ESSnuSB Target Chris Densham, Tristan Davenne STFC Rutherford Appleton Laboratory 26 th May 2014

Target Station Layout Kinematic Mounts Shield Blocks Rest on Vessel Helium Vessel Feedthrough for Services 4 targets in 4 horns ~50 kW per target Particle bed only viable static target option

Targets requirements: simple? HP Target High power proton beam Heat load removal Stress endurance Creep Cyclic stresses (fatigue) Dynamic inertial stresses Quasi-static stresses Material props Rad. Damage Operational safety RadiologicalToxicological Disposal Remote handling Physics performance Operational reliability

Chris Densham Target remote exchange system T2K Target π π Helium flow lines – design optimisation using CFD 400 m/s p Helium cooled graphite rod Design beam power: 750 kW Beam power so far: 230 kW 1 st target & horn just replaced after ~5 years, 6 x protons 1 st measurement of ν e appearance from ν μ beam

Solid Peripherally cooled Target Packed Bed or segmented Target Flowing Target - powder jet, mercury jet Heat Load ~10 kW~100kW ~1 MW Limiting factors Heat Transfer Thermal and Inertial Stress Off axis beam Helium Pressure Radiation damage Window components Reliability Complexity Radiation handling Development Time When to use a Packed Particle Bed Target? Simple, well proven A bit more complex, less experience Much harder, very complex

Particle bed advantages Large surface area for heat transfer Coolant can pass close to maximum energy deposition High heat transfer coefficients Low quasi static thermal stress Low dynamic stress (for oscillation period <<beam spill time)... and challenges High pressure drops, particularly for long thin Superbeam target geometry Need to limit gas pressure for beam windows Transverse flow reduces pressure drops – but Difficult to get uniform temperatures and dimensional stability of container

Simple packed bed target model W Assume parabolic energy deposition profile Obtain gas temperature as a function of transverse position

Sphere Temperature for 3mm Ti6Al4V spheres with ~1MW beam W Sphere core temperature is seen to depend on gas temperature and energy deposition, variation in thermal conductivity with temperature is also accounted for. Empirical Nusselt number correlation for heat transfer in packed bed (Achenbach et al.)

Pressure Drop W Use Ergun equation or similar correlation (e.g. Achenbach) to determine pressure drop through packed bed

W Applicability to ESSnuSB Max possible power density assuming max Titanium temp < 400°C Helium pressure =10bar max helium pressure drop < 0.5bar Max possible power density for packed bed

Packed Bed Target baseline solution: ESSnuSB Packed bed target concept for 5 MW From SPL-Superbeam study (EUROnu) Stress limit reached for solid peripherally cooled target 100 m/s helium Increased surface area. Coolant reaching maximum energy deposition region T.Davenne

Packed Bed Testing Plans Packed bed induction heating theory Duquenne et al. Induction Heating Packed bed placed in an alternating magnetic field. Eddy currents induced in conductive spheres. Resultant Joule heating provides internal heating of spheres. Induction heater test Graydon et al.

Compressed Air Induction heater head unit Infra red temperature gauge Induction coil Safety tube Borosilicate glass test section Holes for coolant tubes and power cables to pass to PSU on lower level Target Thermal imaging camera exhaust IR transparent window Stainless flanges T2T2 T1T1 Flow Meter Rig layout 90cm 40cm 90cm 3.15m 3 Heat applied to target determined from mass flow and temperature difference valve

Investigation of the radiation response of structural window and target materials in new highly intensity proton accelerator particle sources is a promising candidate because of: Beryllium is a promising candidate because of: good “nuclear” properties;good “nuclear” properties; appropriate mechanical propertiesappropriate mechanical properties good “thermal” properties (conductivity, specific heat, melting point);good “thermal” properties (conductivity, specific heat, melting point); high oxidation resistance;high oxidation resistance; positive experience from existing beam windowspositive experience from existing beam windows What about new working conditions?

Microscope and Ion Accelerator for Materials Investigations facility (MIAMI) University of Huddersfield, UK (collaboration with Prof. S E Donnelly) From Ions: He+ Beam energy: ~ 10keV Beam energy: ~ 10keV => peak of damage in the middle of TEM foil (SRIM) Dose: up to 1 dpa Temperature: 200ºC (300ºC, 600ºC) He implantation experiments. Low energy

Surrey Ion Beam Centre, UK (collaboration with Prof. R.Gwilliam) APT sample Pt Pre-tip Ions: He+ Maximum beam energy: Maximum beam energy: 2 MeV => 7.5µm implantation depth (SRIM) Dose: up to 1 dpa Temperature: 200ºC (100ºC, 600ºC) TEM sample 8 × 8 µm 3 He implantation experiments Micromechanical tests

Micro-mechanical testing 1um 3m3m 10  m 4m4m 3m3m Unique materials expertise at Oxford (MFFP Group) Micro-cantilevers machined by Focused Ion Beams Compression tests Tension tests Three Point Bend Cantilever bending New facility NNUF (National Nuclear User Facility) under construction at Culham to carry out such testing of small quantities highly active materials

ESSnuSB Superbeam Target Station R&D Issues Beam windows (target station and target) – Ti6Al4V alloy good for pulsed beams (used for T2K) – Beryllium better at higher currents (used for NuMI/NOvA) – Radiation damage & embrittlement a concern for both Target – Radiation damage of graphite (used in all conventional facilities) Reduction in thermal conductivity, swelling etc Consider beryllium, titanium – Structural integrity & dimensional stability – Heat transfer – High helium volumetric flow rate (and high pressure or high pressure drops) Collector/1 st Horn – Cooling, fatigue strength, hydrolysis, water activation, NO x production if in air Target station emission limitations

Target R&D work list Collaboration between various experts regarding: – Physics performance (maximise useful pion yield) – Engineering & materials performance (maximise lifetime) Engineering studies – Conceptual, FEA, CFD studies Materials – Radiation damage studies – DPA/He/H2 calculations – Cross-referencing with literature data – Devise suitable experiments with irradiation and PIE (Post Irradiation Examination) Prototyping Heating/cooling tests In-beam experiments