Fabrication and test of the LDX levitation coil

The Levitated Dipole Experiment (LDX) was designed by Columbia University and the Massachusetts Institute of Technology to investigate plasma confinement within a dipole magnetic field. The experiment consists of a 5 m diameter by 3 m tall vacuum chamber and three superconductor coils: a Nb₃Sn Floating Coil that provides the dipole field for plasma confinement; a NbTi Charging Coil that inductively charges and discharges the Floating Coil current; and a high temperature superconductor (Bi-2223) Levitation Coil that electromagnetically supports the weight of the 620 kg Floating Coil and controls its vertical position within the vacuum chamber. LDX is the first US plasma confinement experiment to use a high temperature superconductor coil. The use of high temperature superconductor minimizes the electrical and cooling power needed for levitation, allowing additional power for plasma heating. The levitation coil is a 2800 turn, 1.3 m outer diameter, double pancake winding. It is designed to operate at up to 150 A current at 20 K and is cooled by a combination of one stage cryocooler and liquid nitrogen cooled radiation shield. This paper provides details for the design, fabrication and test of the coil.