3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009...

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


Outline

•Context

•Principle

•Technical specifications

•Process

•Characterization

– Electrical tests (RRR, Ic)

– Demonstrators

– Preliminary compression results

•Summary of the results

•The Short Model Coil Program


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


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


Insulation R&D

Wrapping

Heat treatment Very brittle

!

Resin impregnation

Insulated coil with mechanical cohesion

Classical insulation Winding Innova

tive

insu

latio

n


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.


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.


Process (1/3)

•Solution (rheological behavior, stability, quality of impregnation, plasticity)

•Tape impregnation

DryingDrying

Dimensionnal controlDimensionnal control

Impregnated tapeImpregnated tape

ImpregnationImpregnation

TapeTape

StorageStorage


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


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


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


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


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


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


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)


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


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


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


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.


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


Courtesy Pierre MANIL (CEA/iRFU/SIS)

CABLE CARE/NED

COIL TEST#2

MECANICAL STRUCTURESTRUCTURE& SUPPORT

Short Model Coil Program

3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009...

Documents

Transcript of 3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009...