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Engineering simulations and methodologyEngineering simulations and methodologyas applied to the LBNE target study
P. Loveridge, C. Densham, O. Caretta, T. Davenne, M. Fitton, M. Rooney (RAL)P. Hurh, J. Hylen, R. Zwaska (FNAL)
High Power Targets Workshop
MalmöMay 2011
1
What is LBNE?
• The proposed Long Baseline Neutrino Experiment (LBNE) will use the main injector accelerator atthe main injector accelerator at Fermilab to produce 120 GeV protons that collide with a fixed target to generate a beam of g gNeutrinos.
• The Neutrino beam will then travelThe Neutrino beam will then travel several hundred miles to reach a far detector possibly sited at DUSEL, South Dakota.South Dakota.
• Design of a target that is able to withstand the pulsed heating andwithstand the pulsed heating and radiation damage effects from the 2.3 MW beam is a particularly challenging task LBNE will use a fixed target and horn system
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challenging task
LBNE Beam and Target Parameters
Proton Beam Energy (GeV)
Repetition Period (sec) Protons per Spill Proton Beam
Power (MW)Beam sigma, radius (mm)
120 1 33 4 8 e13 0 7 1 5 3 5120 1.33 4.8 e13 0.7 1.5 – 3.5
120 1.33 1.6e14 2.3 1.5 ‐ 3.5
Pulse length (micro‐sec)
Bunches per Pulse
Bunch length (nano‐sec)
Bunch spacing (nano‐sec)
Protons per Bunch
9.78 519 2‐5 18.8 3.1e11
Beryllium Target
Beam
Ø9
-21
mm
R=3σ
1 m (~2 interaction lengths)
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1 m ( 2 interaction lengths)
Concepts Studied
1. ‘Separate’ target and Horn 2. ‘Combined’ target and Horn
• Conventional concept• Target inserted inside horn inner
• Alternative concept• Target doubles as current carryingTarget inserted inside horn inner
conductor• Separate target and horn cooling
systems
Target doubles as current carrying inner conductor
• Must withstand beam interactions and pulsed current effects
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systems and pulsed current effects
Simulation Challenges
• RAL High Power Targets (HPT) group used a suite of simulation tools to study the proposed LBNE target system
Physical Effect Timescale Simulation Software
Beam induced heating micro‐seconds FLUKA
Acoustic stress‐waves micro‐seconds ANSYS, AUTODYN
Violin Modes milli‐seconds ANSYS, AUTODYN
Pulsed current / skin depth milli‐seconds ANSYSPulsed current / skin depth milli seconds ANSYS
Thermal Conduction seconds ANSYS, AUTODYN, CFX
‘Static’ Stress seconds ANSYS
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MonteCarlo Simulations
• Used FLUKA to study the physics and engineering performance of the target:– Physics
• Yield of useful particles investigated using a figure‐of‐merit (FoM)Yield of useful particles investigated using a figure‐of‐merit (FoM)– Engineering
• Deposited energy distribution taken as an input to further engineering simulations
• ‘Figure of Merit’ (FoM) devised by R.Zwaska (FNAL)
• FoM is convolution of selected pion• FoM is convolution of selected pion energy histogram by a weighting function:
– W(E)=E2.5 forW(E) E for • 1.5 GeV < E < 12 GeV• pT <0.4 GeV/c
• Weighting function compensates for lowWeighting function compensates for low abundance of most useful (higher energy) pions
Energy deposition at a section through the target and horn inner conductor
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horn inner conductor
MatLab Interface Developed In‐House
