Transverse Feedbacks against ECE at SPS and LHC W.Hofle CERN BE-RF-FB on behalf of a multi-lab team CERN – SLAC – LBNL – LNF-INFN W. - La Biodola, Elba, Italy June 9, 20121

focused on damping intra-bunch transverse oscillations for proton bunches deriving specifications for a High band width feedback for the SPS from simulations  see talk by K. Li in this workshop, activity with headtail and WARP codes started in 2008 demonstrated damping of headtail instability caused by ecloud future: extend to TMCI caused by impedance (SPS, then PS and LHC ?) prototype hardware development for machine studies and “demonstrator” for proof of principle experiment in SPS  see overview talk by J. Fox designs for new kickers, impedance (SLAC – LBNL – LNF-INFN) collaborating team: J. Cesaratto, J.D. Fox, M. Pivi, K. Pollock, C. Rivetta, O. Turgut, S. Uemura (SLAC) G. Arduini, W. Hofle, K. Li, G. Rumolo, B. Salvant (CERN) M. Furman, M. Venturini, S. De Santis, Z. Paret, R. Secondo, J.-L. Vay (LBNL) A. Drago, S. Gallo, F. Marcellini, M. Zobov (LNF-INFN) Acknowledgements CERN PS team: H. Damerau, S. Gilardoni, A. Blas Multi lab effort W. - La Biodola, Elba, Italy June 9, supported by US-LARP CERN SPS LIU Project

June 9, 2012 W. - La Biodola, Elba, Italy 3/38 Current CERN Accelerator Complex LHC: 450 GeV to 7 TeV, protons 400 MHz SPS: 26 GeV/c to 450 GeV, protons for LHC 200 MHz PS: Protons 1.4 GeV – 26 GeV/c 3 – 10 MHz, 13 MHz, 20 MHz, 40 MHz, 80 MHz bunch structure of 25 ns created PSB: 50 MeV to 1.4 GeV, future: 160 MeV to 2 GeV MHz, MHz LINAC2 (protons), 200 MHz to be replaced by LINAC4 (H-, under construction) 352 MHz

June 9, 2012 W. - La Biodola, Elba, Italy 4 First observations in SPS on pick-ups of transverse feedback 1998/1999 … Top trace: 20  s/div Bottom trace: 1  s /div protons/batch LHC beam 25 ns bunch spacing protons/batch LHC beam 25 ns bunch spacing Observation: baseline drifts on pick-up signals during the passage of an LHC batch what is going on? presented at Ecloud ‘07 1 turn 72 25ns spacing

June 9, 2012 W. - La Biodola, Elba, Italy 5 … Magnetic solenoid field can suppress the effect  electrons without solenoid with solenoid (100 gauss) horizontal vertical The resonant build-up of the electron generation can be disrupted by applying a magnetic solenoid field scales 1  s/div presented at Ecloud ‘07

PS: at very last part of beam manipulations when 25 ns spaced bunches are shortened horizontal coupled bunch instability, also intra bunch motion ? SPS: all along the cycle at 25 ns bunch spacing strong horizontal coupled bunch instability and vertical single bunch instability with intra bunch motion LHC: single bunch instability under study see talk by H. Bartosik; also intra bunch motion ? signature of ecloud with its development along batch without mitigation  instabilities lead to beam losses and transverse emittance blow-up with direct impact on luminosity performance in LHC  Mitigation: Transverse Feedbacks Transverse instabilities caused by ecloud in LHC and its injectors W. - La Biodola, Elba, Italy June 9, 20126

