1. CASA Collider Design Review Retreat HERA The Only Lepton-Hadron Collider Ever Been Built Worldwide Yuhong Zhang February 24, 2010

2. Outline Overview, baseline design and parameters Overview, baseline design and parameters Polarization and cooling Polarization and cooling Luminosity upgrade Luminosity upgrade Interaction region Interaction region

3. e-p Proton on wire target electron on polarized gas target Construction started in April 1984, ended on Dec. 1990 Commissioning took place in 1991 (First collision on Oct. 14, 1991) Data taken in June. 1992

6. HERA Collider Rings Design requirements head-on collisions Energy range p: up to 300 to 820(920) GeV (lower limit by maximum path length adjustment for preserving e and p synchronism) e: up to 30 GeV RF power (SR loss) limit 7.2 MW

7. HERA Collider Rings Ring circumference: 6336 m (determined by maximum p energy) Four quadrants: north, east, south, west Quadrant = two mirror symmetric octants Each octant has 18 FODO cells Ion FODO: 47 m, phase advance 60° 416 SC dipoles (4.6 K), 8.83 m, 4.68 T, radius 584m, 75 mm aperture 6 vertical dipoles, 3.356 m 224 SC quads, 1.5 to 1.86 m, 90 T/m e FODO: 23.5 m, phase advance 60° half of ion FODO cell length Four 360 m straights for four IRs Straights also for injection/ejection, RF, beam dump, collimators, etc Electron straight also includes spin rotators (interleafed vertical & horizontal bending magnets) Small electron betatron functions (strong focusing) in RF sections for reducing bad orbit-RF coupling (eg. single and multiple bunch instabilities) Minimizing dispersion in RF sections for avoiding synchro-betatron resonances Arc Straights

8. HERA Injectors Electron/positron (polarized) Electron/positron (polarized) –An S-band warm linac  450 MeV pulsed current –Accumulator ring PIA (also bunching) into single bunch –Synchrotron DESY II  7 GeV –e-P storage ring PETRA  12 GeV, filling with 60 bunches –HERA collider ring  27.5 GeV –Self-polarization Proton/ions Proton/ions –An H - sources, a 750 KeV RFQ –A 50 MeV H - linac –Synchrotron DESY III  7.5 GeV (transition energy is 9 GeV) –Striping at injection of DESY III –e-P storage ring PEREA  40 GeV (transition energy is 6.5 GeV) –HERA collider ring  920 GeV

9. Synchrotron DESY II and III Proton emittance determined by space charge effect in proton injector Proton emittance determined by space charge effect in proton injector Beam spot size (and luminosity) at IP is determined by Beam spot size (and luminosity) at IP is determined by –Beam emittance –Chromaticity & dynamical aperture  smallest acceptable β* at IP

10. HERA Design Parameters

11. Polarized Lepton Beams

12. (Unrealized) Electron Cooling 120 m Continuous cooling Cooling bunch dimensions can be smaller than ion bunch Wiggler with 1 T A high-β (~500 to 2000) insertion

14. e Ring Lattice & chromaticity Correction Change of FODO cell betatron phase advance Change of FODO cell betatron phase advance –Increasing focusing in FODO lattice reduces electron beam equilibrium emittance, reaching minimum at 135° phase advance per cell –Strong focusing (large betatron phase advance per FODO cell) causes big chromaticity –Needs strong sextupole strengths to correct chromaticity, but reduces dynamical apertures  a compromise: 90° for horzontal and 75° for vertical  equilibrium emittance for 27.5 GeV is 22 nm  equilibrium emittance for 27.5 GeV is 22 nm (In the north, south and east straight sections, (In the north, south and east straight sections, high dispersion caused by bends in spin rotators high dispersion caused by bends in spin rotators contribute significantly to the emittances) contribute significantly to the emittances) Interleaved Chromaticity correction scheme Interleaved Chromaticity correction scheme –Two families in the horizontal plane, three families in the vertical plane –Chromatic correction adequate but worse in the horizontal plane Non-interleaved chromaticity correction scheme Non-interleaved chromaticity correction scheme –Requires stronger sextupole strength

15. Electron Dynamics Study for Luminosity Upgrade Goal: reducing beam emittance through Goal: reducing beam emittance through –Change of RF frequency –Increase focusing (phase advance) Dynamics aperture study (G. Hoffstatter) Dynamics aperture study (G. Hoffstatter)

19. Synchrotron Radiation Detector shielded by 3 movable upstream collimators Detector shielded by 3 movable upstream collimators Two fixed collimators near IP against back scattering Two fixed collimators near IP against back scattering Background conditions very low Background conditions very low No upstream collimators No upstream collimators Radiation fan must pass through IR Radiation fan must pass through IR Main background sources: back-scattering from absorbers 11 to 27 m right of IP Main background sources: back-scattering from absorbers 11 to 27 m right of IP Small central beam pipe Small central beam pipe Total power 18 kW (26 kW at 30 GeV) Total power 18 kW (26 kW at 30 GeV) Critical energy up to 115 keV (150 at 30 GeV) Critical energy up to 115 keV (150 at 30 GeV)

20. Special Magnets

21. Things Still Bother Them at Last Days of HERA 2007

22. End of a Great Machine & Era