Date: Wed, 7 Jul 2004 18:04:11 +0200 (MEST)
From: Peter Schuler
Subject: eddy simulation: first results

....
we have first and preliminary results from the eddy current simulation.
The attached figure

        eddy-sim-I(t).pdf   (25 KB)

shows the expected current transient I(t) for the positron magnet, when
the applied voltage is switched from positive to negative.

The different curves (except for the yellow curve) correspond to different
voltage ramps between 8 and 50 ms, as indicated at the bottom. As one can
read from the curves, the current reverses its sign about 0.25 sec after
switching the sign of the input voltage. At about 0.5 sec appears a hump
in the otherwise nearly exponential curve. So this is eddy effect we were
curious and nervous about. Fortunately it appears to be a relatively
modest perturbation. At 1 sec, the current has reached -47A or 75% of its
asymptotic value (here set to -62.5A). At 2 sec, the current has reached
-60.2A or 96% of its asymptotic value.

The yellow curve was supposed to represent the expected exponential
behavior in the absense of eddy effects, based solely on the L/R
time constant. In the meantime, however, we learned that the inductance
given to us earlier by Efremov appears to be in error. The new value is
larger and would indicate an L/R time constant of about 0.9 sec.

This would bring the yellow curve closer to the other curves.
Of course, we will investigate this further.

Peter