| http://www.w3.org/ns/prov#value | - (b) a pair of superconducting coil units, each said coil unit including a coil of a superconducting material substantially coaxial with said axis, a generally toroidal vacuum vessel coaxial with the axis surrounding the coil and extending around one of said poles, and a thermal shield within the vacuum vessel, each said coil unit further including a service port chamber disposed above one of said
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