of the insulated chromium layers 42 43 applied to the electrodes 40 41 in such a way that a dc current flows through the windings and the chromium layer generating a voltage drop while at the same time the rf alternating voltage is also applied across both ends the resistance layers 42 43 are connected with the hyperbolic electrodes below at position 44 it is therefore possible to generate two independent voltage drops in the sections 45 44 and 44 46 of the quadrupole system the rf alternating voltage of these feeds does not have to supply all the chromium layers 42 43 with rf voltage in this case since there is capacitive coupling between the rf voltage through the insulating paint and the hyperbolic electrodes 40 41 which are good conductors this simple circuit avoids the use of capacitors resistances or inductors to connect the hot side of the transformer windings it is possible to use a litz wire made of three braided strands for the windings for example since the electrically conductive surface layers 42 and 43 which each form a resistance layer insulated from the hyperbolic electrodes 40 and 41 are connected at position 44 with the hyperbolic electrodes 40 and 41 below it is possible to form the voltage drop in the two partial sections 45 44 and 44 46 separately the two independently adjustable potential gradients can be used to greatly vary the size of the pool which results in the overflow a very small voltage drop in the larger part of the quadrupole system.