Time-varying Lens Design Research

Time-varying magnetic lens is a new device in linear induction accelerator (LIA) for the focus of burst multi-pulse beams. In this paper it describes two design schemes for the time-varying lens, using the PIC method to simulate the beam transport and focus after a time-varying magnetic lens. There are two kinds of Time-varying lens:nested time-varying lens and combined time-varying lens. Nested time-varying lens’principle is to change the focusing magnetic field to adjust the focal spot, while the combined time-varying lens’is to change the parameters of a beam in the conventional lens entrance.In the paper we discuss if the beam parameters (emittance, energy spread) and the magnetic field affect the beam focusing by simulation, and find a reasonable way to set the emittance and energy spread during the simulation. It provide theoretical support for the two lens design.We get different magnetic fields by changing the parameters of the single coil in the simulation. Thus we optimize the parameters of the single-turn coil by the result of the simulation. On this basis, we use PIC method to simulate the beam focusing by changing the current loaded on the coil. The results of the simulations prove that this method can regulate the focal spot’s location. In the study of nested temporarily we find there are two problems. We don’t find out useful method to resolve them, so we will research it in the future.We use PIC method to simulate the combined magnetic lens by gradually changing the parameters including the current value and the location of the coil. Finally, by the result analysis, we confirm that the suitable current value is from3to5kA and the distance between the single coil and the entrance of the conventional lens should be10-15cm.Finally in the paper we introduce the theory of pulse power supply and calculate the parameters of the pulsed power supply for design. At last we get a befitting pulse by simulation. The output waveform meets the requirements of our proposed.