CERN, Geneva, Switzerland PAC 2003 – Portland, Oregon, USA DESIGNING AND BUILDING A COLLIMATION SYSTEM FOR THE HIGH-INTENSITY LHC BEAM R.W. Aßmann for the Collimation Team O. Aberle, R. Aßmann, M. Brugger, L. Bruno, H. Burkhardt, E. Chiaveri, B. Dehning, A. Ferrari, J.B. Jeanneret, M. Jimenez, V. Kain, M. Lamont, F. Ruggiero, R. Schmidt, P. Sievers, V. Vlachoudis, L. Vos, J. Wenninger, CERN, Geneva, Switzerland I. Baishev, IHEP, Protvino, Russia D. Kaltchev, TRIUMF, Canada PAC 2003 – Portland, Oregon, USA RWA PAC03

The LHC Challenge for Collimation High stored beam energy ~ 350 MJ/beam (melt 500 kg Cu, required for 1034 cm-2 s-1 luminosity) Small spot sizes at high energy 200 mm (at coll.) (small 7 TeV emittance, no large beta in restricted space) Large transverse energy density 1 GJ/mm2 (beam is destructive, 3 orders beyond Tevatron/HERA) High required cleaning efficiency 99.998 % (~ 10-5) (clean lost protons to avoid SC magnet quenches) Collimation close to beam 6-7 s (available mechanical aperture is at ~10 s) Small collimator gap ~ 3 mm (at 7 TeV) (impedance problem, tight tolerances: ~ 10 mm) Activation of collimation insertions ~ 1-15 mSv/h (good reliability required, very restricted access) Big system 60 coll / 2 insertions RWA PAC03

At less than 1% of nominal intensity LHC enters new territory. There is no easy start-up for collimation! RWA PAC03

Allowable Intensity in the LHC Allowed intensity Quench threshold (7.6 ×106 p/m/s @ 7 TeV) Cleaning inefficiency = Number of escaping p (>10s) Number of impacting p (6s) Beam lifetime (e.g. 0.2 h minimum) Dilution Length (50 m) RWA PAC03

The V6.4 LHC Collimation System Two warm LHC insertions dedicated to cleaning: IR3 Momentum cleaning 1 primary 6 secondary IR7 Betatron cleaning 4 primary 16 secondary Two-stage collimation system 54 movable collimators for high efficiency cleaning, two jaws each + other absorbers for high amplitude protection Significant system: ~ 200 degrees of freedom! RWA PAC03

Beam Halo and Collimation Philosophy Secondary collimators Primary collimators Protection devices Strategy: Primary collimators are closest. Secondary collima- tors are next. Absorbers for protec- tion just outside se- condary halo before cold aperture. Relies on good know- ledge and control of orbit around the ring! Cold aperture RWA PAC03

Achievements… …and open questions System layout has been worked out and provides required cleaning efficiency. Collimation has been integrated into machine optics and layout. Foreseen collimator materials do not withstand the expected beam impact (~8 bunches out of 2808). Require factor 100-200 better resistance! Impedance from collimators is critical (similar to the rest of the machine or larger). High activation imposes severe restrictions for access. How to service the cleaning insertions? Mechanical and operational tolerances are tight. How to maintain, commission, optimize, operate such a system? …and open questions RWA PAC03

Material Studies Irregular dump → Proton impact on jaw → Proton-matter interaction Two possibilities: Find a solution where collimator jaws resist expected failures (preferred). Accept that jaws can be damaged and foresee in-situ repair/exchange. Pursuing possibility 1 for the moment but also getting informed about 2 (LC’s). RWA PAC03

Temperature Increase in Materials Typical length of secondary jaw: 0.5 m (Cu) to 1.0 m (C) RWA PAC03

Stress and Fatigue Analysis Calculated stress in simple Graphite is almost OK Divide numbers by 2.5 for recent improvement in dump re-triggering time. Just 30% too high… Would survive most erratic dumps. Other forms of Carbon are expected to be more robust (Carbon-Carbon). Under study. Beryllium would not sur-vive due to large stress. About factor of 3 beyond limit. FLUKA energy deposition as input to ANSYS calculations RWA PAC03

Impedance Constraint Typical collimator half gap at 7 TeV LHC impedance without colli-mators A doubling can be accepted at 7 TeV with full powering of octupoles Half gap b [m] Graphite requires different collimation strategy (larger openings). Not evident – possibilities under study (local triplet collimation, …). RWA PAC03

Other Ongoing Studies Length of collimator jaws for low Z: 0.2 m/1.0 m for prim./sec. jaws gives sufficient efficiency Re-design of cleaning insertions for longer collimators Vacuum and outgassing studies for C jaws Outbaking, heat treatment, jaw temperature <50ºC, local e-cloud Checks of downstream equipment, activation – damage Mechanical design Moving mechanisms, vacuum tank, cooling design, jaw surface properties: flatness, stability, … Possibilities for experimental tests RWA PAC03

Summary and Outlook Collimation of the high intensity LHC beams is a challenging task with many difficulties. New territory is entered. Requirements are now clearly defined and a strong project team is pursuing a solution at full speed. Design choices will be done in the next few months. The solution will be a compromise between different constraints. April 2004: First prototype. 2004-2005: Production of 56 collimators plus spares. 2006: Installation into the LHC. Ready for beam in 2007. In parallel: Studies on procedures for commissioning, optimization, and operation of such a system. LHC will rely on collimation as no other collider before: Opportunity for all of us to learn more about the handling and control of very high intensity beams! RWA PAC03