Investigation of a “Pencil Shaped” Solid Target Peter Loveridge, Mike Fitton, Ottone Caretta High Power Targets Group Rutherford Appleton Laboratory, UK January

Introduction EUROnu Annual Meeting, January 2011 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 Baseline target technology is a solid beryllium rod, peripherally cooled 2 Beam Separator 4 MW Proton beam from accumulator at 50 Hz 4 x 1MW Proton beam each at 12.5 Hz Decay Volume Target Station (4 targets, 4 horns)

Beryllium Material Properties 3EUROnu Annual Meeting, January 2011

Beryllium Material Properties Note degradation in strength at elevated temperature Suggest to limit T max to, say ~300°C ? Need to define a design stress limit as some fraction of σy say, ~160 MPa ? 4EUROnu Annual Meeting, January 2011

Motivation for a “Pencil shaped” target Need to find a way to reduce the high steady-state thermal stress present in the case of a solid cylindrical beryllium target –Stress driven by large radial temperature variation at thermal equilibrium A potential solution – place the cooling fluid closer to the region peak energy deposition in the target –Shorter conduction path –Reduced ΔT between surface and location of Tmax –Tmax is reduced – more favourable material properties –Lower thermal stress Engineering solutions being considered: –“Pencil shaped” solid target - PL –Packed pebble bed target - TD 5EUROnu Annual Meeting, January 2011

“Pencil” Target Concept Design Pencil shaped Beryllium target contained within a Titanium “can” Pressurised Helium gas cooling, outlet at 10 bar Supported as a cantilever from the upstream end 6 BEAM EUROnu Annual Meeting, January 2011 Drawing not to scale! He In He Out Titanium “Can”Beryllium Target Beam Window Intermediate tube

Geometry Parameterisation 7 Length 800 mm Ø24 mm (r = 3σ) A BC Beam Deposited beam energy in three example beryllium targets Cylinder “Pencil”Cone EUROnu Annual Meeting, January 2011

Deposited Energy (FLUKA) Benefits of a cone shape (compared to a cylinder): –Integrated heat load is reduced (less material in front of the beam?) –Coolant fluid in close proximity to the region of maximum heat deposition Cylinder: Ø24 mm, 800 mm long Integrated Heat Load 2.9 kJ/pulse i.e. 36 kW heating from 1 MW beam 8 Cone: 1 mm < Ø < 24 mm, 800 mm long Integrated Heat Load 2.0 kJ/pulse i.e. 24 kW heating from 1 MW beam EUROnu Annual Meeting, January 2011

Well Centred Beam (Standard Operating Case) Results from steady-state thermo-mechanical analysis: –Need surface HTC of the order 4kW/m 2 K in order to limit Tmax to ~300°C –Gives max stress = 83 MPa Temperature (left) and Von-Mises thermal stress (right) corresponding to a steady state operation with a surface HTC = 4kW/m 2 K, bulk fluid temp = 30°C 9EUROnu Annual Meeting, January 2011 Uniform HTC = 4kW/m 2 K 72°C318°C0MPa83MPa

Off Centre Beam (Accident Case) Results from steady-state thermo-mechanical analysis: –Total heat load is reduced in the case of the beam being mis-steered –Location of Tmax moves downstream Energy deposition (left) and temperature corresponding to a steady state operation with a surface HTC = 4kW/m 2 K, bulk fluid temp = 30°C (right) 10EUROnu Annual Meeting, January 2011 Lateral beam position offset = 2 x beam sigma: Integrated Heat Load 21.2 kJ/pulse i.e. 14 kW heating from 1 MW beam 34°C201°C Uniform HTC = 4kW/m 2 K

Off Centre Beam (Accident Case) Lateral deflection due to steady-state off-centre heating: –13 mm lateral deflection if cantilevered from downstream end –Max stress increased to 120 MPa (recall 83 MPa in well centred beam case) Deflection (left) and Von-Mises thermal stress (right) corresponding to a laterally mis-steered beam 11EUROnu Annual Meeting, January mm13 mm0MPa120MPa

CFX conjugate heat transfer model Cooling fluid = Helium Turbulence model = Shear Stress Transport (SST) Inlet mass flow rate = 60g/s Inlet temperature = 300K Outlet Pressure = 10bar Heat deposition in target = 24kW steady state from Fluka simulation Model of 36° slice (1/10 th of target) with symmetry boundary conditions Cooling channel outer surface defined by 3 radii and connected with spline 12 TargetHelium Inlet Outlet Radius 1Radius 2Radius 3 0.4m EUROnu Annual Meeting, January 2011

Mesh at downstream end of target 13 Boundary layer inflation Fluid Domain Solid Domain EUROnu Annual Meeting, January 2011

Linear cooling channel (Equal area at both ends) Cooling channel R1 = 7.2mm R2 = 10.6mm R3 = 14mm 14 4kW/m 2.K Helium velocity minimum at peak heat Design 1 EUROnu Annual Meeting, January 2011

Constant area (at R1, R2 & R3) cooling channel 15 Cooling channel R1 = 7.2mm R2 = 9.5mm R3 = 14mm 4kW/m 2.K Helium velocity maximum here due to gas heating Design 2 EUROnu Annual Meeting, January 2011

Cooling channel area reduced at centre & increased at ends (2) 16 Cooling channel R1 = 9mm R2 = 9mm R3 = 14.4mm 4kW/m 2.K Design 3 Helium velocity maximum at peak heat EUROnu Annual Meeting, January 2011

Helium Cooling Summary Beryllium target can be cooled with 60g/s helium at 10bar and maintain a steady-state temperature of approximately 300°C Mass flow rate is double that of the T2K target cooling but the volume flow rate is a factor of 3 less due to the target operating at high pressure 10bar & 300K = 135m 3 /hr (Design 3 volumetric flow rate) For comparison 1.6bar & 300K = 421m 3 /hr (T2K volumetric flow rate) Guess total  P (Target + Heat Exchangers + Pipe work) is 5bar Ideal compressor work is then approximately 8kW (T2K = 20kW) Seems reasonable 17 Maximum Temperature [°C] Pressure Drop [bar] Linear cooling channel Uniform area channel “Optimised” channel EUROnu Annual Meeting, January 2011

General Conclusions and further work Pencil target geometry merits further investigation –Steady-state thermal stress within acceptable range –Initial investigation into pressurised helium cooling appears feasible –Off centre beam effects could be problematic..? Need to study pion production for “pencil” target geometry – Andrea?? –Look for any “show-stoppers” Carry out further thermo-mechanical studies including: –Input CFX heat transfer result into ANSYS mechanical model –Profile the target instead of the “can” for ease of manufacture –Helium return flow 18EUROnu Annual Meeting, January 2011