W. - La Biodola, Elba, Italy 7/38 Accelerator Digital / analogue processing Power / kicker / bandwidth Status PS Booster (protons) 50 MeV – 1.4 GeV kin. E. (future: 160 MeV to 2 GeV kin E) no ecloud, long bunches multi turn injection from Linac 2 analogue beam offset signal suppression, analogue delay (cables & switches) 100 W, 50  stripline Limited to 13 MHz in operation But built for 100 MHz bandwidth, baseband H-plane: used and required V-plane: beam stable w/o FB upgrade planned PS (protons, ions) 1.4 GeV – 25 GeV (kinetic E) (future injection at 2 GeV) ecloud observed when beam bunched at 25 ns Spacing, coupled bunch digital system, synergy with LHC Damper for The low level digital processing 80 MHz clock frequency 2 kW solid state power amplifier; 112  stripline (0.9 m length), planned with ~30 MHz bandwidth in baseband, lower cut-off ~50 kHz 2012 under commissioning injection damping and feedback will be beneficial in particular for high intensity CNGS beams and LHC beams. Currently horizontal instabilities are cured by introducing coupling to the vertical plane which constrains the tunes SPS (protons, ions) (14 – 450) GeV/c protons FT (26 – 450) GeV/c LHC beam ecloud observed and is a potential limitation for 25 ns spacing digital notch filter and 1T-delay (Altera FPGA, 80 MHz clock) commissioned in 2000/2001 tetrode amplifiers with two 30 kW tetrodes in push-pull directly coupled to a kicker (base band); feedback bandwidth ~10 kHz to 20 MHz 2001 upgraded for LHC beams H-plane: used in operation V-plane: used in operation used and required for operation above 5x10 12 protons (max ~5.5x10 13 ppp accelerated) SPS High Bandwidth 4 – 5 GS/s clockunder study, GHz BWFeasibility Study LHC (protons, ions) protons: 450 GeV/c – 7 TeV/c ecloud observed and is a potential limtation for 25 ns spacing digital notch filter and 1T-delay, built-in diagnostics 14 bit DAC / DAC Altera FPGA, 40/80 MHz clock 2 um rms resolution tetrode amplifiers with two 30 kW tetrodes in push-pull directly coupled to kicker (base band) similar to SPS system 3 kHz -> 20 MHz 2010 fully commissioned injection damping feedback used in ramp and physics, essential Transverse Feedback Systems in LHC and its injectors

From established LHC operation to LHC High Luminosity operation Statimportant for injectors: two very different scenarios: 25 ns bunch spacing 50 ns bunch spacing LIU (“LHC Injector Upgrade”) project addresses upgrades in the injector chain (LINAC)  PSB  PS  SPS  to meet HL requirements W. - La Biodola, Elba, Italy June 9, LHC 2012 OP LHC nominal HL-LHC 25 ns HL-LHC 50 ns Energy4 TeV7 Tev # Bunches bunch spacing [ns] p/bunch [10 11 ] (0.58A)2.2 (1.11 A)3.5 (0.88 A)  x,y  [  m] Peak lumi [10 34 ] Lumi levellingno 5x10 34 #Pile up Status from May 2012 (L. CM18) 2014+Future upgradetoday

Increase performance  higher brightness LINAC4 (H- linac) is being constructed raise of injection energy into PSB from 50 MeV to 160 MeV (LINAC4) increase injection energy into PS (space charge limits) 1.4  2 GeV SPS: RF upgrade (power), Q20 optics (lower  T )  TMCI vacuum chamber coating in SPS as part of ecloud mitigation high bandwidth feedback LLRF upgrades in PSB,PS,SPS with additional long./cavity feedbacks upgrades for beam transfer, collimation, scraping, instrumentation Increase reliability and lifetimes until 2030 approximately spares, radio-protection, replacement of aging equipment Project timeline: “baseline” completed after LS2 (long shutdown 2 of LHC) > 2017/2018: LIU “baseline” beam commissioning constraints: two long shutdowns LS1 and LS2 for modifications and major installations; LS1 to start at end of 2012 LIU project: Goals and Means W. - La Biodola, Elba, Italy June 9, 20129

objective: cure transverse “single bunch” instability by feedback two collective effects are limiting the SPS performance as LHC injector e-cloud TMCI similarities: both effects cause vertical intra bunch instability high chromaticity suppresses instability to a certain extent feedback expected to permit running at low chromaticity and at intensities beyond which high chromaticity is an established cure particular important to maintain small transverse emittances Motivation for high bandwidth feedback in SPS W. - La Biodola, Elba, Italy June 9,

coherent signals visible for both ecloud and TMCI instability provided reaction time (few turns) shorter than growth times  feedback in principle should work Feedback as cure Frequency (0-2.5 GHz) turns sum difference (delta) instability growing (TMCI) signals up to 1.6 GHz R. de Maria et al. DIPAC 2009, MOPD17 W. - La Biodola, Elba, Italy June 9,

e-cloud vertical instability frequency turns sumdifference (delta) instability growing signals up to 1.2 GHz R. de Maria et al. DIPAC 2009, MOPD17 artifact from pick-up (beam pipe cut-off) quadrupolar motion (longitudinal) at injection due to voltage mismatch W. - La Biodola, Elba, Italy June 9,

e-cloud vertical instability W. - La Biodola, Elba, Italy June 9,

RF, low radiation special instrumentation no RF infrastructure extraction CNGS/LHC injection slow extraction radiation high current transverse FB extraction LHC LSS3 layout to be studied by working group under LIU led by E. Montesinos (BE-RF) alternative location base line location for wide band TFB W. - La Biodola, Elba, Italy June 9, Implementation in SPS: possible locations for transverse feedbacks in SPS

