Miami University

Instrumentation Laboratory Project Page

Project: Coil Driver Project

Department: Physics

Primary Investigator: Dr. Samir Bali

Purpose: At room temperature, atoms typically zing around at speeds on the order of a km/sec.  Our experiment uses laser light and magnetic fields to slow down atoms and actually trap them.  Our goal is to produce cold and dense samples of trapped atoms for future nanotechnological  applications. If you like, you may see a picture of our atom trap. A 50X magnified image of the  trapped atom cloud (about a million atoms) appears as a white blob on the TV screen. The  magnetic fields, while useful for trapping large numbers of atoms, prevent the atoms from  attaining temperatures colder than about a millikelvin (which is still more than ten thousand  times colder than liquid nitrogen!). To reach colder temperatures the magnetic fields need to  be turned off, and turned off quickly (in less than a millisecond). Of course, after a brief interval the magnetic fields need to be turned on again to recapture atoms and reload the trap.
This is where we sought the help of the Instrumentation Lab. Our trap magnetic fields are  produced by 10 Amperes of current running through a pair of current-carrying coils of wire of 150 turns each. Building a circuit to repeatedly turn that much electrical energy off in  less than a millisecond is by no means a trivial task, for potentials of several kilovolts  may build up in parts of the circuit.
The designed circuit is capable of turning off our magnetic fields in 0.8 milliseconds or less.  Thus we can produce cold atoms that are moving so slowly that we can see them move with  our bare eyes!

IL Comment: The key requirement for this circuit was to switch the gradient coil current to zero  in less than 1 millisecond. Depending on coil geometry this can produce voltages in excess of 1000  V. Conventional circuits require tens of milliseconds. The design is versatile enough that coil currents  from 1 to 10 amperes and inductances from 2 to 80 millihenries can be accommodated by changing  one resistor.

Cost to researcher: $243.66

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