Low Energy Antiproton Facility at CERN Christian Carli on behalf of the AD and ELENA team …. with special thanks to P.Beloshitskii, T.Eriksson and S. Maury for help with the slides Brief History of Antiproton Machines at CERN Antiproton Decelerator (AD) Extremely Low ENergy Antiproton ring (ELENA) Summary

Brief History of Antiproton Machines at CERN Conversion of the SPS into a collider (to become ) in the 1970’ies: Conversion of a brand-new machine into a collider First proof of stochastic cooling (proposed several years earlier by S. van der Meer) in ISR ICE for systematic investigations on stochastic cooling and later on electron cooling (proposed by and proof of principle test at BINP) Construction of the Antiproton Accumulator AA with target area …  AA commissioning in 1980  Discovery of the W bosons in 1984 in the 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team

Brief History of Antiproton Machines at CERN 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team Construction and commissioning of the Low Energy Antiproton Ring LEAR Additional facility making use of the p-bar accumulation complex Ultra-slow (and fast) ejection to experiments in south hall and internal targets Commissioning in 1982 with stochastic cooling First machine with electron cooler used for operation First observations of antihydrogen … First proposal to construct ELENA to decelerate to even lower energies (7.85 m circumference to reach 200 keV !!)

Brief History of Antiproton Machines at CERN 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team Construction and commissioning of the Antiproton Collector AC Motivation: increase of the p-bar accumulation rate to increase antiproton intensity in Additional ring with large acceptances to collect and (pre-)cool p-bars before transfer to the AA Commissioned in 1987  Elaborate complex and operation for antiprotons  Linac + PSB + PS for p-bar generation  Two rings AC + AA for accumulation  LEIR with PS again required for transfer  with PS again required as injector (until 1990?)

Brief History of Antiproton Machines at CERN 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team AD Construction and commissioning Around 1995:  AC & AA running only for LEAR  Decision to discontinue p-bar physics with LEIR (several machines and transfers involved … free resources for LHC) Conversion of AC to AD proposed as simplified scheme for low energy p-bar physics  Only one p-bar machine  PS used only for p-bar production Start of AD Commissioning in Autumn 1998 First physics run in summer 2000

AD – Hall and Layout 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team Target Area: 26 GeV/c protons -> 3.57 GeV/c pbars, yield ~ Protons via loop (TTL2, not operational) 4 arcs: chromaticity correction, dispersion suppression Stoch. Cooling kicker Stoch. Cooling pick-up 4 dispersion free straight sections: S-cool, E-cool, RF, diagnostics Experimental Area Electron Cooling

AD – Main Parameters Circumference182 m Production beam1.5*10 13 protons at 26 GeV Injected beam5*10 7 pbars/cycle Beam momenta max-min3.57 – 0.1 GeV/c Momenta for beam cooling:  Stochastic3.57 and 2.0 GeV/c  Electron0.3 and 0.1 GeV/c Acceptances:  Transverse200 (   m  Longitudinal± Ejected beam at 100 MeV/c or 5.3 MeV:  Intensity~  Transverse emittances5   m (dense core ~1   m )  Momentum spread1*10 -4  Bunch Length~200 ns Vacuum pressure, average4* Torr Cycle length100 s 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team

ELENA – Motivation Further deceleration of p-bars coming from the AD to 100 keV  Separation of vacuum system of experiments from the transfer line  100 keV fits the needs of the experiments  Very low energy for synchrotrons  Operation at 100 keV challenging due to very low magnetic fields (in average 94 G along whole circumference, 493 G in Bends) Electron cooling to reduction emittances – compensate increase due to deceleration Expected gain for experiments  About two orders of magnitude more intensity for experiments with thick degraders  About one order of magnitude more intensity for ASACUSA and no delicate RFQD operation  Several experiments operated in parallel Sketch of ELENA magnetic cycle  Expected duration around 10 s to 15 s 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team

ELENA – Proposal in 1982 Proposal for very short ring (11.4 m circumference … longer than in proposal from Jan. 1982) Energy down to 200 keV (discussion on feasibility of 100 keV) Cooler current 0.16 mA 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team From the proceedings of the Workshop on “Physics at LEAR with Low-Energy Cooled Antiprotons”, ERICE (1982)

