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  • 1.
    Achilli, Timothée
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    STATISTICAL STUDY OF THEEARTH'S MAGNETOPAUSEBOUNDARY LAYER PARTICLEPOPULATIONS2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    While double ion populations, with a cold population originating from the solar windand a hotter one from the magnetosphere, are frequently observed in the Earth’s lowlatitudeboundary layers, similar double electron populations are seldom recorded.We performed a statistical study of ion and electron double populations near themagnetopause by using 7 years of THEMIS particle data. After a preliminary study ofmagnetopause crossings characteristics, in particular by determining the typicalenergies of ion and electron populations in regions near the magnetopause, we setup an automated detection algorithm for identifying regions with combined ion andelectron double populations.The statistical study carried out with respect to IMF conditions in the upstream solarwind during and just before the events suggests that such combined ion and electronDouble Population Boundary Layers (DPBL) form preferentially under northward IMFbut with a significant BY component.We interpret this trend as a result of reconnection of the same magnetosheath fieldline in both hemispheres, but with at least one end reconnecting in its hemisphere atlower latitude with a closed magnetospheric field line which already contains a hotelectron source.

  • 2. Aiempanakit, Montri
    et al.
    Aijaz, Asim
    Lundin, Daniel
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Helmersson, Ulf
    Kubart, Tomas
    Understanding the discharge current behavior in reactive high power impulse magnetron sputtering of oxides2013Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, nr 13, s. 133302-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The discharge current behavior in reactive high power impulse magnetron sputtering (HiPIMS) of Ti-O and Al-O is investigated. It is found that for both metals, the discharge peak current significantly increases in the oxide mode in contrast to the behavior in reactive direct current magnetron sputtering where the discharge current increases for Al but decreases for Ti when oxygen is introduced. In order to investigate the increase in the discharge current in HiPIMS-mode, the ionic contribution of the discharge in the oxide and metal mode is measured using time-resolved mass spectrometry. The energy distributions and time evolution are investigated during the pulse-on time as well as in the post-discharge. In the oxide mode, the discharge is dominated by ionized oxygen, which has been preferentially sputtered from the target surface. The ionized oxygen determines the discharge behavior in reactive HiPIMS.

  • 3. Aijaz, Asim
    et al.
    Sarakinos, Kostas
    Lundin, Daniel
    Brenning, Nils
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Helmersson, Ulf
    A strategy for increased carbon ionization in magnetron sputtering discharges2012Ingår i: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 23, s. 1-4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A strategy that facilitates a substantial increase of carbon ionization in magnetron sputtering discharges is presented in this work. The strategy is based on increasing the electron temperature in a high power impulse magnetron sputtering discharge by using Ne as the sputtering gas. This allows for the generation of an energetic C+ ion population and a substantial increase in the C+ ion flux as compared to a conventional Ar-HiPIMS process. A direct consequence of the ionization enhancement is demonstrated by an increase in the mass density of the grown films up to 2.8 g/cm(3); the density values achieved are substantially higher than those obtained from conventional magnetron sputtering methods.

  • 4. Aikio, A T
    et al.
    Blomberg, Lars
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Yamauchi, M
    On the origin of the high-altitude electric field fluctuations in the auroral zone1996Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 101, nr A12, s. 27157-27170Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Intense fluctuations in the electric field at high altitudes in the auroral zone are frequently measured by the Viking satellite. We have made an analysis of the origin of electric and magnetic fluctuations in the frequency range of 0.1 - 1 Hz by assuming four different sources for the signals: (I) spatial structures, (2) spatial structures with a parallel potential drop below the satellite, (3) traveling; shear Alfven waves, and (4) interfering shear Alfven waves. We will shaw that these different sources of the signals may produce similar amplitude ratios and phase differences between the perpendicular electric and magnetic fields. Since the different sources have different frequency dependencies, this can be used as an additional test if the signals are broadband. In other cases, additional information is needed, for example, satellite particle measurements or ground; magnetic measurements. The ideas presented in the theory were tested for one Viking eveningside pass over Scandinavia, where ground-based magnetometer and EISCAT radar measurements were available. The magnetic conditions were active during this pass and several interfering shear Alfven waves were found. Also, a spatial structure with a parallel potential drop below the satellite was identified. The magnitude of the 10-km-wide potential drop was at least 2 kV and the upward field-aligned current 26 mu A m(-2) (value mapped to the ionospheric level). The held-aligned conductance was estimated as 1.3 - 2.2x10(-8) S m(-2).

  • 5.
    Alaniz Flores, Monica
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Experiment Control Electronics for Spinning Quad Ionospheric Deployer SQUID2011Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The Spinning QUad Ionospheric Deployer (SQUID) is a soundingcrocket experiment developed to test and verify a novel mechanism to deploy wire booms. The SQUID consists of the Rocket Mounted Unit (RMU) and the Free Flying Unit (FFU), the former is attached to the rocket and the latter is ejected. The FFU carries the electronics box (eBox) that controls the system and the boom deployment system known as SCALE. The FFU needs to be independent when has been ejected from the rocket. This thesis work covers the design and manufacture of the SQUID electronics system to control the functionality of the experiment. The control is implemented in a Field Programmable Gate Array (FPGA) using the VHDL language. The integration, testing and validation of software and hardware also is presented here. The SQUID experiment was launched onboard the REXUS-10 rocket from ESRANGE the 23rd February 2011.