• FLUKA post‐processing GUI developed in‐house– Reads the FLUKA output file– Writes out the energy deposition data in a suitable– Writes out the energy deposition data in a suitable
format for CFX, ANSYS, AUTODYN
• Semi‐automated process permits multiple case runs CFX: fluid dynamics code
ANSYS: multi physics simulationANSYS: multi-physics simulation
FLUKA:energy deposition
MatLAB:MatLAB:semi-automated interface
[Ottone Caretta]
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Computational Fluid Dynamics (CFD)
• Used CFX to investigate various forced convection cooling options– Water, air, helium,
• Conjugate Heat Transfer AnalysisConjugate Heat Transfer Analysis – Solid and fluid domains solved simultaneously– Local heat-transfer coefficient evaluated at solid/fluid interface
The peak target temperature will oscillate around the steady-state value
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CFX Conjugate Heat Transfer analysis
“Static” Thermal Stress
• Depends primarily on temperature difference between target core and surface• Can be reduced by enlarging the beam sigma and target radius• Smallest (1 5 mm) beam sigma excluded for highest power (2 3 MW) operation• Smallest (1.5 mm) beam sigma excluded for highest power (2.3 MW) operation
Temperat re Von Mises StressTemperature Von‐Mises Stress
300 K 376 K 10 MPa 100 MPa300 K 376 K
Temperature and Von-Mises stress contour plots at the end of the first beam spill (700 kW operation)
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Stress‐Waves
• Are superimposed on top of the “static” stress• (Acoustic) stress waves may be generated if the energy deposition time is short
compared to the characteristic expansion time of the targetcompared to the characteristic expansion time of the target– These are elastic waves that travel at the speed of sound in the target material
• The Longitudinal and shear wave speeds in Beryllium are:
km/sec 13.1
2ν1ν1ρν1E
CL
km/sec 8.9
ρG
CS
Th L i di l d di l i d h
μsec 2.4C2R
TS
R
μsec 150C2L
TL
L
• The Longitudinal and radial stress‐wave periods are then:
Beryllium Target
• Recall the beam spill duration in LBNE was 9.78 µsec
Beam
Ø21
mm
10 Peter Loveridge, May 20111.0 m
m
Gauge PointStress‐Waves
• The response of the target to a single beam spill is recorded at “gauge points” in the model 0 25 m
Beam
Ø21
mm
in the model
Dynamic Stress in LBNE Beryllium Target After a Single Beam Spill at Room Temperature, Tspill = 10 micro-second
Dynamic Stress in LBNE Beryllium Target After a Single Beam Spill at Room Temperature, Tspill = 10 micro-second
1.0 m0.25 m
1.6e14 protons @ 120 GeV, beam sigma = 3.5mm, target diameter = 21 mm
300
400
Rad-Str @ GUAGE PT
Long-Str @ GUAGE PT
VM-Str @ GUAGE PT2.4 µsec
Beam Spill
1.6e14 protons @ 120 GeV, beam sigma = 3.5mm, target diameter = 21 mm
300
400
Rad-Str @ GUAGE PT
Long-Str @ GUAGE PT150 µsec
Beam Spill
100
200
s (M
Pa)
VM Str @ GUAGE PT
100
200
(MPa
)
VM-Str @ GUAGE PT150 µsec
-200
-100
0
Stre
ss
-200
-100
0
Stre
ss
-400
-300
0 10 20 30 40 50
Time (micro-sec)
-400
-300
0.0 0.1 0.2 0.3 0.4 0.5
Time (milli-sec)
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Stress‐Waves
Effect of Spill Duration on Peak Dynamic Stress in the TargetFree Beryllium Cylinder (Ø21mm L1000mm, beam-sigma = 3.5mm)
2.3MW beam power (1.6e14 protons/spill @ 120 GeV, 0.75 Hz rep-rate )
400
500
300
400
Stre
ss (M
Pa)
R=0
, Z=0
.25)
200
ak V
on-M
ises
Sat
gau
ge p
oint
(R
100
Pea
Effect of beam spill time on the peak dynamic stress in the target
01.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02
Energy Deposition time (seconds)
