3nd KEK-CEA Workshop on Superconducting magnets and cryogenics for accelerator frontier - 24/03/2009 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, I c ) –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, Nb 3 Sn best superconductor candidate for high field magnets (> T). But delicate implementation: –Need long heat treatment at °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 °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 Innovative insulation

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 Nb 3 Sn : 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 > 10 7 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 Drying Dimensionnal control Impregnated tape Impregnation Tape 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 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 = 330 RRR = 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 mm Coil 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 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) 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 Exemple of field map in configuration B1 (B Christiane = -5 T / B coil = 5.49 T) Exemple of field map in configuration B2 (B Christiane = -2 T / B coil = 6.57 T) Hoop stress vs. radial location (in the plane z=0) Configuration B : magnets with opposite polarities Tension Compression 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 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 S hort M odel C oil 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 STRUCTURE STRUCTURE & SUPPORT S hort M odel C oil Program