ADT upgrades for HLLHC BERF W Hofle J
ADT upgrades for HL-LHC BE/RF: W. Hofle, J. Komppula, G. Kotzian, S. Rains, M. Soderen, D. Valuch* BE/ABP: X. Buffat * daniel. valuch@cern. ch
Overview o Damper operation, parameters and a bit of history o Key components, parameters and performance of the current system o Potential for evolution o What is needed for HL-LHC? 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 2
ADT: LHC Transverse Feedback System o The LHC transverse damper is a closed loop feedback system: • It measures the bunch-by-bunch oscillations and damps them by signals applied through fast “electrostatic” kickers. o Primarily designed to: • Damp the injection oscillations • Counteract the coupled bunch instability • Preserve the beam transverse emittance 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 3
ADT: LHC Transverse Feedback System o Key parameters for beam physics • Feedback gain / Damping time • Bandwidth (some kind of…) 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 4
ADT: LHC Transverse Feedback System o o Key parameters for beam physics • Feedback gain / Damping time • Bandwidth (some kind of…) Key parameters for the system • Pickup sensitivity (signal µ charges per bunch) • Position measurement resolution • Position measurement noise floor • Deflection strength • Full power bandwidth • Small signal bandwidth • Total loop delay • How the signal is processed • Noise injected to the beam 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 5
ADT modes of operation in LHC Run I o By design, the ADT was intended to operate only for few milliseconds to damp injection oscillations at injection o Soon it turned out, it helps if we keep it ON also for the whole injection o Soon it turned out, it helps if we keep it ON also during the ramp o Did not take too long for someone to come with an idea “what if we keep it ON also during the physics? ” o So, how much off were the original assumptions used for the design? o The longest fill so far >48 hours, vs. 10 milliseconds, that is factor 17’ 280’ 000, i. e. 144 d. B… 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 6
ADT modes of operation in LHC Run I o Many ideas in the control room, how the ADT should be operated o A gain knob in LSA was left at the disposal of who ever had an idea about the gain of the day o Soon a clear pattern started to emerge: 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 7
Lessons learned: Is the damper working? Typical cycle observed every year since 2010: Increase ADT gain Beam unstable Increase octupole current Beam still unstable Reset o Increase ADT gain Call ADT people if damper is working Yes, it does Recursion, see Recursion. Increase octupole current Beam still unstable Octupole current at max Increase ADT gain Repeat n times… ADT gain at max Chamonix 2016 / ADT Post-LS 1 – W. Hofle G. Kotzian, D. Valuch 8
ADT modes of operation LHC Run II o In run II, the bandwidth control and main/witness loops become available o ADT is currently operated at injection with damping time ~40 turns and bunch-by-bunch mode o During ramp, the damping time increases to 50 -80 turns, b-b-b mode o Squeeze: 50 -80 turns, b-b-b mode o In physics: switch over to standard bandwidth mode (pole at 800 k. Hz) • Single bunch damping time ~70 turns • Low coupled bunch modes <40 turns Injection oscillation, bunch by bunch damping time, long train, enhanced bandwidth (b-b-b mode) 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 9
Summary o In the past ~2 years the requirements for ADT had evolved from: • “as fast as possible”, • “as low as possible”, • “as large as possible” o To something like: • “can it be 0. 001 sigma? ”, • “we should try 1 MHz bandwidth”. o This is an unprecedented progress, thank you very much for all the effort! o Having scientific grounds allows us to benchmark the ADT performance against the requested machine parameters/models. On improving the ADT pick up resolution. HL-LHC WP 2 meeting D. Valuch, 10. 4. 2018 10
Performance of the ADT building blocks Digital signal processing SR 4 Pickup, transmission lines, Beam position module Tunnel + SR 4 16 Oct 2018 Drivers, power amplifiers, kickers UX 45, UX 451 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 11
Beam position module o Beam position measurement, bunch by bunch o Two pickups per beam per plane (out of 4 available) o Sensitivity few 108 p/bunch to 1012 p/bunch o Optimal performance within a dynamic range of ~6 d. B o Resolution ~60 nm/bin o Noise floor ~1. 8 mm. RMS* o Not very flexible in terms of setting up (*) The position measurement noise floor is calculated using the real noise coming from electronics superimposed to ideal position signals, and processed by the Beam. Pos module algorithm. Valuch D. : Plans for improved ADT pick up resolution https: //indico. cern. ch/event/718322/ 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 12
