A 50 Mw Pulse-Forming Network with a Voltage Stability within 0.03-Percent

Requirements on electron energy stability are extremely tight for operation of a free-electron laser. In case a radio-frequency field is used to accelerate the electrons, this leads to stringent requirements on the stability of the klystron output power and, hence, on the stability of the source producing the cathode voltage. A pulse-forming network (PFN) capable of delivering a 19 kV pulse with a stability of 0.03%, during 20 mus, is presented. The PFN consists of four parallel lines, each containing 19 cells of a 20 nF capacitor and a 20 muH solenoid. The solenoids are equipped with taps and a plunge tuner. An innovative line switch is used, namely a stack of 32 thyristors in series. Numerical simulations of the pulse shape show that, in order to obtain the best possible pulse flatness, it is essential to arrange the capacitors such that the difference between adjacent capacitances is minimized.