Development Of Pulsed Power Supply In Proton Therapy

Proton therapy centers have been operated worldwide recently. Proton beams provide unique dose distribution governed by the maximum range of the beam. There is no dose beyond the range; hence, the undesirable dose to normal tissues could be significantly reduced in proton beam therapy. The purpose of the injection system of synchronous storage ring in Shanghai proton therapy equipment is to inject proton beams from the low-energy beam line to storage ring in the painting way. The injection system requires two bump magnets. Each bump magnet is powered by a single power supply. Two pulsed power supplies with the adjustable peak current and the consistent waveform have been proposed and developed.The parameter requirements of pulsed power supply involve quick pulsed power, consistent pulsed waveform, excitation current trigger jitter and reproducibility of current. This thesis mainly refer to the main circuit parameter calculation, simulation, how to choose components, protected circuit design, structural design, hardware and software development of the power controller and final tests of the whole power supply system.The principle of pulse forming circuit is that LC series resonance generates when thyristor is turned on by trigger signals. Energy storage capacitor is charged to the setting voltage which determines the amplitude of the pulse waveform based on constant current by charging power supply. The main circuit employs variable inductance to adjust the pulse width. Fast recovery diode in series of thyristor could compensate for the turn-off delay of the thyristor while the peak of reverse current decreases due to saturable inductor. Programmable Logic Controller is selected as CPU of power supply controller. External trigger signal and interlock, control signals are sent to signal regulated board to be controlled by the power supply controller. The purpose of whole power supply system is to realize the process control of charging power supply, pulsed power supply and trigger signal.Test results showed that when the half-sine excitation current peak was set to 3732 A, its trigger jitter and reproducibility were less than ±25 ns and 0.1%, respectively. The consistent of current waveform at the falling edge was less than 1%. Reverse current could be reduced to 3.75% of the peak current. The local and remote process control of the power supply controller was operated correctly.Experimental results indicate that the pulsed power supply reaches to the design requirements and saturable inductor restrains reverse current effectively.