How can I do to remove these flaws in the hair particle system?
Try to change Curve Segments to Line Segments (or the other way round) in the Geometry tab of the Render Settings. Or when using Curve Segments, increase Curve Subdivisions.
What kind of material do you use? It seems to me normals are not calculated as expected for hair (in the Blender version I run), so if normals have a large effect, things might look broken near the connection points of segments. It doesn’t look to me, like this is the point here. It is mostly an emission shader, right?
Exact, I changed Segments to the Curve and it worked. Thanks!
And yes, the material is an emission shader, and composed nodes with blur and glow.