An ionized gas contains both positive and negative ions. If it is subjected simultaneously to an electric field along the $+x$  direction and a magnetic field along the $-z$  direction, then 

As the electric field is switched on, positive ion will start to move along positive x-direction and negative ion along negative x-direction. Current associated with motion of both types of ions is along positive x-direction. According to Fleming's left hand rule force on both types of ions will be along positive y-direction.