New kickers W. - La Biodola, Elba, Italy short (array of) striplines, slotted wave guides, cavities ? Location: dispersion supressor, flat vacuum chamber Frequency reach < 1.5 GHz Cabling can be prepared in LS1 (2013/2014) June 9,

June 9, 2012 W. - La Biodola, Elba, Italy 16 SPS aperture

W. - La Biodola, Elba, Italy Aperture available for feedback kickers and pick-ups in dispersion suppressors June 9, under review: H. Bartosik Y. Papaphilippou aperture available determined by fixed target beams (14 GeV/c) circular or rectangular vacuum chamber possible  input to design of kicker

Boundary conditions: LS1:2012 LS2: Phase 1: The demonstrator  end 2012 minimum goal: damp head tail motion of single bunch existing equipment (amplifiers, BPWs as kicker and PU) “drive experiments”  see presentations in this session electronics (LARP), close FB loop all design specifications for phase 2:end of 2012 Phase 2: New pick-up, new kicker, consolidated electronics, higher power amplifiers, preparation of LSS3 in LS1 for installation of equipment at the end of LS1 or later in a short winter shutdown post-LS1 feedback on multi-bunch beam in presence of e-cloud decide on final implementation and LSS3 vs. LSS5 before LS2 R&D and staged implementation: The Path (1) W. - La Biodola, Elba, Italy June 9,

Phase 3: Final implementation in LS2 depending on desired energy range  upgrade power and if impossible to install in LSS3 for reasons of space or radiation  move to LSS5 add kicker modules if required design and construct final electronics (profit from latest technology) commission after LS2 R&D and staged implementation: The Path (2) W. - La Biodola, Elba, Italy June 9,

“a” Schedule new pick-up design and construction Year 4Year 3Year 2Year 1Year 5 Phase 1: Year 6Year 7 demonstrator power amplifiers for phase 2 tendering (s) kickers design and construction phase 2 beam tests Phase 2: review for phase 2: Phase 3: implementation go / no-go phase 3: June 9, 2012 W. - La Biodola, Elba, Italy 20

W. - La Biodola, Elba, Italy June 9, SLAC committed to provide the yet missing part for the demonstrator J. D. Fox

simulations with impedance model of SPS for TMCI/FB needed address full parameter space with ecloud simulations R&D also need to cover exotic beams, very high single bunch intensities for LHC MDs, feedback for other bunch spacings (5ns ?) R&D recommended also for possible implementation in LHC (SPS is “test bed”), PS (?) design report with choices for kickers at end of phase 1 (end of 2012) impedance of kickers (!) Immediate future towards a design report at end of 2012 W. - La Biodola, Elba, Italy June 9,

June 9, 2012 W. - La Biodola, Elba, Italy 23 Kicker options all kicker options need evaluation of the impact of their beam coupling impedance from machine point of view a lower impedance structure is preferred make impedance only as high as necessary, in case more kick strength required, installation of more power is always an option Computation of required power needs input from headtail or from the demonstrator experiments

Striplines (1) A single 10-cm long stripline seems to be able to provide the necessary transverse kick up to 750 MHz, with acceptable power figures and required voltage. Its response time is capable of targeting at least head and tail of the bunch with independently selected kicks. If a response up to 1.5 GHz is required to deal with the TMCI, multiple shorter striplines ( 4 x 5 cm long) can provide the necessary transverse impedance over the entire frequency range up from DC. We have validated our analytical estimates with 3D electromagnetic simulations, which can also provide information on the field uniformity, etc. Such 3D simulations will be the tool of choice for a careful design of the stripline kicker once a choice is made. S. De Santis Z. Paret, LBNL June 9, 2012 W. - La Biodola, Elba, Italy 24

