A magnetic field $\mathbf{B}=B_0 \hat{\mathbf{j}}$ exists in the region $a < x < 2 a$ and $\mathbf{B}=B_0 \hat{\mathbf{j}}$ in the region $2 a < x < 3 a$, where $B_0$ is a positive constant. A positive point charge moving with a velocity $\mathbf{v}=v_0 \hat{\mathbf{i}}$, where $v_0$ is a positive constant, enters the magnetic field at $x=a$. The trajectory of the charge in this region can be like