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Effect of beam spill time on the peak dynamic stress in the target
Stress‐Waves
• “static” stress component is due to thermal gradients
– Independent of spill time
Effect of Spill Duration on Peak Dynamic Stress in the TargetFree Beryllium Cylinder (Ø21mm L1000mm, beam-sigma = 3.5mm)
2.3MW beam power (1.6e14 protons/spill @ 120 GeV, 0.75 Hz rep-rate )
Independent of spill time
400
500
300
400
Stre
ss (M
Pa)
R=0
, Z=0
.25)
200
ak V
on-M
ises
Sat
gau
ge p
oint
(R
Static StressComponent= 90 MPa
100
Pea
Effect of beam spill time on the peak dynamic stress in the target
90 MPa
01.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02
Energy Deposition time (seconds)
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Effect of beam spill time on the peak dynamic stress in the target
Stress‐Waves
• “static” stress component is due to thermal gradients
– Independent of spill time
Effect of Spill Duration on Peak Dynamic Stress in the TargetFree Beryllium Cylinder (Ø21mm L1000mm, beam-sigma = 3.5mm)
2.3MW beam power (1.6e14 protons/spill @ 120 GeV, 0.75 Hz rep-rate )
Independent of spill time
• “dynamic” stress component is due to stress 400
500
component is due to stress waves
– Spill time dependent 300
400
Stre
ss (M
Pa)
R=0
, Z=0
.25)
Dynamic Stress
Component
200
ak V
on-M
ises
Sat
gau
ge p
oint
(R
Static StressComponent= 90 MPa
pFor 10 µsec spill
= 100 MPa100
Pea
Effect of beam spill time on the peak dynamic stress in the target
90 MPa
01.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02
Energy Deposition time (seconds)
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Effect of beam spill time on the peak dynamic stress in the target
Stress‐Waves
• “static” stress component is due to thermal gradients
– Independent of spill time
Effect of Spill Duration on Peak Dynamic Stress in the TargetFree Beryllium Cylinder (Ø21mm L1000mm, beam-sigma = 3.5mm)
2.3MW beam power (1.6e14 protons/spill @ 120 GeV, 0.75 Hz rep-rate )
Independent of spill time
• “dynamic” stress component is due to stress
Radial
Oscillation P
e= 2.4 µsec400
500
component is due to stress waves
– Spill time dependenteriodc
300
400
Stre
ss (M
Pa)
R=0
, Z=0
.25)
• Tspill > Radial period– Radial stress waves are
not significantDynamic Stress
Component
200
ak V
on-M
ises
Sat
gau
ge p
oint
(Rnot significant
Static StressComponent= 90 MPa
pFor 10 µsec spill
= 100 MPa100
Pea
Effect of beam spill time on the peak dynamic stress in the target
90 MPa
01.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02
Energy Deposition time (seconds)
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Effect of beam spill time on the peak dynamic stress in the target
Stress‐Waves
• “static” stress component is due to thermal gradients
– Independent of spill time
Effect of Spill Duration on Peak Dynamic Stress in the TargetFree Beryllium Cylinder (Ø21mm L1000mm, beam-sigma = 3.5mm)
2.3MW beam power (1.6e14 protons/spill @ 120 GeV, 0.75 Hz rep-rate )
Independent of spill time
• “dynamic” stress component is due to stress
Radial
Oscillation P
e= 2.4 µsec
LongitudinaO
scillation Pe
= 150 µsec400
500
component is due to stress waves
– Spill time dependenteriodc aleriod c
300
400
Stre
ss (M
Pa)
R=0
, Z=0
.25)
• Tspill > Radial period– Radial stress waves are
not significantDynamic Stress
Component
200
ak V
on-M
ises
St g
auge
poi
nt (R
not significant
• Tspill < Longitudinal periodd l
Static StressComponent= 90 MPa
Component For 10 µsec spill
= 100 MPa100
Pea a
– Longitudinal stress waves are important!
