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Magnet Construction. Neil Marks, ASTeC, U. of Liverpool, Daresbury Laboratory, Warrington WA4 4AD, U.K. Tel: (44) (0)1925 603191 Fax: (44) (0)1925 603192. Contents.
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Magnet Construction Neil Marks, ASTeC, U. of Liverpool, Daresbury Laboratory, Warrington WA4 4AD, U.K. Tel: (44) (0)1925 603191 Fax: (44) (0)1925 603192
Contents • The presentation describes the construction of laminated magnets and shows examples of the various stages in a magnet manufacturing factory. • Thanks are given to Tesla Engineering for the provision of photographs of these processes.
Yokes • For dc accelerator magnets, yokes are usually laminated (see material for presentation on ‘Magnetic Materials’). • The use of laminations: • allows shuffling of steel - randomise properties; • prevents eddy time constants ~ minutes; • Laminations are 'stamped' using a 'stamping tool'; very high precision and reproducibility (~20µm) is possible. • The stamping is carried out on a ‘press’ (c 200T!) – see next slide.
Lamination Assembly • The laminations are ‘stacked’ to make ‘blocks’. The assembly is in a jig, with hydraulic pressing. • Small laminations can be glued together; the glue (epoxy type) is now usually coated onto the lamination material at by the steel manufacturer and sets as a thin (c 10 mm) solid layer at room temperature. After stacking the assembly is put under pressure and then placed in an oven; the epoxy liquefies and then cures, producing a solid block. • Large laminations are often welded whilst held in the stacking jig (but Tesla tend still to glue).
Laminations stacked to form blocks. Diamond quadrupole laminations in the ‘stacking fixture’ prior to bonding.
A large GSI dipole block (1/4 of an ‘H’ magnet) stacked in a single stacking fixture.
Diamond quadrupole blocks Two blocks – now machined (see chamfer) and mated together to form half a quadrupole. Note- coils cannot be added in this configuration.
Coils • Coils are wound with the glass insulation wrapped onto the copper conductor.
Coils • The coils then receive an 'outer-ground' insulation of (thicker) glass cloth and wrapped in ‘release tape’ (which will not stick to epoxy resin). They are then placed into a mould and heated in vacuum oven to dry and out-gas.
Coils • The mould is then flooded with liquid epoxy resin and the vacuum tank let up to atmosphere, forcing the resin into the coil. 'Curing' of the resin then occurs at high temperature. Total cleanliness is essential during all stages of this process! Vacuum oven used to ‘cure’ coils
Coil testing • Rigorous testing of coils, including: • water pressure tests to detect leaks from the cooling circuits; • water flow; • thermal cycling (between ambient and operating temperature 50 or 100 times); • then 'flash' testing at high voltage whilst the body of the coil is immersed in water (terminals only clear); • inter-turn voltage tests (using transformer techniques); • is strongly recommended.
