PS-RF for LHC beams and what is new (protons/ions)

PS-RF for LHC beams and what is new (protons/ions) H. Damerau, S. Hancock Acknowledgments: G. Metral 53 BE/OP Shutdown Courses 2012 25 January 2012

Outline • Introduction • LHC multi-bunch beams in the PS • Proton beams • Flat-bottom and acceleration: injection, longitudinal emittance control, triple splitting • Flat-top: synchronization, splitting and bunch rotation • Lead ion beams • Acceleration + manipulations on intermediate flat-top • Rebucketing, synchronization, extraction • Summary

Please interrupt for questions!

Proton and ion beams for LHC For protons: M. Benedikt, LHC-OP-ES-0002 rev. 1.0, edms.cern.ch/document/487892/ p+ beam # bunches el [eVs] Intensity per bunch LHC25ns 12 to 72 0.35 2 · 1010 to 1.3 · 1011 ppb LHC50ns 12 to 36 2 · 1010 to 1.7 · 1011 ppb 0.35 • LHC50ns • Main physics beam in 2011, most probably also in 2012 • LHC25ns • Injected into LHC in 2011, extensive tests and scrubbing (?) in 2012 • LHC100ns  new production scheme in 2012 • Low intensity proton beam for proton-ion collisions in LHC Pb54+ # bunches/spacing el [eVs] Intensity per bunch Early 1 • 10.4 6.5 · 109 charges/bunch Intermediate 2/200 ns Up to 1.3 · 1010 charges/b. 10.4 Nominal 4/100 ns 6.5 · 109 charges/bunch 10.4

The LHC25ns cycle in the PS gtr Eject 72 bunches Inject 4+2 bunches (sketched) Low-energy BUs h = 21 h = 7 High-energy BU h = 84 Triple splitting after 2nd injection Split in four at flat top energy 2nd injection inj2allb.dat foursplitb12.dat 1.4 GeV 26 GeV/c → Each bunch from the Booster divided by 12 → 6 × 3 × 2 × 2 = 72

The LHC50ns cycle in the PS Eject 36 bunches Inject 4+2 bunches gtr Low-energy BUs h = 21 h = 7 h = 84 Triple splitting after 1st injection Split in two at flat top energy 2ndinjection inj2allb.dat twosplitb12.dat 1.4 GeV 26 GeV/c → Each bunch from the Booster divided by 6 → 6 × 3 × 2 = 36

Problems? Need tools Proton Synchrotrons C P S http://cdsweb.cern.ch/record/1398557/files/ATS%20104%20perf.pdf • OASIS, Tomoscope, Bunch shape measurement (BSM)... • Use Tomoscope or OASIS reference files whenever possible!

The first bunch from the booster must arrive 250 ns after the common rising edge of the RF trains First bunch in the PS: protons and ions Local video display With ions, only the RF trains are visible 2. Receive bunch correctly phased, 250 ns after 1. Send RF trains (h = 1, 4, 8) to PSB for phase positioning Convention for PSB → PS transfer: ‘250 ns rule’ • Adjust BA3.PSYNCOFFSET such that this rule is respected • Bucket must then be at the correct phase with respect to the bunch (local)

Injection oscillations • To minimize the glitch when switching to beam signals, check injection oscillations with loops closing after 2 ms 1st injection 1st injection 2nd inj. 3 4 2 1 3 4 2 1 3 4 inj2osc.dat inj1osc.dat • Ring 3 of 1st injection: no or only small correction should be required • Correct oscillations with PSB synchronization offset BAn.PSYNCOFFSET

Second injection Adjust DR EXTFREQPSB/7 → Make frev (closed loop, 2nd inj.) the same as frev at first inj.

