1. LEP3 Machine Design Options Frank Zimmermann LEP3 Day, 18 June 2012 work supported by the European Commission under the FP7 Research Infrastructures project EuCARD, grant agreement no. 227579 cern.ch/accnet

2. LEP3 history in a nutshell “LEP3” idea raised by Alain Blondel at Grenoble EPS-HEP ECFA session in July 2011 LEP3 paper with beam parameters submitted to arXiv on Christmas’ Eve 2011 “SuperTRISTAN” proposals by Katsunobu Oide in January/February 2012 LEP3 was a parenthesis at Chamonix’12 Lots of interest in LEP3 poster at IPAC’12 18 June 2012: first LEP3 day

3. LEP3 at IPAC’12

4. key parameters beam energy: ≥120 GeV luminosity in each of two experiments: ≥ 10 34 cm -2 s -1 at the ‘Higgs energy’ (~240 GeV c.m.) ≥ 10 35 cm -2 s -1 at 2xM W (~160 GeV c.m.) ≥ 5x10 35 cm -2 s -1 at the Z pole (~90 GeV c.m.) LEP3 circular Higgs factory (ee-> ZH)

5. installation in the LHC tunnel “LEP3” + inexpensive (<0.1xLC) + tunnel exists + reusing ATLAS and CMS detectors + reusing LHC cryoplants - interference with LHC and HL-LHC new larger tunnel “DLEP” or “TLEP” + higher energy reach + decoupled from LHC and HL-LHC operation and construction + tunnel can later serve for HE-LHC (factor 2-3 in energy from tunnel alone) with LHC remaining as injector - 3-4x more expensive (new tunnel, cryoplants, detectors?) two options

6. LEP3 double ring Sketch of LEP3 double ring [1]: a first ring accelerates electrons and positrons up to operating energy (120 GeV) and injects them at a few minutes interval into the low-emittance collider ring, which includes high luminosity 10 34 cm -2 s -1 interaction points. A. Blondel

7. LHC tunnel cross section with space reserved for a future lepton machine like LEP3 [blue box above the LHC magnet] and with the presently proposed location of the LHeC ring [red]

8. arc optics same as for LHeC:  x,LHeC <1/3  x,LEP1.5 at equal beam energy, optical structure compatible with present LHC machine small momentum compaction (short bunch length) assume  y /  x ~5x10 -3 similar to LEP (ultimate limit  y ~ 1 fm from opening angle) RF RF freqeuncy 1.3 GHz ILC-type RF cavities high gradient (20 MV/m assumed, 2.5 times LEP gradient) total RF length for LEP3 at 120 GeV similar to LEP at 104.5 GeV short bunch length (small  * y ) cryo power <1/2 LHC synchrotron radiation energy loss / turn: E loss [GeV]=88.5×10 −6 (E b [GeV]) 4 /ρ[m]. higher energy loss than necessary arc dipole field = 0.153 T compact magnet critical photon energy = 1.4 MeV 50 MW per beam (total wall plug power ~200 MW ~ LHC complex)→4x10 12 e ± /beam LEP3 key parameters

9. LHeC Conceptual Design Report M. Klein

10. LEP2LHeCLEP3DLEP beam energy E b [GeV] circumference [km] beam current [mA] #bunches/beam #e − /beam [10 12 ] horizontal emittance [nm] vertical emittance [nm] bending radius [km] partition number J ε momentum compaction α c [10 −5 ] SR power/beam [MW] β ∗ x [m] β ∗ y [cm] σ ∗ x [μm] σ ∗ y [μm] hourglass F hg ΔE SR loss /turn [GeV] 104.5 26.7 4 2.3 48 0.25 3.1 1.1 18.5 11 1.5 5 270 3.5 0.98 3.41 60 26.7 100 2808 56 5 2.5 2.6 1.5 8.1 44 0.18 10 30 16 0.99 0.44 120 26.7 7.2 4 4.0 25 0.10 2.6 1.5 8.1 50 0.2 0.1 71 0.32 0.67 6.99 120 53.4 14.4 60 16.0 10 0.05 5.2 1.5 2.0 50 0.2 0.1 45 0.22 0.75 3.5 LEP3/DLEP parameters in comparison -1

