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  • 1.
    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.

  • 2.
    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.

  • 3.
    Blomberg, Lars G.
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Cumnock, J. A.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Eriksson, A. I.
    The martian plasma environment: Electric field and Langmuir probe diagnostics2003Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 31, nr 6, s. 1232-1236Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The plasma environment of Mars has been studied by a small handful of spacecraft. From the sparse observations that exist, one may conclude that the solar wind-Martian magnetosphere interaction is different in significant ways from the solar wind's interaction with Earth's magnetosphere. Mars offers an opportunity to make significant advances in our understanding of the fundamentals of the solar wind's interaction with cold celestial bodies, with suitable plasma instrumentation orbiting the planet. We briefly review what is known about Mars' plasma environment and address some scientific topics that can be studied by proper plasma instrumentation in Mars' vicinity, in particular the scientific potential of Langmuir probe measurements. Finally, we exemplify how the studies may contribute to an enhanced understanding not only of the plasma surrounding Mars, but also of the planet itself and its neutral atmosphere.

  • 4. Bratman, V. L.
    et al.
    Fedotov, A. E.
    Kalynov, Yu. K.
    Makhalov, Petr B.
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik. Russian Acad Sci, Russia.
    Osharin, I. V.
    Numerical Study of a Low-Voltage Gyrotron ("Gyrotrino") for DNP/NMR Spectroscopy2017Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 45, nr 4, s. 644-648Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Feasibility of a gyrotron for the dynamic nuclear polarization (DNP) purpose, integrated with nuclear magnetic resonance (NMR) spectrometer inside a single cryomagnet, is analyzed on the basis of numerical simulations. The necessary condition for DNP is matching of the gyrotrino and DNP frequencies. This imposes a strong restriction on the gyrotron operating voltage, which should be less than 2 kV. The most part of the uniform magnetic field region in the cryomagnet is occupied by a sample with NMR probe, so there is a very limited space for the gyrotron cavity. This dictates a number of peculiarities for the gyrotrino design, in particular, the diffraction power output from the cathode end of the cavity and collecting of a thin electron beam in a strong magnetic field. According to simulations, the gyrotrino operating at the fundamental cyclotron resonance with a voltage of 1.5 kV can provide an output power of 10-20 W at a frequency of 264 GHz, which is suitable for many NMR-DNP experiments.

  • 5.
    Brenning, Nils
    KTH, Tidigare Institutioner                               , Alfvénlaboratoriet.
    Interaction between a dust cloud and a magnetized plasma in relative motion2001Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 29, nr 2, s. 302-306Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The interaction between a dust cloud and a magnetized plasma is investigated by use of an idealized model where the dust particles have uniform size, a uniform density within the dust cloud, and start with the same velocity across the magnetic field in the plasma's rest frame. The interaction is found to be governed by a dimensionless parameter K which is a function of dust cloud, and ambient plasma, parameters. For K much smaller than unity, the interaction goes on for typically 1/(2 piK) gyro times, with the particles in the dust cloud performing gyro motions with decreasing radius, For K close to unity, the dust motion is stopped on the order of a dust particle gyro time, For the case K much greater than 1, the plasma in the flux tube through the dust cloud is dragged across the magnetic field over a distance of the order of Kr-d, where r(d) is the dust gyro radius, before the motion is stopped. Some expected effects for a more realistic dust cloud with density gradients, and containing dust with a spread in size, are discussed. The results have bearing on dusty plasma in space, e.g., models of the formation of spokes in Saturn's ring system.

  • 6.
    Elfsberg, Mattias
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Möller, Cecilia
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Hurtig, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Larsson, Anders
    Swedish Defence Research Agency (FOI) Defence & Security, Systems and Technology, Grindsjön Research Centre, Tumba, Sweden.
    Nyholm, Sten
    Swedish Defence Research Agency (FOI) Defence & Security, Systems and Technology, Grindsjön Research Centre, Tumba, Sweden.
    Experimental Studies of Anode and Cathode Materials in a Repetitive Driven Axial Vircator2008Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 36, s. 688-693Artikel i tidskrift (Refereegranskat)
    Abstract [en]

     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.