Effect of beam spill time on the peak dynamic stress in the target
90 MPa
01.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02
Energy Deposition time (seconds)
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Effect of beam spill time on the peak dynamic stress in the target
Violin Modes• Asymmetric heating due to an off‐centre (mis‐steered) beam initiates bulk lateralAsymmetric heating due to an off centre (mis steered) beam initiates bulk lateral
vibrations (‘violin modes’)– Modal and transient analyses used to identify the vibration modes and deflection
magnitudes in the target structureg g
1st mode = 38 Hz‘cantilever’
300 K 362 K
Temperature after a 2 sigma offset beam pulse
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Temperature after a 2-sigma offset beam pulse* lateral deflection shown at true scale 2nd mode = 240 Hz
‘bending’
Off‐centre beam effects: dynamic stress
• Consider a gauge point located at the outer radius at the constrained end of the target:target:
BEAM
• Longitudinal stress oscillations dominate• Can clearly identify a number of
superimposed frequencies in thesuperimposed frequencies in the longitudinal stress:
– Longitudinal acoustic wavesBending violin mode– Bending violin mode
– Cantilever violin mode
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A Potential 2MW Target Concept: Beryllium Spheres
• Longitudinal segmentation– Spheres avoid inertial stress
• High Pressure helium cooling loop• High Pressure helium cooling loop– Helical flow guides– 10 bar outlet pressure
Littl d it d i l t– Little energy deposited in coolant– Coolant applied close to region of
peak energy deposition
Mid-plane temperatures
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Combined Target and Horn Concept
Magnetic “pressure” on conductor
22
20
8 RIP
• Multiphysics magneto‐thermo‐structural analysis using ANSYS
22
0 ln RIFlong
Total longitudinal force
I
14 Rlong
B
FF
ANSYS finite element model of a magnetic horn
20 Peter Loveridge, May 2011
Multiphysics simulation
• ANSYS is well suited to multiphysics simulation– Can investigate the combination of effects from several different physics environments
ANSYS
(3D slice) ANSYS
(3D slice) Software: ANSYS
(3D slice) FLUKA
(3D)
Beam heat
Current pulse definition
Inputs: Resistive heat generation rates Nodal forces
Nodal temperatures Proton beam
parameters
generation rates
Thermal Transient
emag Transient Model:
Structural Static
Energy Deposition
Magnetic field Outputs: Current density
Joule heating
f
Temperature distribution
Static stress / strain
Energy density distribution
Lorentz force
Procedure for magneto-thermo-structural analysis of a magnetic horn
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Max current density Max. magnetic field
0 A/mm2 1200 A/mm2 0 Tesla 5.6 Tesla
Max. Lorentz stress Max. temperature
22 Peter Loveridge, May 20110 MPa 129 MPa 300 K 311 K
Max current density Max. magnetic field
• Combined target and horn concept ruled out:– Inner conductor diameter needs
0 A/mm2 1200 A/mm2 0 Tesla 5.6 Teslato be large in order to sustain the longitudinal Lorentz force, and becomes sub‐optimal for
Max. Lorentz stress Max. temperatureparticle production.
– Continuous target incompatible with beam induced longitudinal gstress‐waves. A segmented target is preferred.
23 Peter Loveridge, May 20110 MPa 129 MPa 300 K 311 K
Summary
• RAL High Power Targets (HPT) group used a suite of simulation tools to study the proposed LBNE target system:
– FLUKA (MonteCarlo code)• energy deposited in target components by the beam• optimisation of useful particle yield• optimisation of useful particle yield
– CFX (fluid dynamics code)• Cooling options• conjugate heat transfer analysis• conjugate heat transfer analysis
– ANSYS “classic” (Implicit FEA)• Multiphysics magnetic, thermal, mechanical analyses• ‘Long duration’ dynamic simulations• ‘Long duration’ dynamic simulations
– AUTODYN (Explicit FEA)• ‘Short duration’ dynamic simulations
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