LHC Collimator Materials: Irradiation Studies for Upgrades

1. Collimator Materials for LHC Luminosity Upgrade:Irradiation Studies at BNL BLIPExperimental Safety Review MeetingMarch 27, 2013N. SimosSenior Scientist, BNLInput from: H. Ludewig, A. Aronson(BNL team)N. Mariani, A. Bertarelli, S. Redaelli, L. Lari (CERN-LHC team)T. Markiewicz (SLAC_LARP) N. Simos

2. Overview - Background • Phase I LHC Collimator Study at BLIP • 200 MeV Linac protons for 10-week irradiation of 2D Carbon-Carbon Composite • Study revealed a fluence threshold for the selected composite material • LHC, however, was not expected to reach the fluence achieved at BLIP during Phase I and so 2D C/C was employed • For this Phase II or Luminosity Upgrade of LHC a new set of higher performance materials are being explored • Objective is to reach the threshold fluence of 5 x 1020 p/cm2 N. Simos

3. LHC Collimators General Requirements • Key requirements for LHC Collimation System: High Thermal Stability for SState • High Thermal Stability in steady state conditions; • Tailored Cleaning Efficiency (multistage cleaning); • Low RF Impedance; • High Shock Resistance under accidental cases; • High Radiation Hardness (Lifetime). • Intrinsic limitations C-C Collimators may ultimately limit LHC performances: • Low-Z material (Limited Cleaning Efficiency) • Poor electrical conductivity (High RF impedance) • Limited Radiation Hardness (Reduced Lifetime) • Innovative Materials key element for next-generation Collimators • Need for new materials extensive Characterization CuCD Courtesy: E. Neubauer, M. Kitzmantel– RHP-Tech MoGRCF – CERN - BrevettiBizz N. Simos

4. BNL_BLIP results closer to the anticipated conditions at LHC Post-irradiation data to be compared with similar (but quite different) studies • Proposal for Characterization Program in Brookhaven National Laboratory to assess the radiation damage on: • Molybdenum • Glidcop • CuCD • MoGRCF • Features: • Irradiation with proton beam at 200 MeV • Indirect water cooling and T~100°C (samples encapsulated with inert gas) • Thermo-physical and mechanical characterization for fluence up to 1020 p/cm2 • Possibility to irradiate with neutrons (simulate shower on secondary coll.) • Ongoing Characterization Program in RRC- Kurchatov Institute (Moscow) to assess the radiation damage on: • CuCD • MoCuCD • MoGRCF (ex SiC) • Features: • Irradiation with proton and carbon beam at 35 MeV (and 40 MeV) • Direct water cooling and T~100°C • Thermo-physical and mechanical characterization at different fluencies (1016, 1017, 1018 p/cm2) • Theoretical studies of damage formation N. Simos

5. Composition & physio-mechanical properties of the material matrix to be irradiated N. Simos

6. Objectives of BNL-BLIP Experiment • Assess degradation of physical and mechanical properties of selected materials (Molybdenum, Glidcop, Cu-CD, Mo-GRCF) as a function of dpa (up to 1.0) • Assess irradiation effects on physical and mechanical properties: • Stress-strain behavior up to failure (Tensile Tests on metals, Flexural Tests on composites) • Thermal Conductivity • Thermal Expansion Coefficient (CTE) and swelling • Electrical Conductivity • Possible damage recovery via thermal annealing • Compare dpa level to expected dpa level in LHC at nominal/ultimate operating conditions • Address dpa a sufficient indicator to compare different irradiation environments N. Simos