  • 6.
    Alaniz, Monica
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Belyayev, Serhiy
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Bergman, David
    Casselbrant, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Honeth, Mark
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Huang, Jiangwei
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Ivchenko, Nickolay
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Laukkanen, Mikko
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Michelsen, Jacob
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Pronenko, Vira
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Paulson, Malin
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Schlick, Georg
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Tibert, Gunnar
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Valle, Mario
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    The SQUID sounding rocket experiment2011Ingår i: Proceedings of the 20th ESA Symposium on European Rocket and Balloon Programmes and Related Research, European Space Agency, 2011, s. 159-166Konferensbidrag (Refereegranskat)
    Abstract [en]

    The objective of the SQUID project is to develop and in flight verify a miniature version of a wire boom deployment mechanism to be used for electric field measurements in the ionosphere. In February 2011 a small ejectable payload, built by a team of students from The Royal Institute of Technology (KTH), was launched from Esrange on-board the REXUS-10 sounding rocket. The payload separated from the rocket, deployed and retracted the wire booms, landed with a parachute and was subsequently recovered. Here the design of the experiment and post fight analysis are presented.

  • 7.
    Alday, Juan
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Roth, Lorenz
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ivchenko, Nickolay
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Retherford, Kurt D.
    Becker, Tracy M.
    Molyneux, Philippa
    Saur, Joachim
    New constraints on Ganymede's hydrogen corona: Analysis of Lyman-alpha emissions observed by HST/STIS between 1998 and 20142017Ingår i: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 148, s. 35-44Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Far-ultraviolet observations of Ganymede's atmospheric emissions were obtained with the Space Telescope Imaging Spectrograph (STIS) onboard of the Hubble Space Telescope (HST) on several occasions between 1998 and 2014. We analyze the Lyman-alpha emission from four HST campaigns in order to constrain the abundance and variation of atomic hydrogen in Ganymede's atmosphere. We apply a forward model that estimates surface reflection and resonant scattering in an escaping corona of the solar Lyman-alpha flux, taking into account the effects of the hydrogen in the interplanetary medium. The atmospheric emissions around Ganymede's disk derived for the observations taken between 1998 and 2011 are consistent with a hydrogen corona in the density range of (5-8) x 10(3) cm(-3) at the surface. The hydrogen density appears to be generally stable in that period. In 2014, Ganymede's corona brightness is approximately 3 times lower during two observations of Ganymede's trailing hemisphere and hardly detectable at all during two observations of the leading hemisphere. We also investigate extinction of Ganymede's coronal emissions in the Earth's upper atmosphere or geocorona. For small Doppler shifts, resonant scattering in the geocorona of the moon corona emissions can effectively reduce the brightness observed by HST. In the case of the 2014 leading hemisphere observations, an estimated extinction of 80% might explain the non-detection of Ganymede's hydrogen corona. Geocoronal extinction might also explain a previously detected hemispheric difference from Callisto's hydrogen corona.

  • 8.
    Alday Parejo, Juan
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ganymede's hydrogen corona and FUV albedo from HST/STIS images2017Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Ganymedes är största månen i vårt Solsystem, och är ett föremål för intensiv vetenskaplig forskning under senaste decenier. Sedan 1998, STIS (Space Telescope Imaging Spectrograph) instrumentet ombord rymdteleskopet Hubble (HST) har observerat Ganymedes i UV ljus med våglängder mellan 1150 Å och 1730 Å i fem olika omgångar. Bilder av månen har tagits när Ganymedes var i olika positioner i sin bana. Detta gör det möjligt att jämföra båda hemisfärer av månen, och att undersöka eventuell tidsvariation. I denna rapport HST/STIS observationer av Ganymedes analyseras med målsättningen att undersöka månens exosfär bestående av atomär syre samt månens albedo i FUV våglänger. Väteexosfären, också kallad korona, förväntas sprida Lyman- ljuset vid 1216 Å, som kan observeras av STIS. Observationer i denna våglängd analyseras och en modell är framtagen för olika källor som bidrar vid denna våglängd. En uppskattning görs också av en eventuell absorption av Ganymedes emissioner i Jordens övre atmosfär, som kan uppgå till 85%. Jämförelse av modellen med bilder från HST/STIS tyder på att Ganymedes har en väteexosfär med ytdensiteten av (2-8) 103 cm􀀀3. Under Hubble kampanj 13328 har däremot betydligt lägre antal väteatomer detekterats, som kan bero på skillnader i magnetosfäriska omgivningen av månen jämfört med tidigare observationer. FUV albedo av månens yta har undersökts genom jämförelser av reflektansen vid olika våglängder, inklusive eventuella skillnader mellan olika hemisfärer. Vi finner att bakre (i förhållande till rörelsen i banan, som månen är låst i) hemisfären är ljusare än främre hemisfären för < 1600 Å. För längre våglängder, > 2000 Å, har motsatta resultat rapporterats tidigare, där främre hemisfären var ljusare. Detta tyder på att Ganymedes ytreflektans har en spektral inversion mellan 1600-2000 Å. Vi noterar även att ytreflektansen ökar med kortare våglängd för < 1400 Å, som kan bero på att ytans växelverkan med rymdpartiklar.

  • 9. Alexeev, I. I.
    et al.
    Belenkaya, E. S.
    Bobrovnikov, S. Yu.
    Kalegaev, V. V.
    Cumnock, Judy
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Blomberg, Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Magnetopause mapping to the ionosphere for northward IMF2007Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 25, nr 12, s. 2615-2625Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the topological structure of the magnetosphere for northward IMF. Using a magnetospheric magnetic field model we study the high-latitude response to prolonged periods of northward IMF. For forced solar wind conditions we investigate the location of the polar cap region, the polar cap potential drop, and the field-aligned acceleration potentials, depending on the solar wind pressure and IMF B-y and B-x changes. The open field line bundles, which connect the Earth's polar ionosphere with interplanetary space, are calculated. The locations of the magnetospheric plasma domains relative to the polar ionosphere are studied. The specific features of the open field line regions arising when IMF is northward are demonstrated. The coefficients of attenuation of the solar wind magnetic and electric fields which penetrate into the magnetosphere are determined.