After transfer Observe bunches after injection into the PS with the BSM: • Bunches must have equal intensity as seen by the wall-current monitor in the PS • Transfer losses should be negligible at the same time

Longitudinal emittance control Why bother about longitudinal emittance? • 1.3 eVs is required for triple splitting (LHC50/LHC25) • During acceleration el/Nbunch > 1.4 eVs/5.2 · 1011 ppb for stability • Stringent specification at PS extraction of el = 0.35 eVs/bunch Prepare splitting flat bottom Stability gtr or final el/bunch Stability and final el/bunch (LHC25 only)

Emittance budget of the LHC beam variants Tomoscope: Cxxxbn.dat LHC25ns LHC50nsLHC75 LHC100 LHC150 Injection, h = 7 1.1 eVs 1.0 eVs After 1st blow-up 1.3 eVs 1.3 eVs Splitting on flat bottom triple triple After splitting 0.45 eVs0.45 eVs After 2nd blow-up 0.65 eVs0.65 eVs Acceleration h = 21 h= 21 After 3rd blow-up 1.3 eVsno blow-up Splitting on flat top quadruple double Final emittance per bunch 0.35 eVs0.35 eVs Total emittance increase +280 % +100 % Obsolete • Most of the long. emittance increase is applied via blow-ups • Small contribution by each splitting (only few percent)

Longitudinal emittance along the cycle el per bunch LHC25 gtr Arrival flat-top High-energy BU Triple split Quad split Low-energy BUs el per bunch at extraction C1395b4.dat C1515b12.dat C2205b12.dat Triple split Transition Stability, final el → Wrong el may cause all kind of funny effects later in the cycle!

Triple bunch-splitting (LHC25, LHC50) • Split bunches in three similar parts (h7 → h21) • Three RF harmonics at the same time • Control two relative phases to level of ~ 2º • Control one relative RF amplitude to level of better than ~ 5%

Phase control for triple splitting PA.GSRPB PA.GSRPC CERN-ATS-Note-2011-104 PERF …or just use the amplitude knobs • Tuning Group A (C36, C46): • h7 → h21, phase reference,PA.GSRPA zero everywhere • Tuning Group B (C51, C56, C66, C76, C81, C91): • h21 only, relative forward phase h7/h21, PA.GSRPB • Tuning Group C (C86, C96): • h14 → h21 only, relative forward phase h7/h14, PA.GSRPC

Effect of phase errors during triple split trisplitb1.dat trisplitb1.dat h21 phase 15º too low h14 phase 10º too high • Relative phases must be controlled to well below 5° • Slightly intensity dependent adjustment

Centre to outer bunch symmetry trisplitb1.dat h14 RF voltage 10% too low • RF voltage on h14 defines intensity ratio in inner/outer bunches after splitting • Relative control and stability to the level of few percent

RF Slow signal Digital signal What is a beam control? Loop corrections Reference magnet B+ h·frev B Df frev B- RF-Gen. → Calculate frev, open loop from bending field and multiply by h → Correct with beam measurements to obtain frev, closed loop

RF Slow signal Digital signal Df Df • Phase loop adjusts the RF phase to where the beam would like it • • Suppress phase transients and RF phase noise to avoid blow-up Beam phase loop Phase pick-up RF cavity Cavity phase Beam phase frev, closed loop Loop correction Synchronous phase, fs - Move the wave! frev, open loop

Df Adjustment of phase measurement Phase pick-up RF cavity Cavity phase Beam phase Df (frev) = Dfoffset + 2phfrev·Dt • Every phase measurement is a phase comparison between two signal • Cable lengths of beam and cavity return signals influence measurement How to reference phase, Dfoffsetmeasurement and avoid cable delay, Dt? • Button to compensate offset • Beam reference: Df = 0 on flat-bottom and flat-top • Adjust absolute cable length • Not very sensitive, checked once during start-up

How to measure beam phase? ...independent from RF voltage and beam intensity Crystal filter AVC Df,Dt Beam/ cavity ret. To phase detector Various harmonic components, amplitude not constant hfrev appears at fIF fIF is only component PA.DPC10PA.DPC10ACCPA.DDC20RETPA.DDC40RET LO:hfrev+fIF • Absolute length equalization normally only after hardware changes • BUT: Detection electronics slightly dependent upon beam intensity • Remove remaining offset on flat-bottom and -top with offset knob