7. BNL Accelerator Complex Typical proton beam profile N. Simos

8. LHC_BLIP Target Array N. Simos

9. Challenges • Ensure that the array receives 200 MeV at inlet and provides the right energy for isotope production at exit (~212 MeV)  independent studies have been performed to ensure that the energy budget through the target array is what it should be • Ensure that the water column intercepted by the beam (water cooling channels between target capsules) is minimized and it is less or equal to the water column of 32 mm proven to be a good measure based on the experience of the 181 MeV Run of 2010 for 9 weeks • At issue is the short-lived isotopes produced in the water • The Nominal option for the experiment has a water column width of 17mm • The Alternative option with increased water gap between targets (to 2.5mm) will have a total water column width of 25 mm • In attempting to reduce the gap to the minimum (nominal case ~1.5mm) the potential for water cooling channel reduction due to bowing of the target encapsulation under ABNORMAL conditions increases. Detailed studies for normal and abnormal conditions have been performed. • Assessment of the ability of the encapsulation to withstand both normal and abnormal beam conditions especially in the case of coolant path reduction. N. Simos

10. Challenges (cont.) Assessment of the hydro-dynamic or fluid flow/heat transfer conditions around the targets given the limited flow controls at the BLIP target coolant supply While CFD simulations have been performed, conservative heat transfer coefficients were deduced based on heat transfer calculations (these have been benchmarked and verified in previous studies of target irradiations at BLIP) Mapping and quantification of Isotopes produced during the 8-week irradiation by the LHC target array Identified strong isotope signatures will be used for monitoring of the condition of the target integrity during irradiation by sampling and analyzing the BLIP cooling water Option B will be available and in ready position (i.e. array with increased cooling gaps but still within the safe water column width) in the event that the NOMINAL arrangement, combined with beam abnormal conditions, will lead to a breach in any of the target capsules. The continuous monitoring will ensure that the process will be under control. N. Simos

11. Pre-Experiment Analyses • To ensure that good understanding of the parameters and the need to satisfy the key requirements of safety and of undisturbed isotope production, an array of relevant studies were performed, namely • Beam energy and beam profile evolution to ensure that the appropriate isotope production energy is unaffected: • Beam energy degradation through curve fitting (used also in isotope target energy calculations • A detailed simulation using SRIM/TRIM with all layers of different materials represented exactly as they will be at the experiment (beam energy, beam profile, energy deposition) • A detailed MCNPX-ORIGEN simulation of the exact array for beam energy degradation, energy deposition and isotope mapping and quantification • A FLUKA model calculation for damage (dpa) and confirmation of beam energy, profile and energy deposition • Heat transfer coefficient analytical study. • CFD simulation of velocity profiles through target array • Large-scale linear and non-linear finite element analyses for thermal and thermo-mechanical response of the target capsules in the proposed array N. Simos

12. Linac Energy Degradation Assessment Objective is to precisely degrade the 200.3 MeV Linac energy through the target array in a way that the beam energy leaving the array to be EXACTLY what the isotope target array receives when it normally operates at the 118 MeV mode Four (4) parallel studies were performed to ensure the proper proton energy degradation N. Simos

13. First Screening/Layout of Target Array based on energy degradation fitting curves N. Simos

14. SRIM/TRIM Simulation of the Complete Target Array N. Simos

15. SRIM/TRIM Energy Deposition Simulation of the Complete Target Array N. Simos

16. SRIM/TRIM Simulation of the Complete Target Array N. Simos

17. MCNPX Simulation of LHC Target Array N. Simos

18. MCNPX Energy Deposition of LHC Target Array N. Simos

19. MCNPX Isotope Generation Estimation from LHC Target Array N. Simos

20. MCNPX Isotope Generation Estimation from LHC Target Array N. Simos

21. FLUKA Simulation (L. Lari, CERN) • Impacting p+ @ 201 MeV • Spot beam size: sx=0.892 [cm]; sy=0.679 [cm] • Beam interacting in the center (x=0,y=0) of the target. • 8-9 weeks of continuous irradiation (depends on Linac current) @ 5.94E+14 p+/s More detailed Results in provided Appendix N. Simos

22. N. Simos

23. Results are normalized to 5.94E+14 p+/s !!! • Power density peak in the Molybdenum central specimen • (6th layer) Power density peak [W/cm3] Agreement between SRIM and FLUKA z [cm]

