Amplifier test stand for the CRM cyclotron

The final stage amplifier stability has proved to be an important issue in the commissioning of CRM cyclotron at CIAE. An air cooled 4CX15,000 tube final amplifier was designed to evaluate the anode circuit and neutralization, both of which are weak points of the CRM cyclotron amplifier. Instead of strip line, the new designed anode structure adopts coaxial form, resulting less chance of parasitic resonance in the circuits. A tuneable neutralization circuits was also included in the design, giving an opportunity to fine tune in high power operations. First, the instability in CRM RF system will be analyzed in this paper, followed with the new amplifier designs including the tube operating line calculations, input/output circuits designs and finite integral simulations. The mechanical design for tube socket and anode tank were successfully carried out using the data provided in this paper. The final stage amplifier was then manufactured, assembled and commissioned. In the power test with dummy load, more than 9.2kW RF fundamental power was provided at the frequency of 44.5MHz.