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WP 4: Crab Cavity

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;

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WP 4: Crab Cavity

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

  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! HL-LHC Meeting WP4: Crab Cavity

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

  4. 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? HL-LHC Meeting WP4: Crab Cavity

  5. 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, ...) HL-LHC Meeting WP4: Crab Cavity

  6. Elliptical cavity design Taken from Rama Calaga’s Talk at Chamonix 2010, http://indico.cern.ch/conferenceDisplay.py?confId=67839 HL-LHC Meeting WP4: Crab Cavity

  7. Compact cavity designs EUCARD 4-rod cavity (Lancaster) ODU Parallel Bar Cavity KEK Kota Cavity SLAC Half-wave Spoke Resonator Taken from Graeme Burt’s Highlight Talk at EuCARD Annual Meeting, http://indico.cern.ch/conferenceDisplay.py?confId=73614 HL-LHC Meeting WP4: Crab Cavity

  8. 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? HL-LHC Meeting WP4: Crab Cavity

  9. WP4: Possible design subjects (1/2) Technology Issues HL-LHC Meeting WP4: Crab Cavity

  10. WP4: Possible design subjects (2/2) Beam Issues * Cavity design dependent HL-LHC Meeting WP4: Crab Cavity

  11. WP4: Possible Participants • CERN • Cockcroft Institute (U Lancaster) • US-LARP • KEK • CEA • CNRS • ... HL-LHC Meeting WP4: Crab Cavity

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