Short High Current Pulses Research Articles

Time evolution of plasma parameters in the jet of a low-power vacuum arc thruster

The plasma parameters temporal evolution of a 30 W-class Vacuum Arc Thruster equipped with a Ni-Cr cathode is examined in the far-field region of the plasma jet. Measurements have been performed 20 cm downstream of the arc region where the plasma is created. The thruster operated at 1 Hz with 25 μs duration current pulses. The maximum current intensity reaches 4000 A about 8 μs after the discharge ignition. The change in the electron density, electron temperature and plasma potential during the short high-current pulse has been obtained by means of time-resolved Langmuir probe measurements. A time-of-flight technique based on a planar probe has been used to determine the mean ion velocity in the plasma jet. In addition, a Faraday cup allowed the determination of the ion current density. The electron density peaks at ∼ 8×1017 m−3 at 12 μs. The electron temperature is above 25 eV at 7 μs and then it stabilizes around 5 eV. Several ion populations are identified. The lowest ion mean velocity amounts to 20 km/s. Interestingly, combining all data allows to assess the ion mean electrical charge and its temporal behavior. The mean charge reaches 12 a few μs after ignition. It decays quickly afterwards and stays unchanged at 2 beyond 10 μs. Analysis of all the results support the idea of two distinct plasma discharge regimes.

Failure of electrical vias manufactured in thick-film technology when loaded with short high current pulses

The high-current failure of electrical interconnects (through-metalized vias) manufactured in thick-film technology is investigated. A large number of vias were measured in a four-wire-setup by applying short time high-current pulses. The experimental conditions ensured that approximately half of the tested vias were destroyed during the tests. The high-current failure mechanism was identified to be a kind of a self-accelerating melting process. It was also implemented in a “Finite Element Method” (FEM)-model. The FEM-model delivered not only the time-dependent voltage drops over the through holes (which is proportional to the through hole resistance), but also the time-dependent temperature, conductivity, and current density distributions inside of the vias during current load. Input parameters for the model were material properties and sample geometries. Analyzed cross-section micrographs of destroyed vias and the temperature maxima received from the FEM-model agreed well. Furthermore, measured and modeled voltage drops during failure were compared and agreed also very well.

A model for the self-pulsing regime of microhollow cathode discharges

Microhollow cathode discharges may operate in different regimes depending of the discharge current. They are subject to relaxation oscillations in the so-called self-pulsing regime in which the discharge oscillates between two quasiequilibria: at low current it remains confined in the microhole whereas it expands on the cathode backside during short high-current pulses. A model based on a nonlinear discharge resistance is proposed to describe the phenomenon. The analysis of the dynamics reveals that the current pulse rises in an extremely short time while the characteristic (longer) decay time is imposed by the resistance when the discharge is expanded outside the hole. It is shown how the nonlinear discharge resistance may be inferred from the experimental current-voltage signals.

Enhanced laser shutter using a hard disk drive rotary voice-coil actuator

Rotary voice-coil motors from computer hard disk drives make excellent mechanical shutters for light beams. However, the complexity of the necessary electronic driving circuit can hinder their application. A new design is presented here, using a single integrated circuit originally intended for controlling dc motors. A digital input signal switches a unipolar power supply bidirectionally through the voice coil. Short high-current pulses are generated on the transitions to ensure rapid shutter action, while a low holding current reduces the power requirement and heating of the actuator. The circuit can reverse the current to brake the shutter and reduce the impact at the end of its travel. With a focused laser beam, the shutter achieves rise times below 500 ns. A method for producing variable length pulses is also described, demonstrating durations as short as 700 ns.

Short-time failure of metal interconnect caused by current pulses

It is pointed out that voltage programmable link (VPL) technologies impose a new criterion on the reliability of metal interconnect. Lines of metallization must support the full programming current, which can be many times larger than the signal level current, for very short periods of time. For a sufficiently short high-current pulse, the wire, encapsulated in oxide, will not reach thermal equilibrium and the current-induced heating can be modeled as being adiabatic. Energy conservation predicts a relationship between maximum current density that can be carried by a wire before it fuses, and the pulse duration time, J/sup 2/t=10/sup 8/ A/sup 2/-s/cm/sup 4/. This relationship is based on a temperature rise in the metal line at failure of theta /sub f/*=300 degrees C. The time required for the metal to reach thermal equilibrium at a given current density is shown to be proportional to the square of the oxide thickness. These predictions are experimentally verified with layered AlSi/Ti metallization on thermal oxide on silicon substrates. >