Why Does Current Density Point Downwards in a Magnetic Field?

[loba333]

Homework Statement

Heres the problem:

Homework Equations

F=BIL F=qvB

The Attempt at a Solution

I really don't know where to start. Can you guys give me a hand. Maybe a link to a web page explaining. I understand if it were convention current flowing through the 'pipe' it would experience a force due to the magnetic field. I don't understand why current density which I'm assuming just (J=I/A) is pointing downwards ?

Thank you in advance

 

[Quinzio]

I think this may be just a "mind exercise" of a problem that in reality has no meaning.
It says the pipe is insulating, so it's really not clear where does this current flows through.