping Beam allowed area: ± radius/3 BPMD: 130mm diameter strip-line LHC BPM in front of the Dump transfer line Average error in beam allowed area: 1.1 mm Max error for on-diag beam: 6mm! Average error in beam allowed area: 30 um Max error for on-diag beam: < 100 um Existing non-linearity correction can be improved by using a 2-D cross-term polynomial Especially for IR bumps and Dump line BPMs

6. BPM with DOROS o DOROS is a new technique developed to process collimator BPM signals, robust and simple o Optimised for position resolution, absolute accuracy for centered beams o No bunch-by-bunch measurement but could be gated (not implemented yet !) Tested in SPS on collimator BPM prototype and in LHC @Pt 5 on BPMSW

7. 7 BPM with DOROS Resolution <100nm Non linearity of diode to be taken into account Visible scaling error wrt normaliser (tbu) Preparing the cable infrastructure during LS1 for LSS’s BPMs

8. I could be brief… ORBIT FEEDBACK I could be brief… Orbit correction at IP to bring beams head-on (here B1H correction) Slow drift over the year  not corrected by OFB. The F2F difference is very small and sufficiently good (  squeeze in collision) 80  m 7  m rms o LHC does not work without orbit FB and overall performance 2010-2012 has been remarkable (Jorg W. – BI Day 2012) o Current correction quality limits (not yet a real problem): o Arcs + most of the LSS: BPM F2F reproducibility – 50 um rms. OK! o Common regions 1,2,5 & 8, ~ 200 um rms (directivity of stripline BPM)

9. ORBIT FEEDBACK o Improvements in hardware highly beneficial for OFB o For arcs – limited by residuals after temp control (F2F: <30um) o For IRs : Need to implement local orbit correction in LSSs : better resolution/stability o Regular system improvements with synch orbit + new correction polynominals o DOROS in parallel & could take over once proven (F2F: <1um ?) o Some Software improvements: o Handling of response matrices OFC/OFSU o Filtering of bad elements (use existing unused code + improvements) o A lot done during the last 2 years: Code review and documentation during LS1 (BI-OP- CO) Plan for LS1

10. Interlock BPMs o Purpose o To ensure the orbit at the extraction septum MSD remains below ±4mm, in order to maintain a safe extraction trajectory o Layout o 2 redundant BPMs added near TCDQ and 2 near preceding Q4 o 90° phase advance to minimise chance of an unfortunate orbit bump o use standard LHC BPM analogue electronics BUT specific FPGA firmware o All hardware detection and trigger of beam abort BPMSA (.A/.B) BPMSB (.A/.B) Main window with 70 readings (BD1) out of limits over 100 turns (T1) triggers the system Second window with 250 (BD2) out of limits over 10 turns (T2) to quickly catch fast orbit change

11. I could be brief… Interlock BPMs Note: 1% ~ 130 um for LHC arc, ~220um for BPMSA and ~330um for BPMSB buttons o Modify attenuation to displace dynamic ranges o Current installation BPMSA (80mm ap.) have 4dB and BPMSB (130mm ap.) have 0 dB for P/P run

12. Interlock BPMs o … The system has suffered too many false dumps – No known case where the interlock did not function when it should have o Difficult start in 2012 with initial problems coming from BI database o No more issues once system tuned for the operational high intensity beams (low sensitivity mode – triggering dumps @2E10 bunch intensity) o Not so compatible with other tests (like proton-Lead) – more sensitive to signal reflections in high sensitivity mode o … New version of interlock firmware/fesa has been prepared.. not deployed yet o Version with more diagnostics - Installed on a test system since summer 2012 o Several issues found … i.e. neither BPMS orbit reading nor the position thresholds took into account the electronic non-linearities … o …. Options for LS1 o Optimize the hardware to limit signal reflection (spurious beam count) and adjust the sensitivity ranges to operational scenarios (remotely controlled attenuators ?) o if not enough.....duplicate the system: one for protons and one for lead ions physics ? o New firmware customized for interlock BPMs only (more data for PM analysis) ? o All of these choices have an impact for MP & need to be thoroughly discussed

13. I could be brief… TUNE Systems System hardware settings optimized for different beam configurations

14. TUNE Settings of BBQ FE for different beam conditions Need to be put in operation through sequencer to use full BBQ capabilities

15. TUNE with FB Main ‘issues’ with the LHC Tune system during last years o Tune FB triggering QPS (too fast voltage change) due to poor Q peak quality o Pending request for b/b tune measurements o Low S/N ratio for certain beam conditions o Damper system operated at high gain o Large octupole currents and chromaticity The peak finding challenge Solved by Gated BBQ system o Gating on bunches for which the damper operates at lower gain o Long development resulting in first prototype tested in summer 2012 o Operational in 2012 with basic functionality

16. I could be brief… GATED TUNE I could be brief… gated BBQ = standard BBQ + RF switch + hybrid + attenuation RF switch ∆ input H output H ∆ input V output Vgate input gate driver bipolar detector power supply compartment Gated BBQ front-end Hybrid  signals attenuator

17. TUNE after LS1 Installation of new pick-ups for Gated tune and better measurement of coupling Software required to exploit full functionality of nominal and Gated BBQ – Fesa and logging DB done already – missing GUI’s (bunch selection and bunch scans display …) Tune system compatibility with Damper should be even better (gated BBQ) with upgrades foreseen on the Damper (see Daniel’s talk) QFB compatibility with QPS Better tune signal with Gating TE/MPE considers introducing 3 threshold levels after LS1 (instead of 2). Thresholds are not yet defined….. To be discussed….

