Conic sections of the cone $z^2=x^2+y^2$ by the planes $z-ax=1$

Describe the figures that can be obtained as intersection of the cone \(z ^ { 2 } = x ^ { 2 } + y ^ { 2 }\) with the plane \(z - a x = 1 , 0 < a < \infty\) , in R3.