A Hall Probe Calibration System at Low Temperature for the TPS Cryogenic Permanent Magnet Undulator

A cryogenic permanent-magnet undulator (CPMU) with a 15-mm period length is being constructed for the TPS. Field measurements of this undulator will be performed with a Hall probe at cryogenic temperatures, for which a field strength and temperature-dependent calibration system is necessary. This system consists of a cryo-cooler and a heater to control the Hall probe temperature, a home-made dipole electromagnet, a nuclear magnetic resonant Tesla meter, and two angle adjusting stages. These stages will rotate the Hall probe to adjust the angular accuracy of the Hall probe axes with respect to a reference ceramic surface and to measure the planar Hall effect coefficient. A two-axis compact 0.9-mm SENIS Hall probe is used in the very small gap of 4 mm of this CPMU. Design details and performance of this system, its calibrating process, and calibration results at various temperatures will be discussed in this paper.