Superbeam target work at RAL

1. Superbeam target work at RAL Work by: Ottone Caretta, Tristan Davenne , Peter Loveridge, Chris Densham, Mike Fitton, Matt Rooney (RAL) EURONu collaborators: C. Bobeth, P. Cupial, M. Dracos, M. Kozien, B. Lepers, A. Longhin, F. Osswald, B. Skoczen, A. Wroblewski, M. Zito Presented by Ottone Caretta O.Caretta@rl.ac.uk EuroNu Meeting, RAL January 2011

2. Introduction Beam Separator 4 MW Proton beam from accumulator at 50 Hz Decay Volume 4 x 1MW Proton beam each at 12.5 Hz Target Station (4 targets, 4 horns) • EUROnu target-station scheme has 4 targets and 4 horns • Each target exposed to ¼ of the total beam power (1.11e14 protons/pulse, 4.5 GeV, 12.5 Hz repetition rate) • Reduced Beam induced heating in target by a factor of 4 • roughly 50kW of heat deposited in each target • beam sigma 4mm. Target diameter 30mm (around 780mm long) • Target almost entirely inserted in the bore of the horn Marcos Dracos 2 EUROnu Annual Meeting, January 2011

3. Target design criteria Cost 1. Feasibility 2. Reliability Simplicity Safety 3. Reliability 4. Reliability 5. Physics performance

4. Some issues of interest for the engineering of the target Heat removal beam ~50kW Joule from current (integrated target&horn) ~20kW Thermal/mechanical stresses static dynamic Cooling layout – design & medium water helium peripheral vs transversal cooling Neutron production – heat load/damage of horn (avoid high Z materials) Safety (e.g. Activated mercury vapours) Radiation resistance Reliability! – engineering integration (simple is good!) Pion yield

5. Heat removal Beam heating ~50kW - substantial! cooling is feasible but thermal stresses are an issue Joule heating (if considering an integrated target and horn) ~20kW not much but challenging if added to the beam heating Peter Loveridge P Loveridge

6. Thermal/mechanical stresses Static stresses (related to steady state dT in material) on centre temperature difference between core and surface in a rod generates high mechanical stresses largely independent of the rate of cooling off centre higher stresses and significant deformations are to be expected in a target excited by an off centre beam. Dynamic inertial stresses by instantaneous heating can play an important role P Loveridge

7. Cooling layout & medium • Water • avoidenclosed water in proximity of the beam: • 1K of (instantaneous) beam induced heating generates approximately 5bar of pressure rise which may result in water hammer and/or cavitation • Helium • almost beam “neutral” is good also for transversal flow cooling (across the beam footprint) although pressure has to be kept higher (10bar) to obtain a high cooling efficiency. No generation of stress waves in coolant. Low activation of coolant. No corrosion problems • Peripheral vs transversal cooling • peripheral cooling does not appear sufficient to maintain a low dT within the target material. • A transversal cooling arrangement may be necessary to provide cooling at the core of the target.

8. IG 43 graphite Radiation damage 800oC 400oC Thermal conductivity (After/Before) (dpa) 1 2 3 Mechanical properties of graphite degrade rapidly with irradiation Mike Fitton Matt Rooney Nick Simos, BNL

9. Summary of target options Mercury jet high-Z (too many neutrons & heat load on horn) not chemically compatible with horn Graphite rod thermal conductivity degrades with radiation damage mechanical stress depends on dT hence short life time Beryllium rod thermal stress is significant alternative geometries could overcome the problem (still under investigation) Integrated Be target and hornextra heat load makes it even more challenging combined failure modes could reduce the life time Fluidised powder target potential solution for higher heat load Static pebble bed reduced stresses. Favourable transversal cooling. Good yield

10. Cylindrical Solid Target Steady-State Temperature Steady-State Stress Temperature (left) and and Von-Mises thermal stress (right) corresponding to steady state operation of a peripherally cooled cylindrical beryllium target • Initial baseline was a solid cylindrical beryllium target. This has since been ruled out • At thermal equilibrium (after a few hundred beam pulses) large temperature variations develop within the target • The large ΔT between the target surface and core leads to an excessive steady-state thermal stress • This ΔT depends on the material thermal conductivity and cannot be overcome by more aggressive surface cooling HTC = 10kW/m2K HTC = 10kW/m2K

11. “Pencil Shaped” Solid Target • A potential solution may be found by shaping the upstream end of the target such that the cooling fluid is in close proximity to the region of peak energy deposition • Shorter conduction path to coolant • Reduced ΔT between surface and location of Tmax • Thermal stress is reduced to an acceptable level • Able to operate with a factor 2 x less aggressive surface cooling • Pressurised helium gas cooling appears feasible Steady-State Temperature Steady-State Stress HTC = 5kW/m2K HTC = 5kW/m2K 68 (°C) 306 (°C) 0 (MPa) 110 (MPa) Temperature (left) and Von-Mises thermal stress (right) corresponding to steady state operation of a peripherally cooled “pencil shaped” beryllium target

12. Packed bed Target Concept for EUROnu Tristan Davenne Model of a 12mm radius Titanium alloy cannister containing packed bed of 3mm titanium spheres Offers high surface to volume ratio for good heat transfer throughout target Possible to remove dissipated energy without concerning temperatures and stress Insensitive to off-centre beam Need pressurised gas for high power deposition Bulk density lower than solid density ( use titanium instead of beryllium ) Ideal Transverse flow configuration FLUKA + CFX Physics performance for titanium spheres looks reasonable Induction heater test Graydon et al. 1MW beam Helium mass flow = 93grams/s Helium outlet temperature = 109°C Induction heating may provide an interesting way to test a packed bed Maximum titanium temperature = 673°C