Transcript Diapositive 1

Ceramic insulation for Nb3Sn
accelerator magnets
F.Rondeaux
CEA 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
• Cable wrapped with a mineral tape
– Remove organic sizing with heat treatment
• Coil winding
Wrapping
• Heat treatment at 650-660°C
• Transfer of the coil into the impregnation
mold
• Vacuum impregnation with epoxy resin
Winding
!
Heat treatment
Very brittle
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Resin impregnation
Insulation R&D
Wrapping
Insulated coil with
mechanical cohesion
Winding
Classical insulation
!
Heat treatment
Very brittle
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Resin impregnation
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.
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−
−
−
−
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
Drying
Impregnated tape
Dimensionnal control
Tape
Impregnation
Storage
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
Insulation tape
Wrapped cable
• Glass tape is wrapped around
the conductor
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.
Winding
• Heat treatment occurs to form
the SC material and synthesize
the ceramic material.
• The stack has mechanical
cohesion after heat treatment.
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
RRR = 300
RRR = 330
The strand is covered with impregnation
solution before heat treatment.
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 mm
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Coil on the
sample rod
Critical current measurements: VAMAS + demonstrators
Sample preparation : as
for RRR measurements
- No difference between VAMAS with and without solution
- Good correlation between Ic measurements and quench
in the coil
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Coil on the CétacéS
sample holder
Demonstrators
• Solenoid 180 turns
800
 3.8 T at 740 A
No ageing of
the insulation
700
Quench current (A)
600
2004
2006
10
11
500
400
300
200
100
0
4
5
6
7
8
9
Peak field (T)
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
12
13
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)
Configuration A : both magnets with the same polarity
Maximum induction located in the internal radius of the coil,
Outward Lorentz forces  tension
35

r
30

z
Hoop stress (MPa)
25
20
15
10
0 T / 5,63 T
1 T / 5,06 T
2 T / 4,48 T
3 T / 3,93 T
4 T / 3,47 T
5 T / 3,05 T
6 T / 2,7 T
7 T / 2,39 T
5
0
-5
Peak field max.
-10
10
15
Exemple of field map (BChristiane = 7 T / Bcoil = 2.39 T)
20
25
radius (mm)
30
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
35
Demonstrators
Configuration B : magnets with opposite polarities
Tension

r
20
10

z
Exemple of field map in configuration B1
-10
-20
-30
-40
-50
(BChristiane = -5 T / Bcoil = 5.49 T)
Compression
Peak field max
Hoop stress (MPa)
0
-60
-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
-70
10

r
15
20
25
radius (mm)
30
35
Hoop stress vs. radial location
(in the plane z=0)

z
Peak field max
Exemple of field map in configuration B2
(BChristiane = -2 T / Bcoil = 6.57 T)
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.
Measure of displacement
as a function of stress
Measurement cell
L = 50 mm
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Compression tests
Experimental 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
Courtesy of
R.Hafalia
CAST3M model of a SMC coil
Courtesy of P.Manil
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
Short Model Coil Program
CABLE CARE/NED
COIL TEST#2
Courtesy
Pierre MANIL
(CEA/iRFU/SIS)
MECANICAL STRUCTURE
3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009
STRUCTURE
& SUPPORT