American Magnetics 05100PS-430-601 High Stability Integrated Power Supply System - Manual (Page 194)

176 Rev. 5
Appendix
Model 601 and Energy Absorption
continues to flow driven by the self-induced magnet voltage
1
(refer to
Figure A-7).
With a 4-quadrant power supply capable of reversing both the current and
voltage, the power supply voltage would reduce to zero volts and
ultimately reverse as necessary to control the current downward.
However, a unipolar power supply cannot reverse polarity. With no outside
voltage to reduce the current, it continues to flow at the previous rate,
decaying only at the natural time-constant of the circuit inductance and
resistance, T
sec
= L / R.
The current will be reduced by 63% during each
successive time constant period T. With a typical inductance of 50 Henries
and lead resistance of 0.001 Ohms, (T = 50,000 seconds), it will take over
14 hours to decay to 37%, and many times that to reduce to near zero.
Introduction of the Model 601 Energy Absorber provides the solution,
allowing Model 430 Programmer control of both magnet charge and
1. Magnet power supply design is such that the output resistance is
essentially zero resulting in no significant IR drop at the supply termi-
nals.
Figure A-7. Loop Voltages - Magnet Passively Discharging