  • 7.
    Frassinetti, Lorenzo
    et al.
    Consorzio RFX.
    Gobbin, M
    Piovesan, P
    Marrelli, L
    Martin, P
    Franz, P
    Chapman, BE
    Craig, D.
    Sarff, J. S.
    Soft X-ray pulses in the reversed-field pinch2005Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 33, nr 2, s. 462-463Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Data obtained in the Madison Symmetric Torus reversed-field pinch with a soft X-ray diagnostic will be presented. They have been used to study transient transport events in this device. Fast thermal relaxation events are associated to bursts of magnetohydrodynamic fluctuations.

  • 8.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Electrodynamics of cosmical plasmas - some basic aspects of cosmological importance1990Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 18, s. 11-17Artikel i tidskrift (Refereegranskat)
  • 9.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Magnetosphere-Ionosphere Interactions-Near-Earth Manifestations of the Plasma Universe1986Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 14, s. 616-628Artikel i tidskrift (Refereegranskat)
  • 10.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Plasma physics from laboratory to cosmos - The life and achievements of Hannes Alfven1997Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 25, s. 409-414Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hannes Alfven, Lifetime Fellow of IEEE and 1970 Nobel Laureate for Physics, passed away on April 2, 1995 after a life of exceptional scientific achievement. His discoveries laid the foundations of major parts of modern plasma physics and its applications in areas as diverse as industrial processes, thermonuclear research, space physics, astrophysics, and cosmology. From a family background of high achievers and stimulating childhood experiences he went through an extremely rapid academic career, and his intense scientific activity lasted from his early twenties well into his eighties. His scientific work reveals a profound physical insight and an astounding intuition which allowed him to extract results of great importance and generality from specific problems. His most fundamental discoveries were those which opened a new field of physics, magnetohydrodynamics, and provided plasma physics with powerful new tools. His discovery of a new kind of waves, now called Alfven waves, was initially met with disbelief and accepted only years later. With the evolution of plasma physics, and especially space plasma physics, the significance of this discovery has grown to the extent that Alfven waves, and related terms such as Alfven velocity, Alfven number, etc., have become among the most frequently used terms in plasma physics. His introduction of the guiding center concept vastly simplified the analysis of charged particle motion in electric and magnetic fields and was the embryo from which grew the highly sophisticated adiabatic theory of particle motion. In addition to his most fundamental discoveries, Hannes Alfven made numerous important contributions to the physics of (what we now call) the magnetosphere, especially auroras and magnetic storms, as well as to solar and interplanetary physics, astrophysics, and cosmology. Often his contributions were initially disregarded or opposed but vindicated later, often as a result of new experiments in the laboratory or measurements in space. Some of his ideas remain unaccepted or controversial even today. Finally, it is worth emphasizing that Hannes Alfven contributed to the progress of science not only by his own work but also by the extraordinary inspiration that he gave to his many students as well as to colleagues all over the world.

  • 11.
    Fälthammar, Carl-Gunne
    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.
    Magnetosphere-ionosphere interactions as a key to the plasma Univers1995Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 23, s. 2-9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Almost all known matter in the universe is in a state, the plasma state, that is rare on Earth, and whose physical properties are still incompletely understood. Its complexity is such that a reliable understanding must build on empirical knowledge. While laboratory experiments are still an important source of such knowledge, Earth’s magnetospere-ionosphere system, made accessible by space technology, vastly widens the parameter ranges in which plasma phenomena can be studied. This system contains all three main categories of plasma present in the universe. Furthermore, the interaction between the magnetosphere and the ionosphere excites a wealth of plasma physical phenomena of fundamental importance. These include, among others, formation of magnetic-field aligned electric fields, acceleration of charged particles, release of magnetically stored energy, formation of filamentary and cellular structures, as well as unexpected chemical separation processes. What has been learned, and what stilt remains to be learned, from study of the magnetosphere-ionosphere system should therefore provide a much improved basis for understanding of our universe.

