Beryllium Target studies for Long Baseline Neutrino Experiment - PowerPoint PPT Presentation

Beryllium Target studies for Long Baseline Neutrino Experiment (LBNE) at 0.7 MW and 2 MW operation • RAL High Power Targets Group: Chris Densham, Otto Caretta, Tristan Davenne, Mike Fitton, Peter Loveridge, Matt Rooney • In collaboration with Fermilab: Patrick Hurh, Bob Zwaska, James Hylen, Sam Childress, Vaia Papadimitriou

Beam Parameters used in study Proton Beam Protons per Repetition Proton Beam Beam sigma, Energy Spill Period (sec) Power (MW) (mm) (GeV) 120 4.8 e13 1.33 0.7 1.5 – 3.5 60 5.5 e13 0.76 0.7 1.5 – 3.5 120 1.6e14 1.33 2.3 1.5 - 3.5 60 1.6e14 0.76 2 1.5 - 3.5 Bunch length Bunch spacing Bunches per Protons per Pulse length (nano-sec) (nano-sec) Pulse Bunch (micro-sec) 2-5 18.8 519 3.1e11 9.78

Assumptions for target technology options 1. Target length = 1m, Target diameter between 9mm and 21mm 2. Low z target material – lower heat load per pion produced – lower production of neutrons and other secondary particles – less secondary heating and radiation damage to horn and target station components 3. Candidate materials • Baseline: graphite, water cooled (IHEP study) • Alternative materials for this study: Be and alloys (motivated by radiation damage of graphite) 4. Geometry options: • Target integral with horn inner conductor (water spray cooled) • Separate target and horn inner conductor cooled by: – Water – 2-phase water – Helium – Air

– The ‘Figure of Merit’ is a convolution of the selected pion energy histogram by a FLUKA studies weighting function: ‘Figure of Merit’ • 1.5 GeV < E < 12 GeV • pT <0.4 GeV/c yield in energy range of interest – Weighting function W = E 2.5 0.4 compensates for low 0.35 abundance of most useful yield [pions/proton] 0.3 (higher energy) pions total = 1.43 pions/proton 0.25 – Devised by R.Zwaska (FNAL) 0.2 – Implemented in FLUKA by 0.15 Tristan Davenne 0.1 0.05 0 10.25 10.75 11.25 11.75 1.75 2.25 2.75 3.25 3.75 4.25 4.75 5.25 5.75 6.25 6.75 7.25 7.75 8.25 8.75 9.25 9.75 pion energy [GeV]

Figure of Merit as a Change in FoM with target radius 150 FoM [pions+/-/proton * GeV^2.5] design guide 140 130 Investigate: 120 optimum target radius 110 sensitivity to off centre beam 100 target length 0 2 4 6 8 10 12 beam energy (60 vs 120GeV) etc etc target radius [mm] beam sigma=3.5mm beam sigma=1.5mm large target design radius = 3sigma small target design radius = 3sigma FOM vs length performance drop off with eccentric beam 180 150 FoM [pions+/-/proton * GeV^2.5] 160 140 130 120 140 110 FOM 100 120 1.5mm 90 10.5mm radius cylinder 80 3.5mm 100 70 10.5mm radius spheres 60 80 4.5mm radius cylinder 50 (low statistics) 0 1 2 3 4 5 6 7 8 9 10 11 12 60 80 120 160 200 240 280 320 360 400 parallel off centre deviation [mm] Target length [cm]

Energy deposition contour plots Energy deposition in beryllium target (GeV/cc/proton) Beam energy = 60 GeV Beam sigma = 3.5mm sigma Target radius = 10.5mm Target length = 1 m Integrated energy deposition = 16.9kJ/spill 15% increase in integrated energy deposition with magnetic field target radius Effect of horn focussing of secondary particles

Effect of water and horn inner conductor on FoM Reduction in yield due to water jacket FoM [pions+/-/proton * GeV^2.5] 160 140 4% reduction in FoM due to 120 presence of water 100 80 Target 60 Water jacket 40 20 0 120GeV 120GeV 60GeV 60GeV 1.5mm 3.5mm 1.5mm 3.5mm Significant reduction in FoM due to inncer conductor being in close proximity with target

Stress Calculations Stress Levels exceeding design stress for some design options “Quasi - static” “Stress - wave” Peak “total” Beam Beam thermal stress inertial component Beam sigma stress Energy Power component (inferred through (mm) (AUTODYN) (GeV) (MW) (ANSYS) subtraction) [MPa] [MPa] [MPa] 1.5 177 100 77 120 0.7 3.5 55* 27 28 1.5 575* 334 241 120 2.3 3.5 180 90 90 • Significant Longitudinal Stress Waves

