Showing papers by "Christopher B. Murray published in 1992"

Ignition and extinguishing characteristics of Cs‐Ba tacitron

Abstract: The operation characteristics of the Cs‐Ba tacitron as a switch are investigated experimentally in three modes: (a) breakdown mode; (b) I‐V mode; and (c) current modulation mode. The switching frequency, grid potentials for ignition and extinguishing of discharge, and the Cs pressure and emission conditions (Ba pressure and emitter temperature) for stable current modulation are determined. The experimental data is also used to determine the off time required for successful ignition, and the effects of the aforementioned operation parameters on the ignition duty cycle threshold for stable modulation. Operation parameters measured include switching frequency up to 8 kHz, hold‐off voltage up to 180 V, current densities in excess of 15 A/cm2, switch power density of 1 kW/cm2, and a switching efficiency in excess of 90% at collector voltages greater than 30 V. The voltage drop strongly depends on the Cs pressure and to a lesser extent on the emission conditions. Increasing the Cs pressure and/or the emission current lowers the voltage drop, however, for the same initial Cs pressure and emission conditions, the voltage drop in the I‐V mode is usually lower than that during current modulation. As long as the discharge current is kept lower than the emission current, the voltage drop during stable current modulation could be as low as 3 V.

Cs-Ba Tacitron: I. Extinguishing Characteristics

Abstract: : The extinguishing characteristics of a Cs-Ba tacitron as a switch/inverter are investigated experimentally in three modes of operation: breakdown mode, I-V mode, and current modulation mode Operation parameters measured include switching frequency up to 8 kHz, hold off voltage up to 180 V, current densities in excess of 15 A/cm2, switch power density of 1 kW/cm2, voltage drop as low as 15 volts, for a switching efficiency in excess of 94% at collector voltages greater than 30 V The voltage drop during both the I-V and current modulation modes strongly depend on the Cs pressure and to a lesser extent on the emission properties of the emitter (ie emitter temperature and Ba pressure) Increasing the Cs pressure and/or the emission current decreases the voltage drop in the triode sections However, for the same initial Cs pressure and emission conditions, the voltage drop in the I-V mode is usually lower than that during current modulation Results show that at an initial Cs pressure of 20 mtorr, Ba pressure of 01 mtorr, and emitter temperature of 1400 C, the voltage drop in the triode section in the I-V mode could be as low as 15 V At the same operation condition during stable current modulation, so long as the discharge current is kept lower that the emission current, the voltage drop could be as low as 3 V The Cs pressure, Ba pressure and emitter temperature influence not only the voltage drop but also the stable current modulation of the device (ie ignition and extinguishing of the discharge occur when positive and negative pulses are applied to the grid, respectively) Results show that in order for stable modulation to occur the initial amount of Cs atoms in the discharge volume at the time of ignition should be sufficiently high, however, in order to successfully extinguish the device, the heavy components in the discharge volume should be sufficien

Cs-Ba TACITRON: II. IGNITION CHARACTERISTICS DURING BREAKDOWN AND CURRENT MODULATION MODES

Abstract: : Experiments are performed to determine the effects of the emitter temperature, Cs pressure, Ba pressure, and grid and collector voltages on the ignition of the Cs-Ba tacitron in the breakdown and current modulation modes. The values of off-time required for ignition in the breakdown mode are compared with those in the modulation mode for both stable and unstable current modulation conditions. Results show that in both modes of operation, the off-time required for ignition is strongly dependent on the Cs pressure in the gap and the applied positive grid potential but less dependent on the emitter temperature and the Ba pressure. Increasing the Cs pressure and/or the grid potential causes the off-time for ignition to decrease. It is determined that the net adsorption/desorption of Cs atoms onto the cold electrode surfaces during the off-time is negligible. Reducing the grid potential not only increases the off-time, hence decreasing modulation frequency of the device, but also can under certain conditions, cause current modulation to become unstable. Results show that the ignition duty cycle threshold for stable modulation is about 40-60%, regardless of the values of the applied positive grid potential. This threshold is weakly dependent on the Cs pressure, Ba pressure and the applied modulation frequency to the grid. However, increasing the grid potential for ignition beyond that corresponding to the duty cycle threshold causes the off-time required for ignition to decrease and the duty cycle of the device to increase.