Generation of quadrupole magnetic field for trapping atoms in Cs fountain being developed at NPL India

We describe the development of a constant current source for magneto-optical trap (MOT) coils. The system is designed to supply maximum 5 A current in continuous or pulsed mode to the anti-Helmholtz (AH) coils which produce quadrupole magnetic field inside the chamber for trapping of Cs atoms. To obtain a stable field gradient the coils are operated at low current to minimize current fluctuations. With AH coils having 100 turns and 5 Ω resistances, we achieved rise and fall times of current as 5 ms and 7 ms, respectively. With a field gradient of 6 G/cm at the center of the MOT, 7 number of atoms trapped is about 10. To prevent burning of coils due to failure of current source, a thermal protection circuit has been incorporated. Measurements made for switching times of current profile in coils is also reported.