I've had this happen with both launchers. The logs I sent up are from the Beta Launcher from before it went public beta.check if a java.exe task is still running in taskmanger after it happens.
because there is a log.txt.0.lck file in your zip .. that does suggest the game wasnt closed (or the java session was not ended) at all
the logfile itself also does end in mid air without anything being logged as error.
are you using the old or new launcher ? maybe it is related to the version of java being in use.
Calani just did release the latest beta build maybe check if that works.