  • 10. Alfier, A.
    et al.
    Annibaldi, Silvia Valeria
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. Euratom/ENEA Association, Italy.
    Bonomo, F.
    Buratti, P.
    Franz, P.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marrelli, L.
    Pasqualotto, R.
    Piovesan, P.
    Spizzo, G.
    Energy confinement in high current RFX-mod plasmas2007Ingår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, nr 1, s. 415-418Konferensbidrag (Refereegranskat)
  • 11. Alfsen, K. H.
    et al.
    Bonifazi, C.
    Pedersen, A.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Electric field and plasma observations near the magnetopause and bow shock during a rapid compression.1984Ingår i: Achievements of the International Magnetospheric Study (IMS), s. 99-104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A fast compressional motion of the magnetopause resulting from the interaction of an interplanetary shock and the Earth's magnetosphere is discussed. The ISEE-1 and 2 satellites were in the frontside magnetosphere before the shock. A magnetosonic wave front, the magnetopause, and the bow shock passed them in a very short time. By a combination of electric and magnetic field data it is possible to determine the magnetosonic and the magnetopause velocity. -from STAR, 23(14), 1985

  • 12. ALFSEN, KH
    et al.
    BONIFAZI, C
    PEDERSEN, A
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    INTERACTION BETWEEN AN INTERPLANETARY SHOCK AND THE EARTHS MAGNETOSPHERE ON AUGUST 27, 1978 - ISEE-1 ELECTRIC-FIELD AND ISEE-2 PLASMA OBSERVATIONS1984Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol. 89, nr NA10, s. 8863-8871Artikel i tidskrift (Refereegranskat)
  • 13. ALFVEN, H
    et al.
    AXNAS, I
    BRENNING, N
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    VOYAGER SATURNIAN RING MEASUREMENTS AND THE EARLY HISTORY OF THE SOLAR-SYSTEM1986Ingår i: PLANETARY AND SPACE SCIENCE, ISSN 0032-0633, Vol. 34, nr 2, s. 145-154Artikel i tidskrift (Refereegranskat)
  • 14. Alm, L.
    et al.
    Argall, M. R.
    Torbert, R. B.
    Farrugia, C. J.
    Burch, J. L.
    Ergun, R. E.
    Russell, C. T.
    Strangeway, R. J.
    Khotyaintsev, Y. V.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Giles, B. L.
    Shuster, J.
    EDR signatures observed by MMS in the 16 October event presented in a 2-D parametric space2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 3, s. 3262-3276Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a method for mapping the position of satellites relative to the X line using the measured B-L and B-N components of the magnetic field and apply it to the Magnetospheric multiscale (MMS) encounter with the electron diffusion region (EDR) which occurred on 13:07 UT on 16 October 2015. Mapping the data to our parametric space succeeds in capturing many of the signatures associated with magnetic reconnection and the electron diffusion region. This offers a method for determining where in the reconnection region the satellites were located. In addition, parametric mapping can also be used to present data from numerical simulations. This facilitates comparing data from simulations with data from in situ observations as one can avoid the complicated process using boundary motion analysis to determine the geometry of the reconnection region. In parametric space we can identify the EDR based on the collocation of several reconnection signatures, such as electron nongyrotropy, electron demagnetization, parallel electric fields, and energy dissipation. The EDR extends 2-3km in the normal direction and in excess of 20km in the tangential direction. It is clear that the EDR occurs on the magnetospheric side of the topological X line, which is expected in asymmetric reconnection. Furthermore, we can observe a north-south asymmetry, where the EDR occurs north of the peak in out-of-plane current, which may be due to the small but finite guide field.

  • 15.
    Alm, Love
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Cluster investigations of the extent and altitude distribution of the auroral density cavity2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The auroral density cavity constitutes the boundary between the cold, dense ionospheric plasma and the hot, tenuous plasma sheet plasma. The auroral density cavity is characterized by low electron density and particle populations modified by parallel electric fields. Inside the cavity the electron densities can be as much as a factor 100-1000 lower than same altitude outside the cavity.The Cluster mission's wide range of instruments, long lifetime and ability to make multi-spacecraft observations has been very successful. Over its 15 year lifespan, the Cluster satellites have gathered data on auroral density cavities over a large altitude range and throughout an entire solar cycle, providing a vast data material.The extent of the density cavity and acceleration region is large compared to the typical altitude coverage of a satellite crossing the cavity. This makes it difficult to produce a comprehensive altitude/density profile from a single crossing. In order to facilitate comparisons between data from different events, we introduce a new reference frame, pseudo altitude. Pseudo altitude describes the satellites' position relative to the acceleration region, as opposed to relative to the Earth. This pseudo altitude is constructed by dividing the parallel potential drop below the satellite with the total parallel potential drop. A pseudo altitude of 0 corresponds to the bottom of the acceleration region and a pseudo altitude of 1 to the top of the acceleration region. As expected, the pseudo altitude increases with altitude. The electron density exhibits an anti-correlation with the pseudo altitude, the density becomes lower close to the upper edge of the acceleration region. The upper edge of the acceleration region is located between a geocentric altitude of 4.375 and 5.625 RE. Above the upper edge of the acceleration region, the electron density continues to decrease for the entire range of the study, 3.0-6.5 RE. This is much further than the geocentric altitude range of 2-3 RE which is suggested by previous models. We can conclude that the auroral density cavity is not confined by the auroral acceleration region, as suggested by previous models, and may extend all the way to the plasma sheet.