  • 12. Huang, Shuo
    et al.
    Gudmundsson, Jon Tomas
    Shanghai Jiao Tong University; University of Iceland.
    Ion Energy and Angular Distributions in a Dual-frequency Capacitively Coupled Chlorine Discharge2014Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 42, nr 10, s. 2854-2855Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ion energy distributions (IEDs) and ion angular distributions (IADs) of Cl2 + and Cl+ ions in a dual-frequency capacitively coupled chlorine discharge are obtained through a particle-in-cell/Monte Carlo simulation. Since the ion transit time is less than the low-frequency period, the ions respond to the instantaneous electric field in the sheath region, which leads to bimodal IEDs for Cl2 + and Cl+ ions. When transiting the sheath, the Cl+ ions experience a more collisional sheath than the Cl2 + ions. The IADs of Cl2 + and Cl+ ions at the surface are almost anisotropic. However, a secondary peak is found in the IAD of Cl+ ions, which can be ascribed to dissociative ionization reactions.

  • 13. Hurtig, Lars Tomas Gustav
    et al.
    Brenning, Nils
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Gunell, Herbert
    Investigation Into Relativistic Magnetic Flux Amplification2016Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 44, nr 1, s. 2-6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Amplification of magnetic flux and electric polarization fields caused by a plasma streaming at relativistic velocity into a magnetic field is discussed. It is shown that the electrostatic polarization field that arises in a plasma beam streaming across magnetic field lines at relativistic velocities will cause amplification of the magnetic flux. This effect is in complete contrast to the expulsion of the magnetic field from the plasma interior that can be expected in high beta(K) plasmas, where beta(K) is the kinetic energy density in the plasma stream divided by the energy density in the magnetic field. The amplification is shown to be caused by the relativistic motion of the space charge layers setting up the polarization field. 3-D electromagnetic particle-in-cell simulations that support this theory are presented.

  • 14.
    Höök, Josef
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    An Adaptive delta f Monte Carlo Method2010Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 38, nr 9, s. 2190-2197Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new adaptive delta f Monte Carlo method is presented with an application to radio frequency heating and transport in fusion plasmas. The method is suitable when an initial zeroth-order approximation of the distribution function is known. The difference between our method and earlier delta f methods is that we model the source term, obtained from the delta f ansatz, by adding particles. The rate of particles is defined by the inhomogeneous term in the Fokker-Planck equation. We develop an adaptive scheme for modifying the unperturbed part G(x) such that the number of particles used in the simulation for a fixed weight is minimized. This implicitly reduces the variance and improves computational efficiency. The method is tested on a one-dimensional Fokker-Planck model for RF-heating and compared against the analytical stationary solution.

  • 15.
    Liu, Lipeng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Becerra, Marley
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    An Efficient Semi-Lagrangian Algorithm for Simulation of Corona Discharges: The Position-State Separation Method2016Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 44, nr 11, s. 1-10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An efficient algorithm without flux correction for simulation of corona discharges is proposed. The algorithm referred to as the position-state separation method (POSS) is used to solve convection-dominated continuity equations commonly present in corona discharges modelling. The proposed solution method combines an Eulerian scheme for the solution of the convective acceleration, the diffusion and the reaction subproblems, and a Lagrangian scheme for the solution of the linear convection subproblem. Several classical numerical experiments in different dimensions and coordinate systems are conducted to demonstrate the excellent performance of POSS regarding low computational cost, robustness, and high-resolution. It is shown that the time complexity of the method when dealing with the convection of charged particles increases linearly with the number of unknowns. For the simulation of corona discharges where local electric fields do not change strongly in time, the time step of POSS could be much larger than the Courant–Friedrichs–Lewy (CFL) time step. These special features enable POSS to have great potential in modeling of corona discharges in long interelectrode gaps and for long simulation times.

  • 16.
    Liu, Lipeng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Becerra, Marley
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Application of the Position-State Separation Method to Simulate Streamer Discharges in Arbitrary Geometries2017Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we extended the recent work of Liu and Becerra to employ the position-state separation (POSS) method to simulate filamentary streamer discharges. POSS is a semi-Lagrangian method, which solves convection-dominated continuity equations without numerical flux correction. An improved interpolation strategy for POSS is here introduced to overcome the excessive numerical diffusion of the method when very small time step is used. Several benchmark tests in the literature are used to validate the improved method. Numerical experiments show that POSS is an accurate, efficient, and robust numerical method to simulate streamer discharges in arbitrary geometries when combined with finite-element method.