Phase loop offset during acceleration What is the phase reference for the phase loop? → Remote button to adjust the offset of the phase measurement! OASIS global ‘LHC50ns RF adjustments’ • One button for each phase loop or harmonic number • PA.DPC10: h7 phase loops offset • PA.DPC10ACC: h21 (LHC50, LHC25)

Synchronization: in two steps 1. Coarse synchronization, h1: Move the whole batch Reference given by frev SPS • Batch at the correct position 2. Fine synchronization, h84: Put bunch to bucket centre • Improve precision • Phase error of 1º at h = 1 • corresponds to 84º at h = 84 (40 MHz) • corresponds to 420º at h = 420 (200 MHz) More than one SPS bucket

Coarse synchronization • Coarse synchronization before RF manipulations on flat-top • Set radial steering to adjust beam frequency  Smooth lock! OASIS global ‘LHC25ns RF adjustments’ tbeat • • Time constraint: • Synchronization loop must lock before voltage program of 13.3/20 MHz cavity starts • Fine synchronization later, before extraction

RF Slow signal Digital signal Df How to change frev? Radial loop Beam Hybrid D S D/S frev, closed loop • Normally: Keep beam in the centre of the radial loop pick-ups • Move beam radially by adding perturbation function PA.GSRPOS • Change revolution frequency • Change beating between closed loop frev and fRF,SPS/420 Loop correction - frev, open loop Steering: PA.GSRPOS

LHC50ns bunch splitting at flat-top energy • Long. emittance: ~ 0.65 eVs • Bucket area (h21): ~ 3.2 eVs • Synchrotron freq.: 120 Hz • Splitting duration: 118 ms twosplitb12.dat • RF harmonics (h21 → h42) the same as for a 25 ns beam, but half longitudinal emittance • Sensitive to RF phases → prone to drift → PA.DPC20

Rebucketingor splitting? • LHC25 and LHC50 (ns) seem to be very similar at first sight: Just turn the last bunch splitting (h42 → h84) into a rebucketing h = 84 h = 84 LHC25 LHC50 h = 42 h = 42 • Splitting and rebucketingvery similar manipulations • Relative RF phase determines what happens (180º) • Rebucketingis much more robust to phase errors

Adjustment of rebucketing 1. Change PA.DPC40 by ~ 180º and search phase where bunches jump from one side to the other rebucketing.dat rebucketing.dat 2. Change PA.DPC40 by exactly 180º to go back to stable phase

Well adjusted rebucketing Switching of RF trains PAX.SSWTDISTSPS disabled rebucketing.dat rebucketing.dat • Rebucketingis a very robust process • No problem even with a forward phase error of 20º on PA.DPC40 • There should be not much to see…

Fine synchronization h84LOC Delay Df fRF SPS, 200 MHz (h = 420) Multi- plier × 4 h84REF Divider by 5 Internal h = 21, synchronous to cavity RF Fine sync. phase PA.DDCSYNCF Reset PA.DCNBEJ Df Reset Divider by 21 (MHS) Divider by 84 h1LOC h1REF Coarse sync. phase • Coarse (PA.PSYNCDISC-LHCC) and fine (PA.PSYNCDISC-LHCF) synchronisation phase discriminators compare the same signals, but: • Fine synchronisation 84 times more sensitive (h = 84/h = 1) • New after start-up 2011: Remote delay PA.DDCSYNCF to align synchros

Phase discriminators on the flat top • The harmonic number for the phase loop must follow the harmonics of the cavities active Zero at switch-over DPC10ACC DDC20RET OASIS global ‘LHC50ns RF adjustments’ DDC40RET DDCSYNCF • The offset of each phase loop harmonic must be compensated: • PA.DPC10ACC: h21 phase loop • PA.DDC20RET: h42 phase loop • PA.DDC40RET: h84 phase loop (only LHC25) → No h = 84 phase loop with LHC50ns → Rebucketing directly to fRF,SPS divided by 5

