WP 4: Crab Cavity Ed Ciapala, Erk Jensen BE-RF, CERN HL-LHC Meeting, CERN, 20 July 2010

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 integrated rather than peak luminosity! 20 July HL-LHC Meeting WP4: Crab Cavity

Local and Global Scheme Local Scheme: Global Scheme: 20 July 2010 HL-LHC Meeting WP4: Crab Cavity3 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: Requires novel Compact Cavities (194 mm separation), which are not validated; Requires 4 cavities per IP; What if a cavity trips?

CERN Strategy Aim ultimately at a significant luminosity increase using the local scheme with compact crab cavities around the IPs. ◦ This requires a substantial R&D program, but first results are encouraging (see below). To mitigate the risk, and in parallel to the above, design and implement a elliptical cavity in IR4 to obtain measurable luminosity increase in a global scheme. ◦ Conceptual design exists (US-LARP), including coupler, cryostat, wrong-order-mode dampers,... ◦ Space is available in IR4 (was foreseen for ACN200 system). ◦ What could a test of the KEK crab cavity in SPS tell us? 20 July 2010 HL-LHC Meeting WP4: Crab Cavity4

Collaboration In order to encourage collaboration and to assure its consistency and continuity, CERN has to take the lead in the world wide Crab Cavity development program. This is also a necessary strong sign to assure partners! In the past, CERN was merely observer; results obtained by collaborators so far: ◦ US-LARP: design of elliptical cavity system, some 3 compact designs, ◦ EuCARD WP 10.3: specifications, compact cavity design (Lancaster), ◦ KEK-B positive results, compact cavity design (“Kota” cavity). CERN is in the process of defining the strategy and a work plan (in parallel to ongoing efforts), which it will then adhere to. Expected in September 2010: “Statement of Need”, Initial Cost & Schedule, work plan! This will allow identification of work packages for partners. HL-LHC is one important element of the overall strategy (focussing on “design” questions); other elements – coordinated with it – are: ◦ US-LARP and maybe APUL, EuCARD, the French “Grand Emprunt” in Rhône-Alpes region, DoE SBIR & MTTR programs,...) 20 July 2010 HL-LHC Meeting WP4: Crab Cavity5

Elliptical cavity design 20 July 2010 HL-LHC Meeting WP4: Crab Cavity6 Taken from Rama Calaga’s Talk at Chamonix 2010, Taken from Rama Calaga’s Talk at Chamonix 2010,

Compact cavity designs 20 July 2010 HL-LHC Meeting WP4: Crab Cavity7 EUCARD 4-rod cavity (Lancaster)ODU Parallel Bar Cavity SLAC Half-wave Spoke Resonator KEK Kota Cavity Taken from Graeme Burt’s Highlight Talk at EuCARD Annual Meeting, Taken from Graeme Burt’s Highlight Talk at EuCARD Annual Meeting,

The possible issues Will it work? Machine protection! ◦ Major concern: single turn failure! Requires study! Collimation efficiency and hierarchy ◦ Initial calculations indicate that this might be OK – still, it requires more study! Crab cavity induced noise ◦ Phase noise leads to beam offset – requires study! Impedance, both longitudinal and transverse! Operational: how to make “invisible”, how to commission? What happens during the ramp? 20 July 2010 HL-LHC Meeting WP4: Crab Cavity8

WP4: Possible design subjects (1/2) 20 July 2010 HL-LHC Meeting WP4: Crab Cavity9 TasksCollaborator 1Design optimization for novel schemes (minimum # of peripherals)CI, LARP, CERN,KEK 2Cavity and cryomodule specifications (LHC report)CERN, KEK, CNRS 3Local IR layout and spatial integrationCERN, KEK 4Multipacting simulations of cavity & couplersCI, LARP 5FEM simulations: mechanical & thermal aspectsCI, LARP 6 Fabrication and measurements on copper models: field profile, impedance, error sensitivity) CI, LARP 7Demonstration of field gradients in compact cavities (4 structures)LARP, CERN, CI 8Q-slope, onset of field emission and quenchLARP, CERN 9Performance difference between 2 K & 4 KLARP, CERN 10Coupler development and testingCERN, CEA 11Tuner concepts and mock up on copper modelsCERN, CEA 12Study of mech. resonances, microphonicsCERN, CEA 13Performance with couplers and horizontal cryostatCERN, CEA 14Performance with beam (e.g. SPS – impedance, collimation, …)CERN, LARP 15Interlocks and fast Feedback (other measures like Qext)CERN, 16Common power and cryogenic systems across the IPs (?)CERN, CEA? 17LLRF and controls – (phase control!)CERN, CI Technology Issues

20 July 2010 HL-LHC Meeting WP4: Crab Cavity10 WP4: Possible design subjects (2/2) TasksCollaborator 1RF behavior for cavity quench or turbulent behavior *CERN, LARP, KEK 2Tracking simulations for loss maps for fast failure modesCERN, LARP, KEK 3 Beam-beam simulations to investigate instabilities, noise issues and DA CI, LARP, CERN 4 Impedance and growth rate estimates for specific HOMs to specify exact damping and feedback measures* CERN, LARP 5Effect of non-zero dispersion and stable working pointsCERN, LARP 6Crab consistent opticsCERN, LARP, KEK Beam Issues * Cavity design dependent

WP4: Possible Participants CERN Cockcroft Institute (U Lancaster) US-LARP KEK CEA CNRS July 2010 HL-LHC Meeting WP4: Crab Cavity11