1. for a neutrinos factory
Magnetic horn
for a neutrinos factory
Thermal and mechanical issues
Sandry Wallon
Linear Accelerator Laboratory
(LAL-IN2P3-CNRS)
Orsay, France
Horn for a neutrinos factory - thermal and mechanical issues (8/07/2003)

2. Magnetic horn for a neutrinos factory
Thermal and mechanical issues
CONTENT
Horn prototype at Cern - features
Thermal issues
Material and mechanical issues
Heat transfert rate – tests at LAL
Fatigue strength – fatigue tests
Summary
Horn for a neutrinos factory - thermal and mechanical issues (8/07/2003)
Sandry Wallon

3. 1. Horn prototype at Cern Sandry Wallon
Horn for a neutrinos factory - thermal and mechanical issues (8/07/2003)
Sandry Wallon

4. Drawing from S. Rangod / S. Gilardoni
1. Horn prototype at Cern
Very 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
Horn for a neutrinos factory - thermal and mechanical issues (8/07/2003)

5. Water flow in annular channel
2. Thermal issues
Cooling system used
for horn prototype
Water curtain
Electrical skin
Water flow in annular channel
Jacket
Horn for a neutrinos factory - thermal and mechanical issues (8/07/2003)
Sandry Wallon

6. Inner cond. waist’s shape
2. Thermal issues
Heat
removal
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
Inner cond. waist’s shape t
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)
Horn for a neutrinos factory - thermal and mechanical issues (8/07/2003)
Sandry Wallon

7. 2. Thermal issues Thermal stress
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)
Horn for a neutrinos factory - thermal and mechanical issues (8/07/2003)
Sandry Wallon

8. 3. Material and mechanical issues
Lifetime/
Fatigue limit
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
Horn for a neutrinos factory - thermal and mechanical issues (8/07/2003)
Sandry Wallon

9. 3. Material and mechanical issues
Dynamical
stress
Static stress(1) due to magnetic pressure
sq = 12 MPa
sz = 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 analysis
shows 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
Horn for a neutrinos factory - thermal and mechanical issues (8/07/2003)
Sandry Wallon

10. 3. Material and mechanical issues
Limit of
‘thickness
reducing’
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]
Inner cond. waist’s shape t
Horn for a neutrinos factory - thermal and mechanical issues (8/07/2003)
Sandry Wallon

11. 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)
Horn for a neutrinos factory - thermal and mechanical issues (8/07/2003)
Sandry Wallon

12. 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
Horn for a neutrinos factory - thermal and mechanical issues (8/07/2003)
Sandry Wallon

13. 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…
Horn for a neutrinos factory - thermal and mechanical issues (8/07/2003)
Sandry Wallon