1. Compact Crab Cavity Status E. Jensen for WP4 R. Appleby, T. Baer, J. Barranco, I. Ben-Zvi, G. Burt, R. Calaga, E. Ciapala, S. Da Silva, J. Delayen, L. Ficcadenti, R. De Maria, B. Hall, Z. Li, A. Grudiev, R. Rimmer, J. Tückmantel, J. Wenninger and many more … (excuses)

2. Crab Cavities – context Many bunches require non-zero crossing angle to avoid parasitic collisions and to reduce beam-beam effects; Many bunches require non-zero crossing angle to avoid parasitic collisions and to reduce beam-beam effects; With non-zero crossing angle, luminosity gain by squeezing beams further is small (red curve below). With non-zero crossing angle, luminosity gain by squeezing beams further is small (red curve below). Crab cavities can compensate for this geometric effect and thus allow for a luminosity increase of about 50 % at β* of 25 cm. Crab cavities can compensate for this geometric effect and thus allow for a luminosity increase of about 50 % at β* of 25 cm. In addition, crab cavities provide an ideal knob for luminosity levelling; In addition, crab cavities provide an ideal knob for luminosity levelling; This allows optimizing for integrated rather than peak luminosity! This allows optimizing for integrated rather than peak luminosity!

3. Local vs. Global Scheme Local Scheme: Local Scheme: Global Scheme: Global Scheme: Advantages: Only one cavity per beam; Larger beam separation near IP4; Elliptical cavity of known technology. Disadvantages: Constraining betatron phase advance; Requires larger collimator settings; Works only for H or V crossing; Only 800 MHz or higher fits. Advantages: Individual luminosity control at each IP; Adapted to H or V crossing; Orbit perturbed only locally; Could work lower f – better performance. Disadvantages/concerns: Requires novel Compact Cavities (194 mm separation), well advancing, but not yet validated; Requires 4 cavities per IP; What if 1 cavity trips?

4. Compact Crab Cavities are in need! The nominal LHC beam separation in the LHC is 194 mm; Conventional (elliptical) cavities scale with λ – they are too large even at 800 MHz! The nominal LHC beam separation in the LHC is 194 mm; Conventional (elliptical) cavities scale with λ – they are too large even at 800 MHz! … but at higher f, the RF curvature is non-linear! … but at higher f, the RF curvature is non-linear! This is a real challenge! This is a real challenge!

5. Progress with Compact Crab Cavities They appeared in LHC-CC08 (in the box “Exotic Designs”); seriously considered from 2009. They appeared in LHC-CC08 (in the box “Exotic Designs”); seriously considered from 2009. They made remarkable progress since then. They made remarkable progress since then. Truly global effort: Truly global effort: FNAL, SLAC, BNL, KEK, LBNL, ODU/JLAB, ULANC & CERN

6. Truly global design effort R. Calaga, SRF2011

7. SLAC (&ODU/JLAB) : Double-ridged cavity Double ridge cavity – now teamed up with ODU/JLAB. Excellent! Double ridge cavity – now teamed up with ODU/JLAB. Excellent! Field flatness < 0.6% @ ± 10 mm Field flatness < 0.6% @ ± 10 mm first OOM far away, HOM damping relatively simple (below cut-off) first OOM far away, HOM damping relatively simple (below cut-off) HOM below (stringent) impedance budget. HOM below (stringent) impedance budget. LHC-CC11, CERN, 15 Nov 2011 Zenghai Li

8. ODU/JLAB (&SLAC) : Parallel bar to double ridged waveguide – evolution J. Delayen, S. da Silva

9. Progress with ODU/JLAB/SLAC design Flattening field profile OK: Flattening field profile OK: MP: cavity quite clean; issue maybe in the couplers – under study! MP: cavity quite clean; issue maybe in the couplers – under study! Engineering design has started: sensitivity to pressure variation done. Engineering design has started: sensitivity to pressure variation done. Prototype “square outer conductor”; size 295 mm Prototype “square outer conductor”; size 295 mm OK @ 3 MV, marginal for 5 MV OK @ 3 MV, marginal for 5 MV First CU, then Nb prototypes: First CU, then Nb prototypes: LHC-CC11, CERN, 15 Nov 2011

