Investigations of two-stage-pseudospark switches for high-currentapplications

To avoid the lowering of the holdoff voltage due to the electrode erosion in one stage high current pseudospark switches (PSS), a two stage PSS with no axial aperture in the intermediate electrode was tested. For investigations a pulse generator was used generating peak currents up to 120 kA at a maximum voltage of 30 kV with a period length of 5 μs of a weakly damped sine wave with 90% current reversal. In comparison with a one stage PSS the breakdown characteristic was shifted to higher pressure. With a free floating intermediate electrode, the device could not be triggered, however, with additional capacities of a few nF between the three electrodes the discharge was ignited. The discharge in the second gap is triggered by the pseudospark discharge in the cathode gap, discharging the auxiliary capacities. Simultaneously, observation of both gaps with fast shutter photography showed an independent movement of the discharges in the two gaps. In the cathode gap as current increases, the discharge moves away from the center to the plane electrode surface as has been observed in the one stage PSS. However, in the anode gap the discharge moves away from the center after a contraction to the center. The two discharges are transmitted to metal vapor arc type discharges as the erosion patterns prove. With this kind of a two stage PSS holdoff voltages exceeding 35 kV would be possible. The characteristic switch data, i.e., delay and jitter, are nearly equal to a one stage PSS     

Orphan-Free Anisotropic Voronoi Diagrams

We describe conditions under which an appropriately defined anisotropic Voronoi diagram of a set of sites in Euclidean space is guaranteed to be composed of connected cells in any number of dimensions. These conditions are natural for problems in optimization and approximation, and algorithms already exist to produce sets of sites that satisfy them.     

Triggering of radial multichannel pseudospark switches by a pulsedhollow cathode discharge

We report on a special trigger discharge for pulsed high-power pseudospark switches. The switch used is a radial three-channel pseudospark switch. For triggering, a cylindrical trigger electrode is inserted into the hollow cathode of the main gap. This electrode acts as a hollow cathode for the dc preionization, while the hollow cathode of the main gap is the anode. A negative high-voltage pulse supplied to the trigger electrode ignites the main discharge. We report the temporal evolution of the trigger discharge observed with a fast camera. This trigger method gives an excellent current distribution among the discharge channels, as can be proven by fast photography. The switch has a delay of 220 ns and a jitter of 15 ns     

Investigation of the different discharge mechanisms in pseudosparkdischarges

The intention of this paper is to give an overview of recent experiments explaining the development and transition of the discharge phases in a pseudospark. The reported experiments include single gap pseudospark discharges in ultra-high-vacuum systems with hydrogen as working gas, as well as multigap pseudospark discharges in argon. Temporally and spatially resolved framing photography, spectrometry, raster electron microscopy and time resolved electrical measurements are presented. The experiments comprise a current range of some hundreds of amps to 60 kA. The results are used to specify the four characteristic phases of the pseudospark: Townsend-, hollow cathode-, high current- and metal vapor arc phase     

Development of a high current pseudospark switch and measurement ofelectron density

The pseudospark, a low-pressure gas discharge in a special geometry, is suitable for high-current switching. A single-channel prototype is tested with a 3.3-μF capacitor bank, voltages up to 30 kV, and peak currents up to 120 kA. The electrical circuit, not comprising any load resistor causes weakly damped sinusoidal pulses of 5-μs duration at 90% current reversal. For lifetime tests, a switch with an alumina insulator and copper seals is used. Hydrogen is the working gas. Several electrode materials like molybdenum, tungsten, graphite and chromium-copper are tested. Optical investigations of the discharge and of plasma parameters are done with an O-ring sealed pseudospark switch. The light of the discharge is observed spectrally integrated with a streak camera. Spectral resolution is obtained by using a high-speed shutter in combination with a monochromator. The radial electron density is determined by measuring the Stark broadening of the Balmer H_β-line. At 60 kA a maximum electron density of about 2×10¹⁷cm^-3 is calculated     

Private Philanthropy and Basic Research in Mid-Twentieth Century America: The Hickrill Chemical Research Foundation

