Booster Beam Dynamics Christian Carli

1. Booster Beam DynamicsChristian Carli On behalf of the team working on and contributing to the study: M. Aiba did all ORBIT simulations (Booster modelling …. injection) R. Garoby: elaboration of longitudinal painting scheme, Booster with Linac4 in the CERN complex B. Goddard and team: injection hardware, help implementing it in ORBIT M. Martini carried out ACCSIM simulations M. Chanel: experience on PS Booster operation and 160 MeV measurements S. Cousinau and her colleagues at SNS for help and advice on ORBIT F. Ostiguy for advice and help with ESME F. Gerigk, D. Montillot …..

2. Overview of the presentation • Introduction • PS Booster Overview • PS Booster with Linac4 • Injection studies • Active longitudinal Painting • Simulations of longitudinal Painting • ORBIT Simulations of the PS Booster Injection • Benchmark effort ACCSIM versus Measurements • Integration in the CERN complex • Further potential Topics and Studies • Summary Linac4 Machine Advisory Committee - Booster beam dynamics

3. Introduction - PS Booster Overview • Constructed in the 70ies to improve the performance (intensity) of the PS • Four superimposed rings (chosen instead of fast cycling synchrotron or 200 MeV Linac) • 16 cells with triplet focusing, phase advance >90o per period • Large acceptances: 180  m and 120  m in the horizontal and vertical plane, respectively • Multiturn injection with betatron stacking and septum at 50 MeV • Acceleration to 1400 MeV (was 800 MeV at the beginning) • Double harmonic RF (now: h=1 and h=2), resonance compensation, dynamic working point … • Intensities of up to 1013 protons per ring (i.e. four times design) obtained • Maximum direct space charge tune shifts larger than 0.5 in the vertical plane • Vesatile machine - many different beams with different caracteristics Sketch of the PS Booster with: - Distribution of Linac beam into 4 rings - Recombination prior to transfer Linac4 Machine Advisory Committee - Booster beam dynamics

4. Introduction - PS Booster with Linac4 • PSB to PS transfer energy increased in two steps from 800 MeV to 1400 MeV: • To alleviate direct space charge effects at PS injection • Creation of a bottleneck due to direct space charge in the Booster at low energy • PS Booster with Linac4: • Increase of PS Booster injection energy from 50 MeV to 160 MeV and 2 by factor 2 • (Beam stays (a bit) longer with large direct space charge detuning) • Goal: Increase of intensity within given emittances by factor 2 • > Nominal LHC beam with PS single batch filling, • Save generation of ultimate LHC beam with PS double (and single ?) batch filling, • Increase of number of protons available for other experiments • H- charge exchange injection and Linac4 beam chopping: • Opens possibility for painting (in all three planes ?) and further gain in performance • Losses and activation ?? • Losses (on septum) inherent to conventional multiturn injection disappear • Losses (during times with large direct space charge detuning) at higher energy • Some bottleneck at transfers PS Booster -> PS and PS -> SPS ?! Linac4 Machine Advisory Committee - Booster beam dynamics

5. Introduction - PS Booster with Linac4 Beams to delivered: • Beams considered challenging: • In addition various beams (less challenging ?): • LHC single bunch beams: Pilot beam, Probe beam, single bunch physics beam • Beams for PS physics: Slow ejection east hall, AD, nTof … • MD beams … • Many of these beam may be even easier with Linac4 (Painting of small longitudinal emittances, no sieve reducing the Linac2 intensity needed … ) Linac4 Machine Advisory Committee - Booster beam dynamics

6. Injection - active longitudinal Painting • With Linac4: similar RF system than at present • Double harmonic • fundamental h=1 and h=2 systems to flatten bunches • reduces maximum tune shifts • Injection with d(B)/dt = 10 Tm/s (no need for injection with small ramp rate with painting any more) • Little (but not negligible) motion in longitudinal phase space. • No way for painting from synchrotron motion (large harmonic numbers and RF voltages ruled out) • Need for active painting (aim: fill bucket homogeneously) and energy modulation Linac4 Machine Advisory Committee - Booster beam dynamics

7. Injection - active longitudinal Painting • Principle: • Triangular energy modulation (slow, ~20 turns for LHC) • Beam on/off if mean energy inside a contur ~80% of acceptance • Nominal LHC: intensity with 41mA (!!!) after 20 turns • High intensity: several and/or longer modulation periods • Potential limitations: Linac4 jitter, debunching of Linac4 structure in Booster Linac4 Machine Advisory Committee - Booster beam dynamics

8. Injection - Simulations of longitudinal motion • Simulation with ESME for nominal LHC beam: • Energy modulation 1.1 MeV, plus rms spread 120 keV • About 98 % of particles at the and buching factor ~0.60. • High intensity (reduced bucket hight due to direct space charge): • Similar results with reduced E modulation After 10 turns after 20 turns (completed injection) after~3000 turns Linac4 Machine Advisory Committee - Booster beam dynamics

9. Injection - first Results with ORBIT • Combines: • Transverse painting as designed by team working on new injection hardware • Active longitudinal painting • In Case of Dispersion Missmatch: Blow-up of horizontal emittance • Large/small emittance dependant on position in longitudinal phase space • Investigations with/without dispersion mismatch from M. Aiba Evolution of rms emittances after injection - blow-up (extrapolation ?) may be too large(slightly larger relative blow-up for 99% and 100% emittances) Linac4 Machine Advisory Committee - Booster beam dynamics

