CLIC parameters at 500 GeV

1. CLIC parameters at 500 GeV Grudiev for CLIC study 02/09/2008

2. Strategy • 3 TeV nominal parameters based on nominal beam parameters • Emittances @ IP smaller than ILC by 15 in H, 2 in V for 5*smaller Qb • Paper design and prototypes of key components • No feasibility demonstration of all parameters by 2010 • Define (more) conservative beam parameters (Emittances, Focusing, beam sizes at IP) which will have been addressed (or demonstrated) by 2010: • In facilities in operation or being approved for construction • In test facilities (ATF) • Base 500 GeV design (first stage) on more conservative parameters • Strategy recommended at CLIC07 and supported by ACE • Increase credibility of the first stage (first to be built) • Larger beam dimensions at IP easier to achieve and measure • Relaxed stability tolerances

3. Conservative Final Focus parameters • What is conservative after ATF2? • Scaling ATF2 parameters (L*=1m, βx*= 4mm, βy*= 0.1mm ) to L*=4.3m givesβx*= 17mm, βy*= 0.43mm (ILC betas!) • ATF2-based-conservatism is too bad for CLIC! • Why not lowering ATF2 betas?: • P. Bambade has already proposed a factor 2 • Strategy: Join P. Bambade and push ATF2 betas as low as possible (and/or push L* up). • Assuming ATF2 betas reach 2,0.05 mm (factor 2 lower than design). The conservative CLIC betas would be • (8.6, 0.21)mm for L*=4.3m • (7.0, 0.17)mm for L*=3.5m • Rogelio Tomas Garcia Conservative FFS after the ATF2 ? 19/02/08

4. Vertical emittance from SLS Y. Papaphilippou physical vertical emittance [pm] • Swiss Light Source achieved 2.8pm, the lowest geometrical vertical emittance, at 2.4 GeV, corresponding to ~10nm of normalised emittance • Below 2pm, necessitates challenging alignment tolerances and low emittance tuning (coupling + vertical dispersion correction) • Seems a “safe” target vertical emittance for CLIC damping rings

5. Horizontal emittance scaled from NSLS II physical horizontal emittance [nm] • Scaling of emittance with beam energy and bunch population including longitudinal emittance and IBS yields: = 2.4µm • In this respect, a normalised horizontal emittance of 2µm is reasonable Y. Papaphilippou 5

6. CLIC emittances: present and conservative Factor 6 in luminosity is missing

7. Optimization constraints at 3TeV • Beam dynamics (BD) constraints based on the simulation of the main linac, BDS and beam-beam collision at the IP: • N – bunch population depends on <a>/λ, Δa/<a>, f and <Ea> because of short-range wakes • Ns – bunch separation depends on the long-range dipole wake and is determined by the condition: • Wt,2 · N / Ea= 10 V/pC/mm/m · 4x109 / 150 MV/m • RF breakdown and pulsed surface heating (rf) constraints: • ΔTmax(Hsurfmax, tp) < 56 K • Esurfmax < 250 MV/m • Pin/Cin·(tpP)1/3 = 18 MW·ns1/3/mm

8. Difference in BD constraints for 3TeV and 500GeV D. Schulte

9. Difference in BD constraints for 3TeV and 500GeV L0.01/L = 0.4 at 3 TeV D. Schulte

10. Beam dynamics constraints at 500GeV and conservative emittance Short range wake limits bunch charge εx,y = 3μm, 40nm βx,y = 8mm, 0.1mm Long range wake amplitude on the second bunch limits the bunch spacing: Wt(2) * N / <Ea> < 20 V/pC/m/mm* 4x109 / 150 MV/m 10 V/pC/m/mm has been used for 3TeV

11. Other constraints • RF constraints remains the same as for 3TeV: • P/C*tp1/3 < 18 Wu(MW/mm*ns1/3) • Esmax < 260 MV/m • ΔTmax < 56 K • RF phase advance per cell: 120 or 150 degree • No 3TeV constraints: • Structure length Ls more than 200 mm; • Pulse length tp is free • Bunch spacing Ns is free • 3TeV constraints Ns = 6: • Ls = 230 mm; tp = 242 ns • Ls = 480 mm; tp = 242 ns • Ls = 480 mm; tp = 483 ns

12. Figure of Merit CLIC_G@3TeV: 9.1

13. Rf-to-beam efficiency

14. Repetition rate for L1 = 2 [1034/s·cm2] CLIC_G@3TeV: 50 Hz

15. If repetition rate is limited to 50 Hz 1 • Case 2 has been chosen: • As close as possible to 100 MV/m • Cost considerations which were not included in the optimization • Beam current in injectors is only ~2 times higher than for 3 TeV • RF constraints for PETS are the lowest 2 3

16. Parameters of CLIC main linac in different cases • Case 0: if we do not change anything then Luminosity reduction is ~6 • Case 1: Changing the scheme but keeping CLIC_G. Reducing gradient to 67 MV/m but doubling pulse length results in Luminosity reduction only ~4. It implies twice less PETS per meter as well as twice less turn-arounds. • Case 2: Keeping the nominal scheme but replacing only the accelerating structures. Luminosity reduction ~2. • Case 3: Both the scheme and the structures are changed. Reducing gradient by 2 and increasing structure length and pulse length by 2. No luminosity reduction. It implies twice less PETS and turn-arounds.

17. Parameters of the structures for 500 GeV

18. Conclusions • Conservative set of parameters for emittances and final focusing has been elaborated based on the existing or approved for construction facilities • Based on this set, beam dynamics (BD) constraints has been modified. • Optimization of CLIC main linac accelerating structure has been performed taking into account the modified BD constraints, the RF constraints (the same as for 3 TeV) and additional constraints coming from the compatibility to the 3TeV CLIC. • As a result, new optimum structure with bigger aperture operating at 80 MV/m is proposed for 500 GeV CLIC. The use of this structure instead of CLIC_G increases the luminosity by factor 3. • It also implies doubling the bunch charge which, on the other hand, seems to be feasible.

19. Beam power for L1 = 2 [1034/s·cm2] CLIC_G@3TeV: 14 MW/beam

20. Input power for L1 = 2 [1034/s·cm2] CLIC_G@3TeV: 50.4 MW/linac

21. If power loss per meter is limited to nominal (Pl-Pb)*<Ea> = const