3 MeV H - Chopper Beam Dump Pre-design study

1. 3 MeV H- Chopper Beam Dump Pre-design study By L.Bruno AB/ATB M.MagistrisAB/OP M.Silari TIS/RP

2. The Pre-design study OUTLINE 1. Introduction 2. Engineering baseline proposal 3. Radiation studies 4. Engineering studies 5. Issues & future work 6. Summary

3. Driving Parameters The chopper beam dump has to … … continuously intercept a 3 MeV H- beam pulsed at 50 Hzwith 2.8 ms long pulses. The maximum average beam current to be absorbed is 1.1 mA, with a mean power of 3.3 kW. The beam is circular and has a uniform profile of 6 mm radius, which results in a surface heat flux of ~30 MW m-2 .

4. Beam time-structure 20 ms Coarse structure 2.8 ms Fine structure 5 bunches to the end-of-line 3 bunches to the dump Because of inertia, the fine bunch time-structure does not affect the mechanical behaviour of the dump.

5. Lay-out of the chopper line 135 mm flange-to-flange only ! End-of-line dump Chopper dump The dump placed after the chopper would be able to absorb also the beam at the end of the 3 MeV test facility.

6. Engineering baseline Front view Side view Dump core Water ~ 100 mm Water Un-chopped beam Vacuum Chopped beam a Air Vacuum flange Water Cooling tubes Jacket a = 10 degrees The dump core is shrink-fit into an actively-cooled metal jacket. The cooling tubes are bonded by plastic deformation to the jacket

7. Materials Tubes: • Stainless steel 316 LN • Duplex st. steel (1.4462) Jacket: • Aluminium • Dispersion strengthened copper - Cu Al2O3 Core: • Graphite / C-C composite • Hexagonal boron nitride • Aluminium nitride • Molybdenum alloy (TZM) • Copper

8. Radiation study by the Monte Carlo codeFLUKA The baseline was studied to investigate: • Elastic scattering of protons It depends on the composition of the dump core • Inelastic interactions Scored with an energy threshold of 1 keV • Ionization Production of X-rays, estimated with an energy threshold of 1 keV • Transport of photons and electrons Simulation of the whole electromagnetic cascade; energy threshold for particle transport = 1 keV

9. Energy distribution Per primary 3 MeV proton Energydeposited in the dump core: A = 0.525 keV +/- 0.17% B = 2.9801 MeV +/- 0.004% (99.3%) Energy escaping from the dump: X-Rays, e- : 0.1029 keV +/- 0.4% p, X-rays, e- : 14.60 keV +/- 0.5% ( = 0.029% of the beam energy) Energy deposition occurs at the inner surface of the dump core. A B Beam spot

10. Induced radioactivity There is no (p,n) reaction !!! Cross-check: No inelastic interactions were scored with FLUKA on C, Cu, AlN, BN and TZM.

11. Scattered proton flux Per primary 3 MeV proton Downstream of the dump, there is a flux of scattered protons. The colour plots give the fraction of the primary protons scattered per square centimeter at 6 cm distance downstream of the dump.The maximum of this flux ranges from 0.1 per mil (carbon) to 3 per mil (TZM) of the incoming protons (6.85 1016 p+s-1) C AlN Cu TZM

12. Scattered proton spectrum at 20 cm downstream of the dump 1.5 MeV The spectrum of scattered protons 20 cm downstream of the dump at 0°, 15° and 30° with respect to the beam axis peaks at 1.5 MeV.

13. Electron flux [cm-2 proton-1] Top view C TZM 5 cm downstream of the dump, a maximum energy of~6 keV was scored for the electrons emitted from copper. The corresponding x-ray flux (1-4 keV, 1 keV being the FLUKA lower threshold) is about 3 10-6 cm-2 per proton.

14. Finite Element Analysis The baseline was studied to investigate: • 2D Steady-state thermal field for a 10-fold geometric dilution of the heat flux • 2D Steady-state stress field cooling tubes are checked against the ASME rules (American Society of Mech. Engineers) • Material choice results are shown for the most promising Copper-based configuration • Opportunities to optimize water cooling parameters and structural behavior

15. Finite Element Models Ø8.4/8 2D STEADY-STATE THERMAL ANALYSIS Boundary Conditions: Subcooled flow boiling at 20 °C, 40 bars, 12 ms-1 with turbulence promoter. Minimum heat transfer coeff. is 54 kWm-2. Load: Heat flux of 3 MWm-2 . (geometrical dilution factor of 10). 2D STEADY-STATE MECH. ANALYSIS Boundary Conditions: simple support (x-symmetry plus fixed point), GPS (Generalized Plane Strain) without bending. Load: Thermal field plus 40 bar water pressure. Cu Al2O3 Duplex St.Steel R21 3 MWm-2 4 12 6 Water cooling Fixed point

16. Temperature [°C] Subcooled flow-boiling is effective in limiting the maximum temperature of the dump core (Tmax=90°C). The maximum heat flux at the inner surface of the cooling tubes is1.13 MWm-2,which is far below the critical heat flux (>100 MWm-2) for the given cooling parameters. Tmax= 90°C

17. Von Mises Stress [Pa] The maximum Von Mises stresses are below 2/3 of the yield stress at the working temperature in the dump core (177 MPa for CuAl2O3) and below the ASME allowable Sm value in the cooling tubes (207 MPa for the duplex stainless steel). sVM,max=134 MPa in Cu Al2O3 sVM,max=142 MPa in St. Steel

18. None expected To be validatedUnknown Issues and further work Temperature / Thermal gradient Dumpcore Dynamic effects / Mech. strength Radiation damage Geometrical accuracy Background Dumpassembly Vacuum / Outgassing Heat removal principle Handling Dump system Cooling system Alignment Problems? ...

19. Summary Status in April 2003 A proposal for the engineering baseline of the chopper beam dump is available; The pre-design study of its physical and mechanicalbehavior was performed; The most promising materials have been identified; The interfaces for handling, cooling, instrumentation and control are being defined. A detailed technical study is to be performed next.

20. Design guidelines • The dump should be… • a reliable,permanentcomponent; • easilyinstalled, serviced and dismantled; • compact, robust with possibly in-situ spares; • “Cost-effective”: the same design should be re-usable within an SPL-like machine.