From looking this up online, I should have a "Stop" option under the Actions Tab of the Device Manager's tool window?
But I only see six options: Duplicate, Wipe Data, Cold Boot Now, Show On Disk, Details, Delete.
Seems the only way I have to stop it is by holding down the (virtual) power button to then shut it down.
Only closing the emulator window with (x) works for me. Pressing the power off button just turns of the screen. The ADB manual in android developer says there should be a "Stop" in device manager but that is removed.