Spark gap triggering with photoconductive switches
Photoconductive switches are well suited for triggering spark gaps since the triggering event is short and requires very little energy. Photoswitches offer fast-rising pulses of short duration with voltage levels of several tens of kV and tens of ps jitter and can be very simple in design, whereas typical trigger sources require multiple stages to generate tens of kV needed to effectively trigger a spark gap of the same potential and usually suffer from slow risetimes. This paper presents methods aimed at triggering spark gaps with photoswitches. Both linear and nonlinear photoswitches are discussed and their associated problems are presented.
Pulse Compression Characteristics of an Opposed-Electrode Nonlinear GaAs Photoconductive Semiconductor Switch at 2 μJ Excitation
The investigation of nonlinear transient characteristics of gallium arsenide (GaAs) photoconductive semiconductor switches (PCSS) is of great significance for its applications in pulsed power technology. In this letter, the laser diode (LD) energy of $2~\mu \text{J}$ is employed to trigger the opposed-electrode GaAs PCSS. The compressed pulse width and increased amplitude are obtained as the bias electric field increases from 6kV/cm to 34kV/cm. It is numerically modeled the transient electric field distribution along the photogenerated carriers’ transport. Results reveal that pulse compression effect (PCE) can be attributed to the negative differential mobility (NDM) and electric-field screening (EFS) effect. The compression of pulse width on time scale provides a possibility to relieve the heat accumulation on time scale, and further to suppress the device failure for the potential high-repetition-rate applications.
DESIGN CONSIDERATION TO PPM KLYSTRONS FOR INDUSTRIAL LINAC
Toshiba has been developing the C-band and X-band Periodic Permanent Magnet (PPM) focused klystron in collaboration with KEK and manufactured prototypes for the JLC project. [1] The PPM klystron has an advantage to enhance the total efficiency as a result of eliminating the electric power for the focusing magnet. From experience on the development the PPM focused klystrons for the JLC project, we plan to apply the PPM focused klystron to the medical and industrial linac. The periodic magnet focusing scheme has some technical difficulties such as stop band voltage. To design the PPM klystron for the medical and industrial linac, it is necessary to give heed to electron beam instability; so that the tube parameters of the PPM focused klystrons have some constraints. The size of the accelerator system is substantially reduced if a PPM focused klystron is used. The majority of medical and industrial linacs use frequencies of S-band range. We discuss the availability of the S-band PPM focused klystron in this paper.