Figures of Merit for target design for neutrons

Figures of Merit for target design for neutrons, neutrinos… Chris Densham Rutherford Appleton Laboratory Chris Densham

Motivations for ‘Figures of Merit’ • End-to-end simulations of accelerator driven facilities highly sophisticated & complex – – Computationally expensive – e. g. genetic algorithm ‘Black box’ type output Can be difficult to identify ‘design guidelines’ ‘Listen to the robot’ for the answer • Useful to have a tool that (ref R. Zwaska) : – Can factorise problems – orthogonal to genetic algorithm – Is readily understood – Can apply to a distribution • Also useful to have a tool to compare reliability (materials or engineering issues) Chris Densham

Neutron Economy at SNS F. X. Gallmeier • 1. 4 MW SNS produces: 2 × 1017 n/s • Thermal neutrons at beamline start: 2× 1012 n/s • Neutrons at sample position (white): 2× 1011 n/s • Neutrons at sample (chopped): 2× 1010 n/s • Neutrons scattered: 2× 108 n/s • Neutrons counted: 5× 107 n/s Neutron counted/Neutrons produced: 3× 10 -10 3 Presentation name

Figures of Merit for Physics & Engineering? • Chris Densham 29 February 2016 4

ISIS First Target Station Upgrade Project • • To upgrade key elements of TS 1 including moderators, reflectors and target infrastructure Aims to achieve a factor of 2 or more increase in neutronic performance for a modest cost. Use modern software and analysis techniques to improve neutronic efficiency without increasing the beam power. Develop a more efficient spallation reflector, moderator, target system. Target, moderators and reflector assembly The ISIS First Target Station

ISIS TS 1 Upgrade • Maximise neutronic output • Optimise beam power (~200 k. W seems just fine) g e st n Tu n ‒ Make more compact ‒ Less neutron-absorbing material Water flow lines ons prot Ambient Water Hydrogen Temperatures Methane Existing TS 1 target & moderator assembly 6

Increasing Beam Power – Neutronics • Stuart Ansell and Goran Skoro modelled neutronic gain as a function of beam current for several target types: • Higher beam power => more plates required => more water in target => longer neutron pulse width Chris Densham

Neutrinos: LBNF/DUNE Experiment • Muon neutrinos/antineutrinos generated by 1. 2 – 2. 4 MW proton beam at Fermilab • Long baseline -> large matter effects (unlike T 2 K, Hyper-K) – Measurement of neutrino mass hierarchy • On-axis, wide-band beam (wide range of neutrino energies ~ few Ge. V) – Measurement of different oscillation rates for νs and anti-νs – Unfold CP-violation from matter effects through E dependence – Can capture both 1 st and 2 nd oscillation maxima 1300 km Chris Densham 8

Laura Fields Chris Densham

Laura Fields Chris Densham

Chris Densham

Results of optimisation Chris Densham 12

High Z cooling tube or downstream plug? c/o Mary Bishai • High z plug downstream of the target and/or high z target outer tube • Increase pion yield relative to a 2 interaction length graphite target. • Graphite cylinder inside a High-Z tube gives best increase in yield • A comparative Figure of Merit would be useful to compare & optimise different designs Chris Densham

‘Figure of Merit’ for LBNF Fo. M= • • • (R Zwaska) Ni = Number of pions in bins from 1. 5 Ge. V < E < 12 Ge. V for pt < 0. 4 Ge. V Useful indication of physics performance to inform engineering studies Weights higher energy (more interesting) pions to balance drop in production at higher energies NB needs to be modified to take into account 2 nd oscillation max at c. 1 Ge. V FLUKA simulations T. Davenne, O. Caretta Chris Densham

Figure of Merit Comparison for different target and beam sizes FLUKA simulations Target radius Chris Densham

π p T 2 K Target & horn π Helium cooled graphite rod Design beam power: 750 k. W Beam power so far >350 k. W σ = c. 4. 2 mm 3% beam power deposited in target • 1 st target & horn replaced after 4 years, 6. 5 e 20 p. o. t. • 2 nd target repaired after 5 e 20 p. o. t. • • • Target exchange system

Effect of pulsed beam on T 2 K target 8 MPa p 0. 5 µs beam spill Radial stress waves – on centre beam spill Inertial ‘violin modes’ Stress distribution after off-centre beam spill

Effects of pulsed beams: Nu. MI target Autopsy of water-cooled Nu. MI target NT-03 (photo courtesy of V. Sidarov) Possible explanation: high tensile stress after beam pulse (damage may also have occurred during removal of target tube)

Fast neutron radiation damage data for graphite (IG 110)

Radiation damage – any chance of a Fo. M? C. A. English (2011)

Figures of Merit for target/collimator materials (proposed by A. Bertarelli, CERN) • Chris Densham 29 February 2016 21

Limitations of target technologies Flowing or rotating targets Segmented Peripherally cooled monolith

Particle Production Target ‘Optimum’ Performance • For particle flux – small beam σ is favoured – A ‘Figure of Merit’ can indicate physics performance • For target lifetime – bigger is better. – – Lower power density – lower temperatures, lower stresses Lower radiation damage rate Lower amplitude ‘violin’ modes (and lower stresses) Need another Figure of Merit for target engineering issues • For integrated particle flux, need to take both these factors into account – E. g. How to achieve best physics performance possible for a target lifetime of a minimum of 1 year? – Answer will depend on Beam Power Chris Densham

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