A.P.J. van Deursen

Multiple x-ray bursts from long discharges in air

A lightning surge generator generates a high-voltage surge with a 1.2 µs rise time. The generator fed a spark gap of two pointed electrodes at 0.7 to 1.2 m distances. Gap breakdown occurred between 0.1 and 3 µs after the maximum generator voltage of approximately 850 kV. Various scintillator detectors with different response times recorded bursts of hard radiation in nearly all surges. The bursts were detected over the time span between approximately half of the maximum surge voltage and full gap breakdown. The consistent timing of the bursts with the high-voltage surge excluded background radiation as the source for the high intensity pulses. In spite of the symmetry of the gap, negative surges produced more intense radiation than positive. This has been attributed to additional positive discharges from the measurement cabinet which occurred for negative surges. Some hard radiation signals were equivalent to several megaelectronvolts. Pile-up occurs of lesser energy x-ray quanta, but still with a large fraction of these with an energy of the order of 100 keV. The bursts occurred within the 4 ns time resolution of the fastest detector. The relation between the energy of the x-ray quanta and the signal from the scintillation detector is quite complicated, as shown by the measurements.

X-ray emission in streamer-corona plasma

X-ray emission has been detected occasionally during the streamer-corona propagation in a wire-plate corona reactor open to ambient air. A 65 kV pulse with 15 ns rise time is applied to the wire anode superimposed on a 20 kV dc bias. The duration of the driving voltage pulse (110 ns) is less than 2.5 times the primary streamer transit time. Under this condition no arc discharge occurs between the wire and the cathode plates separated by 6 cm air. The onset of x-ray emission coincides with the initiation of the primary streamers near the wire anode. No x-rays were detected later, during or after the primary or secondary streamer development. X-ray energies ranged between 10 and 42 keV, as detected by a LaBr3 (Ce) scintillator–photomultiplier combination. Time resolved imaging of the streamer propagation highlights the different stages in the streamer discharge process. The energetic electrons originate near the anode, at the moment of streamer initialization.

Experimental investigation of small He clusters

The question of the existence of a bound state for He2 has been investigated by observing ionized Hen+ clusters produced in a low temperature molecular beam. The results agree with the prediction that there is no bound state for He2. (AIP)

Intensities and cross-sections of Ar clusters in a molecular beam

Ar-cluster beams were produced by supersonic expansion under various source conditions. The experimental intensities have been scaled such that universal curves are obtained, up to moderate source pressures. The ratio of dimer/monomer cross-sections has been determined.

Molecular beam intensities and collision cross-sections of small Ne, H2, N2, NO and O2 clusters☆

Abstract The temperature- and pressure-dependence of cluster intensities were determined in a molecular beam from a supersonic nozzle source. The ratio σ2/σ1 for the total cross-section of the monomeric and dimeric systems investigated was found to be between 1.34 and 1.55 with a heavy inert gas as scattering partner. The magnetic deflection properties of H2−, O2−, and NO-dimer beams are discussed.

Differentiating/integrating measurement setup applied to railway environment

Large-scale tests at the new Harbor Railway Line in The Netherlands asked for a dedicated measuring system for all currents at eight cross sections of the railway. The differentiating/integrating measurement scheme with adapted versions of Rogowski coils and special integrators fulfilled the requirements with respect to accuracy, bandwidth, electromagnetic compatibility, life-time, and environmental constraints. Three types of current sensors were developed; their air-core guaranteed linearity over the full current range up to 20 kA. Most importantly, the sensors allowed unimpeded rail transport. The paper discusses the sensors, the rationale, and tests, as well as the integrators. The system has been successfully employed, before and after the large-scale tests, in Luxembourg and Portugal. A few out of much data gathered show the broad applicability of the system.

Measurements of intensity and velocity distribution of clusters from a H2 supersonic nozzle beam

Abstract Measurements on the production of (H2)n clusters of small size are reported. The abundance of different clusters is found to rise to a flat maximum, at optimum source conditions for a specific cluster size. These maxima reach values of about 10% of the H2+ signal without a strong tendency to decrease with increasing mass. The possibility of production of neutral cluster beams of known cluster size is discussed, which can be used in molecular beam scattering experiments.

Fermi surfaces and effective masses in LnB6, Ln La, Ce and Pr

Abstract The Fermi surface has been compared for the three compounds LnB6 (Ln  La, Ce and Pr) by measurement of the de Haas-van Alphen effect. The major part is observed to be similar in each compound, most likely consisting of X-centred ellipsoids with a total effective volume of about 1 electron per formula unit. Differences occur in the details of the shape of the FS, clearly seen for PrB6. Large effective masses, m ∗ , are observed for CeB6 and PrB6, m ∗ = 6 and about 1.8, respectively. These have to be compared with m ∗ = 6.0 for LaB6.

Transfer impedance of nonmagnetic conduits of various shapes

Metallic conduits provide mechanical support for cables, and may also protect the cables against interference caused by currents induced by external electromagnetic fields. The conduit transfer impedance Z/sub t/ then is a good measure for the provided protection. We studied Z/sub t/ by means of conformal transformations and of the method of moments in a quasistatic, two-dimensional (2-D) approach. Practical U-, H-, L-, and T-shaped conduits are discussed. Conformal transformations provide simple engineering expressions for the mutual inductance part of Z/sub t/ for cable positions inside the conduit. The method of moments formulation results in useful approximations for the crossover frequencies in Z/sub t/ between DC and high frequency. Measurements on U-shaped conduits confirm the calculations.

Fermi surface measurements of UPd3

The Fermi surface of the DO24 compound UPd3 has been investigated by the de Haas-van Alphen effect in magnetic fields up to 46 Tesla. Two sheets are detected, one with a high frequency, about 4 103 Tesla, and one having low frequencies, about 4 102 Tesla. Values of the effectives mass obtained are in accordance with a non-f character of the electron wave function on the orbits investigated.