Yutaka Murai

Anode discharge mode and cathodic plasma state in high‐current vacuum arcs

Anode surface states and traces of the cathode spots after arcing of various anode discharge modes in vacuum have been studied in the current range of 5–20 kA. Spectroscopic measurements of the radial electron temperature profile in the cathode region, which is related to the distribution of the current density, have also been performed to investigate the cathodic plasma state of the arcs in the various anode modes. The arc of a half‐wave sinusoidal current of 60 Hz was burned between a 60‐mm‐diam anode and a 30‐mm‐diam cathode spaced 4 mm apart. The electrodes were made of oxygen‐free, high‐conductivity copper. The cathode spots spread uniformly over the entire cathode and a uniform current density profile was obtained in the diffuse‐arc mode. It was found, however, that the cathode spots bunch together and the current density profiles peak at the center of the discharge in the anode‐spot mode. The cathode‐spot bunching and the nonuniformity in the current density profile become significant with a suffic...

Voltage Escalation in the Switching of the Motor Control Circuit by the Vacuum Contactor

A turn-to-turn fault of a high-voltage motor which was controlled by a vacuum contactor prompted this study. The study revealed that a voltage escalation can certainly occur by the repetition of re-ignitions as indicated by recent several papers,1,2, but the cause of the escalation is different from that reported. This paper presents a new theory for the voltage escalation, makes clear the conditions for the occurrence of the escalation, and leads to the conclusion that protectors are indispensable in the application of the contactors to the motor control circuit.

Statistical Property of the Breakdown of Vacuum Circuit Breakers and its Influence on the Surge Generation in Capacitive and Reactive Current Interruption

The statistical property of the breakdown of a contact in vacuum has been studied experimentally. The results are summarized so as to express the cumulative probability of breakdown as a function of the applied voltage and the spacing of the contact. The expression of the probability distribution is applied to analyze the switching surge generation by a vacuum circuit breaker in the load current interruption of capacitive and inductive circuits. It was shown that a completely restriking -free condition is quite difficult to realize particularly at high system voltages. The statistics of the switching surges due to the restrikings and the problems of circuit protection for them are given based on the analysis.

Protection of Motor from Switching Surge by Vacuum Switch

A way of surge suppression by a reactor is presented for the protection of turn-to-turn insulation of motors from steep front surges produced by vacuum switch. In the first part of this paper, the construction and the functions of the reactor are explained. Discussions are given on the possibilities of turn-to-turn faults by the switching surges under the effect of the reactor, taking voltage distribution in motor winding into account. The result is expressed as the probability of turn-to-turn fault per switching operation for a given circuit condition. Examples of numerical evaluation of probability are obtained for a circuit breaker with average chopping current of 4A and for a contactor with average chopping current of 1 A.

High repetition rate operation of a long pulse excimer laser

The high repetition rate operation of a long pulse XeCl laser is demonstrated. The laser is found to work successfully when the reverse voltage mode operation of a spiker‐sustainer circuit is employed. This produces the steep voltage rise between the main electrodes resulting in an initiation of a homogeneous discharge and supplies excitation energy from the sustainer circuit with no time delay. These features enable the laser to operate at a repetition rate of greater than 500 Hz with a long pulse duration of 340 ns. An average power of 505 W is achieved.

Ion beam generation by field ionization of laser-excited Rydberg atoms

Sodium atoms (108–1011 cm−3) effused from an oven where excited by two pulsed dye lasers (∼8–15 ns, ∼100 μJ) from the ground state 3s, via an intermediate state 3p, to a Rydberg state ns or nd (20≤n≤25). About 50 ns after the laser irradiation, a pulsed electric field (0.5–5.5 kV/cm) was applied to the Rydberg atoms to ionize them and accelerate the resulting ions. Thus, a pulsed ion beam was obtained with a maximum total electric charge of ∼5 pC, corresponding to a peak current of ∼25 μA with an output pulse of ∼200 ns full width at half‐maximum.

Vapour flow patterns observed in free-burning arcs

The vapour flow pattern of a free-burning arc of 20 mm length is studied varying the cathode and anode diameters independently from 5 to 22 mm. Roughly speaking, there are two flow patterns which depend on the electrode arrangement. One is a bidirectional flow pattern and the other a unidirectional flow pattern. In both cases, outward flow are always observed without any indication of the air entrainment. A rough estimation shows that the radiation loss is more than 84% of the total energy loss in the vapour dominant arc generated in the present condition.

Generation of pure ion beams by field ionization of laser‐excited Rydberg atoms

Sodium atoms (108–1011 cm−3) effused from an oven were stepwise excited from their ground state to a Rydberg state ns or nd (20≤n≤26) by two pulsed dye lasers (∼5–10 ns, ∼100 μJ, ∼1.6‐mm‐diam spot). The laser energy density necessary to saturate the excitation processes from the ground state to the Rydberg state is ∼ several mJ/cm2. About 50 ns after the laser irradiation, a pulsed electric field (0.5–5.5 kV/cm) was applied to the Rydberg atoms to ionize them and accelerate the resulting ions. Thus, a pulsed sodium ion beam of purity >99.99% was obtained with a maximum total electric charge of ∼5 pC and a pulse width of ∼120 ns full width at half maximum. The total electric charge of the ion beam is estimated including the effect of space‐charge field of the beam ions, and is in good agreement with the experimental values.

Generation of pure gallium ion beams by field ionization of laser-excited rydberg atoms

Abstract Gallium atoms (10 8 −10 11 cm −3 ) effused from an oven were excited stepwise from their 4p ground state to a Rydberg state n p (20 ≤ n ≤ 52) by two pulsed dye lasers ( ∼ 2–10 ns, ∼ 10–100 μJ). About 50 ns after the laser irradiation, a pulsed electric field (0 kV/cm) was applied to the Rydberg atoms to ionize and accelerate the resulting ions. Thus, a pulsed gallium ion beam of purity >99.99% was obtained with a maximum total electric charge of ∼ 2 pC and a pulse width of ∼ 200 ns full width at half maximum.

High repetition rate operation of a high power long pulse XeC1 laser

An excitation system using a surface corona preionization scheme and a spiker-sustainer circuit is being developed to realize 2 kW XeC1 laser. An average power of 650 W is obtained so far at the repetition rate of 500 Hz.