3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Ceramic insulation for Nb3Sn accelerator magnets
F.RondeauxCEA Saclay - IRFU - SACM - LEAS
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Outline
•Context
•Principle
•Technical specifications
•Process
•Characterization
– Electrical tests (RRR, Ic)
– Demonstrators
– Preliminary compression results
•Summary of the results
•The Short Model Coil Program
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Context
•At the present time, Nb3Sn best superconductor candidate for high field magnets (> 10 - 11 T).
•But delicate implementation:
– Need long heat treatment at 650 - 660°C in argon flow no organic material before treatment.
– Great brittleness and strain sensitivity of the material after heat treatment “Wind and React” technique
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Wind & React principle with classical insulation
Wrapping
Heat treatment Very brittle
!
Resin impregnation
Winding
•Cable wrapped with a mineral tape – Remove organic sizing with heat treatment
•Coil winding
•Heat treatment at 650-660°C
•Transfer of the coil into the impregnation mold
•Vacuum impregnation with epoxy resin
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Insulation R&D
Wrapping
Heat treatment Very brittle
!
Resin impregnation
Insulated coil with mechanical cohesion
Classical insulation Winding Innova
tive
insu
latio
n
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Technical specifications (1/2)
Follow the heat treatment imposed by the formation of Nb3Sn : ramp at 6°C/h, 240 h at 660°C in argon flow.
Appropriate electrical insulation.• Dielectric strength at 4.2 K > 75 V between turns
Mechanical cohesion of the coil during handling and running phases.
Transverse compression strength . • (100 MPa at room Temp. and 70 MPa at 4.2K) / 200 MPa at 300K and 4K
Dimensional control of the coil.
Support thermal cycles and running cycles without degradation.
Radiation hardness > 107 Gy.
Porosity.
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Technical specifications (2/2)
+ conditions for industrial transfer:
No change in the superconductor synthesis and shaping.
Minimize the changes in the process.
Various stages from manufacture to winding clearly separated to facilitate the implementation.
− Preparation of solutions
− Tape impregnation
− Cable wrapping
− Winding
− Heat treatment
Basis materials easily available and no toxic.
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Process (1/3)
•Solution (rheological behavior, stability, quality of impregnation, plasticity)
•Tape impregnation
DryingDrying
Dimensionnal controlDimensionnal control
Impregnated tapeImpregnated tape
ImpregnationImpregnation
TapeTape
StorageStorage
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Process (2/3)
•Glass tape is impregnated with a thick layer of ceramic precursor
Ceramic penetrates entirely the fibers
•Glass tape is wrapped around the conductor
Wrapped cable
Insulation tape
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Process (3/3)
•Plasticity of impregnated ribbon allows the manufacture of coil according to traditional techniques.
•Heat treatment occurs to form the SC material and synthesize the ceramic material.
• The stack has mechanical cohesion after heat treatment.
Winding
Stack of cables
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Electrical tests •On ceramic sample: dielectric strength > 7.3 kV/mm at 4.2 K
•On wires covered/not covered with the ceramic solution and
reacted: verify there is no modification in electrical properties due to
insulation.
– RRR measurements
The strand is covered with impregnation solution before heat treatment.
RRR = 330RRR = 300
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Critical current measurements : experimental setup
Cétacés (Cryostat d’Essai Température Ajustable Champ Élevé Saclay)
Bmax = 17 T / useful diameter: 49 mm / Temp. from 1.8 K to 200 K
CHRISTIANE
Bmax = 7 T / useful diameter: 90 mmCoil on the sample rod
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Critical current measurements: VAMAS + demonstrators
- No difference between VAMAS with and without solution
- Good correlation between Ic measurements and quench in the coil
Sample preparation : as for RRR measurements
Coil on the CétacéS sample holder
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Demonstrators
•Solenoid 180 turns
3.8 T at 740 A
0
100
200
300
400
500
600
700
800
4 5 6 7 8 9 10 11 12 13
Peak field (T)
Que
nch
curr
ent
(A) 2004 2006
No ageing of the insulation
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Demonstrators
•Solenoid 400 turns
5,63 T at 590 A• 30 MPa in tension
• 65 MPa in compression(Stress levels evaluated with simulations in Roxie)
-10
-5
0
5
10
15
20
25
30
35
10 15 20 25 30 35radius (mm)
Hoo
p st
ress
(M
Pa)
0 T / 5,63 T1 T / 5,06 T2 T / 4,48 T3 T / 3,93 T4 T / 3,47 T5 T / 3,05 T6 T / 2,7 T7 T / 2,39 T
z
r
Configuration A : both magnets with the same polarity
Maximum induction located in the internal radius of the coil, Outward Lorentz forces tension
Peak field max.
Exemple of field map (BChristiane = 7 T / Bcoil = 2.39 T)Hoop stress vs. radial location (in the plane z=0)
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Demonstrators
z
r
Exemple of field map in configuration B1
(BChristiane = -5 T / Bcoil = 5.49 T)
z
r
Exemple of field map in configuration B2
(BChristiane = -2 T / Bcoil = 6.57 T)
-70
-60
-50
-40
-30
-20
-10
0
10
20
10 15 20 25 30 35radius (mm)
Hoo
p st
ress
(M
Pa)
-1 T / 6,19 T -2 T / 6,67 T
-3 T / 6,87 T -4 T / 6,36 T
-5 T / 5,49 T -6 T / 4,87 T
-7 T / 4,19 T
Hoop stress vs. radial location (in the plane z=0)
Configuration B : magnets with opposite polarities
Te
nsi
on
Co
mp
ress
ion
Peak field max
Peak field max Case B1 : Maximum induction located in the external radius / Inward Lorentz force compression
Case B2 : Maximum induction located in the internal radius / Outward Lorentz force tension
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Compression tests
Firsts tests on stacks: 3 cycles of uniaxial compression from 0 to 150kN max.
Measurement cell
L = 50 mm
Measure of displacement as a function of stress
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Compression testsExperimental problems on short stacks
development of more efficient samples
Performing “stack tests” on ‘very little’ racetrack coils - 5 turns, approx. 5 x 10 cm size = 10-stack + steel mandrel- Without and with insulation
- avoid tin losses
- limit the structural relaxing effect du to twist pitch
- improve the sample cohesion when reaction pre-stress is relaxed
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Summary of the results
•Precursors solution adapted to the insulation process. Typical rheological behavior
•Impregnation setup. Deposit homogeneous on important lengths of tape Variation of thickness controlled
•No degradation in the properties of the strand by using this insulation.
•Ceramic insulation tested with 2 solenoid demonstrators of 180 and 400 turns :
• No degradation of the solenoids during the test • They have produced a field of 3.8 T / 5.63 T
•Heat Transfer measurements on stack of five insulated conductors under mechanical constraint.
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Short Model Coil Program
Conceiving a short model coil package in the aim of:
• testing short model coils in charge (in NED dipole configuration)
– safe stress limit?
– peak field in the straight section
•being able to apply very high or low pre-σ bladders and keys, rods
– what happens without pre-σ? variable pre-σ
•being easy to assemble and disassemble subscale racetrack coils
•being able to test different coils coherent conception
•Conceiving the associated tooling
Built and test the coil packages
CAST3M model of a SMC coil Courtesy of P.Manil
Courtesy of R.Hafalia
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Courtesy Pierre MANIL (CEA/iRFU/SIS)
CABLE CARE/NED
COIL TEST#2
MECANICAL STRUCTURESTRUCTURE& SUPPORT
Short Model Coil Program