  • 16.
    Alm, Love
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Li, Bin
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Statistical altitude distribution of the auroral density cavity2015Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, nr 2, s. 996-1006Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The statistical altitude distribution of auroral density cavities located between 3.0 and 6.5 R-E is investigated using in situ observations from flux tubes exhibiting auroral acceleration. The locations of the observations are described using a pseudo altitude derived from the distribution of the parallel potential drop above and below the satellite. The upper edge of the auroral acceleration region is observed between 4.375 and 5.625 R-E. Above 6.125 R-E, none of the events exhibit precipitating inverted V electrons, though the upward ion beam can be observed. This indicates that the satellites are located inside the same flux tube as, but above, the auroral acceleration region. The electron density decreases as we move higher into the acceleration region. The spacecraft potential continues to decrease once above the acceleration region, indicating that the density cavity extends above the acceleration region. From 3.0 to 4.375 R-E the pseudo altitude increases by 0.20 per R-E, consistent with a distributed parallel electric field. Between 4.375 and 5.625 R-E the pseudo altitude increases weakly, by 0.01 per R-E, due to an increasing number of events per altitude bin, which are occurring above the acceleration region. Above 5.625 R-E the pseudo altitude increases by 0.28 per R-E, due to a rapid increase in the number of events per altitude bin occurring above the acceleration region, indicating that the remaining parallel potential drop is concentrated in a narrow region at the upper edge of the acceleration region, rather than in a distributed parallel electric field.

  • 17.
    Alm, Love
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Electron density and parallel electric field distribution of the auroral density cavity2015Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 120, nr 11, s. 9428-9441Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present an event study in which Cluster satellites C1 and C3 encounters the flux tube of a stable auroral arc in the pre-midnight sector. C1 observes the mid cavity, while C3 enters the flux tube of the auroral arc at an altitude which is below the acceleration region, before crossing into the top half of the acceleration region. This allows us to study the boundary between the ionosphere and the density cavity, as well as large portion of the upper density cavity. The position of the two satellites, in relation to the acceleration region, is described using a pseudo altitude derived from the distribution of the parallel potential drop above and below the satellites.The electron density exhibits an anti-correlation with the pseudo altitude, indicating that the lowest electron densities are found near the top of the density cavity. Over the entire pseudo altitude range, the electron density distribution is similar to a planar sheath, formed out of a plasma sheet dominated electron distribution, in response to the parallel electric field of the acceleration region. This indicates that the parallel electric fields on the ionosphere-cavity boundary, as well as the mid cavity parallel electric fields, are part of one unified structure rather than two discrete entities.The results highlight the strong connection between the auroral density cavity and auroral acceleration as well as the necessity of studying them in a unified fashion.

  • 18.
    Alm, Love
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran T.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    In situ observations of density cavities extending above the auroral acceleration region2014Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, nr 7, s. 5286-5294Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The uppermost part of a stable potential structure in the auroral acceleration region was studied using simultaneous observations of Cluster satellites C1 and C3. Both satellites observe a monotonically decreasing electron density as they ascend through the auroral acceleration region. As C1 exits the top of the auroral acceleration region, the electron densities continue to decrease, and the minimum electron density is reached 14 km above the upper edge of the auroral acceleration region. The electron density does not return to noncavity values until the spacecraft exits the potential structure's flux tube. The data indicate that the auroral density cavity is not confined by the potential structure and may extend above the auroral acceleration region.

  • 19.
    Alm, Love
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran T.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Masson, A.
    Pseudo altitude: A new perspective on the auroral density cavity2013Ingår i: Journal of Geophysical Research A: Space Physics, ISSN 2169-9380, Vol. 118, nr 7, s. 4341-4351Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Studying the density distribution inside the auroral density cavity is complicated by the difficulties in achieving simultaneous measurements within the same flux tube at different altitudes. Comparisons between different events are complicated by variations in both the location of the density cavity and the location of the related potential structure. Describing the spacecraft's location inside the density cavity relative to the potential structure instead of the Earth offers a more practical and consistent frame of reference, a pseudo altitude. The pseudo altitude is determined by comparing the potential drop above the spacecraft, as determined from the characteristic energy of the downward electrons, with the parallel potential drop below the spacecraft, determined from the characteristic energy of the upward ions. A pseudo altitude of 0 corresponds to the bottom of the potential structure and a pseudo altitude of 1 to the top of the structure. Seven events from 2008 were selected, each of which corresponds to a Cluster crossing of a mainly quasi-static potential structure. All of the events exhibit a consistent anticorrelation between the pseudo altitude and the electron density. No upper limit of the density cavity can be observed, while all cavities have a lower limit above a pseudo altitude of 0.33. These observations show that the auroral density cavity is predominately concentrated to the upper parts of the quasi-static potential structure.

  • 20.
    Andersson, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Currrent disruptions in a magnetised plasma stream1997Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 21. Andre, M.
    et al.
    Li, W.
    Toledo-Redondo, S.
    Khotyaintsev, Yu. V.
    Vaivads, A.
    Graham, D. B.
    Norgren, C.
    Burch, J.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ergun, R.
    Torbert, R.
    Magnes, W.
    Russell, C. T.
    Giles, B.
    Moore, T. E.
    Chandler, M. O.
    Pollock, C.
    Young, D. T.
    Avanov, L. A.
    Dorelli, J. C.
    Gershman, D. J.
    Paterson, W. R.
    Lavraud, B.
    Saito, Y.
    Magnetic reconnection and modification of the Hall physics due to cold ions at the magnetopause2016Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 13, s. 6705-6712Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohm's law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the vxB drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.