18. I could be brief… SCHOTTKY MONITORS Run With IONS in 2011 Run With Protons in 2012 o The Schottky transverse signals are still good on B1H, for single and multi bunch measurements at injection and at stable beam. o Too large coherent signals saturate and destroy the pre-amps in the other systems! (B2H pre-amp killed already) o Good, high level Schottky signals on all ion fills, for B1H, B1V and B2H. o Reliable single bunch measurements for the tune, and possible also for the chromaticity measurements. o Modification on the gating procedure of the B2V pick- up: Significant reduction of the coherent signal peaks, but no improvement of the transverse Schottky signal bumps. Figure : Analogue Processing Chain describing the modified pickup plate with the addition of a gate and a 24 MHz filter (elements unlighted in yellow).

19. I could be brief… SCHOTTKY MONITORS Plan for LS1: Make all 4 Schottky Monitors fit for Protons! Overhaul of the Schottky pick-ups Reduction of the reflections for better return loss using a better overall match on the waveguide-to-coaxial transition (new transitions have to be manufactured) Systematic checks on test bench with stretched wire measurements Improve the symmetry of opposite electrodes, e.g. lower tolerances, mechanical tuning Check the transverse coupling impedance Replace all internal SiO2 coaxial cables (some have a vacuum leak) Overhaul of the RF signal processing Modify the gating of all front-ends! New RF input filter to better cope with 25 ns bunch spacing. Probably new input amplifiers ? Controls and software Extend the attenuator / phase shifter control to all systems. Adapt the front-end control software to the hardware modifications. Complete rearrangement / replacement of the Java user application software!

20. MONITORING INSTABILITIES o Observation of instabilities in 2012 relied mainly on BBQ spectra and ADT activity (see daniel’s talk) o LHC head tail monitors using fast sampling oscilloscopes limited to the detection of 100um oscillation amplitudes and limited in memory Development of high senstivity frequency domain detection system based on bandpass filters and diodes m=1 m=2 m=5 m=1 m=2 m=5 sum or 'm=0' signal Channel index 0 1 2 3 4 5... HT modes Time Frequency

21. Input Δ-Signal Output full-range 1.6 GHz 1.2 GHz 0.8 GHz 0.4 GHz High modulation-index @ 400 MHz → indicates 'm≥1' head-tail motion Prototype tested on SPS in Summer 2012 ; Installed shortly after on LHC MONITORING INSTABILITIES

22. Proposal for LS1 – more for discussion ! Put the ‘Multi Band Instability Monitor’ in operation with several functionalities Providing observation system for beam oscillation in several frequency bands with high resolution (<100nm) (to be discussed how many channels and which frequency bands) Generate an appropriate ’instability Trigger’ (software or hardware) for Head-Tail oscilloscope for intra-bunch oscillations (100um) Damper pick-up (400MHz) for B/B measurement @ 1um resolution Possibility to use a set of high-frequency tickler (BQK) to excite and measure the growth/damping time of specific instability modes Upgrades the HT oscilloscopes with fast digitizers providing more memory (not budgeted yet) Guzik’s GSA & ADC 6000series - 4 (2,1) channels @ 4 (6.5, 13) GHz - 16 (32) GB samplig buffer (1.6s of beam data) - Online FGPA processing: FFT & DFT

23. I could be brief… CONCLUSIONS o Improving the stability and accuracy of Beam Position Monitors o Install thermalized racks for WBTN o Use synchronous orbit mode for common region BPMs o Implement better correction of non-linearities o Attractive option for high-resolution BPM using DOROS in LSS’s BPMs o Modifications of Interlock BPMs to improve the system performance without compromising on reliability….. o Gated Tune system has solved many issues in 2012 – Full functionalities after LS1 o OFB and QFB will get better with hardware upgrades – Software review during LS1 o Several technical solutions on offer for Instability measurements o Need to agree on system architecture to be deployed after LS1 (BI, ABP, OP, RF)

24. I could be brief… Thanks again all the contributors to this talk ! BI WATCH

25. Orbit resolution in LSS Subject: Cross-talk between both beams in insertion BPMs (stripline). Solution: Use synchronous mode with orbit calculated from single bunch which has no long range collision close to BPM location. Firmware deployed since January 2011. Action 2012: Mask needs to be configured for each BPM and dynamically as filling progresses There is a (OP) person working on an application to do this automatically.

