DUNE/LBNF Target Studies: Physics

John Back

University of Warwick

12th April 2016

1

Introduction • DUNE/LBNF: international program for future neutrino experiment based at

Fermilab: simultaneously measure mass hierarchy and CP violation

– Effort underway to optimise beam & target to maximise physics potential

• Current “baseline” is water-cooled NuMI-like target

– Proton beam: 60 120 GeV/c, width = 1 4 mm; 1.2MW, ~1021 POT/year

• Investigating other target options:

– Be Spherical Array Target (SAT) with He cooling

– T2K-like graphite cylinder with He cooling

• Using Geant4 software to simulate target and comparing performance:

– Estimated significance (“# of ”) of measuring CP-violating phase CP

– Similar figure of merit: integrated flux between E = 0 to 4 GeV

2

= n

Gauss beam path length

Solve for N spheres: given R, beam and required n physical length of SAT 15% longer than cylinder

Convolution of Gauss beam path length along SAT

Target module geometry

p beam

Be

He

Ti

He

SAT support “helix” 3

He

Ti

Ti

He

Be R

SAT (or cylinder) encased in double Ti can filled with He gas inside Horn1 (3-Horn set-up)

Simulation parameters: Target radius R: 3 12 mm = 3 x beam Gauss width Target length equivalent to 2 5 Proton beam momentum: 60 120 GeV/c Assume 1.2 MW beam power

Example CP sensitivity

4

2m NuMI target, pbeam = 60 GeV, 3 years running, 1.2 MW Horizontal dotted line: “CP sensitivity” = containing top 75% of values Need CP sensitivity to be as high as possible

Estimated significance for measuring CP violation phase CP using GLoBES software and Geant4 simulated neutrino flux at the far detector (1300km)

75%

Be SAT: 75% vs p

5

L = 2 L = 3

L = 4 L = 5

C cylinder: 75% vs p

6

L = 2 L = 3

L = 4 L = 5

Summary • Target module CP sensitivities compared to 2m (4) NuMI target

(assuming 3 horn set-up optimal for NuMI), all for 3 yrs running @ 1.2 MW:

– Be SAT needs L = 5, R 7 2 mm, p 10515 GeV for similar performance • Longer length required owing to gaps between the spheres

– C Cylinder best performance: L = 5 (2.4m), R 6 2 mm, p 110 20 GeV

• Caveats/issues: – The 3-horn set-up that is optimal for the NuMI target is probably not optimal

for the other target modules – Horn design has strong influence on performance:

• Need to see what critical horn parameters we can (slightly) change • Reduce target module length via horn geometry optimisation?

• Further work:

– Split up target into two equal “mirror image” sections: • Quantify impact on performance

– Investigate target hybrids: low atomic Z start & high Z end • Increases secondary interactions for producing useful low energy ’s • Potential problems with too high energy deposition in high Z end?

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LBNF Target Studies : Engineering Tristan Davenne

Rutherford Appleton Laboratory High Power Targets Group

Engineering Challenges • Total Power Deposited [kW thermal] • Pulsed power density [J/cc] • Radiation damage [Protons/cm2] → dpa LBNF Requirements • Beam Power = 1.2MW baseline increasing to 2.4MW with PIP • Kinetic Energy = 60 – 120GeV • Beam Sigma tuneable between 1mm and 4mm

Target Options • ‘Numi-like’ water cooled graphite target • ‘T2K-like’ Cylindrical helium cooled graphite target • SAT (spherical array target)

NUMI-like target

• Stress calculation assumes normal (unirradiated) graphite material properties, radiation damage may be highest at water cooling operating temperatures

• Stress calculated based on beam spill applied to fin initially at uniform temperature, any residual thermal stress from last pulse?

• Cyclic fatigue loading of a brittle material

Based on the NuMI design but with: Increased target width to 10mm Increased beam sigma from 1 to 1.7mm Increased beam power from 400kW to 1,2MW

Numi stress prediction at 400kW P.Loveridge

C.Crowley

At 1.2MW stress levels reduced from 35MPa to 10MPa

C.Crowley

Titanium tubes to reduce stress in cooling pipes

O.Caretta

C.Crowley

NUMI-like target

May require additional helium cooling for downstream window and outer can?

