A digital feedback controller for stabilizing large electric currents to the ppm level for Feshbach resonance studies

Area of Science:

• Atomic, Molecular, and Optical Physics
• Quantum Gases
• Magnetics

Background:

• Magnetic Feshbach resonances are crucial for ultracold quantum gases.
• Achieving high magnetic fields (up to 1000 G) with high stability (<10⁻⁴) is necessary.
• Electromagnets often require high currents (>100 A) and specific design features.

Purpose of the Study:

• To develop a simple digital current controller for generating large, stable magnetic fields.
• To enable optimal control of current sources with non-linear actuators.
• To meet the stringent requirements for magnetic field stability in quantum gas experiments.

Main Methods:

• A digital proportional-integral-derivative (PID) current controller was designed using a field-programmable gate array (FPGA).
• The controller incorporates gain scheduling for optimal performance with non-linear actuators.
• Off-the-shelf evaluation boards were utilized for construction.

Main Results:

• The controller successfully stabilized an electric current of 337.5 A.
• Fractional stability of 7.5 × 10⁻⁷ was achieved within a 10-minute averaging time.
• A control bandwidth of 2 kHz was demonstrated.

Conclusions:

• The developed digital PID controller provides a simple yet effective solution for generating highly stable, large magnetic fields.
• This technology is vital for advancing research in ultracold quantum gases and magnetic Feshbach resonances.
• The controller's performance meets the demanding specifications for precision quantum experiments.