Luminosity Limitations of e-p Colliders

1. Luminosity Limitations of e-p Colliders • Extrapolation from HERA Experience • Examples for IR Layout • LINAC-Ring Limitations • HERA Limitations F. Willeke, Snowmass 2001

2. HERA Luminosity • 2001 PARAMETERS • Np number of protons per bunch = 1 x 1011 • Ne number of leptons per bunch = 3 x 1010 • nb number of bunches = 174 • f0 revolution frequency = 47.3kHz • sx,y,p,e hor./vert. beam dimensions of leptons & protons = 114mm/ 30mm • half crossing angle = 0 L luminosity = 7 x 1031cm-2sec-1 F. Willeke, Snowmass 2001

3. HERA Luminosity Constraints & Limitations L = 7 x 1031cm-2sec-1 • Constraints: q< 1mr (beam-beam tracking Sen‘95) =>q set 0(head on coll.) • sx,yp=~ sx,ye (Brinkmann, Willeke PAC’93) • Dne not (yet) limiting Limitations: Np / eN proton beam brightness = 1 x 1011/ 4mm (injector, ibs, bb-e) Ie total lepton beam current = 60mA (rf power, bb-p) gp proton relativistic factor = 981 (max field, circumference) bx,y p hor.& vert. Betafunctions at the IP = 2.45m/0.18m (ir layout, sp) To what extend are these fundamental? F. Willeke, Snowmass 2001

4. Proton Beam Brightness Limitations Present design Np / eN =1 x 1011 / 4 x 10-6 m Laslett Tuneshift in DESY III Booster Synchrotron 50MeV (kin.energy) injection • Dnsc ~ R Np / ( eN b2gB ) = 0.6@ 1.3 1011&eN=2mm Can be overcome by smaller ring are higher injection energy in the booster No principal limitation `just´ costs Example: DESYIII Inj. Energy from 50MeV120MeV @ 10M$ F. Willeke, Snowmass 2001

5. Proton Beam Brightness Limitations:IBS Scaling from HERA F. Willeke, Snowmass 2001

6. F. Willeke, Snowmass 2001

7. Scaling IBS ts~eN1.42~es1.52~URF1/4 • Increasing Np/eN increases growth time: •  larger es Larger ss  larger b* (hourglass effect) • Luminosity almost independent of Np/eN Possible Cure: More RF Voltage tibs~URF0.25however se ~ URF0.25 L / L0 = (se / se )2= (URF/ URF0)1/2 (expensive) HERA Experience: Running with 2x nominal se still ok but effect already noticeable (increased backgrounds) F. Willeke, Snowmass 2001

8. Cooling Bunched Beam Stochastic Cooling at High Energy  Not very promising perspective Bunched e-Beam Cooling: -May be cost effective way to provide bright beams -Doesn‘t look promising for high energies -May work for ions  See K.Balewski‘s presentation F. Willeke, Snowmass 2001

9. Lepton Beam-Beam Effect Dney=0.045 This is already a rather large value which potentially limits the proton beam brigthness. What are the margins? beam-beam experiments F. Willeke, Snowmass 2001

10. Too Strong Beam-Beam Force on e? Ls So far no reduction of Ls by the bunch current Ippb No reduction of Ls by the second experiment No reduction of Ls by a larger b-funktionen F. Willeke, Snowmass 2001

11. Where are the Beam-Beam Limits? Upgrade and Ip=140mA: emittance starts to grow F. Willeke, Snowmass 2001

12. Conclusion of Proton Beam Brightness Limitation For a machine with the circumfrence and the energy range of HERA there is no large increase factor in p beam brightness possible. A factor of >2 might be compatible with lepton beam beam effect and controlling IBS Lepton Beam-Beam Effect: Could be mitigated By smaller beta, however: D.A. limitations present HERA optics DA=~15-20 sx F. Willeke, Snowmass 2001

13. Electron Beam Current Limitations RF RF installation costs, operation costs Not fundamental Now: RF power 12 MW, RS1.5GW  60mA @ 27.5GeV Cost example: prov RF to increase I by factor 1.6  5M$ Vacuum costs, not fundamental SR losses 5.2MW @ 1000W/m (~B-Factories ) Presumably no big current increase factor reasonable! (factor 2-3?) costs! Feedback System: designed for 60mA, upgrade no technical problem Proton Beam Beam Effect(stability, background, lifetime concerns) tb=96ns, unproblematic For IR design & paras. Resonances f: fill factor Dnpx=1.4 x 10-3 limit? F. Willeke, Snowmass 2001

14. Too Strong Beam-Beam Force on p? 16mA 73mA Corresponding e-current after upgrade Lsis independent of e-current Tp depends on e-current Tails depend on e-current F. Willeke, Snowmass 2001

15. Conclusions: Electron Beam Current Limitations Educated guess: BesidesCOSTS, the beam current is limited by IR designconsiderations andbeam-beam effects. For HERA, the e-beam current could be increased bya factor ~2 if costs could be disregarded F. Willeke, Snowmass 2001

16. Limitations to Focussing • Chromatic effects Dynamic Aperture Limitations • Hourglass Effect • Interaction Region Layout and IR Magnet Design: • Need e & p lenses close to IP • Crossing angle • separate quickly beam dynamics, geometry • Magnetic Separation • Concern about SR F. Willeke, Snowmass 2001

17. Luminosity ( ) Lumi Reduction by Hourglass Effect bunch length: 6cm p e 20cm 30cm Length19cm: 12cm: F. Willeke, Snowmass 2001

18. New HERA Inter Action Region (==>see M. Seidel)strong magnetic combined function separation e-focusing DF p-focusing D-F-D-F Half Quadrupoles Superconducting Separator/Quads p-focusing sc sc p-beam e-beam F. Willeke, Snowmass 2001

19. Superconducting Magnets in the Detectors F. Willeke, Snowmass 2001

20. Ring Linac Collider Become interesting at Lepton Energies beyond capability of Storage Rings Ee>100GeV Np 10-6m gp 10cm Pe 250GeV L= 4.8 x 1030cm-2sec-1 1011eN 1066 b* 26.6MW Ee High Energy bunched beam Cooling! Energy Recovery F. Willeke, Snowmass 2001

21. THERA LINAC-Ring Lattice (proposed)small crossing angleprotons focussed by 2 electron low beta triplets, b*=10cm bmax 8kmprotons deflected from e-orbit by a long off-center quadrupoleelectron orbit straightenergy range Ep/Ee: 4/1 - 1/1 Proton Optics 1TeV Electron Optics 250GeV-800GeV F. Willeke, Snowmass 2001

22. Conclusions • Ring-Ring HERA L=~1032cm-2sec-1 New Collider in the range of HERA Energies: L=1033cm-2sec-1 is an ambitious goal and may be considered as a target for new designs • Ring-LINAC L>1031cm-2sec-1 :only feasible witg bunched beam cooling F. Willeke, Snowmass 2001