Stripline (2) 100 mm 20 mm 30 mm 40 mm 59 mm S. De Santis Z. Paret, LBNL June 9, 2012 W. - La Biodola, Elba, Italy 25

Stripline (3) A 5 cm long stripline offers maximum shunt impedance at 1.5 GHz, equal to about 250 Ω. The required deflecting voltage increases to 3.1 kV therefore multiple striplines are needed. GHz Ω 4×5 cm 10 cm Total impedance Frequency (MHz)V/moduleP max (W)/mod.P avg (W)/mod Adding four 5 cm stripline modules is sufficient to obtain manageable values for voltage and power figures at 1.5 GHz and can possibly replace the single 10 cm module at lower frequencies! S. De Santis Z. Paret, LBNL June 9, 2012 W. - La Biodola, Elba, Italy 26

W. - La Biodola, Elba, Italy June 9, Slotted waveguide kicker (1)

W. - La Biodola, Elba, Italy June 9, Slotted waveguide kicker (2)

Kicker #1Kicker #2Kicker #3 TypeStriplineCavity, TM110 defl. mode 3-dB bandwidthDC – 400 MHz800 ± 16 MHz1200 ± 16 MHz Length17 cm15 cm10 cm Filling time0.6 ns10 ns QLQL Shunt Impedance≈ 1.5 kΩ DC)≈ 1.5 kΩ 800 MHz)≈ 2.2 kΩ 1200 MHz) Resulting transverse voltage transferred to the beam as a function of the frequency, assuming the system of kickers driven by a 1 kW source. June 9, 2012 W. - La Biodola, Elba, Italy 29 A. Gallo, F. Marcellini, LNF-INFN Proposal by A. Gallo and F. Marcellini Stripline plus cavities (1) need check in headtail

Verify with simulations that the wanted cavity parameters (frequency, Q and shunt impedance) are feasible. Simple geometry considered: single cell cavities input/output wgs coupled by means of 2 identical and large apertures working mode: TM110 Rectangular beam pipe (100x36 mm^2) assumed. June 9, 2012 W. - La Biodola, Elba, Italy 30 A. Gallo, F. Marcellini, LNF-INFN Proposal by A. Gallo and F. Marcellini Stripline plus cavities (2)

Extension to PS and LHC: Comparison with SPS High bandwidth feedback R&D for hardware directly applicable to PS and LHC application to LHC and for SPS at top energy may require higher sampling rate than the present hardware (4 GS/s), 12 GS/s seems current technology barrier, still very expensive required power at 7 TeV in LHC also a concern address bandwidth and power for full parameter space in simulations for LHC, PS and SPS along the ramp potential to damp within bunch oscillations observed both in PS (transition) and in LHC not related to ecloud W. - La Biodola, Elba, Italy June 9, PSSPSLHC nominal energy (inj) GeV1.4 (kin.)26450 top energy GeV bunch spacing [ns]25 cycle length3.6 s18 s approximatel y up to many hours time with ecloudfew msfull cycleentire store scrubbingNoNoyes bunch lengths3.7 ns3.7 ns – 1.7 ns ns expect to require 3x bandwidth & sampling rate for LHC system at top energy when compared with SPS at injection (scaling with bunch length)

What happens before the extraction of LHC beam from the PS? 80 MHz (h = 168) 40 MHz (h = 84) 4  = 14 ns 11 ns 4 ns Adiabatic shortening Bunch rotation Bunch splittings Extractio n H. Damerau see also talk by Ch. Bhat at this workshop PS: no time for scrubbing (low duty cycle !) ecloud observed, but no intra bunch instability (yet ?) June 9, 2012 W. - La Biodola, Elba, Italy 32

,  R,  V signals E. Métral et al., 2003 S. Aumon, 2010 also candidate for cure by high bandwidth feedback if it were / became a limitation Transverse instability in PS at transition

Summary W. - La Biodola, Elba, Italy Multi lab effort ramped up, for kicker design study collaborators from LNF-INFN Frascati recently joined Simulations: first results from Kevin Li confirm previous results, very encouraging Hardware (SLAC) critical for demonstrator tests in 2012 Evaluate impedance and aperture from kickers (down select process !) Shutdown 1 preparations and design report at end of year are next milestones Results in SPS also applicable to PS and LHC, challenging in case of LHC June 9,