  • 17.
    Montaño, Raúl
    et al.
    Division for Electricity, Uppsala University.
    Becerra, Marley
    Division for Electricity, Uppsala University.
    Cooray, Vernon
    Division for Electricity, Uppsala University.
    Rahman, Mahbubur
    Liyanage, Prasanna
    Resistance of spark channels2006Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 34, nr 5, s. 1610-1619Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A study undertaken to measure the resistance ofspark channels in air with two different current waveforms ispresented. In one experiment, the spark was created by a Marxgenerator. In this case, the gap length was maintained at 12.8 cm,and the current flowing through the spark had a peak currentlying in the range of 0.2–2.2 kA. The decay time of the currentwas larger than 100 μs. In the other experiment, the spark wascreated by a current generator. In that experiment, the gap lengthwasmaintained at 1 cm, and the current flowing through the sparkhad peak-current amplitudes in the range of 35–48 kA. The decaytime of the current was larger than 500 μs. The results showthat the resistance of spark channels initially decreases, reaches aminimum value, and then recovers as the current in the spark gapdecreases. The minimum resistance of the spark channel decreaseswith an increasing peak current. The results are compared withvarious theories that attempt to predict the temporal variationof the resistance of spark channels. The comparison shows thatfurther developments in the existing theoretical models are neededin order to reproduce with better accuracy the dynamic behaviorof the channel resistance.

  • 18.
    Mukhtar, Qaisar
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    On Solving Singular Diffusion Equations With Monte Carlo Methods2010Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 38, nr 9, s. 2185-2189Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Diffusion equations in one, two, or three dimensions with inhomogeneous diffusion coefficients are usually solved with finite-difference or finite-element methods. For higher dimensional problems, Monte Carlo solutions to the corresponding stochastic differential equations can be more effective. The inhomogeneities of the diffusion constants restrict the time steps. When the coefficient in front of the highest derivative of the corresponding differential equation goes to zero, the equation is said to be singular. For a 1-D stochastic differential equation, this corresponds to the diffusion coefficient that goes to zero, making the coefficient strongly inhomogeneous, which, however, is a natural condition when the process is limited to a region in phase space. The standard methods to solve stochastic differential equations near the boundaries are to reduce the time step and to use reflection. The strong inhomogeneity at the boundary will strongly limit the time steps. To allow for longer time steps for Monte Carlo codes, higher order methods have been developed with better convergence in phase space. The aim of our investigation is to find operators producing converged results for large time steps for higher dimensional problems. Here, we compare new and standard algorithms with known steady-state solutions.

  • 19.
    Möller, Cecilia
    et al.
    FOI.
    Elfsberg, Mattias
    FOI.
    Hurtig, Tomas
    FOI.
    Larsson, Anders
    FOI.
    Nyholm, Sten E.
    FOI.
    Proof of Principle Experiments on Direct Generation of the TE11 Mode in a Coaxial Vircator2010Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 38, nr 1, s. 26-31Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experiments on a coaxial vircator with a sectioned emitter are reported. The emitting area is sectioned to form two opposing emitters in order to favor growth of the TE11 mode and inhibit growth of the TM01 mode that is usually excited in a coaxial vircator. Experiments are performed using a compact 320-J 400-kV Marx generator and a compact coaxial vircator built in a standard 8 '' vacuum tube. The radiated magnetic-field strength is measured by means of four free-field (B-dot) probes, and experiments show that sectioning the emitter does, in fact, lead to generation of the TE11 mode.