11. LEP2LHeCLEP3DLEP E SR loss /turn [GeV] V RF,tot [GV] d max,RF [%] ξ x /IP ξ y /IP f s [kHz] E acc [MV/m] eff. RF length [m] f RF [MHz] δ SR rms [%] σ SR z,rms [cm] L/IP[10 32 cm −2 s −1 ] number of IPs beam lifetime [min] ϒ BS [10 −4 ] n γ /collision  BS /collision [MeV]  BS rms /collision [MeV] 3.41 3.64 0.77 0.025 0.065 1.6 7.5 485 352 0.22 1.61 1.25 4 360 0.2 0.08 0.1 0.3 0.44 0.5 0.66 N/A 0.65 11.9 42 721 0.12 0.69 N/A 1 N/A 0.05 0.16 0.02 0.07 6.99 12.0 4.2 0.09 0.08 3.91 20 606 1300 0.23 107 2 16 10 0.60 33 48 3.5 4.6 5.0 0.05 0.91 418 376 1300 0.16 0.17 142 2 22 8 0.25 12 26 LEP3/DLEP parameters in comparison -2

12. IR design large aspect ratio  x /  y ~200 to limit beamstrahlung  * y ~ 1 mm: close to the value giving the maximum geometric luminosity for  z ~ 2-3 mm (hourglass effect); realized by o short free length from the IP, l* ~ 4 m o quadrupole length ~ 4 m o quadrupole gradient ~ 17 T/m o and aperture (radius) ~ 5 cm (>20σ y )

13. quadrupoles inside CMS? J. Nash CARE-HHH IR’07 Had Barrel: HB Had Endcaps:HE Had Forward: HF HB HE HF HO The important regions for forward jet tagging are in HE/HF 10.8m 14.3 m 3.0 m 6.5 m z=4.0-10.0 m R max ≥40 cm

14. quadrupoles inside ATLAS? z=3.49-4.58 m r max =18 cm z=6.8-8.66 m r max =43 cm z=8.69-12.870 m r max =87 cm M. Nessi CARE-HHH IR’07 z=12.95-18.60 m r max =150 cm

15. bunch intensity limits beam-beam tune shift up to ~0.1 OK (see talk by R. Assmann) TMCI LEP2: limit of 5x10 11 at 22 GeV injection LEP3: gain factor 5.5 from higher energy; lose factor (1.3/0.7) 3 from wake field (different RF frequency); gain factor >2 from larger Q s [other:  functions at RF, bunch length?] => N b ~10 12 OK; 4 bunches per beam

16. beam lifetime LEP2: beam lifetime ~ 6 h dominated by radiative Bhahba scattering with cross section  ~0.215 barn [11] LEP3: with L~10 34 cm −2 s −1 at each of two IPs:  beam,LEP3 ~16 minutes additional beam lifetime limit due to beamstrahlung > 30 minutes if  max,RF ≥ 4% (see talk by Marco Zanetti)

17. Upsilon parameter P. Chen, K. Yokoya [7] beamstrahlung formulae photons emitted per collision average energy loss per collision for LEP3 the longitudinal damping time is 17 turns and the number of collisions per damping time 34 rms energy spread per collision K. Yokoya [8]

18. RF momentum acceptance synchronous phase overvoltage momentum acceptance

19. e + production rate top-up interval << beam lifetime → average luminosity ≈ peak luminosity! for the top-up to work: we need about 4×10 12 e + every few minutes, or of order 2×10 10 e + per second for comparison: LEP injector complex delivered of order 10 11 e + per second [12]

20. ramping speed of accelerator ring nominal ramp rate of LEP: 500 MeV/s [13] at the same speed acceleration to 120 GeV would take less than 4 minutes this would be sufficient, but faster ramp rate would be even better for maintaining a constant luminosity

21. two ambitious time schedules

22. LEP3 robustness & novelties storage-ring colliders: well-established, robust technology novel features of LEP3: 15% more energy than LEP2 top-up injection ultralow vertical  * (but still 3-4 x SuperB) significant beamstrahlung