Bunch rotation in two steps: 1. 290 ms before extraction: h = 84 (40 Mhz): 100 → 300 kV 2. 90 ms before extraction: h = 168 (80 Mhz): 0 → 600 kV For the second step: Bunches must be shorter than 12.5 ns (full length)! R. Garoby, CERN PS/RF/Note 93-17 Bunch rotation for LHC-type beams h = 168 h = 84 80 MHz phase controlled by PA. DPC80

The first bunch from the must be aligned within ± 2.5 ns with respect to the rising edge of the frev marker from the SPS Synchronization check and ejection bucket frev marker PS ejection video pulse switch • from SPS • RF simulation Beam signal from wall current monitor Move beam with PA.DCNBEJ • The bucket number PA.DCNBEJ is integer by definition • 2012: New fine delay to correct extracted bunch position -2.5...2.5 ns

What is finally delivered • 36 bunches with up to 1.7 · 1011 ppb →6.1 · 1012ppp • Separate PPM users to switch between 12/36 bunches • 50 ns beam already well above nominal intensity

2012: Study alternative production schemes h2+1PSB → h9PS and h = 9 → 10 → 20 → 21 Pure h = 21 Voltage programs: C. Carli, Chamonix 2011 h = 21 h = 9 h = 20 h = 10 Pure h = 9 OR Becoming operational in 2012 for LHC100ns for p-Pb collisions and CNGS, small emittance LHC beam R. Garoby, 2011 h = 7→ 8 → 9 → 10 → 11 → 12 → 13 → 14 → 7 → 21  Initial MDs in 2012

Injecting and accelerating lead ions • PS with ions is like TGV at 10 km/h: • You don’t feel that it moves • The PS RF does not feel the beam • RF wise a textbook accelerator!  Only few remote adjustments needed for the ion beam control

Lead ion Pb54+ beam variants for LHC MSWG 04/12/2009 VLEIR=2.8kV, VPS=15kV VLEIR=2.8kV, VPS=25kV • New in 2011: Intermediate beam • Turn bunch splitting of nominal beam into rebucketing • Twice more intensity per bunch • No margin for long. emittance in PS → Luminosity production beam in LHC of 2011 run. Also in 2012?

The early ion cycle in the PS Eject 2 bunches spaced 200 ns Inject 1 bunch h = 169 h = 16 gtr h = 16 Intermediate flat-top No manipulation Rebucket Single bunch injected from LEIR Accelerate from flat-bottom to flat-top on h = 16 (2.8  7.6 MHz) Synchronized (h = 1/ h = 9) Rebucketed to h = 169 for adia-batic bunch shortening to < 4 ns Extraction rebucketing.dat 1.4 GeV 26 GeV/c →Single bunch from LEIR results in one bunch at ejection

The nominal ion cycle in the PS Eject 4 bunches spaced 100 ns Inject 2 bunches h = 169 h = 21 gtr h = 16 Intermediate flat-top Batch expansion Rebucket rebucketing.dat bexpand.dat 0.38 GeV/u 5.9 GeV/u → Each bunch from LEIR divided by 2 → 2× 2 = 4

The intermediate ion cycle in the PS Eject 2 bunches spaced 200 ns Inject 2 bunches h = 169 h = 21 gtr h = 16 Intermediate flat-top Batch expansion Rebucket rebucketing.dat bexpand.dat 0.38 GeV/u 5.9 GeV/u → Each bunch from LEIR results in one bunch at ejection

199.81 Main challenges with Pb54+ beam • Low signals from due to low beam intensity, especially on the flat bottom • Mechanical relay to switch wall-current monitor to beam control • Sensitive beam phase detection • Huge and fast frequency swing frev,ej/frev,inj = 2.7 (1.09 for protons) • Signal path length of beam and (simulated) cavity return well equilibrated • Compensate frequency dependent delay t(fRF) of power amplifiers • Sophisticated RF manipulation for “Intermediate” and “Nominal” beams • Inverse batch compression (cf., AD beam) • Bunch splitting (cf., proton LHC beams) • Four different phase loop harmonics: hPL = 16, 12, 21, 169 • Delicate rebucketing from h = 16 or 21 to h = 169

PS-RF for LHC beams and what is new (protons/ions)