10. Prototype status

11. BNL: ¼ wave cavity Compact and simple, mechanically stable. Compact and simple, mechanically stable. Synergy with eRHIC (181 MHz) Synergy with eRHIC (181 MHz) Large separation to next HOM (theor. factor 3, realistically 1.4, high-pass filter enough!) Large separation to next HOM (theor. factor 3, realistically 1.4, high-pass filter enough!) Non-zero longitudinal field – issue? Non-zero longitudinal field – issue? Easy tuning. Easy tuning. Field flattening OK (<1% over ± 20 mm) Field flattening OK (<1% over ± 20 mm) MP: easy to condition through. MP: easy to condition through. Topology similar to double ridge! Topology similar to double ridge! Technology is at hand (S. Bousson) Technology is at hand (S. Bousson) LHC-CC11, CERN, 15 Nov 2011 I. Ben-Zvi, R. Calaga

12. 4-rod cavity: Evolution from JLAB proposal to ULANC Design supported by

13. ULANC (CI/DL): LHC-4R Flattening field profile led to new shape: Flattening field profile led to new shape: Aluminium prototype arrived: Aluminium prototype arrived: MP studied – OK for clean cavity, MP free after discharge cleaning (with SEY 1.25) MP studied – OK for clean cavity, MP free after discharge cleaning (with SEY 1.25) Bead-pull OK, Bead-pull OK, Couplers and HOM damper studies started. Couplers and HOM damper studies started. LHC-CC11, CERN, 15 Nov 2011 G. Burt, B. Hall, R. Rimmer (JLAB)

14. Aluminium Prototype Beadpull measurements are being performed on a to scale aluminium prototype. Beadpull measurements are being performed on a to scale aluminium prototype. Coupler ports present to allow verification of damping. Coupler ports present to allow verification of damping.

15. 4R-LHC: Fabrication techniques 1.Nb sheets, multiple pressed sections; EBW complicated. 2.Offset rods, slanted rods to make EBW easier. 3.End plates from 1 Nb solid; Wire-etch two end-plates from 1 Nb block – modified modify shape to make compatible with EDM.  LHC-CC11, CERN, 15 Nov 2011

16. Comparing 400 MHz compacts LHC-CC11, CERN, 15 Nov 2011 400 MHz, 3 MV kick 500

17. Common concerns Field linearity Field linearity Power coupler Power coupler HOM impedance/HOM coupler/HOM damping HOM impedance/HOM coupler/HOM damping Multipactor Multipactor Fabrication techniques Fabrication techniques Machine protection Machine protection RF phase noise RF phase noise

18. Field linearity: Studied for example with multipole expansion. Studied for example with multipole expansion. Effect of B (2) on tune shift dominating; with the above estimates ξ < 7E-4. Effect of B (2) on tune shift dominating; with the above estimates ξ < 7E-4. ODUCAVSRHWKEKCAVUKCAVQWAVERFRSCAV Vz(x=0) [kV]0.0-2.1 - 2.5i-4 +1378i0.00 +85.7i-0.1 -0.2i Vx [MV]555555 B (2) [mTm/m]00 -0.04i-32.7 - 0.1i0.02 + 0i25 + 0i0 +108i B (3) [mTm/m 2 ] 1250 + 0i 229 + 0i250 - 0i2452 - 0.5i464 + 0i-233 +1i B (4) [mTm/m 3 ]00266 - 5i0540 +0i-189 -14209i R. Appleby, R. De Maria, A. Grudiev, J. Barranco

19. Machine Protection Requirement: Stay below 1 MJ in 5 turns! Requirement: Stay below 1 MJ in 5 turns! For upgraded optics, one gets 4 σ offset at CC voltage maximum. (10 MV kick, single cavity) For upgraded optics, one gets 4 σ offset at CC voltage maximum. (10 MV kick, single cavity) Dynamics dominated by Q ext. (τ = 1 ms for 1E6) Dynamics dominated by Q ext. (τ = 1 ms for 1E6) up to 0.5 σ per turn! 2.2 σ after 5 turns. up to 0.5 σ per turn! 2.2 σ after 5 turns. Voltage failure – bunch centre not affected Voltage failure – bunch centre not affected Phase failure – bunch centre affected Phase failure – bunch centre affected Scenarios to stay below 1 MJ loss in 5 turns: Scenarios to stay below 1 MJ loss in 5 turns: Highly overpopulated tails observed: Highly overpopulated tails observed: In horizontal plane about 4% of beam beyond 4σ meas. In horizontal plane about 4% of beam beyond 4σ meas. Corresponds to ≈20MJ with HL-LHC parameters. Corresponds to ≈20MJ with HL-LHC parameters. Collimation system designed for fast accidental loss of up to 1MJ. Collimation system designed for fast accidental loss of up to 1MJ. Hollow electron lens to deplete tails gives add’l failure margin. Hollow electron lens to deplete tails gives add’l failure margin. LHC-CC11, CERN, 15 Nov 2011 T. Baer, J. Wenninger

20. RF Phase Noise

21. Overall planning

22. Testing-commissioning