10. Injection - first Results with ORBIT from M. Aiba Dispersion at injection matched D mismatch (line ends with D=0m, Dbooster~-1.4m) -3 x’ (mrad) 3 -3 x’ (mrad) 3 0 x(m) 100 0 x(m) 100 -20 x(mm) 20 -20 x(mm) 20 -6 y’ (mrad) 6 -6 y’ (mrad) 6 0 y(m) 100 0 y(m) 100 -15 y(mm) 15 -15 y(mm) 15 -2 E (MeV) 2 -2 E (MeV) 2 -180o phase 180o -180o phase 180o -180o phase 180o -180o phase 180o Linac4 Machine Advisory Committee - Booster beam dynamics

11. Injection - first Results with ORBIT from M. Aiba • Only nominal LHC beam considered so far • No simulations for high intensity yet • 240 000 macro-particles over 5000 turns (~5ms) • Feasible within a reasonable time for the job to run • No acceleration, nor injection foil scattering, nor machine imperfections • No dramatic effect of dispersion mismatch • Blow-up difficult to extrapolate (straight line, saturation …) • Simulation over more turns and with more particles ? Linac4 Machine Advisory Committee - Booster beam dynamics

12. Benchmark measur’ts (M. Chanel): High intensity (1013 protons in one ring) beam at 160 MeV plateau Time evolution of emittances and intensity Long bunches (see fig.) tune shifts ~0.25 Short bunches (second harmonic RF in phase) -> more losses Different working points …. Simulation (M. Martini) with ACCSIM: Only short times (computation time) In general overestimation of growth rates (except long bunches & and hor. plane) Insufficient statistics ? Attempt to compare with ORBIT ? As well significant ACCSIMORBIT benchmark effort: Moderate agreement only so far Benchmark Efforts -ACCSIM versus Measurements H*short bunch Dashed: measurement (interpolatio) Solid: simulation e(2s)= (93, 52) pm 0 rms* 20 H*long bunch - fair agreement e(2s)=(100, 47) pm v*short bunch 0 protons 1013 v*long bunch 0 time(ms) 200 200 Time (ms) 1000 Linac4 Machine Advisory Committee - Booster beam dynamics

13. Integration into the CERN Complex -present Ideas, under Investigation Proposals made (R. Garoby et al.) for demanding Beams: • Nominal LHC Beam with single batch PS transfer: • Splitting in the Booster, transfer of beam from three rings into hPS=7 buckets (rest similar to present scheme with Linac2, but no double batch), details/options under discussion: • hPSB=1 (and hPSB=3) component to adjust spacing to hPS= 7 • Shorter bunches due to ejection kicker, bunch rotation in PS, adiabatic RF voltage decrease … • No hPSB=1 component and injection off the bucket center for blow-up • Ultimate LHC Beam (several options): • Increase intensity (if feasible) of scheme for nominal LHC beam • With double batch PS filling: • Like with Linac2 for nominal LHC beam, but higher intensities • Tunes shifts and spreads in PS acceptable ? (some margin for bunch length) • “Exotic” schemes with single batch PS filling using all four PSB rings: • Four Booster rings with hPSB=3 fill 12 out hPS=14 buckets … • Four Booster rings with hPSB=2 fill 8 out hPS=10 buckets … • High Intensity (CNGS like): • Schemes similar to present case hPSB=2 and hPS=8 with Linac2 (possibly higher intensities) Other beams with similar characteristics to present situation with Linac2: • No problems for transfer to PS (just the injection into the Booster changes) Linac4 Machine Advisory Committee - Booster beam dynamics

14. Further Studies • Injection studies with validation & optimization of the painting scheme: • Add acceleration and injection foil, possibly machine imperfections • Tracking over longer times, check parameters to avoid numerics problems • Check filamentation of structure from injection - especially with dispersion mismatch • Limitations: Linac4 energy jitter, debunching in Booster and associated energy spread • Elaborate scenarios for the generation of all beams needed • Integration into the CERN Complex - Elaborate detailed scenarios for all beams needed • Check limitations of present Booster hardware: • Instabilities (existing damper with higher intensities) • (Cure beam loading problems of h=2 cavities for h=1 beams to remove a potential limitations for ISOLDE beams) • Injection losses and associated activation (“normal” losses, failure scenarios …): • Desirable, in collaboration with or by injection hardware team (resources ?) • Possibly advanced Studies on slow Beam Losses, and Activation and Collimation ….: • Feasibility (computational tools, resources) unclear • Most (all) accelerators with large direct space charge designed without detailed simulations • Losses in ring during period with large direct space charge effects: • Prerequisite: Benchmark measurements/simulations (160 MeV) to judge feasibility • Estimate losses and induced radiation • Possibly devise simple collimation (scraping needed before PS transfer) Linac4 Machine Advisory Committee - Booster beam dynamics

15. Summary • Linac4 to improve Booster performance • Double 2 and, thus, intensities (within fixed emittances) by a factor two • Versatility of the Booster must be maintained • Active longitudinal Painting proposed: gain: ~10 % intensity for fixed emittances • Studies carried out so far • ESME simulations for longitudinal painting • First ORBIT Runs of the complete Injection • Benchmarks ORBITACCSIM and ACCSIMMeasurements • agreement not (yet?) satisfying • Outlook • Complete injection simulations (acceleration, foils …) • Validate longitudinal painting (energy jitter, Linac4 debunching) • Complete study on integration of Linac4 & Booster into the CERN complex • Injection Losses highly desirable • Possibly check other potential problems (cavities, instabilities & damper …) • Possibly advanced performance estimates with simulations: • Agreement simulations/measurements a prerequisite • Study of Losses & Blow-up during Acceleration, Activation, Rudimentary Collimation ? Linac4 Machine Advisory Committee - Booster beam dynamics