Experiments with Supersonic Beams as a Source of Cold Atoms

Figure 5.5: Photograph of the hydrogen coilgun coil driver circuit. The board on the
right is the circuit which drives the coils, while the board on the left is the circuit
which drives the gate of the IGBT.
are the component that failed at the highest rate. The down side of removing the
thyristor though is that each coil requires its own IGBT (changed to a Powerex
CM600HA-24H 1200 V 600 A IGBT for higher current carrying capability), which is
feasible (each IGBT and gate driver costs $250) as only 18 coils are needed because
of the high magnetic moment to mass ratio of hydrogen.
There are a few other changes made to the circuit, most notably the return
to a resistor in series with the coil, and a freewheel diode and resistor to lower the
voltage spikes produced by switching the coil. The series resistor is required because
the new coil has significantly lower resistance, leading to too great a current for the
IGBT without this resistor. Similarly, the greater current and increased inductance
of the coil produces a damaging voltage spike on the IGBT without the freewheel
diode. Even with these additions, the snubber capacitor must be doubled in size to
limit the switching voltage.
The final change in the coilgun electronics is the addition of two more discharge
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