The design and testing of an automatic rf conditioning system for the compact medical cyclotron

The multipacting phenomenon for the compact medical cyclotrons is special, due to the present of the fringing magnet filed inside the accelerating structure. And it will become more interesting, when the vacuum system is equipped with diffusion pump. A method used for CYCIAE-14 cyclotron cavity conditioning was reported in this paper, together with the testing results of an automatic conditioning circuits designed on such basis. Apart from traditional Low Level RF control, in which close-loop regulation is played as an important role, the automatic conditioning system emphasis on the cavity startup process. It takes advantage of the modern digital signal processing technique, combined with the direct digital synthesizer to accurately limit the reflection, will condition the cavity by means of the sweeping frequency, using the low RF driven power, in continuous wave mode. After successful establishment of the accelerating voltage, the system would maintain turning of the resonator and would decrease driven power once in a while, until the driven power is below a preset limit or the Dee voltage collapse again. In the latter case, the system will repeat the whole process until reaches the first one or interrupt by the operator. The electronics are designed and tested first; it will be used later in the commissioning of the RF system of other compact medical cyclotrons built by BRIF division of CIAE.