The Hickrill Chemical Research Foundation, located north of New York City on the estate of its patrons, Sylvan and Ruth Alice Norman Weil, had a short (1948–59) but productive life. Ruth Alice Weil received a Ph.D. in organic chemistry in 1947, directed by William von Eggers Doering of Columbia University. She intended that Hickrill contribute to cancer chemotherapy while providing resources for Doering's more speculative research. Ultimately, Doering's commitment to theoretical organic chemistry set Hickrill's research agenda. Lawrence Knox, an African American with a Harvard Ph.D., supervised the laboratory's daily activities. Hickrill's two dozen postdoctoral fellows produced path-breaking results in Hückel aromatic theory and reactive intermediate chemistry, fostering the postwar emphasis on “basic science.” This essay places the Laboratory's successes in the wider context of postwar politics and scientific priorities. Private philanthropic support of basic science arose because it received little pre-World War II government support. In the immediate postwar period, modest organisations like Hickrill still met a need, but the increasing governmental defence- and non-defence-related support for science eventually rendered them unnecessary.     

Trigger devices for pseudospark switches

Effective triggering of pseudospark switches with long lifetime and low jitter remains an important problem. This paper presents results of investigations of trigger methods for pseudospark switches. based upon pulsed glow discharges in planar and hollow electrode geometry for charge injection. The influence of different wiring and geometries of the electrodes for preionization is investigated. The effect of additional blocking potentials in the hollow cathode to improve different trigger systems was measured. Calculations of the static potential in the hollow cathode with or without blocking potential are compared with parameters of the discharge     

Pseudospark switches-technological aspects and application

We report results of the development of fast closing switches, so-called pseudospark switches, at Erlangen University. Two different parameter regimes are under investigation: medium power switches (32 kV anode voltage, 30 kA anode current and 0.02 C charge transfer per shot) for pulsed gas discharge lasers and high power switches (30 kV anode voltage, 400 kA anode current and 3.4 C charge transfer per shot) for high current applications. The lifetime of these switches is determined by erosion of the cathode. The total charge transfer of devices with one discharge channel is about 220 kC for the medium and 27 kC for the high power switch. At currents exceeding 45 kA a sudden increase in erosion rate was observed. Multichannel devices are suited to increase lifetime as the current per channel can be reduced. Successful experiments with radial and coaxial arrangements of the discharge channels were performed. In these systems the discharge channels move due to magnetic forces. A skilful use of this phenomena will result in a considerably increase of switch lifetime. Multigap devices enable an increase of anode voltage. A three gap switch has run reliably at an anode voltage of 70 kV     

Pseudospark switches for high repetition rates and high currentapplications

The state-of-the-art of pseudospark switch (PSS) development is reported. In addition to the replacement of thyratrons for high power applications in TE-gas-discharge lasers, PSSs have been tested at high repetition rates up to 2 kHz. In order to minimize the erosion rate and to reduce total switch inductance, multichannel PSSs with various geometrical configurations have been investigated: linear, coaxial, and radial arrangements of the parallel discharge channels. All three configurations possess distinct advantages in pulsed power technology, i.e. linear systems fit well into striplines. Beyond this, PSSs gain increasing importance in high current devices like fast pinches, plasma foci, or powerful modulators, i.e. for magnetoforming. A single-channel switch for hold-off voltages up to 30 kV at peak currents of ≈100 kA has been tested for a damped sinusoidal pulse of a 5 μs duration at a repetition rate of up to 0.2 Hz, with and without electrode cooling     

High-repetition rate sealed-off pseudospark switches for pulsedmodulators

Experimental results of high-repetition-rate pseudospark switch testing are reported. Typical test parameters are hold-off voltage of about 20 kV, peak currents on the order of 10 kA, and pulse durations between 50 and 100 ns. The discharge circuit, with discrete ceramic capacitors up to 10.8 nF total, produced a ringing discharge with peak currents on the order of 10 kA. Current reversal under these conditions was up to 80% of the peak current. A sealed-off, ceramic-metal pseudospark switch with integral deuterium reservoir tested in this setup achieved repetition rates of up to 1.8 kHz without latching or triggering failures. Some 10⁷ shots have been performed without degradation of the switch performance