  • 22. Andre, M
    et al.
    Norqvist, P
    Andersson, L
    Eliasson, L
    Eriksson, A I
    Blomberg, Lars
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Erlandson, R E
    Waldemark, J
    Ion energization mechanisms at 1700 km in the auroral region1998Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, ISSN 0148-0227, Vol. 103, nr A3, s. 4199-4222Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Observations obtained by the Freja satellite at altitudes around 1700 km in the high-latitude magnetosphere are used to study ion energization perpendicular to the geomagnetic field. Investigations of ions, electrons, plasma densities, electric and magnetic wave fields, and field-aligned currents are used to study O+ heating mechanisms. Three ion heating events are studied in detail, and 20 events are used in a detailed statistical study. More than 200 events are classified as belonging to one of four major types of ion heating and are ordered as a function of magnetic local time. The most common types of ion heating are associated with broadband low-frequency electric wave fields occurring at all local times. These waves cover frequencies from below one up to several hundred hertz and correspond to the most intense O+ energization. Heating by these waves at frequencies of the order of the O+ gyrofrequency at 25 Hz seems to be the important energization mechanism, causing O+ ion mean energies up to hundreds of eV. The broadband waves are associated with Alfven waves with frequencies up to at least a few hertz and with field-aligned currents. Other types of O+ energization events are less common. During these events the ions are heated by waves near the lower hybrid frequency or near half the proton gyrofrequency. These waves are generated by auroral electrons or in a few cases by precipitating ions.

  • 23. Andriopoulou, M.
    et al.
    Nakamura, R.
    Torkar, K.
    Baumjohann, W.
    Torbert, R. B.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Khotyaintsev, Y. V.
    Dorelli, J.
    Burch, J. L.
    Russell, C. T.
    Study of the spacecraft potential under active control and plasma density estimates during the MMS commissioning phase2016Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, nr 10, s. 4858-4864Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Each spacecraft of the recently launched magnetospheric multiscale MMS mission is equipped with Active Spacecraft Potential Control (ASPOC) instruments, which control the spacecraft potential in order to reduce spacecraft charging effects. ASPOC typically reduces the spacecraft potential to a few volts. On several occasions during the commissioning phase of the mission, the ASPOC instruments were operating only on one spacecraft at a time. Taking advantage of such intervals, we derive photoelectron curves and also perform reconstructions of the uncontrolled spacecraft potential for the spacecraft with active control and estimate the electron plasma density during those periods. We also establish the criteria under which our methods can be applied.

  • 24. André, Mats
    et al.
    Odelstad, Elias
    Graham, Daniel
    Eriksson, Anders
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Stenberg Wieser, Gabriella
    Vigren, Erik
    Norgren, Cecilia
    Johansson, Fredrik
    Henri, Pierre
    Rubin, M.
    Richter, Ingo
    Lower Hybrid Waves at Comet 67P/Churyumov-Gerasimenko2017Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the generation of waves in the lower hybrid frequency range by density gradients in the near plasma environment of comet 67P/Churyumov–Gerasimenko. When the plasma is dominated by water ions from the comet, a situation with magnetized electrons and unmagnetized ions is favourable for the generation of lower hybrid waves. These waves can transfer energy between ions and electrons and reshape the plasma environment of the comet. We consider cometocentric distances out to a few hundred km. We find that when the electron motion is not significantly interrupted by collisions with neutrals, large average gradients within tens of km of the comet, as well as often observed local large density gradients at larger distances, are often likely to be favourable for the generation of lower hybrid waves. Overall, we find that waves in the lower hybrid frequency range are likely to be common in the near plasma environment.

  • 25. Annibaldi, S. V.
    et al.
    Ivlev, A. V.
    Konopka, U.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Thomas, H. M.
    Morfill, G. E.
    Lipaev, A. M.
    Molotkov, V. I.
    Petrov, O. F.
    Fortov, V. E.
    Dust-acoustic dispersion relation in three-dimensional complex plasmas under microgravity2007Ingår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A series of dedicated experiments with the Plasma Kristal Experiment ( PKE)-Nefedov ( Nefedov et al 2003 New J. Phys. 5 33) set-up were performed on board the International Space Station to measure the dispersion relation ( DR) for the longitudinal dust-acoustic ( DA) waves in quasi-isotropic three-dimensional ( 3D) complex plasmas. The waves were excited by applying ac electric modulation of variable frequency to the radio frequency ( rf) electrodes. The amplitude of excitation was varied with frequency to ensure a 'sufficiently linear' regime of the dust density perturbations. The DR was obtained by measuring the induced density perturbations, revealing fairly good agreement with a simple multispecies theory of DA waves.

  • 26.
    Annibaldi, Silvia Valeria
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Bonomo, F.
    Pasqualotto, R.
    Spizzo, G.
    Alfier, A.
    Buratti, P.
    Piovesan, P.
    Terranova, D.
    Strong transport reduction in the helical core of the reversed-field pinch2007Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 14, nr 11, s. 112515-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An explanation of the strong heating observed in the core of a reversed-field pinch in the quasi-single-helicity state is presented. A magnetic island is formed, in which the heat transport coefficient is much smaller than in the surrounding chaotic sea, because of the formation of well defined magnetic surfaces. The values of the thermal conductivity obtained with the M1TEV [F. Porcelli , Phys. Rev. Lett 82, 1458 (1999)] two-dimensional transport code are in very good agreement with the estimates of the ion diffusion coefficient inside the island, given by a Hamiltonian guiding center code. Moreover, the values of thermal conductivity are in the tokamak range, and are consistent with the peak temperatures measured in the Reversed Field eXperiment [P. Sonato , Fusion Eng. Des. 66-68, 161 (2003)] at Consorzio RFX, Padova, Italy. The effect of the island width and the different powers deposited inside the island on the final temperature peak are also investigated.

