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| 2. |
- Appelgren, Patrik, et al.
(författare)
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Modelling of a small helical magnetic flux compression generator
- 2007
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Ingår i: PPPS-2007 - Pulsed Power Plasma Science 2007. - 1424409144 - 9781424409143 ; , s. 1155-1158
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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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| 3. |
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| 4. |
- Appelgren, Patrik, et al.
(författare)
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Parametric studies of an electrohydrodynamic plasma actuator for boundary layer flow control
- 2009
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Ingår i: PPC '09. IEEE Pulsed Power Conference, 2009. - : IEEE. - 9781424440658 ; , s. 1069-1074
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Konferensbidrag (refereegranskat)abstract
- An electrohydrodynamic plasma actuator can be used as an aerodynamic flow control device. A plasma actuator is realised as a surface-mounted dielectric barrier discharge (DBD) that transfers directed energy from ions in the discharge to the surrounding air. Parametric studies have been performed in order to investigate the relative efficiency in terms of electrical power into the actuator versus mechanical power in the generated boundary flow. The parametric study includes variations of the applied driving voltage and frequency as well as different electrode and dielectric materials. It is found that, within the range tested, for each value of electrical power into the actuator there exists an optimum driving frequency in terms of boundary layer flow velocity. It is also found that the same trend seems to be true when analyzing electric to mechanical efficiency of the device, i.e. for a given input power there exists an optimum driving frequency that produces the highest efficiency. However, this peak in efficiency of the actuator lies on the edge of the parametric space tested so that further experiments are needed to validate these results.
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| 5. |
- Appelgren, Patrik, et al.
(författare)
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Small helical magnetic flux compression generators : Experiments and analysis
- 2007
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Ingår i: PPPS-2007 - Pulsed Power Plasma Science 2007. - : IEEE. - 1424409144 - 9781424409143 ; , s. 1151-1154
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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. |
- Brenning, Nils, et al.
(författare)
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Conditions for plasmoid penetration across abrupt magnetic barriers
- 2005
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- The penetration of plasma clouds, or plasmoids, across abrupt magnetic barriers (of the scale less than a few ion gyro radii, using the plasmoid directed velocity) is studied. The insight gained earlier, from detailed experimental and computer simulation investigations of a case study, is generalized into other parameter regimes. It is concluded for what parameters a plasi-noid should be expected to penetrate the magnetic barrier through self-polarization, penetrate through magnetic expulsion, or be rejected from the barrier. The scaling parameters are n(e), upsilon(o), B-perpendicular to, m(i), T-i, and the width w of the plasmoid. The scaling is based on a model for strongly driven, nonlinear magnetic field diffusion into a plasma which is a generalization of the earlier laboratory findings. The results are applied to experiments earlier reported in the literature, and also to the proposed application of impulsive penetration of plasmoids from the solar wind into the Earth's magnetosphere.
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| 8. |
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| 9. |
- Gunell, H., et al.
(författare)
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Numerical experiments on plasmoids entering a transverse magnetic field
- 2009
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 16:11
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Tidskriftsartikel (refereegranskat)abstract
- Plasma from the Earth's magnetosheath has previously been observed inside the magnetosphere. Inhomogeneities in the magnetosheath plasma, here called plasmoids, can impact the magnetopause and doing so set up a polarizing field that allows it to penetrate the magnetopause and enter the magnetosphere. A set of simulations of plasmoids with different dimensions is presented in this paper. For plasmoids that are longer than those previously published, waves propagating upstream from the barrier are found. It is also found that the penetration process causes the part of the plasmoid that is upstream of the barrier to rotate. The role of plasmoid width and cross sectional shape in penetration is studied, and for plasmoids that are less than half an ion gyroradius wide, the plasmoid is compressed to obtain a vertically oriented elliptical cross section, regardless of the initial shape. When the initial plasmoid width exceeds the ion gyroradius, the plasmoid still penetrates through a mechanism involving a potential that propagates upstream from the magnetic barrier.
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| 10. |
- Gunell, H., et al.