  • 20.
    Möller, Cecilia
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Elfsberg, Mattias
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Larsson, Anders
    Swedish Defence Research Agency (FOI) Defence & Security, Systems and Technology, Grindsjön Research Centre, Tumba, Sweden.
    Nyholm, Sten
    Swedish Defence Research Agency (FOI) Defence & Security, Systems and Technology, Grindsjön Research Centre, Tumba, Sweden.
    Experimental Studies of the Influence of a Resonance Cavity in an Axial Vircator2010Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 38, nr 6, s. 1318-1324Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experiments on an axial virtual-cathode oscillator (vircator) with a resonance cavity enclosing the virtual cathode are reported. The vircator is driven by a repetitive Marx generator operating in a single-shot mode. To be able to separate different radiation mechanisms, the design of the vircator allows adjustment of the cavity depth as well as the way microwave radiation is extracted. The microwave radiation is measured with a pair of free-field B-dot sensors. The maximum field strengths were registered when the bandwidth was very narrow.

  • 21. Nakamura, R.
    et al.
    Torkar, K.
    Andriopoulou, M.
    Jeszenszky, H.
    Escoubet, C. P.
    Cipriani, F.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Fuselier, S. A.
    Pollock, C. J.
    Giles, B. L.
    Khotyaintsev, Y.
    Initial Results From the Active Spacecraft Potential Control Onboard Magnetospheric Multiscale Mission2017Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 45, nr 8, s. 1847-1852Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    NASA's magnetospheric multiscale (MMS) mission was successfully launched in March 2015. The scientific objectives of MMS are to explore and understand fundamental plasma physics processes in the earth's magnetosphere: magnetic reconnection, particle acceleration, and turbulence. The region of scientific interest of MMS is in a tenuous plasma environment where the positive spacecraft potential may reach an equilibrium as high as several tens of volts. The active spacecraft potential control (ASPOC) instrument neutralizes the spacecraft potential by releasing the positive charge produced by indium ion emitters. While the method has successfully been applied to other spacecraft such as Cluster and Double Star, new developments in the design of the emitters and the electronics are enabling lower spacecraft potentials and higher reliability compared to previous missions. In this paper, we report the initial results from the tests of the ASPOC performance during the commissioning phase and discuss the different effects on the particle and field instruments observed at different plasma environments in the magnetosphere.

  • 22.
    Olofsson, Erik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Closed-Loop System Identification and Controller Reconfiguration for EXTRAP T2R Reversed-Field Pinch2010Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 38, nr 3, s. 365-370Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We first briefly summarize a supposedly efficient novel method for measuring the external plasma response as applied to the inherently unstable reversed-field pinch EXTRAP T2R. Second, the set of parameters estimated with this particular method is harvested and fed as input to a discrete-time fixed-order fast-Fourier-transform-decoupled multi-input-multioutput controller synthesis. The thus reconfigured feedback system is implemented and experimentally tested on the real plant T2R. The recorded first-deployment results are encouraging. The overall methodology followed throughout this paper is emphasized and strongly exemplifies applied process control thinking for the stabilization of magnetically confined toroidal plasmas.

  • 23. Peratt, Anthony
    et al.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Guest Editorial Sixth Special Issue on Space and Cosmic Plasma2003Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 31, nr 6, s. 1109-1111Artikel i tidskrift (Övrigt vetenskapligt)
  • 24.
    Pettersson, Jonas
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Becerra Garcia, Marley
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Franke, Steffen
    Leibniz Inst Plasma Sci & Technol, D-17489 Greifswald, Germany..
    Gortschakow, Sergey
    Leibniz Inst Plasma Sci & Technol, D-17489 Greifswald, Germany..
    Spectroscopic and Photographic Evaluation of the Near-Surface Layer Produced by Arc-Induced Polymer Ablation2019Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 47, nr 4, s. 1851-1858Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-intensity plasmas can release material from the surface of polymers by a process known as arc-induced ablation. As consequence, the formation of a near-surface layer of polymeric vapor is generally assumed. In order to investigate the near-surface layer formed by the ablation of polyoxymethylene, high-speed photography and space-resolved optical emission spectroscopy are used. Transient arc plasmas generated under a 1.9-kA, 50-Hz current semicycle are used as ablation source in air. It is found that the near-surface ablation layer strongly scatters radiation emitted by the arc core. This effect is caused by light scattering of micrometer-size fragments released by the ablating polymer. This finding shows that the near-surface layer is not only composed of vapor but also contains a significant density of large-sized polymer fragments. These fragments are formed a few milliseconds after the ignition of the arc plasma, and their density rapidly decreases with the distance to the surface.

