Superconducting Magnet Group Superconducting magnet development for ex-situ NMR LDRD 2003 Paolo Ferracin, Scott Bartlett 03/31/2003

Superconducting Magnet Group 03/31/2003 Paolo Ferracin Contents Introduction Description of the prototype –Conductor and cable –Superconducting coil –Coil pack –Mechanical structure Magnetic design –Analytical analysis –Coil configuration Lorentz forces Mechanical design –Stress analysis Work plan update Conclusions

Superconducting Magnet Group 03/31/2003 Paolo Ferracin Introduction Proof of principle of an ex-situ NMR superconducting magnet –Volume (sweet spot) with high and homogeneous field in a “free region” LDRD proposal prototype design –Three horizontal coils (NbTi) –Field of ~ 2000 Gauss –Sweet spot: 3 mm volume at 15 mm –Homogeneity of 10 -3

Superconducting Magnet Group 03/31/2003 Paolo Ferracin Prototype: conductor and cable Strands –  0.7 mm –Nb 3 Sn filaments in a copper matrix Cable –20 strands –8 mm wide and 1.3 mm thick –0.1 mm insulation (fiberglass)

Superconducting Magnet Group 03/31/2003 Paolo Ferracin Prototype: superconducting coil Coil design: subscale magnet program Cable is wound around an iron island Two layers, 20 turns each Coil main dimensions –300 mm X 110 mm X 15 mm Coil confinement: horse shoe Heat treatment, epoxy impregnation

Superconducting Magnet Group 03/31/2003 Paolo Ferracin Prototype: coil pack Four coils: –SC-11 and SC-12 (under fabrication) –SC-01 and SC-02 (SM baseline) Sweet spot sideConnection side

Superconducting Magnet Group 03/31/2003 Paolo Ferracin Prototype: mechanical structure Steel pads Iron yoke Aluminum shell Diameter: 620 mm Thickness: 110 mm Assembly: –Key and bladder ( new LBNL technology ) Cool-down to 4.3 K

Superconducting Magnet Group 03/31/2003 Paolo Ferracin Magnetic design: analytical analysis Analytical study –Line currents –Accelerator magnet formalism: - I x y + I d t –Field expressed in a series of harmonics: B 1 : dipole; B 3 : sextupole; B 5 : decapole Goal: maximize the B 1 and minimize the higher order harmonics

Superconducting Magnet Group 03/31/2003 Paolo Ferracin Magnetic design: coil configuration Optimization with blocks of conductors instead of line currents Once fixed the position (and the number) of the blocks, two possible coil configurations: x y d t Vertical configuration Horizontal configuration

Superconducting Magnet Group 03/31/2003 Paolo Ferracin Magnetic design: prototype coils The vertical configuration was chosen –Less efficient but more degrees of freedom –More suitable for field quality optimization Main features –4 subscale magnet coils –Current: 11 kA –Field in the sweet spot: 2600 Gauss –Distance of sweet spot from the structure: 45 mm –Homogeneity: limited by the choice of the subscale magnet coils (~10 -2 in 3 mm volume)

Superconducting Magnet Group 03/31/2003 Paolo Ferracin Lorentz forces Horizontal Lorentz forces –tend to separate the coils –F X1 = 600 kN –F X2 = 664 kN Vertical Lorentz forces –No vertical support (sweet spot region) –Magnetic design must limit outward forces –In the prototype negligible outward forces Pre-stress –To limit the conductor movement (quench) the coils are pre-compressed by the mechanical structure

Superconducting Magnet Group 03/31/2003 Paolo Ferracin Mechanical design: stress analysis The pre-compression is provided by –Bladders and keys: 40 % –Different thermal contraction between aluminum shell and iron yoke: 60 % Final stress in the shell: 200 MPa The stress in the shell transferred (via yoke and pad) to the coils No vertical support Full access to the sweet spot

Superconducting Magnet Group 03/31/2003 Paolo Ferracin Work plan update Design: –Basic magnetic/mechanical analysis completed –Design studies of optimized magnets will continue through September Drawings: –ProE model and drawings are being completed Parts: –Support structure parts available by end of April Fabrication: –New coils already wound; heat treatment and impregnation completed by mid April –Assembly completed by end of May Test: –June-July time frame Analysis: –August-September (abstract will be submitted for MT18)

Superconducting Magnet Group 03/31/2003 Paolo Ferracin Conclusions The prototype demonstrates the main design features of the ex-situ magnet: –Mechanical structure with full access to saddle point –Field in the sweet spot –Distance of the sweet spot –Coil configuration –Fabrication and assembly techniques Next steps –Field homogeneity –First ex-situ NMR experiment