(författare)
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Simulations of a plasmoid penetrating a magnetic barrier
- 2008
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 50:7
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Tidskriftsartikel (refereegranskat)abstract
- Plasma structures, here typified by the term 'plasmoids', in the solar wind impacting on the magnetopause, i. e. the boundary between the solar wind and the Earth's magnetosphere, can penetrate this boundary and be injected into the magnetosphere. This can happen either by expulsion of the magnetic field from the structure and subsequent diffusion of the magnetic field into the structure or by the formation of a polarization electric field that lets the plasma structure E x B- drift into the earth's magnetic field. In both cases a collisionless resistivity is required at some stage of the process. While magnetic expulsion requires electromagnetic models for its description, polarization can be modelled electrostatically and both processes can be, and have been, studied in laboratory experiments. We present three-dimensional electrostatic particle-in-cell simulations that reproduce large-amplitude waves, in the lower-hybrid range, that have been observed in laboratory experiments. Lower-hybrid waves have also been seen at the magnetopause of the earth. We consider the implications for spacecraft-based studies of magnetopause penetration, and suggest that the search for penetrating plasma structures should emphasize cases in which the interplanetary magnetic field is oriented northwards, as this configuration is less likely for reconnection. The application of theoretical predictions to the magnetopause environment shows that a plasma structure penetrating via polarization needs to be small, i. e. less than 10-100 km wide for typical parameters, and that wave processes at the magnetopause are needed to create such small structures. A larger structure can penetrate by means of magnetic expulsion.
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| 11. |
- Hurtig, T., et al.
(författare)
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The role of high frequency oscillations in the penetration of plasma clouds across magnetic boundaries
- 2005
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Experiments are reported where a collissionfree plasma cloud penetrates a magnetic barrier by self-polarization. Three closely related effects, all fundamental for the penetration mechanism, are studied quantitatively: (1) anomalous fast magnetic field penetration (two orders of magnitude faster than classical), (2) anomalous fast electron transport (three orders of magnitude faster than classical and two orders of magnitude faster than Bohm diffusion), and (3) the ion energy budget as ions enter the potential structure set up by the self-polarized plasma cloud. It is concluded that all three phenomena are closely related and that they are mediated by highly nonlinear oscillations in the lower hybrid range, driven by a strong diamagnetic current loop which is set up in the plasma in the penetration process. The fast magnetic field penetration occurs as a consequence of the anomalous resistivity caused by the wave field and the fast electron transport across magnetic field lines is caused by the correlation between electric field and density oscillations in the wave field. It is also found that ions do not lose energy in proportion to the potential hill they have to climb, rather they are transported against the dc potential structure by the same correlation that is responsible for the electron transport. The results obtained through direct measurements are compared to particle in cell simulations that reproduce most aspects of the high frequency wave field.
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| 12. |
- Lindblom, A., et al.
(författare)
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First Trials with a 45 GW Cable-Based Pulsed-Power Generator
- 2009
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Ingår i: Acta Physica Polonica. A. - 0587-4246 .- 1898-794X. ; 115:6, s. 976-977
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Tidskriftsartikel (refereegranskat)abstract
- The output from narrow-band high-power microwave (HPM) sources, such as the virtual cathode oscillator (vircator) and the magnetically insulated line oscillator (MILO), is strongly dependent on the voltage pulse feed. A rectangular, flat-top voltage pulse can be achieved by the use of a transmission line as a pulse-forming unit. The development in high-voltage cable technology has made them useful as parts of high-voltage and high-power generator systems. The generator is designed to deliver a 200 ns voltage pulse of 500 kV into a 10 Omega unmatched load with an electric power of 25 GW. The generator has an impedance of 2 Q. The primary energy storage of the generator consists of a 50 kV, 20 U capacitor bank. The 50 kV is discharged into a transformer that charges a pulse-forming line to 550 kV. When charged, the pulse-forming line is discharged into the load via a spark gap. This paper presents results from initial testing of the generator.
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| 13. |
- Lindblom, Adam, et al.
(författare)
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High-voltage pulsed-power cable generator
- 2009
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Ingår i: IEEE Transactions on Plasma Science. - USA : IEEE. - 0093-3813 .- 1939-9375. ; 37:1, s. 236-242
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Tidskriftsartikel (refereegranskat)abstract
- A cable-based 25-GW pulsed-power generator with output impedance of 2 is presented. It is designed to deliver a 200-ns-long 500-kV pulse into a 10 load. The primary energy storage of the generator consists of a 50-kV 20-kJ capacitor bank. The 50-kV capacitor bank is discharged into a 1 : 12 transformer. The transformer is designed to charge a pulse-forming line (PFL) to 600 kV. When charged, the PFL is discharged into a load via a spark gap. The spark gap is located in a coaxial system containing deionized water together with the cable endings of the PFL and transformer. The electric field at the cable endings is refractively graded by the high permittivity of the surrounding water. The primary and secondary windings consist of high-voltage cables that are interleaved and wound together. The PFL consists of eight 40-m-long 110-kV coaxial cables with both ends connected to the load. Each cable screen is grounded in the middle and connected in parallel. The cables have a characteristic impedance of 30 . The parallel cable setup gives the PFL an impedance of 2 . The total length, height, and width of the pulse generator are 4, 2, and 1.2 m, respectively.
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