as applied to the lbne target study - technology · pdf fileas applied to the lbne target...

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

2 Peter Loveridge, May 2011

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)


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


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


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


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]

7 Peter Loveridge, May 2011AUTODYN: dynamic simulation

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


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)


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)


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)



Stress‐Waves

• “static” stress component is due to thermal gradients

– Independent of spill time



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


90 MPa

01.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02




Stress‐Waves






• “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


pFor 10 µsec spill

= 100 MPa100

Pea


90 MPa

01.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02




Stress‐Waves






• “dynamic” stress component is due to stress

Radial

Oscillation P

e= 2.4 µsec400

500


– 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


pFor 10 µsec spill

= 100 MPa100

Pea


90 MPa

01.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02




Stress‐Waves






• “dynamic” stress component is due to stress

Radial

Oscillation P

e= 2.4 µsec

LongitudinaO

scillation Pe

= 150 µsec400

500


– 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


Component For 10 µsec spill

= 100 MPa100

Pea a

– Longitudinal stress waves are important!


90 MPa

01.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02




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


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


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


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


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


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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