  • 27.
    Annibaldi, Silvia Valeria
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. Associazione EURATOM-ENEA, Italy .
    Zonca, F.
    Buratti, P.
    Excitation of beta-induced Alfvén eigenmodes in the presence of a magnetic island2007Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 49, nr 4, s. 475-483Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Observation of magnetic activity in several discharges in the Frascati Tokamak Upgrade has revealed high-frequency oscillations that accompany the development of large magnetic islands in ohmic plasmas. The frequency of these oscillations is one order of magnitude above the typical island rotation frequency and one order of magnitude below the toroidicity-induced gap of the shear-Alfvén continuum. By writing a precise dispersion relation, we interpret these modes as beta-induced Alfvén eigenmodes, i.e. Alfvén eigenmodes located in the low frequency gap which is caused by finite compressibility.

  • 28.
    Appelgren, Patrik
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Experiments with and modelling of explosively driven mangetic flux compression generators2008Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis presents work performed on explosively driven magnetic flux compression generators. This kind of devices converts the chemically stored energy in a high explosive into electromagnetic energy in the form of a powerful current pulse. The high energy density of the high explosives makes flux compression generators attractive as compact power sources. In order to study these devices a generator was designed at FOI in the mid-90ies. Two generators remained unused and became available for this licentiate work.

    The thesis reports experiments with, and simulations of, the operation of the two remaining generators. The aim was to fully understand the performance of the generator design and be able to accurately simulate its behaviour. The generators were improved and fitted with various types of diagnostics to monitor the generator operation.

    Two experiments were performed of which the first generator was operated well below its current capability limits while the second was stressed far above its limits. Since the generator generates a rapidly increasing current, a current measurement is the most important diagnostic revealing the current amplification of the generator and its overall performance. Further it is important to measure the timing of various events in the generator. With a common time reference it is possible to combine data from different probes and extract interesting information which cannot be directly obtained with a single measurement.

    Two types of numerical simulations have been performed: Hydrodynamic simulations of the high explosive interaction with the armature were used to verify the measured armature dynamics. A zero-dimensional code was used to perform circuit simulations of the generator. The model takes into account the inductance reduction due to the compression of the generator as well as the change in conductivity due to heating of the conductors in the generators.

  • 29.
    Appelgren, Patrik
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Gigawatt pulsed power technologies and applications2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 30.
    Appelgren, Patrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. Swedish Defence Research Agency, Sweden .
    Andreasson, S.
    Hurtig, T.
    Larsson, A.
    Nyholm, S. E.
    Modelling of a small helical magnetic flux compression generator2007Ingår i: PPPS-2007 - Pulsed Power Plasma Science 2007, 2007, s. 1155-1158Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 31.
    Appelgren, Patrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. wedish Defence Research Agency, Sweden.
    Bjarnholt, G.
    Elfsberg, M.
    Hurtig, T.
    Larsson, Anders
    Nyholm, S. E.
    Small helical magnetic flux compression generators: Experiments and analysis2007Ingår i: PPPS-2007 - Pulsed Power Plasma Science 2007, IEEE , 2007, s. 1151-1154Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 32.
    Appelgren, Patrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Brenning, Nils
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Hurtig, Tomas
    Larsson, Anders
    Novac, Bucur
    Nyholm, Sten E.
    Modeling of a small helical magnetic flux compression generator2008Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 36, nr 5, s. 2662-2672Artikel i tidskrift (Refereegranskat)
    Abstract [en]

     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.

  • 33.
    Appelgren, Patrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Brenning, Nils
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Nyholm, Sten E.
    Small helical magnetic flux compression generators: experiments and analysis2008Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 36, nr 5, s. 2673-2683Artikel i tidskrift (Refereegranskat)
    Abstract [en]

     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.

  • 34.
    Appelgren, Patrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Carlsson, Torgny E.
    Helte, Andreas
    Hurtig, Tomas
    Larsson, Anders
    Lundberg, Patrik
    Skoglund, Melker
    Westerling, Lars
    Interaction between solid copper jets and powerful electrical current pulses2011Ingår i: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 78, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 35.
    Appelgren, Patrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. Swedish Defence Research Agency (FOI), Sweden.
    Hurtig, T.
    Larsson, A.
    Skoglund, M.
    Parametric studies of an electrohydrodynamic plasma actuator for boundary layer flow control2009Ingår i: PPC '09. IEEE Pulsed Power Conference, 2009, IEEE , 2009, s. 1069-1074Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 36.
    Appelgren, Patrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Larsson, Anders
    Nyholm, Sten E.
    Numerical simulations of flux compression generator systems2007Ingår i: Proceedings of the 20th IET Pulsed Power Symposium, 2007, s. 123-127Konferensbidrag (Övrigt vetenskapligt)
  • 37.
    Appelgren, Patrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Skoglund, Melker
    Lundberg, Patrik
    Westerling, Lars
    Larsson, Anders
    Hurtig, Tomas
    Disruption mechanisms in electrified solid copper jets2011Ingår i: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 78, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Interaction between a solid copper jet and an electric current pulse is a complex process that has been experimentally studied by letting a jet created by a shaped charge device pass through an electrode configuration consisting of two aluminum plates with a separation distance of 150 mm. When the jet bridged the electrodes, which are connected to a charged pulsed power supply, current pulses with amplitude up to 250 kA were passed through the jet. By using flash X-ray diagnostics, the disruption of the electrified jets could be studied. In this paper, the disruption of the electrified jets is discussed and compared with disruption phenomena observed in electrically exploded metal rods in a static setup. Necks are naturally formed along a stretching jet, and in the experiments with current interaction these necks explode electrically. In the static experiments, the metal rods have small notches distributed along the rod to resemble the necks of the jet. When two neighboring necks or notches explode, the shock of the explosion compresses the intermediate jet or rod segment axially and the material is forced out radially. The disruption phenomena in the jet and rod experiments are similar with rapid expansion of the metal at explosion and at comparable velocities.

