Koichi Tsuruta

Velocities of copper and silver ions generated from an impulse vacuum arc

Vacuum gaps with a copper and silver needle-cathode were fired by a 13 /spl mu/s duration half-cycle sinusoidal arc and metal ions were analyzed by a time of flight (TOF) method at variable positions of the acceleration space. Velocities of the ions of each charge state were determined assuming collisionless flight from the cathode region to the outside of the gap. Ions generated at the ignition of the arc flew fast and the velocities were 2.7/spl times/10/sup 4/ and 2.0/spl times/10/sup 4/ m/s for copper and silver, respectively, regardless of the charge state. The velocities of the ions released with the arc extinction were lower and changed depend on the charge state.

Experimental study of the voltage recovery characteristics of small air gaps

The electrical recovery characteristics of relatively small air gaps between 0.3 and 9 mm were determined using a two-pulse method. The first pulse was used to over-volt the gap and initiate the arc current. The second pulse was used to determine the recovery voltage of the gap. A plot of the recovery voltage with time was obtained by varying the time delay of the second pulse relative to the arc extinction time of the first arc, in the time range form 50 mu s to 100 ms. It is found that the recovery characteristics are independent of the electrode materials (Cu, Al , St) and the arc current in the range from 40 to 200 A. It is also found that the shorter gaps and the rod plane gaps recover their dielectric strength faster than the longer gaps and the sphere gaps, respectively. >

Effect of Axially Symmetric Magnetic Fields for Dynamics of Low-Current DC Vacuum Arc Plasma

In this paper, effects of four types of axially symmetric magnetic fields on the dynamics of low-current dc vacuum arc plasma, which is less than 30 A, were examined. Arcs were ignited by the opening of the butt contacts made of zinc. In the axial magnetic field, the arc plasma was restricted within a column, and the arc voltage rose with increasing gap length. When a magnet was arranged behind the cathode, the cathode spot rotated in the opposite direction to the Lorentz force (-J times B) on the edge of the circular-rod cathode. On the other hand, when a magnet was arranged behind the anode, the arc plasma was constricted on the anode side, and the lifetimes of the arcs became longer, although the arc voltage rose with increasing gap length. The compression effect of the axial component of the magnetic field was analyzed by introducing a simple magnetic piston model, and the experimental diameters of the arc column showed a good agreement with the model.

Ignition and instability of low-current DC vacuum arcs ignited by the opening of the electrodes

The ignition, lifetime, and instability of low-current DC vacuum arcs, which were ignited by the opening of the electrodes, were investigated experimentally. Copper electrodes were used and the arc current was less than 50 A. Waveforms of the voltage and current between the electrodes at the moment of arc ignition and during the arc continuation were measured. It was confirmed that, for the ignition of the arc, a voltage which was larger than a critical value should appear between the electrodes at the moment of the opening of the electrodes. The lifetime of the arc is short, less than 1 s in the present condition, and increases with an increase in arc current and output voltage of the current source. The arc voltage consists of a certain DC level, around 20 V, and an additive high-frequency component. The arc current consists of a certain DC level and a subtractive high-frequency component.

Soft x-ray generation after arc extinction of a short vacuum gap operated with low-current, repetitive discharge

Soft x-ray emission from a short vacuum gap, operated with a repetitive low-current arc with a period of ~2??s and peak current of 200?A, was investigated. Electrons are accelerated by an electric field in the cathode sheath that is formed after arc extinction, and soft x-rays were emitted in the period between arc extinction and subsequent breakdown. The bulk of the radiation was detected in the 1?3?keV soft x-ray range when a tungsten anode was employed. The dimension of the point-like x-ray source in the radial direction was less than 170??m. The current density at the time of x-ray emission was ~107?A?m?2.

Effect of magnetic field on sustainment of low-current DC vacuum arcs

Effect of magnetic fields on the instability of low current DC vacuum arcs, less than 10A, were examined experimentally. An axial magnetic field less than 100mT composed of a pair of disc magnets, an axial magnetic field by a solenoid coil in a range of 70 to 300mT, and an axial magnetic filed with a radial component by a disc magnet less than 40mT were used. It appeared that the arcs become unstable and the arc voltages rise by applying axial fields. As a result the lifetimes of the arcs rather decreased with increasing magnetic fields.

Experimental characterization of vacuum arc instabilities for different electrode metals

Arc voltages and instabilities of low-current, dc vacuum arcs, less than 30 A, ignited by the opening of electrodes were investigated for eight kinds of electrode metals. The low-current dc arcs were always unstable, but the dc components of the arc voltages showed peculiar values to the metals. The intensity of the instability differed depending on the electrode material, and it was confirmed that the waveform of the spike voltage was the same with the voltage drop of the inductive resistor of the circuit. The spike voltage excites an oscillation of the arc current as a result of inductance and capacitance resonance of the circuit. The oscillations were observed by adding a parallel capacitance and a series inductance to the circuit, and the waveforms of the oscillation agreed with simulated waveforms.

Ignition and lifetime of low current DC vacuum arc ignited by the opening of the electrodes

The ignition and lifetime of a low current DC vacuum arc, which was ignited by the opening of the electrodes, were investigated experimentally. Copper electrodes were used and the arc current was less than 50 A. Waveforms of the voltage and current between the electrodes at the moment of the arc ignition and during the arc were measured. Lifetime of the arc was measured as a function of the arc current and output voltage of the DC current source. It appeared that, for the ignition of the arc, a voltage which was larger than a critical value should come out between the electrodes at the moment of the opening of the electrodes. After the ignition, the arc voltage consists of a certain DC level, around 20 V, and an additive high frequency component. The arc current consists of a certain DC level and a subtractive high frequency component. The lifetime of the arc is short, less than in the present condition, and increases with increasing arc current and output voltage of the current source.

Charge state and residence time of metal ions generated from a microsecond vacuum arc

Metal ions generated from a microsecond vacuum arc were measured using a time-of-flight (TOF) method. A point-plane vacuum gap was fired by an impulse voltage to generate metal ions. The risetime and time constant for the decay of the arc current were 0.1 and 4.5 mu s, respectively. TOF ion currents were measured for variable ion extraction times after the arc ignition. At a lead cathode, Pb/sup +/ and Pb/sup ++/ ions were detected for ion extraction times less than 45 mu s. The average charge-state fractions of the Pb/sup +/ and Pb/sup ++/ ions were 91 and 9%, respectively. At a copper cathode, Cu/sup +/, Cu/sup ++/, and Cu/sup +++/ ions were detected for ion-extraction times less than 12.5 mu s, and the average charge-state fractions were 42, 41, and 17%, respectively. The residence times of the generated lead and copper ions were also discussed. >

Temporal evolution of micro-plasma in a low-current, repetitive vacuum spark soft X-ray source

Temporal evolution of micro-plasma and soft X-ray emission in a short vacuum gap, operated with a repetitive low-current (/spl sim/100 A) discharge was investigated. The device consists of two resonant circuits having different resonant frequencies for energy storage. Micro-plasma of diameter less than 1 mm is formed during spark phase with a very high-frequency (VHF) voltage, and electrodes are heated by successive high-frequency (HF) current. Thermo-field electrons are accelerated by an electric field in a cathode sheath that is formed after arc extinction. Soft X-rays were emitted mainly in the period between arc extinction and subsequent breakdown.