[tlaplus] Simulation mode

If I select "Simulation Mode" in the Toolbox's "TLC Options", the "Maximum number of traces" empty, then it runs indefinitely (as expected), but when I hit "Cancel" I don't see any trace output in the Toolbox GUI. I can't find any trace files either. How does simulation mode work by default in the Toolbox?
If I set "Maximum number of traces" to 100, then TLC logs "Progress(600) at 2021-08-05 11:14:00: 16221 states generated, -1 distinct states found, -1 states left on queue", then terminates. I still can't figure out how to view the traces it produced.
Switching to the command line, if I run "java -cp tla2tools.jar tlc2.TLC MySpec.tla -simulate", it runs indefinitely as expected, and I hit Ctrl-C, I can't find the generated traces anywhere. The .out files in the .toolbox directory don't include any traces.
I tried passing "-simulate file=foo,num=100" but TLC complained, "Error: Error: more than one input files: MCSliceMerge and file=foo,num=100". I can't figure out what the syntax is for specifying an output file or number of traces, even after reading Current Versions of the TLA+ Tools and the source of TLC.java.

Thanks for your help.