The file corrupted_SWN5k349Qx2lZY1fWq0n1g is a marker indicating that something else in the folder (_fe_Lucene50_0.tim) was discovered to be corrupt.
The corruption in _fe_Lucene50_0.tim indicates that the content of this file is now different from the content that Elasticsearch wrote and is likely due to a problem with your storage system (disk, filesystem etc.)
Normally Elasticsearch would recover automatically using a good copy on a different node, but you only seem to have one data node so that won't work. You can manually recover this index by closing it and restoring it from a snapshot.