Cathode and anode are both grounded to zero potential. An electron with kinetic energy received by the heated cathode approaches the neutral anode. There on the anode, by induction, opposite positive charges, are accumulated, which attract and accelerate the electron. The electron passes the new hole again, which a negative concetretic negative ring is placed, as shown. The negative ring repells and farther accelerates the electron to the right towards the next anode. The whole process is repeated, increasing the velocity of the electron, farther and farther,..., making U_0, <U_1., < U_2,< U₃   .....