Thanks for the information. Looking through your logs, you're not running Alpha 15. You're on a much older version of the game, that has a known OpenCL bug, that has since been fixed.
You may be in an old testing branch, or have Steam's automatic updates disabled.
[Checking if you're in on an old or beta version]
If your right click on the game in your Steam Library, go to properties, and select the "Betas" tab.
In the drop down box select "None - Opt out of all beta programs". Then click close. Steam should automatically download the new version, if you are connected to the internet.
[Checking your update settings]
Go to your Steam Library, right click on the game and select properties. From there, click on the "Updates" tab. Under the header of Automatic updates, select "Always keep this game up to date".