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Sökning: swepub > Larsson Anders > Kungliga Tekniska Högskolan

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1.
  • Appelgren, Patrik, et al. (författare)
  • Experimental Study of Electromagnetic Effects on Solid Copper Jets
  • 2010
  • Ingår i: Journal of applied mechanics. - 0021-8936. ; 77:1, s. 011010
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper we present a study of the interaction between all electric current pulse and a solid copper jet. Experiments were performed using a dedicated pulsed power supply delivering a current pulse of such amplitude, rise little, and duration that the jet is efficiently affected. The copper jet was created by using a shaped charge warhead. All electrode configuration consisting of two aluminum plates with a separation distance of 150 mm was used. The discharge current pulse and the voltages at the capacitors and at the electrodes were measured to obtain data oil energy deposition in and the resistance of the jet and electrode contact region. X-ray diagnostics were used to radiograph the jet, and by analyzing the radiograph, the degree of disruption of the electrified jet could be obtained. It was found that a current pulse with an amplitude of 200-250 kA and a rise time of 16 mu s could strongly enhance the natural fragmentation of the jet. In this case, the initial electric energy was 100 kJ and about 90% of the electric energy was deposited in the jet and electrodes. At the exit of the electrode region, the jet fragments formed rings with a radial velocity of up to 200 m/s, depending oil the initial electric energy in the pulsed power supply. [DOI: 10.1115/1.3172251]
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2.
  • Appelgren, Patrik, et al. (författare)
  • Interaction between solid copper jets and powerful electrical current pulses
  • 2011
  • Ingår i: Journal of applied mechanics. - 0021-8936. ; 78:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The interaction between a solid copper jet and an electric current pulse is studied. Copper jets that were created by a shaped-charge device were passed through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. The electrodes were connected to a pulsed-power supply delivering a current pulse with amplitudes up to 250 kA. The current and voltages were measured, providing data on energy deposition in the jet and electrode contact region, and flash X-ray diagnostics were used to depict the jet during and after electrification. The shape of, and the velocity distributions along, the jet has been used to estimate the correlation between the jet mass flow through the electrodes and the electrical energy deposition. On average, 2.8 kJ/g was deposited in the jet and electrode region, which is sufficient to bring the jet up to the boiling point. A model based on the assumption of a homogenous current flow through the jet between the electrodes underestimates the energy deposition and the jet resistance by a factor 5 compared with the experiments, indicating a more complex current flow through the jet. The experimental results indicate the following mechanism for the enhancement of jet breakup. When electrified, the natural-formed necks in the jet are subjected to a higher current density compared with other parts of the jet. The higher current density results in a stronger heating and a stronger magnetic pinch force. Eventually, the jet material in the neck is evaporated and explodes electrically, resulting in a radial ejection of vaporized jet material.
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3.
  • Appelgren, Patrik, et al. (författare)
  • Modeling of a small helical magnetic flux compression generator
  • 2008
  • Ingår i: IEEE Transactions on Plasma Science. - 0093-3813. ; 36:5, s. 2662-2672
  • Tidskriftsartikel (refereegranskat)abstract
    •  In order to gain experience in explosive pulsed power and to provide experimental data as the basis for computer modeling, a small high-explosive-driven helical magnetic flux-compression generator (FCG) was designed at the Swedish Defence Research Agency. The generator, of which three have been built, has an overall length of 300 mm and a diameter of 70 mm. It could serve as the energy source in a pulse-forming network to generate high-power pulses for various loads. This paper presents a simulation model of this helical FCG. The model, which was implemented in Matlab-Simulink, uses analytical expressions for the generator inductance. The model of resistive losses takes into account the heating of the conductors and the diffusion of the magnetic field into the conductors. The simulation results are compared with experimental data from two experiments with identical generators but with different seed currents, influencing the resistive losses. The model is used to analyze the performance of the generator.
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4.
  • Appelgren, P, et al. (författare)
  • Modelling of a small helical magnetic flux compression generator
  • 2007
  • Ingår i: PPPS-2007 - Pulsed Power Plasma Science 2007. - 1424409144 - 978-142440914-3 ; s. 1155-1158
  • Konferensbidrag (refereegranskat)abstract
    • Helical flux-compression generators convert the chemical energy bond in explosives into electric energy. This paper briefly presents a model of, implemented in Matlab-Simulink, and simulation results for such a device. The simulation results are compared to experimental data from two experiments with identical generators but with different seed currents, influencing the resistive losses and thus the current amplification. The model is used to analyse the performance of the generator.
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5.
  • Appelgren, Patrik, et al. (författare)
  • Small Helical Magnetic Flux-Compression Generators : Experiments and Analysis
  • 2008
  • Ingår i: IEEE Transactions on Plasma Science. - 0093-3813. ; 36:5, s. 2673-2683
  • Tidskriftsartikel (refereegranskat)abstract
    • In order to gain experience in explosive pulsed power and to provide experimental data for modeling, a small high-explosive-driven helical magnetic flux-compression generator (FCG) was designed at the Swedish Defence Research Agency (FOI). The generator, of which three have been built, has an overall length of 300 mm and a diameter of 70 mm. It could serve as the energy source in a pulse-forming network to generate high power pulses for various loads. This paper presents the design of, and tests with, this helical FCG. The generator had an initial inductance of 23 mu H and was operated into a load of 0.2 mu H. The generator is charged with 0.27 kg of high explosives (PBXN-5). Various types of diagnostics were used to monitor the operation of the generator, including current probes, optical fibers, and piezo gauges. With seed currents of 5.7 and 11.2 kA, final currents of 269 and 436 kA were obtained, corresponding to current amplification factors of 47 and 39. The peak of the current was reached about 30 mu s after the time of crowbar. The two generators showed only small losses in terms of 2 pi-clocking. Using signals from optical fibers, the deflection angle of the armature could be determined to be 10 degrees in good agreement with hydrodynamic simulations of the detonation process and the detonation velocity to be 8.7 km/s in agreement with tabulated value.
