x,y,z,t = var('x,y,z,t')

p = implicit_plot3d(x^2+y^2==4, (x,-2,2), (y,-2,2), (z,0,4), opacity=0.75)

p += parametric_plot3d( (2*cos(t), 2*sin(t), t/4), (t,0,5*pi), color='green', thickness=2.5)

p.show()