Research On Digital Scanning Power Supply Technology In Proton Accelerator For Medical Use

Proton has great advantages in the field of cancer radiotherapy because of its goodcharacteristic of Bragg peak. Scanning power supplies are placed in the nozzle of theproton therapy device and they are required high accuracy, high speed and high stability.In this paper，some surveys on the scheme of scanning power supplies of existing protonor heavy ion therapy devices in the world provide reference for the design of scanningpower supplies. Power supply cannot work without control system and because digitalcontrol mode has become increasingly popular for the control of switching powersupplies, thus, digital power controller becomes the key part of digital control system.One of my work is to design the interface for users to monitor the new digital powercontrollers so as to modify parameters, to monitor real-time state, to download digitalwaveforms and to trigger waveforms for the power supplies. With the help of theinterface, users can control the power controller either at local places or at remote places.Simulation design for the power supply is conducted with Simulink in MATLAB,and power simulation performs the working current, voltage and power of the powersupplies. After the frequency analysis of the circuit, it was found that the syntonic polegenerating from the main filter would exert great influence on the closed loop stabilityof the system and at the same time it is not conducive to increase the bandwidth for thecontrol system, therefore, in order to overcome the disadvantages brought by thesyntonic pole, a compensation circuit of a RC branch, which is parallel to the magnetload, is added, the circuit not only can compensate off the syntonic pole produced bythe filter but also can broaden the bandwidth and increase the stability of the system.The closed loop bandwidth of the simulation system can reach at1KHz.In order to verify the correctness of the simulation, several performances of a smallpower supply based on this idea in our laboratory are tested. The result from this testshows that the regulation time of the power supply is about0.4ms, and the bandwidthof the power supply is1KHz, which means that it can satisfy the demand of the scanningpower supply. The test verifies the feasibility of the simulation, which provides referencefor developing scanning power supply in future.