ELENA – Present Layout Circumference increased to 1/6 the AD Space for all equipment required  Magnets (bends, quadrupoles, correctors) with low fields  RF cavities with very low fields  Fully bakeable vacuum system for pressure ~ Torr (beam life- time)  Electron cooler (plus compensators)  Injection and two ejection lines possible (all in dedicated straight)  Instrumentation suitable for low intensity and energy Machine compatible with layout of the AD/ELENA hall (existing experiments) 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team

ELENA – Present Layout in AD/ELENA Hall 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team

ELENA – present estimate for parameter Parameters to be revised and refined for Technical Design Report (TDR) 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team Momentum range MeV/c Energy range MeV Circumference C30.4 m Tunes horizontal/vertical~1.34 / ~2.45 Electron cooling100 keV and ~650 keV Intensity of injected beam3 × 10 7 Intensity of ejected beam1.8 × 10 7 Efficiency60 % Number of extracted bunches1 to 4 Transverse emittances (95%) at ejection at 100 keV 4 / 4  m ∆p/p after cooling, [95%]10 −4 Bunch length L b at 100 keV1.3 m (300 ns) Required (dynamic) vacuum, Torr3 × 10 −12 Torr

ELENA – Present Lattice With perturbation due to cooler (100 G only) periodicity reduced from two to one Few quadrupoles and constraints imply somewhat irregular lattice, but with small beam sizes No section without dispersion – difficult without adding many more quad’s (giving longer machine) 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team Injection E-cooler  H (m) D (m)  V (m)

ELENA – possible limitations, questions Direct space charge effects  Additional defocusing due to Coulomb repulsion  Non-linear, depending on position in bunch  Tune shift and spread (rule of thumb: maximum -0.2 just an indication – true for low periodicity and energy?) Lattice and stray fields  Deflection due to ~0.5 G earth magnetic field at 100 keV (beam rigidity 457 Gm): > 1 mrad  Careful investigations on stray fields to be expected … good closed orbit control  Ratio between magnet gap and curvature radius not (that) small: correct modeling of magnet entrance/exit 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team Anti-

ELENA – possible limitations, questions Electron cooling  Weak magnetic field (100 G planned at present) to limit lattice perturbations  Twiss parameter at cooler D ≈ 3 m,  x ≈  y ≈ 2 m  Expected (cooled) p-bar parameters  rms =(2/3)  m and  p /p =  Temperatures of cooled pbars kT T ≈ 0.07 eV  Electron beam potential creates parabolic electron velocity profile (plotted for 0.5, 1 and 2mA at 100 keV)  Azimuthal electron drift velocity (crossed magnetic and electric field) for 2 mA: v  /v || = r/3.4 m Studies  Cooling times and equilibrium parameters (with cooling and blow-up mechanisms)  Optimum lattice functions and cooler parameter 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team

ELENA – possible limitations, questions Instabilities  Possibly despite low intensity with small emittances (momentum spread) and energy  Large direct space charge impedance due to low energy Mechanisms provoking blow-up and beam loss  IBS, scattering on gas molecules, heating by electron cooler => equilibrium with cooling, blow-up after cooling until ejection Transfer lines  Electrostatic lines proposed: cheap and magnetic shielding simpler H - (or other ion) source for commissioning  Motivation: ELENA commissioning in parallel to AD run, H - with same mass and charge  Life-time (gas stripping) probably o.k., start commissioning at low energy  Possibly switch to H - after very first commissioning with p-bars 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team

ELENA - Tentative Planning Tentative planning  Next step: detailed study and Technical Design Report TDR 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team

Summary and Outlook Antiproton Rings now have a long tradition at CERN  In the 1980’ies: p-bars for the high energy frontier and at low energy  Now: Protons for the high energy frontier (luminosity in LHC) but still a low energy program with very active & successful experiments ELENA has been approved as a CERN project and will become reality  Thanks to everybody involved for making this project reality  Help and contributions to ELENA construction from interested institutes vital (see ADUC & ELENA meeting on 28 th and 29 th September)  We now have to build it and make it work successfully ELENA a synchrotron operated at an unusually low energy range Next step: detailed study and Technical Design Report (TDR)  AD to be operated for at least one more decade and, thus, serious consolidation required New era for antiproton physics at CERN for many years 11th October 2011 Low Energy Antiproton Facility C.Carli on behalf of the ELENA and AD team

Thanks for your attention !