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