26. BPM – non-linearity corrections o Issue with 10-20% scaling error in LSS’s stripline BPMs o Normaliser non-linearity and error in test-bench using BPM simulator o Check with fixed attenuator – found >8% error in worst case o Limitation due to limited directivity of stripline BPM in common vacuum chambers : (Cross talk between both beams) o Mitigation using Synchronous Orbit Mode and selecting appropriate bunch – Tested in MD’s on one BPM– To be deployed…(contributions from OP)

27. Beam Position Monitors: BI MD4 IR8 scan (29 Nov. 2012) 27 BPMSW.1L8.B1 B1 Vertical orbit. Snapshot in time Single-term poly used Difference btw Optics prediction and BPM measurement: ~2mm EM Model: prediction map Cross-term poly used Difference between positions: ~1.8mm Overlay of scan trajectory over prediction map. Single-term poly correction Single-term poly VS. Cross-term poly

28. GATED TUNE  The RF switch can accept some ≈ 30 Vpp, so smaller amplitudes needed (the standard BBQ handles ≈ 500 Vpp straight form the PU electrodes). An RF 180º hybrid used to subtract the pick-up electrode signals to decrease the signal level at the input of the RF switch. The hybrid cannot take the whole electrode signal power (>10 W). 10 dB attenuators are used, causing a sensitivity loss w.r.t. the regular BBQ.  Sensitivity of the gated BBQ is decreased less than the attenuation, as the gated BBQ detector has only one diode, while the standard detector has 6 diodes to deal with the high electrode signal amplitude.  The gated BBQ operates as the standard BBQ with one bunch (or a few bunches) in the machine. The whole acquisition chain and its software is the same.  The above scheme started to be studied only in 2012, as a result of difficulties with the previous development based on a floating gate, which did not require signal attenuation. The current scheme with a series RF switch works only due to the fact that an RF switch was found, accepting signals with sufficiently high amplitudes, which are well above its data sheet spec. standard BBQ gated BBQ = standard BBQ + RF switch + hybrid + attenuation

29. GATED TUNE operation with positive beam offsets the implemented configuration: for operation with bipolar beam signals operation with negative beam offsets

30. MONITORING INSTABILITIES frevfrev+fqfrev-fqfrevfrev+fqfrev-fq

31. This year 4 firmware versions were developed, but only the first was deployed to all the crates. The rest were “under test” is only special crates in P1,P5 and P6. Current deployed DAB firmware: v.2012-1 (24-1-2012) added an automatic IIR setting. - Count the number of received Strobes during a programmable window, in order to Auto-select the Orbit filter according to this number. - Set the Interlock Alarm level = 0, in order to use the Alarm counter to count the received triggers. Versions not yet deployed in all the creates: v.2012-2 (4-4-12) : As. Orbit with increased resolution. v.2012-3 (15-6-12): Split criteria for interlocks triggering: bad acquisitions are not counted as bad positions. Different settings for triggering through errors or positions. More post-mortem data for analysis. v.2012-4 (10-10-12): Interlock Stop Trigger from BST P0 trigger. Allows freezing the PM buffers of all the interlocked channels when one of them triggers the interlock system. DAB firmware in 2012:

32. 1) New tool developed by OP and used at beginning of the year to check the BPM quality from the point of view of inverted polarities and scalar factors. The tool is based on kicks from 2 correctors at (almost) 90 deg phase advance. Fast (< 1 minute / beam /plane) check of the BPM response. Results: - Some scale issue possible (~ 20%) for IR BPMs. (from Jorg) - BPMS[WXY] calibrations are systematically 10% lower while the BPMS[AB] seem to be 10% higher (the data is in the logbook). We assumed that they should be the same. If we could confirm that the BPMSA have the same geometry/design as e.g. (from Ralph’s email) - Warm BPM in LSS seems to have a 10-15% error on scaling factors according to Jorg's measurements. Witold said that he came up last year to the same feeling when analysing VdM scans data. (From Jean Jacques email). - It allowed to detect BPM wrong polarities at BPMSW1.L5 (due to an error when connecting the RF switches). 2012 software upgrades/modifications

33. 2) Sequencer task to calibrate automatically the SPS-LHC transfer lines before every LHC fill. 3) Expert GUI to calculate the temperature gradients of the LTI lines + FESA modifications to used the found them and compensate for temperature effects in the LTI trajectory. 4) New sequencer task selects the bunches without beam crosstalk to setup properly the synchronous orbit. - Required a FESA modification (orbitBunch) that was only deployed for testing in a special crate at P1. - Unfortunately, this crate overwrite some settings (bunch delay and phase clock) with every sequencer calibration, leading to a malfunction of the synchronous orbit. - Solution is found, make an LSA trim to correct the settings. - Tested at P1 during the collide and squeeze MD (MD#3) and during the 1km β*. - Results were nice and seem to be ready to deploy. 2012 software upgrades/modifications