Thomas Jefferson National Accelerator Facility Newport News, Virginia, USA ELIC: A HIGH LUMINOSITY AND EFFICIENT SPIN MANIPULATION ELECTRON-LIGHT ION COLLIDER BASED AT CEBAF* L. Merminga, Ya. Derbenev, A. Hutton, M. Poelker, and Y. Zhang, Jefferson Lab, 12000 Jefferson Ave., Newport News, VA 23606 *Work supported by the U.S. Department of Energy, contract DE-AC05- 84ER401050 Abstract Electron-light ion colliders with center of mass energy between 20 and 100 GeV, luminosity between 10 33 and 10 35 cm -2 sec -1 , and polarization of both beams at or above 80% has been proposed for the study of hadronic structure. The proposed scheme would accelerate the electron beam using the CEBAF recirculating linac with energy recovery. If 20-40 MV/m accelerating structures are installed in the CEBAF tunnel, then a single recirculation can result in electron beam energy of about 5-10 GeV. After colliding with protons/light ions circulating in a storage ring under electron cooling at an energy of 50-100 GeV or above, the electrons are re-injected into the CEBAF accelerator for deceleration and energy recovery. In this report several innovative features of electron and ion beam designs and their advantages in delivering the luminosity and spin are described. These features include: electron circulator ring to reduce electron polarized source and energy recovering linac requirements, twisted spin booster and collider ring; low energy electron cooling accumulator as option for stacking beams from positive polarized ion sources; interaction points with low beta-star and crab-crossing using the short, cooled ion bunches. Accelerator physics and technology issues for both protons/ions and electrons are discussed. The feasibility of an integrated fixed target program at 25 GeV and collider program with center of mass energy between 20 and 45 GeV is also explored. and NUCLEAR PHYSICS MOTIVATION INTEGRATION WITH 25 GeV FIXED TARGET PROGRAM [1] R&D STRATEGY ELECTRON COOLING IN ELIC [4] CONCLUSIONS [1] L. Merminga, et al., “ELIC: An Electron-Light Ion Collider Based at CEBAF,” Proceedings of EPAC 2002 [2] Ya. Derbenev, “Luminosity Potentials in Colliders with Electron Cooling,” These proceedings TPPB081 [3] Ya. Derbenev, “Advanced Concepts for Electron-Ion Collider,” Proceedings of EPAC 2002 [4] Ya. Derbenev, Proceedings of ECOOL’03 Workshop [5] Ya. Derbenev, Proceedings of EPAC 2000 [6] A. Bogacz et al., and C. Tennant et al., These proceedings TOAC006 and RPPG032 Ion S ource RFQ DTL CCL IR IR Beam D um p S nake S nake CEBA F w ith Energy Recovery 5 GeV electrons 50-100 G eV light ions Solenoid Injector Ion S ource RFQ DTL CCL IR IR Beam D um p S nake S nake CEBA F w ith Energy Recovery 5 GeV electrons 50-100 G eV light ions Solenoid Ion S ource RFQ DTL CCL IR IR Beam D um p S nake S nake CEBA F w ith Energy Recovery 5 GeV electrons 50-100 G eV light ions Solenoid Injector Yes Yes No CR cm -2 sec -1 Lum i - 0.1 2/1 10 4.5/3.2 1500 1x10 10 - 5 e - Point D esign 3 0.09 0.01 1 0.1 4.5/3.2 2.5 1x10 10 Yes 50/100 Protons 0.05 - - - L 0.01 0.006 - e / i 0.1 5 0.1 cm z 1 4 5 20 cm * 0.2 10 10 m n 6 6 14 14 m * 0.4 0.6 0.24 A I ave 150 MHz f c 5x10 9 2x10 10 2.5x10 10 1x10 10 ppb N bunch Yes - Yes - - Cooling 50 5 50 5 G eV Energy Protons e - Protons e - Point D esign 2 Point D esign 1 Units Param eter Yes Yes No CR 6x10 34 / 1x10 35 1 x 10 34 1 x 10 33 cm -2 sec -1 Lum i - 0.2 0.1 2/1 10 4.5/3.2 2.5 1500 1x10 10 - 5 e - Point D esign 3 0.09 0.01 1 1 0.1 4.5/3.2 2.5 1x10 10 Yes 50/100 Protons 0.05 - 0.05 - - L 0.01 0.1 0.006 0.5 - e / i 1 0.1 5 0.1 cm z 1 4 5 20 cm * 0.2 10 0.2 10 m n 6 6 14 14 m * 0.4 1.6 0.6 0.24 A I ave 500 150 MHz f c 5x10 9 2x10 10 2.5x10 10 1x10 10 ppb N bunch Yes - Yes - - Cooling 50 5 50 5 G eV Energy Protons e - Protons e - Point D esign 2 Point D esign 1 Units Param eter A B C 25 cryomodules 25 cryomodu J t CirculatorRing Injector J t 1/f c C CR /c f ~100 C CR /c f CEBAF with energy recovery is used for rf power savings and beam dump requirements “Figure-8” storage ring is used for the ions for flexible spin manipulations of all light-ion species of interest Circulator ring for the electrons may be used to ease high current polarized photoinjector requirements spi n Soleno id A high luminosity polarized electron – light ion collider has been proposed as a powerful new microscope to probe the partonic structure of matter Over the past two decades we have learned a great amount about the hadronic structure Some crucial questions remain open: • What is the structure of hadrons in terms of their quark and gluon constituents? • How do quarks and gluons evolve into hadrons? Implement 5-pass recirculator, at 5 GeV/pass, as in present CEBAF (One accelerating & one decelerating pass through CEBAF 20-45 GeV CM Collider Program) NUCLEAR PHYSICS REQUIREMENTS Center-of-mass energy between 20 GeV and 100 GeV with energy asymmetry of ~10, which yields E e ~ 3 GeV on E i ~ 30 GeV up to E e ~ 5 GeV on E i ~ 100 GeV CW Luminosity from 10 33 to 10 35 cm -2 sec -1 Ion species of interest: protons, deuterons, 3 He Longitudinal polarization of