  • 38.
    Appelgren, Patrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Skoglund, Melker
    Lundberg, Patrik
    Westerling, Lars
    Larsson, Anders
    Hurtig, Tomas
    Experimental Study of Electromagnetic Effects on Solid Copper Jets2010Ingår i: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 77, nr 1, s. 011010-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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]

  • 39.
    Archer, Jenny
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Dynamics and characteristics of blackaurora as observed by high resolution ground-based imagers and radar2009Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 40.
    Archer, Jenny
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Dahlgren, Hanna
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ivchenko, Nickolay
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Lanchester, Betty
    School of Physics and Astronomy, University of Southampton, UK.
    Marklund, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Dynamics and characteristics of black aurora as observed by high resolution ground-based imagers and radar2011Ingår i: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 32, nr 11, s. 2973-2985Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-resolution, multi-spectral data from the ground-based low-light auroral imager ASK (Auroral Structure and Kinetics) are used to characterize the fine structure of black aurora. Sixteen events comprising sheared and unsheared black arcs, as well as black patches and rings, constitute the analysed dataset. Simultaneous measurements of emissions caused by high- and low-energy precipitation make it possible to relate the characteristics of different black structures to the energy of the precipitating electrons. The reductions of high-energy particles versus low-energy particles in the black regions compared to the diffuse background are investigated for the different forms of black aurora. Two separate mechanisms have been suggested to cause black aurora. The larger reduction of high-energy precipitation within the fine-scale black structures discussed here favours a magnetospheric mechanism that blocks high-energy electrons from being scattered into the loss cone. European Incoherent SCATter radar (EISCAT) electron density profiles are available for one of the nights, and are compared to the optical measurements.

  • 41. Arriaga, I.
    et al.
    Ivchenko, Nickolay
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Olsson, Göran F
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Alaniz, M.
    Belyayev, Serhiy
    Marusenkov, A.
    SMILE - A miniaturized fluxgate magnetometer2007Ingår i: 18TH ESA SYMPOSIUM ON EUROPEAN ROCKET AND BALLOON PROGRAMMES AND RELATED RESEARCH, 2007, Vol. 647, s. 569-572Konferensbidrag (Refereegranskat)
    Abstract [en]

    The SMILE (Small Magnetometer in Low-mass Experiment) instrument is a miniaturized digital fluxgate magnetometer that combines a miniature triaxial sensor with volume compensation with digital data processing implemented in a single FPGA. This report presents first results of numerical simulations of the sensor. We also discuss the digital solutions used in SMILE.

  • 42.
    Arriaga Trejo, Israel Alejandro
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Numerical Modeling and Evaluation of the Small Magnetometer in Low-Mass Experiment (SMILE)2007Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Fluxgate magnetometers have played a major role in space missions due to their stability, range of operation and low energy consumption. Their principle of operation is relatively simple and easy to implement, a nonlinear magnetic material is driven into saturation by an alternating excitation current inducing a voltage that is modulated by the external field intended to be measured. With the increasing use of nanosatellites the instruments and payload on board have been reduced considerably in size and weight. The Small Magnetometer in Low-Mass Experiment, SMILE, is a miniaturised triaxial fluxgate magnetometer with volume compensation incorporating efficient signal processing algorithms within a field programmable gate array (FPGA). SMILE was designed in collaboration between the Lviv Centre of Institute of Space Research in Ukraine where the sensor was developed and the Royal Institute of Technology (KTH) in Stockholm, Sweden where the electronics used to operate the instrument were designed and programmed. The characteristic dimensions of the SMILE magnetometer and geometry of its parts make impractical the task to find an analytical expression for the voltages induced in the pick-up coils to evaluate its performance. In this report, the results of numerical simulations of the SMILE magnetometer using a commercial finite element method (FEM) based software are presented. The results obtained are compared with the experimental data available and will serve as a first step to understand the behaviour of the nonlinear components that could lead to improvements of its design in a future.

  • 43. Ashrafi, M.
    et al.
    Lanchester, B. S.
    Lummerzheim, D.
    Ivchenko, Nickolay V.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Jokiaho, O.
    Modelling of N(2)1P emission rates in aurora using various cross sections for excitation2009Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 27, nr 6, s. 2545-2553Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Measurements of N(2)1P auroral emissions from the (4,1) and (5,2) bands have been made at high temporal and spatial resolution in the region of the magnetic zenith. The instrument used was the auroral imager ASK, situated at Ramfjordmoen, Norway (69.6 N, 19.2 E) on 22 October 2006. Measurements from the European Incoherent Scatter Radar (EISCAT) have been combined with the optical measurements, and incorporated into an ionospheric model to obtain height profiles of electron density and emission rates of the N(2)1P bands. The radar data provide essential verification that the energy flux used in the model is correct. One of the most important inputs to the model is the cross section for excitation to the B-3 Pi(g) electronic state, as well as the cross sections to higher states from which cascading into the B state occurs. The balance equations for production and loss of the populations of all levels in each state are solved in order to find the cascade contributions. Several sets of cross sections have been considered, and selected cross sections have been used to construct "emission" cross sections for the observed bands. The resulting brightnesses are compared with those measured by ASK. The importance of specific contributions from cascading is found, with more than 50% of the total brightness resulting from cascading. The cross sections used are found to produce a range of brightnesses well within the uncertainty of both the modelled and measured values.

