Field Trimming by Iron Pieces and Coils in a Superconducting Undulator

Trim-iron-pieces and trim-coils were used to correct the magnetic field error in a superconducting undulator with a magnet period of 15 mm. The main-coils were wound with NbTi wires of 0.77 times 0.51 mm² rectangular cross section. The entire iron pole array was electrically insulated from the main-coils using Teflon to avoid degradation of the superconducting wire when the main-coils were trained to a large current. The trim-coils were wound with NbTi wires of 0.33 mm diameter. The trim-iron-pieces and trim-coils were mounted directly on the iron pole. The electric current of these trim-coils were generated by a single power supply with a constant voltage. A variable resistor and two golden-case resistors were connected in parallel to adjust the current that passed through each trim-coil. In this work, three trim-iron-pieces and one trim-coil were fabricated and mounted on each of the upper and lower arrays, and their effect on correcting the magnetic field error of the undulator is measured and compared to a model simulation.