23. LEP3 R&D 3-D integration in LHC tunnel & cohabitation with HL-LHC and LHeC ; RF integration; beam dynamics studies and optics design for the collider ring ; HOM heating w. large bunch currents and short bunch lengths; vertical emittance tuning, single-bunch charge limits, longitudinal effects for Q s ~ 0.35, low beta insertion with large momentum acceptance, parameter optimization, beam-beam effects, including beamstrahlung, and top-up scheme optics & beam dynamics for accelerator ring magnets : collider-ring dipole magnet, acc.-ring dipole, and low-beta quad.; 100 MW SR effects SRF & cryogenics ; optimum RF gradient & RF frequency; engineering study of new larger tunnel for DLEP or TLEP cost and performance comparison double vs single ring; injector complex, including e+ source dual use LEP3 and LHeC MDI; integration of warm low-beta quadrupoles inside ATLAS & CMS detector performance and upgrade studies LEP3 physics studies Synergies: LHeC, HP-SPL, XFEL, HE-LHC

24. conclusions & questions circular Higgs factory with 240 GeV c.m. and L~10 34 cm -2 s -1 appears possible in the LHC tunnel or in a larger tunnel both LEP3 and/or DLEP/TLEP look feasible is such machine important for particle physics? - going much beyond 120 GeV looks challenging, in particular in the LHC tunnel - how critical are H-H-Z production & t-t studies? which of the two options is more realistic/preferred? can LEP3/DLEP wait until after the HL-LHC (~2035)?

25. circular Higgs factories become popular around the world LEP3 2011 SuperTristan 2012 LEP3 on LI, 2012 LEP3 in Texas, 2012

26. References : [1] A. Blondel, F. Zimmermann, ‘A High Luminosity e+e- Collider in the LHC tunnel to study the Higgs Boson,’ V2.1-V2.7, arXiv:1112.2518v1, 24.12.2011 [2] C. Adolphsen et al, ‘LHeC, A Large Hadron Electron Collider at CERN,’ LHeC working group, LHeC-Note-2011-001 GEN. [3] H. Schopper, The Lord of the Collider Rings at CERN 1980-2000, Springer-Verlag Berlin Heidelberg 2009 [4] K. Oide, ‘SuperTRISTAN - A possibility of ring collider for Higgs factory,’ KEK Seminar, 13 February 2012 [5] R.W. Assmann, ‘LEP Operation and Performance with Electron-Positron Collisions at 209 GeV,’ presented at 11 th Workshop of the LHC, Chamonix, France, 15 - 19 January 2001 [6] A. Butterworth et al, ‘The LEP2 superconducting RF system,’ NIMA Vol. 587, Issues 2-3, 2008, pp. 151 [7] K. Yokoya, P. Chen, CERN US PAS 1990, Lect.Notes Phys. 400 (1992) 415-445 [8] K. Yokoya, Nucl.Instrum.Meth. A251 (1986) 1 [9] K. Yokoya, ‘Scaling of High-Energy e + e - Ring Colliders,’ KEK Accelerator Seminar, 15.03.2012 [10] V. Telnov, ‘Restriction on the energy and luminosity of e + e - storage rings due to beamstrahlung,’ arXiv:1203.6563v, 29 March 2012 [11] H. Burkhardt, ‘Beam Lifetime and Beam Tails in LEP,’ CERN-SL-99-061-AP (1999) [12] R. Bossart et al, ‘The LEP Injector Linac,’ CERN-PS-90-56-LP (1990) [13] P. Collier and G. Roy, `Removal of the LEP Ramp Rate Limitation,’ SL-MD Note 195 (1995).

27. thanks to: Alain Blondel for getting me involved in this exciting project and for organizing a LEP3 BBQ tonight! Katsunobu Oide for his interest and excellent ideas Mike Koratzinos for many stimulating discussions Kaoru Yokoya and Valery Telnov for pointing out the importance of beamstrahlung Marco Zanetti for addressing the beamstrahlung issue all speakers and participants of the LEP3 day Andrzej Siemko for lending us a piece of LEP2 beam pipe Steve Myers and Jean-Pierre Koutchouk for supporting the initiative

28. recruiting an SRF expert for LEP3? thank you for your attention!