both beams in the interaction region 80% required for the study of generalized parton distributions and transversity Transverse polarization of ions extremely desirable Spin-flip of both beams extremely desirable BASIS OF ELIC PROPOSAL THE ELIC PROPOSAL [1] CEBAF with upgraded cryomodules and energy recovery “Figure 8” storage ring and boosters Circulator Ring Conceptual development “Circulator Ring” concept promises to ease high current polarized photoinjector and ERL requirements significantly Additional concepts for luminosity improvements are being explored Analysis/Simulations Electron cooling and short bunches Beam-beam physics Circulator ring dynamics ERL physics Experiments • JLab FEL (10mA), Cornell/JLab ERL Prototype (100mA), BNL Cooling Prototype (100mA) to address high current ERL issues • CEBAF-ER: The Energy Recovery experiment at CEBAF to address ERL issues in large scale systems [6] ELIC DESIGN INNOVATIONS [2,3] • Electron circulator ring • Twisted spin booster and collider ring • Short ion bunches resulting from electron cooling • Low beta-star (~ 5 mm) • Crab-crossing • Traveling ion focus Beam energy GeV 150/7 Energy ofcooling beam MeV 75 Bunch collision rate GHz 1.5 Num berofparticles/bunch 10 10 0.2/1 Beam current A 0.5/2.5 Horizontalem ittance, norm m 1/100 Verticalem ittance, norm m 0.01/1 N um berofinteraction points 4 Totalbeam -beam tune shift 0.04/0.16 Space charge tune shiftin proton beam 0.02 Lum inosity over4 interaction points 10 35 /cm 2 .s 2 Cooling/IBS tim e in proton beam core min 5 Core and lum inosity Touschek’s lifetim e hours 20 Electron Cooler for ELIC Electron cooling time grows with beam energy in the first or second power and with normalized beam emittances - in the third power. Therefore, it seems critically important to organize the cooling process in two stages: cool the ion beam initially at injection energy after stacking it in collider ring (in parallel or after re-bunching), and continue the cooling during and/or after acceleration to a high energy. REFERENCES It is important to distinguish between multiple IBS and single scattering or Touschek effect. Multiple scattering contributs to ion Focker-Plank equilibrium i.e. beam core, while single scattering kicks the particles out of the core. To overwhelm multiple IBS, current of cooling beam must well exceed a critical value, proportional to ion current. After the cooling starts, the ion beam will shrink to the Focker-Plank equilibrium. Following this stage, an interplay between Touschek scattering and particle damping due to electron cooling beyond the core will determine the core i.e. luminosity lifetime. At ion energies far above transition value, the area of the cooling beam should frequently exceed that of the ion beam, in order to extend the ion core lifetime. Using this phenomenology one can estimate an optimum set of parameters for maximum average luminosity of a collider. See Table below. At energies above the transition value, energy exchange at intra-beam collisions leads to horizontal emittance blow up due to energy- orbit coupling, and vertical emittance – due to x-y coupling. Since luminosity is determined by the product of two emittances, reduction of transverse coupling to a minimum - while conserving the beam area - would result in decrease of energy scattering, hence, decrease of the impact of IBS on luminosity. Electron cooling then leads to a flat equilibrium with a large aspect ratio [5]. A flat ion beam should collide with a correspondently flat electron beam. INTRABEAM SCATTERING AND FLAT BEAMS [2] The same electron accelerator can also provide 25 GeV electrons for fixed target experiments for physics. The hadron physics community is asking for a high luminosity, polarized electron-light ion collider Our design studies have led to an approach that promises luminosities up to 10 35 cm -2 sec -1 This design can be realized cost- effectively using energy recovery on the JLab site and can be integrated with a 25 GeV fixed target program for physics Planned R&D will address open issues M ax. energy ofe-beam MeV 75-125 Charge/bunch nC 1.7 Currentin EC ring A 2.5 Bunch rep.rate M Hz 1500 Currentin ER L mA 25 Cooling section length m 15 Coolerring circum ference m 60 N um berofelectron revolutionsin circulator 100 Circulation duration secs 20 Bunch length cm 1 Energy spread 3-5x10 -4 Solenoid field T 2 (m ax) Beam radiusin solenoid mm 1 Larmorbeta-function m 0.6 Therm alcyclotron radius m 2 Beam radiusatcathode mm 3 Solenoid field atcathode kG 2 Driftemittance m 1000 Laslett’stune shiftin CR at10 M eV 0.03 Tim eoflongitudinalinter-beam heating secs 200 C ooling at20 G eV Proton em ittancenorm m 4 Proton bunch length (fullw idth) cm 20 Proton charge/bunch nC 0.17x(1-10) Energy spread 3x10 -4 Cooling tim e min 10 IBS equilibrium Emittance m 1 Bunch length cm 2 Laslett’stune shift, m ax 0.1 Cooling tim e min 0.5 C ooling at150 G eV Initialcooling tim e min 3.5 IBS/beam -beam equilibrium Cooling tim e (extended orscanning e-beam ) min 10 X /Y em ittancenorm m 1.6/0.016 Energy spread 2x10 -4 Bunch length cm 1