The effectiveness of the closed field configuration is shown inFig. 4, which is taken from a study at Salford University [27]. As can be seen, operating in the closed field mode results in an ion-to-atom ratio incident at the substrate some 2–3 times greater than that obtained under the same conditions in the mirrored, or single unbalanced magnetron configurations. Also, the influence of the closed magnetic field on the ion-to-atom ratio becomes more marked as the distance from the target increases.