Vertical lines in printed cylinder

[THX1138 1]

I printed a cylinder with a 2 mm wall using a 0.4 mm nozzle and temperature 230 °C with RepRapper transparent PLA. For some reason it has evenly-spaced vertical lines running through it which I don't really want it to have.

The model was made using 123D Design which were saved as STL files an opened in Cura. I have no idea what I'm doing.

The 123D Design and STL files are available here in my Dropbox:

https://www.dropbox.com/s/27c1eu857l9vvcp/Test%20diffusion%20tube%2C%2038%20mm%2C%202%20mm%2C%20bottom.stl?dl=0

https://www.dropbox.com/s/916a7xcliburppj/Tubular%20diffuser%203D%20print%20design%20file%2038%20mm%20diameter%2C%202%20mm%20wall%2C%202%20parts.123dx?dl=0

The GCODE file is on someone elses computer which I don't have access to.

Thanks for any advice or insight.