• Good physics performance due to small beam sigma • Could eliptical beam spot improve physics further? • Water cooling means graphite operates at less than

400C, not benefitting from damage annealing effects that occur at higher temperatures in NoVA & T2K

C.Crowley Stress concentrations at join between graphite fins and cooling tubes

C.Crowley

T2K-like Helium cooled cylindrical graphite target preliminary calculations with LBNF beam parameters

Beam Parameters Beam Energy = 120GeV Beam pulse length = 10μs Beam sigma = 3.5mm Repetition period = 1.33s Beam Power = 2.3MW Protons per pulse = 1.6x1014

FLUKA output for 2m long cylinder of graphite Plan to have two targets back to back about 1m long each

Power deposited in target 1 (i.e. 0m<z<1m) = 30kW

Power deposited in target 2 (i.e. 1m<z<2m) = 19kW

T2K 750kW 30GeV 4.24mm sigma 3.3e14ppp 2.1s 266J/cc/pulse 15kW LBNF 2.3MW 120GeV 3.5mm sigma 1.6e14 ppp 1.33s 280J/cc/pulse 30kW

Predicted operating Temperature of target 1 Assume target has average surface heat transfer coefficient of 1000W/m2K feasible with pressurised helium, IG43 temperature dependant thermal conductivity reduced by factor of a third

before beam pulse after beam pulse

Predicted stress in target 1

before beam pulse after beam pulse

Pulsed energy density no higher than T2K at 750kW Stress levels higher than T2K predictions but in same ball park Off axis beam?

Spherical array target

• Good cooling near target core • Scalability to 2.4MW • Smaller beam sigma than for the graphite cylinder maybe possible • Use of beryllium target material possible in the event that radiation damage becomes a

limiting factor for graphite • Possibility of using different density target materials, although much higher density

than beryllium will be hard without going to very small segments

Stress Wave simulations

• Common theme for neutrino facilities is large pulsed energy deposition which result in stress waves in beam windows and targets

• Simulations often done with Autodyn, LS-Dyna, ANSYS • However simulations are sensitive to parameters such as Courant

number but also mesh size and cell type • As such attractive to have an exact solution for stress wave propagation

in order to benchmark simulations

• Search for an analytical solution for the case of stress waves in a disc -Sievers 1974 and 2000 –uniform heating case and initial energy deposition with a discontinuity (top-hat profile) -Zheng & Taleyarkhan 2004 –solution with smooth energy deposition but appears unstable when increasing number of terms in summation? -Bertarelli – modal summation method for analytical stress wave simulations

After some years of searching we arrived at the following expression for stress waves propagation in a disc as a result of an initial Gaussian temperature distribution

𝑃 𝑟, 𝑡 =𝐶Γ𝑄

𝑉𝑅2𝜎2 −1 − 𝑒

− 𝑅2

2𝜎2

+ 𝐽0 𝜆𝑛

𝑟𝑅

𝐽0 𝜆𝑛2

∞

𝑛=1

𝑐𝑜𝑠𝜆𝑛𝑐𝑠𝑡

𝑅𝑥 𝑒

−𝑟2

2𝜎2 𝐽0 𝜆𝑛𝑟

𝑅𝑑𝑟

𝑅

0

A. D. Polyanin. Handbook of Linear Partial Differential Equations for Engineers and Scientists. CRC Press, 2002.

P Loveridge

Backup

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Be SAT: CP 75% for L = 5

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Bold: Maximum CP for NuMI Red : CP higher than NuMI maximum 0 Blue: CP below but within NuMI maximum; 0 - < |0| + || Uncertainties are 0.02 for all CP

C Cylinder: CP 75% for L = 5

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Bold: Maximum CP for NuMI Red : CP higher than NuMI maximum 0 Blue: CP below but within NuMI maximum; 0 - < |0| + || Uncertainties are 0.02 for all CP

Mary Bishai

BACK UP SLIDES High z cooling tube or downstream plug?

A high z plug downstream of the target and/or high z target outer tube shown to increase pion yield relative to a 2 interaction length graphite target. Graphite cylinder inside a tantalum tube gives best increase in yield

How could we make a downstream high z target plug?

Longer (2m) target helps some what Tantalum plug looks challenging If downstream plug made of an inconel packed bed - max temp jump per pulse would be 265K - power density 0.7kW/cc

Merits further investigation

Steady state test Air mass flow = 34grams/s Inductive power transferred to packed bed = 3.9kW Maximum sphere surface temperature = 165°C Outlet air temperature = 112°C Average power density = 0.19kW/cc Average heat transfer coefficient = 2kW/m2K

Induction heating test at RAL with packed bed of 3mm diameter spheres