Today's results:

I abandoned my search for saturation. I will not be applying the kind
of voltage to the coil that will get it anywhere near saturation. Also,
with the kind of force that I've measured already, I don't need to saturate.

What the limiting factor will be is heat. Exciting the MOT's secondary
causes a lot more current that when it's used in the microwave. I
gathered some data on heating: with 160v AC applied to the bridge, it
drew 1.8A initially and dropped to 1.2A after running for 4 minutes and
heating up. The average coil temperature had risen 210F, to 280F!
(There was some bubbling sound from the coil potting material!) This is
24ga wire+-.

I let it cool for 13 minutes (to give a 30% duty cycle) and ran through
a couple of iterations of 3 minutes on, 7 minutes off. The peak
temperature kept climbing, reaching a max of 240F rise to 310F.

At this point I decided that this test is not realistic. The 30% duty
cycle would likely give the same average temperature as an operating
brake, but the long on period was giving exaggerated max temperatures.
In use, the full on time would only be seconds and 1/2 power on a few
seconds more. I am going to build a rig that will do 30% duty cycle
with short on times (10sec maybe). And maybe do 10% duty cycle also.

Let me add that the temperatures that I was seeing were not alarming me.
I had looked into transformer temperature ratings and found some
interesting stuff. First, their ratings are not so much limits above
which they shouldn't operated, rather they are values which can be
expected to not be exceeded when the transformer is operating at
capacity (80, 115, & 150 degree C rise). It's more a rating of
transformer efficiency (hot is less efficient). And, independently, the
real limiting parameter is the winding insulation temperature limit.
Typically 220C (428F). I was not anywhere near this insulation limit. See
http://www.copper.org/applications/e...fficiency.html

Damn, I'm having more fun than a boy in a sandbox,
Bob