  • 44.
    Axnäs, Ingvar
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Brenning, Nils
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Experiments on the Magnetic Field and Neutral Density Limits on CIV Interaction1988Rapport (Övrigt vetenskapligt)
  • 45.
    Backrud, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Evaluation of the SPEDE instrument on SMART-12007Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 46. Bahnsen, A.
    et al.
    Ungstrup, E.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Fahleson, Ulf
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Olesen, J.K.
    Primdahl, F.
    Spangslev, F.
    Pedersen, A.
    Electrostatic Waves Observed in an Unstable Polar Cap Ionosphere1978Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol. 83, s. 5191-5197Artikel i tidskrift (Refereegranskat)
  • 47. Bahnsen, Axel
    et al.
    PEDERSEN, BM
    JESPERSEN, M
    UNGSTRUP, E
    ELIASSON, L
    MURPHREE, JS
    ELPHINSTONE, RD
    Blomberg, Lars
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    HOLMGREN, G
    ZANETTI, LJ
    Viking observations at the source region of auroral kilometric radiation1989Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, ISSN 0148-0227, Vol. 94, nr A6, s. 6643-&Artikel i tidskrift (Refereegranskat)
  • 48. Bale, S. D.
    et al.
    Maksimovic, M.
    Vaivads, A.
    Andre, M.
    Blomberg, Lars
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Antenna design considerations for the Radio and Plasma Wave (RPW) experiment on solar orbiter2006Ingår i: European Space Agency, (Special Publication) ESA SP, Athens, 2006, nr SP-641Konferensbidrag (Refereegranskat)
    Abstract [en]

    Electric fields in the solar wind are very poorly studied; there have been no instruments dedicated to measuring solar wind electric fields and plasma waves at low frequencies. Here we discuss some of the important physics of LF electric fields, including dissipation of MHD turbulence, shock acceleration of particles, and solar wind magnetic reconnection. We then present some antenna sensor and instrument designs that will potentially satisfy the goal of measuring both DC/low frequency electric fields AND higher frequency radio and thermal noise emissions. We discuss trades between science goals and complexity of the designs.

  • 49. Balmer, G.
    et al.
    Berquand, A.
    Company-Vallet, E.
    Granberg, V.
    Grigore, V.
    Ivchenko, Nickolay
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Kevorkov, R.
    Lundkvist, E.
    Olentsenko, Georgi
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Pacheco-Labrador, J.
    Tibert, Gunnar
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Yuan, Yunxia
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    ISAAC: A REXUS STUDENT EXPERIMENT TO DEMONSTRATE AN EJECTION SYSTEM WITH PREDEFINED DIRECTION2015Ingår i: EUROPEAN ROCKET AND BALLOON: PROGRAMMES AND RELATED RESEARCH, 2015, s. 235-242Konferensbidrag (Refereegranskat)
    Abstract [en]

    ISAAC - Infrared Spectroscopy to Analyse the middle Atmosphere Composition was a student experiment launched from SSC's Esrange Space Centre, Sweden, on 29th May 2014, on board the sounding rocket REXUS 15 in the frame of the REXUS/BEXUS programme. The main focus of the experiment was to implement an ejection system for two large Free Falling Units (FFUs) (240 mm x 80 mm) to be ejected from a spinning rocket into a predefined direction. The system design relied on a spring-based ejection system. Sun and angular rate sensors were used to control and time the ejection. The flight data includes telemetry from the Rocket Mounted Unit (RMU), received and saved during flight, as well as video footage from the GoPro camera mounted inside the RMU and recovered after the flight. The FFUs' direction, speed and spin frequency as well as the rocket spin frequency were determined by analyzing the video footage. The FFU-Rocket-Sun angles were 64.3 degrees and 104.3 degrees, within the required margins of 90 degrees +/- 45 degrees. The FFU speeds were 3.98 m/s and 3.74 m/s, lower than the expected 5 +/- 1 m/s. The FFUs' spin frequencies were 1.38 Hz and 1.60 Hz, approximately half the rocket's spin frequency. The rocket spin rate slightly changed from 3.163 Hz before the ejection to 3.117 Hz after the ejection of the two FFUs. The angular rate, sun sensor data and temperature on the inside of the rocket module skin were also recorded. The experiment design and results of the data analysis are presented in this paper.

  • 50.
    Banon, Jean-Philippe
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Modelling of Dust Transport in Reverse Field Pinch Configuration2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The DDFTU code has been modified and updated to study the transport of dust in the reverse field pinch (RFP) EXTRAP-T2R. The DDFTU code solves the coupled equations of charging, heating and motion of a dust grain immersed in a plasma whose profiles are given. Updates of the code have been introduced to include (i) non-steady state heat balance and phase transitions models, (ii) realistic boundary conditions for dust-wall collisions, and (iii) a radius and temperature-dependent thermal radiation model, for which a dedicated code has been developed. The models for secondary electron emission (SEE), thermionic emission and magnetic dipole force have been refined as well, the sensitivity to SEE and thermal radiation modelling being highlighted. Similarly to limiter tokamak configuration, the ion drag is confirmed to be the main force driving the dust dynamics. However for RFP configurations, the strong contribution of the electric force is demonstrated. The latter plays an important role in the RFP edge plasma due to (i) the large value of the radial electric field and (ii) its sign which is opposite to typical tokamak edge electric fields. A comparison with available experimental data - dust collection in the mid-plane - has been carried out. For this purpose, the dust toroidal transport asymmetry has been evaluated numerically from the computation of the time dependent velocity distribution of an ensemble of many particles launched from the vessel wall. An empirical scaling law for the asymmetry has been found in the high dust inertia regime.

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