Investigation of overvoltages in the anode-grid cavity of the 200 MHz pulse power amplifier of the MMF

RF system of the Moscow Meson Factory DTL consists of the 198.2 MHz four stage amplifier with the last one (PA) connected to the high quality tank (Q_T~10⁵) by a long coaxial transmitting line (CTL). During the PA tuning it is not only needed to reach the demanded level of the accelerating field in the tank but to decrease cross coupling links between the two fast feedback control systems, stabilizing an amplitude and phase of the RF accelerating voltage in the tank, and to obtain the necessary RF pulse shape. As a rule the best PA efficiency is achieved by tuning of the PA anode-grid cavity and adjusting the coupling with CTL usually matched with the tank input impedance. The changing of the CTL length could allow to decide the next two tasks but for over voltages in the PA anode-grid cavity, caused by discharging of the RF energy, stored in the tank. They may achieve a value a few times higher than a steady state one and cause breakdowns in the anode-grid cavity. That is why particular attention should be paid to a study of transients which take place at a RF pulse trailing edge. An analysis of overvoltages in the paper is based on knowledge of free oscillation frequencies (FOF) of the tank and of the PA anode-grid cavity, whose values depend on CTL length. We estimate the influence of the output PA vacuum tube, installed in the anode-grid cavity, on transients in this one