Beam position module o The dominating noise source currently is the position measurement noise o Development of new electronics ongoing, aim to lower the noise floor by at least 10 d. B (/3), o With some advanced tricks another few d. B probably possible o Already at the limit of current technology, further improvements possible by optics (increase of b), moving some electronics to the tunnel, sophisticated active control during the cycle… o First results with beam promising Effort D, R&D Time 1 year Cost 100 k 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 13
Digital signal processing o Receives position signals from 4 pickups o Correction signal calculated by means of digital filters o Four independent, fully configurable feedback paths o Feedback loop bandwidth control o Group delay of 4. 5 turns o Synthesis of all excitation signals (cleaning, ADT-AC dipole) o Considered to be noise-free o Combined noise floor running with two current pickups and standard bandwidth ~0. 8 mm. RMS 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 14
Digital signal processing o Current algorithm limits the minimum damping time to ~10 turns, it is also not compatible with close to half integer tunes o Used already 572 (90%) of the 48 -bit signal processing blocks in FPGA. Not much room to grow o Ready to receive signals from 4 pickups per beam per plane (reducing the feedback noise floor), tests with beam ongoing o Alternative signal processing tested (Komppula algorithm), flexible in terms of group delay/noise/tune acceptance. Promising… o These units are usually upgraded every LS, to provide resources for constantly growing functionality Effort D Time months++ Cost 50 k 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 15
Power amplifiers and kickers o Maximum deflection 2 mrad @ 450 Ge. V (large signal operation, <1 MHz bandwidth) o Frequency response: 1 st order low pass with dominant pole at ~800 k. Hz (2 nd at 7 MHz) o Usable up to 20 MHz (20 x lower deflection) 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 16
Power amplifiers and kickers o The full strength deflection can be achieved only with low bandwidth (<1 MHz) o Full bandwidth (20 MHz) available only at 20 x lower deflection, what can be a limiting factor in bunch by bunch operation at flat top (further 16 x reduction) o The power amplifiers use vacuum tubes (tetrodes), which are consumable (<20 k hours), expensive (>10 k. CHF/piece) and prone to obsolesence in the industry o Design of new amplifier + kicker system requires an extensive and expensive R&D. If we start now, will be ready for LS 4… Effort R &D Time >5 years Cost 1 -5 M 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 17
End of Run II status, plans for LS 2 and outlook for HL o Two most common interactions today: 1. “Can you do this, it will be a very interesting study…” (it becomes an operational mode shortly afterwards) 2. “The damper works, why do you need beam time? ” o Transverse feedback in LHC is a very complex system, it was (over)designed to be flexible and face the new requirements, but this has its limits • Some things are possible already now (Effort). • Some things are possible with certain effort (Development). • Some things are possible with a major effort (Research and Development). • Some things will be possible only with a major effort and a large investment. • … and some things are not possible. 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 18
o It is flexible in terms of optics and per bunch intensities o A development work is ongoing to reduce the feedback noise floor by a factor for after LS 2, triggered by ABP studies (X. Buffat et al) and in a view of the future Crab cavity noise feedback o Otherwise, “ADT works” TM (from an equipment group point of view), so the baseline for LS 2 is to modify nothing and restart with the same parameters and performance as in Run II, unless… Q 8+Q 10 Q 7, Q 8, Q 9, Q 10 to ADTObs. Box Current ADT can do 50 turns damping time through the whole cycle with a noise floor of ~0. 8 mm. RMS Q 9 o Q 7 Baseline for Run III and HL-LHC (summary) m. DSPU Q 7, Q 8, Q 9, Q 10 “Optical distribution network” ADT, HB 1, October 2018 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 19
Baseline for Run III and HL-LHC (summary) o You – the accelerator physics community – have to tell us, what you want the damper for HL-LHC (Run III) to be… o We need concrete numbers to assess the feasibility, required effort, estimate the lead time and set a price tag • Damping time through the cycle • Bandwidth, noise floor, per bunch intensity • Max. deflection • The operational flexibility (what should be changing through the cycle) etc. o As good as possible does not work (obviously, you have it already…) o Do not over-specify – keep in mind some parts are already the limits of the current technology o Keep in mind the required effort counts in years. Even for simple things for Run III, we need the input already now, to be available for restart in 2021 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 20
Thank you for your attention 16 Oct 2018 D. Valuch: ADT upgrades for HL-LHC 8 th HL-LHC Collaboration Meeting, 16. 10. 2018 21
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