A. Bertarelli – A. DallocchioWorkshop on Materials for Collimators and Beam absorbers, 4 th Sept 2007 LHC Collimators (Phase II): What is an ideal material Workshop on Materials for Collimators and Beam Absorbers 3-5 Septermber, 2007 CERN Geneva Alessandro Bertarelli 1 Alessandro Dallocchio 1,2 1 TS department – Mechanical and Material Engineering Group CERN, Geneva 2 Mechanical Engineering Department– Politecnico di Torino, Italy

A. Bertarelli – A. DallocchioWorkshop on Materials for Collimators and Beam absorbers, 4 th Sept 2007 Outline Introduction to the Collimation System Introduction to the Collimation System Phase I Collimators Phase I Collimators Limits of Phase I Collimators Limits of Phase I Collimators Phase II Collimator ideal material Phase II Collimator ideal material

A. Bertarelli – A. DallocchioWorkshop on Materials for Collimators and Beam absorbers, 4 th Sept 2007 Introduction to the Collimation System The first goal of the collimators is to protect the critical LHC components from beam losses (SC magnets quench threshold 30 mJ/cm 3. i.e. 4 x 10 7 protons) The Collimators are the closest elements to the beam! Factor ~ 200 LHC beam parameters: Stored energy 350 MJ per beam (factor 100 higher than others) … Beam transverse density ~1 GJ/mm2 (factor 1000 higher than others) … This makes the LHC beam highly destructive!!!

A. Bertarelli – A. DallocchioWorkshop on Materials for Collimators and Beam absorbers, 4 th Sept 2007 Phase I Collimator Functional Requirements  Low-Z material (C, BN, Be …) long jaw (1200 mm)  Very accurate geometric stability (40  m on 1200mm)  High robustness in accident cases (450 GeV and 7 TeV)  High absorbed heat load (up to ~25 kW)  Limited maximum temperatures (<~50º C)  Low electrical resistivity and RF efficiency  Maintain UH vacuum  …

A. Bertarelli – A. DallocchioWorkshop on Materials for Collimators and Beam absorbers, 4 th Sept 2007 Collimator Main Features RF efficiency is obtained by a system of Cu-Be Silver coated contacts placed on top and bottom of jaws and in transitions. Impedance is minimized and trapped modes reduced. RF contact Transition fingers (Cu-Be) RF contact Longitudinal strip (Cu-Be)

A. Bertarelli – A. DallocchioWorkshop on Materials for Collimators and Beam absorbers, 4 th Sept 2007 Phase I Collimator Main Features (1) Collimating Jaw (C/C composite) (2) Main support beam (Glidcop) (3) Cooling-circuit (Cu-Ni pipes) (4) Counter-plates (Stainless steel) (5) Clamping plates (Glidcop) (6) Preloaded springs (Stainless steel) Jaw Bloc Assembly (1) (2) (4) (3) (6) (1) (2) (3) (4) (6)

A. Bertarelli – A. DallocchioWorkshop on Materials for Collimators and Beam absorbers, 4 th Sept 2007 Jaw. 2-D short fiber Carbon-Carbon composite. Key properties: low-Z material, good thermal and fair electric conductivity. Good shock resilience (higher than isotropic graphite). Processable in long thick plates. Support beam, Clamps, Contact Plate. Glidcop ® AL-15 LOX (Low Oxygen). Glidcop is a Copper based material strengthened by a dispersion of alumium oxide (0.15%). It allies high mechanical properties (even after heat treatment) and very good thermal properties. Cooling Pipes. Cu-Ni10. Vacuum Tank, Counter-plates, Springs. Stainless steel – different grades. Stands, Cradles, Supports. Aluminun alloy AW-6082 T6. Phase I Collimator Materials

A. Bertarelli – A. DallocchioWorkshop on Materials for Collimators and Beam absorbers, 4 th Sept 2007 Limits of Phase I Collimators 1. 1.Resistive Impedance According to RF simulations, Phase I Collimator Impedance would limit LHC beam intensity to ~40% of its nominal value! 2. 2.Cleaning efficiency Cleaning efficiency (i.e. ratio escaping protons / impacting protons) should be better than 99.9% to limit risks of quench at SuperConducting triplets

A. Bertarelli – A. DallocchioWorkshop on Materials for Collimators and Beam absorbers, 4 th Sept 2007 Phase II Collimator Materials To overcome this limit, new secondary collimators with an improved jaw material /design should complement the existing system (Phase II) To achieve the new goal, we need a magic material having: 1. 1.High electrical conductivity to improve RF stability 2. 2.High thermo-mechanical stability and robustness, i.e.: a. a.Low Coefficient of Thermal Expansion b. b.High Yield Strength c. c.Low Young’s Modulus d. d.High Thermal Conductivity e. e.High Specific Heat 3. 3.High density (high Z) to improve collimation efficiency (i.e. intercepted and stop a higher number of particles), possibly depending on final jaw length … 4. 4.Strong resistance to particle radiation …

A. Bertarelli – A. DallocchioWorkshop on Materials for Collimators and Beam absorbers, 4 th Sept 2007  Electrical conductivity [1/  m]  Electrical conductivity [1/  m] Directly related to resistive impedance  Steady-state geometrical stability parameter [W/m]  Steady-state geometrical stability parameter [W/m] Indicates power required to induce a given deflection  Transient Thermal Shock parameter [J/kg]  Transient Thermal Shock parameter [J/kg] Gives an indication of the highest acceptable deposited energy during a beam impact before damage occurs  Mass density [kg/m 3 ]  Mass density [kg/m 3 ] Related to cleaning efficiency Phase II Collimator Materials Relevant figures of merit:

A. Bertarelli – A. DallocchioWorkshop on Materials for Collimators and Beam absorbers, 4 th Sept 2007 Phase II Collimator Materials

A. Bertarelli – A. DallocchioWorkshop on Materials for Collimators and Beam absorbers, 4 th Sept 2007 Phase II Collimator Materials Phase I injection error Max energy density

A. Bertarelli – A. DallocchioWorkshop on Materials for Collimators and Beam absorbers, 4 th Sept 2007 Phase II Collimator Materials