Design And Implementation Of RF Power Supply For 10MeV Compact Cyclotron

With the rapid development of nuclear medicine, the technology of positron emission tomography (PET) has been the most advanced means which is used in medical research on the molecular level. PET tumor detection equipment for early detection and early treatment has a great advantage, so the major hospitals at home and abroad continue to introduce it. Small cyclotron is an important part of the PET system for the production of radioisotopes for medical detection. As a small medical cyclotron, especially low-energy compact cyclotron, is a complex system, and should be of high reliability, the technical requirements for design and manufacture is very high. In our country, all of small cyclotrons for PET detectors are imported from abroad at present, and the price and maintenance costs are high, so to develop the low-energy compact cyclotron by ourselves is necessary.Radio frequency (RF) power supply is an important part of Cyclotron, which supplies the RF power for the D box resonator to generate Dee electrode accelerating voltage, and adjusts the level of output power to maintain the amplitude of Dee electrode voltage stability. This paper describes the system configuration of the RF system of low-energy compact cyclotron in detail, and presents the requirements for RF power supply. Theoretical analysis on how to search the resonance frequency of D box resonator has been stated, and the method of searching resonant frequency has been put forward. The RF signal source should be of variable output frequency, so we make comparison of direct analog synthesizers, phase-locked loop synthesis and direct digital synthesis (DDS), and present the respective advantages and disadvantages of three methods. From the theoretical analysis of the sample spectrum of DDS output signal, proposing the method of selecting the special aliased signal from the DDS output signal as the RF signal source output signal, and the experimental results prove the correctness of theoretical analysis and feasibility of engineering practice. In addition, the paper carries out the research of RF signal detection and closed-loop control, and gives the circuit schematic and simulation results. Basing on the theoretical analysis, gives the mathematical model of tetrode, which is validated by MATLAB simulation. And then establishes the Pspice model of tetrode. According to MATLAB simulation data, the theoretical calculations for tetrode amplifier are stated. By the simulation of tetrode amplifier using tetrode Pspice model, finding the simulation results in good agreement with the data of theoretical analysis, and providing supports for engineering practice. For the tetrode amplifiers, gives the driver stage amplifier circuit design.This paper chooses the triode amplifier as final stage amplifier, selects the fundamental wave of DDS output signal as the RF signal source output signal, completes the circuit designs of RF signal source, RF signal detection, driver amplifier and final stage amplifier, describes the operation of the circuit, and gives the software simulation results. Basing on the prototype machine of RF power supply, some test results have been present.Finally, the paper gives the overall design of RF control system, develops RF control system of the PC monitor and slave control program, and describes the control system approach. Control unit carried out the test of RF cavity load which is designed for low-power experiment, and experimental results verify the correctness and reliability of control procedures.