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6.
  • Appelgren, P, et al. (författare)
  • Small helical magnetic flux compression generators : Experiments and analysis
  • 2007
  • Ingår i: PPPS-2007 - Pulsed Power Plasma Science 2007. - IEEE. - 1424409144 - 978-142440914-3 ; s. 1151-1154
  • Konferensbidrag (refereegranskat)abstract
    • This paper presents experimental results with helical magnetic flux-compression generators (FCGs). FCGs convert the chemical energy bond in explosives into electric energy. The generator had an initial inductance of 23 μH and was operated into a load of 0.2 μH. The generator is charged with 0.27 kg of high-explosives (PBXN-5). Various types of diagnostics were used to monitor the operation of the generator, including current probes, optical fibres, and piezo gauges. The results are analysed and the expansion of the armature compared with hydrodynamic simulations.
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7.
  • Elfsberg, Mattias, et al. (författare)
  • Experimental Studies of Anode and Cathode Materials in a Repetitive Driven Axial Vircator
  • 2008
  • Ingår i: IEEE Transactions on Plasma Science. - 0093-3813. ; 36, s. 688-693
  • Tidskriftsartikel (refereegranskat)abstract
    •  Repetitive use of a high-power microwave (HPM) radiation source implies strong erosion on cathode and anode materials. Electrode material endurance has been studied in a series of experiments with an axial vircator powered by a compact Marx generator. The Marx generator operated in a 10 Hz repetitive mode with a burst of ten pulses. Velvet and graphite was used as electron-emitting materials, and they showed markedly different pulse characteristics. Three different anode materials were used; stainless steel mesh, stainless steel wires and molybdenum wires, which all had different influence on the pulse characteristics.
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8.
  • Midya, Surajit, et al. (författare)
  • Understanding Pantograph Arcing in Electrified Railways - Influence of Various Parameters
  • 2008
  • Ingår i: IEEE International Symposium on Electromagnetic Compatibility Detroit, MI, AUG 18-22, 2008. - NEW YORK : IEEE. ; s. 592-597
  • Konferensbidrag (refereegranskat)abstract
    • The most common and yet unavoidable EMC problems with electrified railways are due to pantograph arcing. This distorts the waveform of the supply voltage and current, can generates transients during the zero crossings of the current and can cause interference with the traction power and signalling system. Pantograph arcing is a complex phenomenon and depends on speed of the train, current, presence of inductance etc. In a sliding contact like pantograph and contact wire, the am root moves across both electrodes because of the relative motion between them. In this paper, we will present an experimental analyses of the are root movement and influence of different parameters on it using a laboratory setup.
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9.
  • Fu, Ying, et al. (författare)
  • Energy band structure and spectral gain characteristics of dilute-nitride zinc blende InGaNAs quantum wells embedded in GaAs and GaNAs barriers
  • 2006
  • Ingår i: Journal of Applied Physics. - 00218979. ; 100:7
  • Tidskriftsartikel (refereegranskat)abstract
    • The spectral gain characteristics of dilute-nitride zinc blende InxGa1-xNyAs1-y quantum wells embedded in GaNy1As1-y1 barriers have been investigated experimentally and theoretically. Two samples, both with the gain peak at 1300 nm, were studied for comparison. One has a high nitrogen concentration in the quantum well with the surrounding barriers being pure GaAs. The other has a lower and uniform nitrogen concentration in the quantum well and the barriers (GaNAs barriers). Measurements show the redshift of the gain peak induced by the incorporation of nitrogen and difference in the spectral gain characteristics. The energy band structures and spectral gain characteristics are analyzed theoretically using the standard eight-band k center dot p theory. It is shown that the introduction of nitrogen atoms in the GaAs barriers reduces the barrier height for the central quantum well so that the energy sublevels in the conduction band becomes condensed. The condensation of the conduction-band energy sublevels reduces the peak gain and makes the gain spectrum narrower, in agreement with measurements.
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10.
  • Soderberg, Emma, et al. (författare)
  • Suppression of higher order transverse modes and oxide modes in 1.3 µm InGaAs VCSELs by an inverted surface relief
  • 2007
  • Ingår i: IEEE Photonics Technology Letters. ; 19
  • Tidskriftsartikel (refereegranskat)abstract
    • It is shown, by a systematic variation of design parameters, that the use of an inverted surface relief is very effective for suppressing higher order transverse modes in oxide confined 1.3-mu m InGaAs vertical-cavity surface-emitting lasers (VCSELs). Single-mode emission is achieved for a large variety of oxide aperture and surface relief diameters, with optimum designs, having a surface relief with a diameter half of that of the oxide aperture, producing 1.1-1.3 mW of single-mode power. It is also shown that the anti-phase layer employed to enable the use of an inverted surface relief is effective for suppressing oxide modes that otherwise appear in oxide confined VCSELs with a large detuning between the gain peak and the cavity resonance.
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