Effects of accidental 2 σ off-centre beam on integrated target & horn inner conductor

Otto Caretta

Target segmentation • Segmenting reduces inertial stress by reducing target expansion time • Also removes problem of an off-centre beam inducing vibration modes • Spheres avoid stress concentrations associated with corners

Effects of accidental 2 σ off-centre beam on stress waves in simply supported target rod Peak stress with off centre beam 800 Peak Von-mises stress as a result of 2sigma off centre beam [MPa] 0.7MW spheres 700 2.3 Mw spheres 0.7 MW cylinder 600 Limited range 2.3 MW cylinder of design nominal yield strength and 500 endurance limit for beryllium parameters Max design stress (as specified by Fermilab) fall below 400 design stress 300 200 100 0 5 10 15 20 25 Diameter of cylinder or sphere [mm]

Physics vs Engineering Optimisation ? Target and Beam Dimensions • For pion yield – smaller is better – Maximum production and minimum absorption (shown by FoM) • For target lifetime – larger diameter and shorter length is better – Lower power density – lower temperatures, lower stresses – Lower radiation damage density • For integrated neutrino flux, need to take both neutrino flux and lifetime factors into account – Want to make an assessment of trade off between target lifetime vs beam and target dimensions – Answer will depend on Target Station engineering (time to change over target and horn systems)

Combined target and horn inner conductor

Combined target and horn inner conductor • Analysis procedure (Peter Loveridge) FLUKA ANSYS ANSYS ANSYS Software: (3D) (3D slice) (3D slice) (3D slice) Beam heat generation rates Nodal temperatures Proton beam Current pulse Resistive heat Inputs: definition parameters generation rates Nodal forces emag Thermal Structural Energy Model: Transient Transient Static Deposition Magnetic field Energy density Temperature Static stress / Outputs: distribution distribution strain Current density Joule heating Lorentz force

Magnetic modelling Longitudinal force in inner conductor  2   I R   0  2 F long ln    4 R   1 I B F Peter Loveridge

Solid beryllium inner conductor diameter = 21mm Max current density Max. magnetic field 0 A/mm 2 1200 A/mm 2 0 Tesla 5.6 Tesla Max. Lorentz stress Max. temperature 0 MPa 129 MPa 300 K 311 K

Ø21mm Beryllium Combined Target / Conductor Beam Heat + Joule Heat + Lorentz Force Combined 380 160 effects of: 370 140 1 ms 300 kA Min. Temperature current pulse 360 120 Max. Temperature Von-Mises Stress [MPa] + 2.3 MW 120 Max. VM-Stress Temperature [K] 350 100 GeV beam pulse 340 80 330 60 320 40 310 20 300 0 0.0 0.5 1.0 1.5 2.0 Time [msec]

Conclusions on combined target/horn IC • Complex, combined horn current pulse and beam pulse effects • Need to reduce longitudinal Lorentz stresses requires target diameter to be larger than desired for optimum pion yield • At 2.3MW target segmentation required so can’t use target as a conductor • Recommend looking at longitudinally segmented target separate from horn

Advantages & disadvantages of different cooling methods Advantages Disadvantages   High heat transfer Not compatible with separate target & horn   No shock issues Patchy/non uniform cooling   Experience for horn cooling Reliability of nozzles Water spray cooling   Good for integrated target/horn Tritium production  Dissociation of water   Uniform cooling Shock/water hammer issues   High heat transfer Heat deposition in water Water forced   Simple hardware requirements Tritium production convection cooling   Low temperature rise of water Dissociation of water   Uniform cooling Lower density than water Helium cooling   No shock issues High pressures required to reduce pressure forced convection  Low radiation drop and obtain sufficient mass flow   Simple hardware requirements Lower density than water   Uniform cooling Most attractive for low beam powers   Low cost Consequences of NO x production and other Air cooling  Can exhaust cooling air into target station radiochemistry effects forced convection  Non re-circulating system, no activation of compressor

LBNE target study: conclusions for 2 – 2.3 MW • Combined target/horn inner conductor – Not recommended as dimensions dominated by horn current pulse Lorentz forces rather than pion production • Candidate beryllium target technologies for further study: 1. Water cooled longitudinally segmented 2. Pressurised helium cooled separate spheres • Further recommendation for 0.7 MW operation – Air cooled target appears an attractive option for LBNE target station configuration

Water cooled target concept (2.3 MW) NB stress waves in water (need helium bubble population?) Mike Fitton

Water cooled target concept (2.3 MW) Pressure drop vs flow rate Δ T=5.7K Target core temperature vs flow rate Δ T=29K Mike Fitton