Binal Bhukhanwala, Purdue University

Ph.D. Thesis, Purdue University

The PRIME Lab uses an 8 MeV FN tandem Van de Graaff accelerator for accelerator mass spectrometry (AMS). The isotope ratios are measured by cycling the magnetic field in the large accelerator magnets. The ion cores of these magnets are not laminated, and therefore give rise to eddy currents, which increase the settling time of the magnetic field. To improve the precision of the measurements of the radioisotope ratios, it is important to minimize the settling-time.

We have designed a dual controller to speed up the changes in the magnetic field. The dual controller consists of a settling-time optimizer and a fuzzy logic controller. The settling-time optimizer stores the current and the field values at every sampling instant into vectors and updates the current vector after every cycle depending on the field vector. During the next cycle, the elements of the updated current vector are applied to the magnet power supply at every sampling instant and the settling-time of the magnetic field is minimized. After the curret vector is updated and applied to the magnet power supply, the fuzzy logic controller adjusts the current after every magnetic field measurement to compensate for any disturbances in the system. Also, the fuzzy logic controller prevents drifting of the magnetic field from its setpoint while the isotopes are being measured.