24. Binning used 1mm (x) * 1mm (y) * 1mm (z) Power deposition maps x [cm] The power density peak in the Molybdenum - 6th layer - is also visible in the power deposition map, cut at the depth of the maximum (i.e. y ~= 0) Vacuum gap Logarithmic scale [W/cm3] y [cm] The power density peak is in the middle of the central “bone” shape Molybdenum specimen Linear scale [W/cm3] z [cm] x [cm]

25. Prompt Dose map The prompt dose map in Gy, cut at the depth of the maximum (i.e. y ~= 0) is shown. Dose peak almost uniform in all the seven material layers  ~ 2e-10 Gy Vacuum gap x [cm] Logarithmic scale [Gy] z [cm]

26. Irradiation profile used In order to evaluate the Radioactive Isotope Production during irradiation, different cooling times where taken into account Start irradiation Stop irradiation Scoring after … 1 hour 8 hours 1 day 7 days 1 month 4 months 10 weeks of irradiation @ 5.94E14 p+/s

27. Molybdenum -3mm- 1st layer Tot. ~7.1e+12 Bq/cm3 +/-0.3% Tot. ~5.3e+12 Bq/cm3 +/-0.3% Tot. ~4.1+12 Bq/cm3 +/-0.3% After 1 hour After 8 hours After 1 day Bq/cm3 Bq/cm3 Bq/cm3 Mass Number A Mass Number A Mass Number A Tot. ~1.7e+12 Bq/cm3 +/-0.4% Tot. ~8.8e+11 Bq/cm3 +/-0.4% Tot. ~4.1e+11 Bq/cm3 +/-0.5% After 7 days After 1 month After 4 months Bq/cm3 Bq/cm3 Bq/cm3 Mass Number A Mass Number A Mass Number A

28. Thermo-mechanical Analysis Objectives/Concerns: Energy deposition and energy removal from the encapsulated targets through the encapsulation windows and from the passing water through the channels Survivability of the encapsulation 304 steel windows for both the degrader and all the targets under normal and off-normal conditions Uncertainties in the value of CONDUCTANCE between the target material encapsulated and the inner face of the encapsulation window (sensitivity studies required) Uncertainties in the impedence of velocity of coolant through the water gaps affecting the heat transfer coefficient and thus heat removal Highly non-linear and benchmarked thermo-mechanical models were employed to address all questions above N. Simos

29. Computational Fluid Dynamics Analysis – Convection Film Coefficients As a result of the effect of channel width on the velocity through the narrow channels seen by the CFD analysis, VERY conservative heat transfer coefficients were used in the subsequent analyses. The film coefficients were based on the hydraulic diameter of the gap, the wall temperatures, estimated velocities, Reynolds, Pradtl and Nusselt numbers. The estimated film coefficient values were significantly reduced for conservatism N. Simos

30. Parenthesis – Analytical Estimation of heat transfer coefficient through the target capsules Estimation of Reynolds number related to the velocity of flow Uf through the hydraulic diameter (gap between targets), NRe = Uf De/ν where ν is the dynamic viscosity Estimate Reynold’s number from Nusselt number NuDe = 0.023 (Re)0.8 (Pr)0.3 where Pr is the Prandtl number By relating the film coefficient to the Nusselt number NuDe NuDe = hf De/ k De = hydraulic diameter Obtain a good estimate of the forced convection film coefficient. N. Simos

