Because of the anode heel effect, where is the intensity of the x-ray beam the greatest?

Along the anode-cathode axis

Explanation:

The Anode Heel Effect, in an X-ray tube states that the direction of emission of X-rays by the anode along the cathode-anode axis causes a variation in the intensity of X-rays.

The geometry of the anode causes the X-ray emitted perpendicular to the cathode-anode axis less intense than the X-rays emitted towards the cathode along the axis.