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Simulating radiation damage effects in LHC collimators (code development status)

Simulating radiation damage effects in LHC collimators (code development status). R. Assmann, H.-H Braun, A. Ferrari, S. Gilardoni, J.M. Jowett, G.I. Smirnov and V. Vlachoudis. Introduction Role of theoretical and model uncertainties Algorithms for dpa calclulation FLUKA upgrade Summary.

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Simulating radiation damage effects in LHC collimators (code development status)

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  1. Simulating radiation damage effects in LHC collimators(code development status) R. Assmann, H.-H Braun, A. Ferrari, S. Gilardoni, J.M. Jowett, G.I. Smirnov and V. Vlachoudis • Introduction • Role of theoretical and modeluncertainties • Algorithms for dpa calclulation • FLUKA upgrade • Summary Materials for Collimators and Beam Absorbers, 05.09.2007

  2. 1. Introduction Radiation damage in graphite : • Dimensional changes • length • diameter • volume • Property changes • thermal conductivity (reduction) • electrical resistivity (increase) • Structure changes • Hydrogen (and helium) retention • Surface sublimation AC150K Tatsuno, Jpn. 2D C/C (CFC) composite LHC collimator jaws Materials for Collimators and Beam Absorbers, 05.09.2007

  3. 2. Role of theoretical and model uncertainties Monte Carlo models for secondary and recoil particles (recoil spectra, damage energy) p + C p + X at 7 TeV X : 12C, 11C, …, 4He, 3He, t, D, p, n, pions, ... • Dpa damage functions can be different if calculated in the USA or Europe — • different models are used for : • Evaluation of the partitioning of damage energy between ionisation and displacements • Treatment of the displaced atoms motion and recombination: • Binary collision approximation (BCA) • Molecular dynamics (MD) approach Materials for Collimators and Beam Absorbers, 05.09.2007

  4. Major uncertainty is anticipated in establishing relation between dpa and macroscopic damage effect • Results of experimental tests of CFC (various beams, different energies) must be analyzed together with the Monte Carlo simulation results. Kurchatov studies (A. Ryazanov) 5 MeV 12C ions 35 MeV protons BNL studies (N. Simos) 200 MeV protons FLUKA 7 TeV protons Materials for Collimators and Beam Absorbers, 05.09.2007

  5. 3. Algorithms for dpa calculation Number of defects in the modified Kinchin-Pease model: Norgert-Robinson-Torrens (NRT)* ND = 0.8 NIEL / 2Eth Total number of defects for one kind (i) of particles (fragments) initiating cascades: NDtot(i) = ∫(dND(i)/dE) dE Total damage in terms of displacements per atom: dpa = 1/ (NA/A) ΣND tot(i) * • Also used in NJOY • CFC — displacement threshold energy Eth = 35 eV Materials for Collimators and Beam Absorbers, 05.09.2007

  6. Energy transfer to the lattice atom« partition function » Theories : 1) Lindhard (Lindhard, Nielsen and Scharf) 2) Firsov Partition of the primary recoil energy E : E = E1 + E2 Where E1 is nonionising energy loss (NIEL) E2 is ionisation loss Three region in the Lindhard theory: 1) Nuclear stopping is dominating 2) Nuclear stopping starts decreasing 3) Ionisation loss dominates Materials for Collimators and Beam Absorbers, 05.09.2007

  7. Results from Lindhard and Firsov theoriesconviniently represented by T. Robinson as: NIEL= 0 if E < Eth (threshold energy) Non ionizing energy loss — NIEL in Carbon lattice for 4He, 10C and 12C Materials for Collimators and Beam Absorbers, 05.09.2007

  8. « Partition function » Portion of recoil energy going into ionization Lindhard theory Robinson C-ion in C-lattice Si-ion in Si-lattice Materials for Collimators and Beam Absorbers, 05.09.2007

  9. Average threshold energy* * Some typical values used in the NJOY99 code system Materials for Collimators and Beam Absorbers, 05.09.2007

  10. Cascade damage formation Lifetime of defects — 10 ps • Molecular dynamicsfor cascade evolution: R. E. Stoller, J. Nucl. Mat., 276 (2000) 22 • weak dependence on the material • virtually independent on temperature • larger damage for near surface cascades Number of defects : ND = k NIEL / 2Eth Iron, T = 100 K 600 K 900 K k(Ep) Solid line — our approximation : Ep Materials for Collimators and Beam Absorbers, 05.09.2007

  11. 4. FLUKA upgrade p + A p + X elastic inelastic Pion production elastic (carbon) ions Fission products Neutrons inelastic elastic inelastic Production of light fragments elastic inelastic elastic inelastic Recoils from spallation reactions Ionisation loss NIEL NIEL NIEL Ionisation loss elastic inelastic  NIEL Ionisation loss dpa Schematic diagram of FLUKA algorithm Materials for Collimators and Beam Absorbers, 05.09.2007

  12. NJOY99 Code System Nuclear reactions (elastic and inelastic) at low neutron energies Modular computer code used for converting evaluated nuclear data files (ENDF) into libraries useful for applications calculations. NJOY99 (latest release of the NJOY system) handles a wide variety of nuclear effects in the energy range from thermal neutrons up to 150 MeV. Materials for Collimators and Beam Absorbers, 05.09.2007

  13. 5. Summary  • Damage effects in LHC collimator jaws evaluation: • FLUKA Monte Carlo code • Binary collision model (primary cascades) • Results from Molecular Dynamics simulation (recombination of defects) • Results from NJOY (nuclear effects innAreactions below 150 MeV ) • Cross checks by employing results of CFC irradiation at low energies Only protons, neutrons and pions are expected to be important for the radiation effects in CFC material at LHC energies Materials for Collimators and Beam Absorbers, 05.09.2007

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