  • 25.
    Raadu, Michael A.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Effective distribution functions for electrostatic waves in dusty plasmas with a dust-size distribution2001Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 29, nr 2, s. 182-185Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The kinetic theory for the electrostatic modes of dusty plasmas with a distribution of grain sizes is examined. It is assumed that the size distribution predominantly decreases exponentially with the mass for large sizes, and that a power law prevails for small sizes. Thermodynamic equilibrium leads to Maxwellian distributions over velocity with a fixed temperature and continuously varying mass. Smaller particles have higher thermal velocity and dominate the tail of the velocity distribution. The contribution of the dust component to the dispersion function is found to be non-Maxwellian and is equivalent to that for a kappa (generalized Lorentzian) distribution of monosized particles, Known results for kappa distributions may be exploited, However, the nonlinear response of the charge density of the dust to an electrostatic potential is quite different to that of a monosized kappa distribution. In general, the definition of an effective dust distribution function for linearized electrostatic modes leads to a useful straightforward procedure to find the dispersion function. It is important to realize that the combined effects of velocity and size distribution can, in general, strongly modify the kinetic behavior of the plasma dust component.

  • 26. Ratynskaia, Svetlana V.
    et al.
    Kretschmer, M.
    Khrapak, S.
    Quinn, R. A.
    Thoma, M. H.
    Morfill, G. E.
    Zobnin, A.
    Usachev, A.
    Petrov, O.
    Fortov, V.
    Dust mode in collisionally dominated complex plasmas with particle drift2004Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 32, nr 2, s. 613-616Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experiments with flow of microparticles were conducted in a de discharge. A sharp threshold in the neutral gas pressure for the onset of an unstable low-frequency dust wave mode was observed. Highly space- and time-resolved measurements of the microparticle flow combined with probe measurements of the plasma parameters have allowed detailed comparison with a theoretical model. The model demonstrates good qualitative and quantitative agreement with the experimental results providing accurate estimates of the particle charge.

  • 27. Rothwell, P L
    et al.
    Silevitch, M B
    Block, Lars P
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    The role of O+ ions in channeling solar wind energy to the ionosphere2000Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 28, s. 1912-1919Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In space weather prediction, the transport of solar wind energy through the magnetosphere is a major aspect. For the transport of energy from the magnetosphere to the ionosphere, magnetic field-aligned (Birkeland) currents are a very important agent. In the present paper, we discuss the role of O+ ions for driving field-aligned currents of spatially alternating polarity that may explain multiple auroral arcs, It is known from earlier work that nonadiabatic motion of O+ ions in the magnetotail plasma can lead to the formation of density striations that are stationary in the GSM frame, As the magnetospheric plasma drifts through these density striations, magnetic field-aligned currents of alternating signs are forced to flow in and out of the oxygen-rich region to maintain quasineutrality. This generates Alfven waves that propagate in the drifting plasma but can form stationary structures in the GSM frame. As the currents close in the ionosphere, the equatorial plasma constitutes a generator from which spatially alternating magnetic field-aligned currents carry energy to the ionospheric load, The wavelength of the density striations, mapped to the ionosphere, is compatible with the spacing of stable auroral arcs, and the power supplied by the equatorial generator region is estimated to be compatible with what is needed to drive auroral arcs, Thus, the consequences of nonadiabatic motion of O+ ions may explain how part of the energy extracted from the solar wind is channeled into multiple auroral arcs.

  • 28. Rothwell, P.L.
    et al.
    Block, Lars P
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Silevitch, M.B.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    A new model for auroral breakup during substorms1989Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 17, s. 150-157Artikel i tidskrift (Refereegranskat)
  • 29.
    Shafiq, Mohammad
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Raadu, Michael. A.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Delayed shielding of a test charge due to dynamical grain charging in a dusty plasma2004Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 32, s. 627-631Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dynamical charging of grains in a dusty plasma modifies the plasma dielectric response function and the nature of the electrostatic wave modes. The grain charging leads to an additional shielding effect that acts in the same way as Debye shielding. Both the additional shielding and the charging rate are important in determining the response of a dusty plasma to a moving test charge. The dynamics of the charging can be approximated by using a time delay. An alternative analysis of the potential of a slowly moving test charge is performed introducing a delay operator for the grain charge response. The terms in the potential that depend on the charging dynamics involve a spatial shift given by the test charge velocity and the charging time. This gives a physical interpretation of earlier results which are identical to first order in the test charge velocity.

