High voltage experiments for the electrostatic deflector of the Milan Superconducting Cyclotron

The electrostatic deflector for the extraction system of the Milan Superconducting Cyclotron is presently under development. The operating electric field should be up to 140 kV/cm across a 8mm gap. In this paper we report the results so far obtained in the breakdown voltage in a 10 kG magnetic field with different types of electrodes in order to select the optimal combination of materials for the cathode and the anode. The effect of current limiting resistor to control the discharge energy has also been investigated, changing the value of the resistor placed in the circuit between the power supply and the vacuum chamber and also testing a small wire resistor placed directly inside the vacuum, as near as possible to the deflector. The results of Poisson calculation for the optimization of the HV electrode in order to minimize the electric field value outside the gap region are presented. (author)