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Compact Crab Cavity Status

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).

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Compact Crab Cavity Status

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  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; • 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. • In addition, crab cavities provide an ideal knob for luminosity levelling; • This allows optimizing for integratedrather than peak luminosity!

  3. Local vs. Global Scheme • Global Scheme: • Local Scheme: now discarded • 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 separationin 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 curvatureisnon-linear! 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 made remarkable progress since then. 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! Field flatness < 0.6% @ ± 10 mm first OOM far away, HOM damping relatively simple (below cut-off) HOM below (stringent) impedance budget. Zenghai Li LHC-CC11, CERN, 15 Nov 2011

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

  10. Prototype status

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

  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: Aluminium prototype arrived: MP studied – OK for cleancavity, MP free after discharge cleaning (with SEY 1.25) Bead-pull OK, Couplers and HOM damperstudies started. G. Burt, B. Hall, R. Rimmer (JLAB) LHC-CC11, CERN, 15 Nov 2011

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

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

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

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

  18. Field linearity: R. Appleby, R. De Maria, A. Grudiev, J. Barranco Studied for example with multipole expansion. Effect of B(2) on tune shift dominating; with the above estimates ξ < 7E-4.

  19. Machine Protection T. Baer, J. Wenninger • 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) • Dynamics dominated by Qext. (τ= 1 ms for 1E6) • up to 0.5 σ per turn! 2.2 σ after 5 turns. • Voltage failure – bunch centre not affected • Phase failure – bunch centre affected • Scenarios to stay below 1 MJ loss in 5 turns: • Highlyoverpopulatedtailsobserved: • In horizontal plane about4%of beam beyond4σmeas. • Correspondsto≈20MJ with HL-LHC parameters. • Collimationsystemdesignedfor fast accidentallossofupto1MJ. • Hollow electron lens to deplete tails gives add’l failure margin. LHC-CC11, CERN, 15 Nov 2011

  20. RF Phase Noise

  21. Overall planning

  22. Testing-commissioning

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