The Photosmith Lightroom plugin relies on a small background process named psahttp on Mac, or psahttp.exe on Windows. This service facilitates several automatic processes, such as the discovery on your local network of your iPad and Lightroom.
The psahttp service launches automatically when Lightroom is launched. The psahttp service will automatically terminate when you close Lightroom.
It is expected and normal behavior to see psahttp or psahttp.exe running in the background of your Mac or PC when you have Lightroom running.
The system resources used by psahttp are exceedingly minimal; Only uses a few megabytes of RAM are used.
If you absolutely must kill the psahttp service (if it remains running after you quit Lightroom), you may safely do so only after shutting down Lightroom.