31. Computational Fluid Dynamics Analysis – Convection Film Coefficients animation N. Simos

32. Computational Fluid Dynamics Analysis – Convection Film Coefficients animation N. Simos

33. Computational Fluid Dynamics Analysis – Convection Film Coefficients animation N. Simos

34. Thermo-mechanical Analysis • Extensive thermal and thermal stress analyses were performed for all the targets but in particular for two very critical elements of the array: • The front degrader which displaces a significant column of water so the beam/water interaction is minimized. The degrader is under vacuum. Any failure of any of its beam windows will result in filling of its volume with water and thus the SIGNIFICANT increase of the intercepting water column • Two options were entertained: One is to use the 0.012-inch thick 304 steel windows used continuously in the isotope production array and with no failure. The PRIMARY option is to use a degrader with 0.030 inch windows given that the energy of the beam has been increased to 200 MeV from 118 MeV. • As the subsequent results will show, the analysis confirms what is normally observed regarding the 0.012 inch-thick degraders and the inward deformation of ~ 0.050 inches (1.25 mm). • The 0.030-inch thick window degrader is adopted as the nominal one (~0.020 mm inward displacement) • The 3-mm thick Mo target (towards the back of the array) experiencing the highest energy deposition (as seen and confirmed by the various analyses) • Thermal and heat transfer calculations based on conservative estimates of energy deposition • Sensitivity analyses of heat transfer through contact between window rear and encapsulated target surface • Abnormal conditions of very rapid heating (rather than steady state) leading to window deformation and thermal stress conditions N. Simos

35. Degrader (vacuum) with 0.030” 304 SSTL windows N. Simos

36. Degrader (vacuum) with 0.030” 304 SSTL windows N. Simos

37. Degrader (vacuum) with 0.030” 304 SSTL windows N. Simos

38. Degrader (vacuum) with 0.012” 304 SSTL windows Predicted value by the analysis confirms what is normally measured on the BLIP degraders used in the isotope production array with the same 0.012” thick 304 steel window !!!! The permanent deformation observed is due to plastic strain that develops at the rim (also confirmed by this analysis) N. Simos

39. Mo Target Thermal and Thermal Stress Analysis The 3-mm thick Mo target (towards the back of the array) experiencing the highest energy deposition (as seen and confirmed by the various analyses) Thermal and heat transfer calculations based on conservative estimates of energy deposition Sensitivity analyses of heat transfer through contact between window rear and encapsulated target surface* Abnormal conditions of very rapid heating (rather than steady state) leading to window deformation and thermal stress conditions *During the 2010 181 MeV run but on graphite, C/C and h-BN the conductance issue and the sensitivity was validated based on post-irradiation studies and the temperatures experienced by the target material contents (inferred from the annealing temperature thresholds) N. Simos

40. Mo Target Thermal Conditions (SState – K = 1000 W/cm2-s) 304 steel window temperature N. Simos

41. Mo Target Thermal Conditions (SState – K = 400 W/cm2-s) 304 steel window temperature N. Simos

42. Mo Target Stress (Normal Conditions) N. Simos

43. Mo Target Stress (Extreme Conditions of very rapid heating) Stresses shown are in Pa – maximum von Mises stress of 261 MPa is ~half the ultimate strength of 304 steel NO plastic strain seen (contact between window and encapsulated target prevents plastic zone formation in window) N. Simos

44. Mo Target Stress (Extreme Conditions of very rapid heating) Under this extreme of rapid heating (window does not have time to accommodate and distribute its thermal expansion) the deformation is towards the water gap. To address and respond to this possibility (which increases the potential for window failure due to gap closure at the very center of the target in the event of abnormal beam heating situation) an arrangement which will accommodate larger water gaps is being designed as a back-up option. N. Simos

45. Mo Target Stress (Extreme Condition) Note that heating is so rapid in off normal condition that there is no heat load dissipation or diffusion N. Simos

46. SUMMARY • We believe with the extensive analyses and effort put behind the preparation of this experiment that we have ensured • Uninterrupted Isotope Production • Safety Conditions with plan B in place for unforeseen off-normal conditions of the Linac Beam • Based on previous experience of similar irradiation experiments we minimized further the beam-water column interaction and the short-lived isotope production • Over the past decade we have performed similar experiments with up to 200 MeV Linac beam (including experiments for Phase I LHC collimators) • The fabrication of all the components is almost complete. Final assembly and tuning will be required prior to irradiation start N. Simos