Sandry WallonHorn for a neutrinos factory - thermal and mechanical issues (8/07/2003) 1

Magnetic hornfor a neutrinos factory

Thermal and mechanical issues

Sandry Wallon

Linear Accelerator Laboratory(LAL-IN2P3-CNRS)Orsay, France

Sandry WallonHorn for a neutrinos factory - thermal and mechanical issues (8/07/2003) 2

CONTENT

1. Horn prototype at Cern - features2. Thermal issues3. Material and mechanical issues4. Heat transfert rate – tests at LAL5. Fatigue strength – fatigue tests6. Summary

Magnetic horn for a neutrinos factoryThermal and mechanical issues

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1. Horn prototype at Cern

Sandry WallonHorn for a neutrinos factory - thermal and mechanical issues (8/07/2003) 4

1. Horn prototype at CernVery high heat load at the horn’s waist• 78.7 kW (energy particles losses) (for a 6+2mm thickness)• 8 kW (Joule losses)

Drawing from S. Rangod / S. Gilardoni

Sandry WallonHorn for a neutrinos factory - thermal and mechanical issues (8/07/2003) 5

NEUTRINO FACTORY PROJECT - HORN PROTOTYPEGENERAL ASSEMBLY

S. Rangod 18/10/2001

Ø420

1030

Magnetic measurements plane

2. Thermal issues

Water curtain

Electrical skin

Jacket

Water flow in annular channel

Cooling system usedfor horn prototype

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2. Thermal issues

We have to evacuate a very high heat load (86.7 kW) thanks to :• sprinklers producing a water curtain• internal jacket giving an annular channel

Other approach : reduce thickness (t) ! heat load cooling can be performed with a single surface

(stress but lifetime can be kept)

Limit of this approach• cooling achievement t < 3 mm Twaist = 85°C (for Twater = 9°C)

(80-90°C : Max temp allowed to use DI water)

Heatremoval

Inner cond. waist’s shape

t

Sandry WallonHorn for a neutrinos factory - thermal and mechanical issues (8/07/2003) 7

2. Thermal issues

Temperature rising after one pulse : 1.2°C !(thanks to a high repetition rate [50Hz])

low thermal expansion dynamical stress < 2 Mpa

(All calculations done for a 3 mm thick cylinder)

Thermalstress

Sandry WallonHorn for a neutrinos factory - thermal and mechanical issues (8/07/2003) 8

3. Material and mechanical issues

Cern’s horn prototype is said to have a 6 weeks lifetime!

Neutrons irradiation of aluminum alloy (6000 family) : yield stress and ultimate tensile stress but material becomes brittle

but for a flux ~ 1022 fast neutrons/cm2 (6 weeks working), some bubbles appear in the material potential fatigue crack

What about the Al alloy fatigue limit? it’s unknown fatigue limit confidence ! fatigue tests of irradiated material is very expensive (~300 k€) available irradiated samples come from nuclear reactor (thermal neutrons flux > fast neutrons flux)

we have to aim for a 6 weeks (guaranteed) lifetime

Lifetime/Fatigue limit

Sandry WallonHorn for a neutrinos factory - thermal and mechanical issues (8/07/2003) 9

3. Material and mechanical issuesDynamical

stress

Static stress(1) due to magnetic pressure = 12 MPaz = 20 Mpa (2 or 3 times smaller than expected fatigue

limit perfect)

(1) analytical calculations performed for t=3mm, realistic for :• Radial vibration freq. << mag. pressure pulse freq.• Axial vibration freq. << mag. pressure pulse freq. highly depends on end flanges design, but end flanges stiffness can be easily tuned

To be done : dynamical coeffs calculation FEM transient analysisshows inner cond. behavior during start up (and ‘continuous’ behavior in case of using a low repetition rate power supply [~1Hz])

FEM harmonic state analysis (at 50 Hz)shows inner cond. behavior after start up

static

dyn

Sandry WallonHorn for a neutrinos factory - thermal and mechanical issues (8/07/2003) 10

Inner cond. waist’s shape

t

3. Material and mechanical issuesLimit of

‘thicknessreducing’

Reducing inner cond. waist’s thickness heat load but buckling Safety Factor (SF)

Limit of this inner cond. waist’s thickness reducing• t > 2.5 mm (buckling SF > 5 [usual value])• t > 2.1 mm (buckling SF > 3 [probably acceptable for a well known load and a perfect shape]

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4. Heat transfer rate – tests at LAL

Heat transfer for forced convection in thin liquid film : results come from measurement with heat flux up to 80 kW/m2

We are close to 500 kW/m2

To be compared to a 2 MW/m2 heat flux for tokamak (cooling liquid : Lithium or molten salt)

Tests at LAL will be performed up to 400 kW/m2

Heat exchange surface (cylinder) will be machined and jacketed to measure the heat transfer rate for Cern’s horn prototype)

Spreadsheet for heat study (steady state)

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5. Fatigue strength – fatigue tests

Al alloy first choice : 6082 instead of 6061 (used for nuclear vessel) : 6082 is an improved 6061 but there’s a lack of ‘good’ fatigue curves

Ultrasonic fatigue tests will be performed up to 1010 cycles

to show a real fatigue limit

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6. Summary

Heat removal is critical heat load coming from target is not welcome!

According to first calculations, heat removal (from inner

cond.) is achieved for a inner conductor with :• a double skin (Cern’s prototype)• a single heat exchange surface (LAL proposal)

Single heat exchange surface design brings :• better transparency• lower manufacturing cost• well known dynamical behavior (easy FEM modelisation)

With a good confidence, lifetime is reasonably around 6 weeks, but it could be more…