  • 30. Thoma, Markus H.
    et al.
    Fink, Martin A.
    Hoefner, Herwig
    Kretschmer, Michael
    Khrapak, Sergey A.
    Ratynskaia, Svetlana V.
    Yaroshenko, Victoria V.
    Morfill, Gregor E.
    Petrov, Oleg F.
    Usachev, Alexander D.
    Zobnin, Andrey V.
    Fortov, Vladimir E.
    PK-4: Complex plasmas in space - The next generation2007Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 35, nr 2, s. 255-259Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    PK-4 is an experiment designed to investigate complex plasmas in a combined dc/RF discharge under microgravity conditions on board of the International Space Station. The dc,discharge is produced in a glass tube with a length of 35 cm and, a diameter of 3 cm. In addition, an RF discharge can be applied by external RF coils. The setup is especially suited for studying the liquid phase of the complex plasmas, e.g., flow phenomena such as turbulence or nozzles, and forces acting on the microparticles. Experiments in the laboratory and in parabolic flights have been used to determine the charge of the microparticles as well as the ion drag force acting on them.

  • 31. Torkar, K.
    et al.
    Eriksson, A. I.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Steiger, W.
    Long-Term Study of Active Spacecraft Potential Control2008Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 36, nr 5, s. 2294-2300Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Emitters based on the liquid metal ion source principle have been operating on the Cluster spacecraft between 2000 and 2004, in order to control the spacecraft potential. The resulting reduction of positive spacecraft potential reduces perturbations to the plasma measurements on board. Ion currents up to 40 [LA have been applied, which reduced the energy band in which photoelectrons disturb the plasma electron measurements to values close to the lower detection limit of the instrument. The experience with this method, meanwhile, covers both the maximum and minimum of the present solar cycle and allows one to study the variations of photoemission and other long-term trends and their effects on the measurements. A long-term trend of the controlled spacecraft potential is indeed observed. In addition, it appears that reconstruction of the uncontrolled spacecraft potential from the controlled one is possible if certain conditions are fulfilled. Spacecraft potential control can thereby improve the plasma measurements while still allowing one to estimate the total plasma density from the residual potential.

  • 32.
    Torkar, K.
    et al.
    Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria..
    Nakamura, R.
    Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria..
    Wellenzohn, S.
    Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria..
    Jeszenszky, H.
    Austrian Acad Sci, Space Res Inst, A-8042 Graz, Austria..
    Torbert, R. B.
    Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Ergun, R. E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80303 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA..
    Improved Determination of Plasma Density Based on Spacecraft Potential of the Magnetospheric Multiscale Mission Under Active Potential Control2019Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 47, nr 8, s. 3636-3647Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Data from the Magnetospheric Multiscale (MMS) mission, in particular, the spacecraft potential measured with and without the ion beams of the active spacecraft potential control (ASPOC) instruments, plasma electron moments, and the electric field, have been employed for an improved determination of plasma density based on spacecraft potential. The known technique to derive plasma density from spacecraft potential sees the spacecraft behaving as a plasma probe which adopts a potential at which the ambient plasma current and one of photoelectrons produced at the surface and leaving into space are in equilibrium. Thus, the potential is a function of the plasma current, and plasma density can be determined using measurements or assumptions on plasma temperature. This method is especially useful during periods when the plasma instruments are not in operation or when spacecraft potential data have significantly higher time resolution than particle detectors. However, the applicable current-voltage characteristic of the spacecraft has to be known with high accuracy, particularly when the potential is actively controlled and shows only minor residual variations. This paper demonstrates recent refinements of the density determination coming from: 1) the reduction of artifacts in the potential data due to the geometry of the spinning spacecraft and due to effects of the ambient electric field on the potential measurements and 2) a calibration of the plasma current to the spacecraft surfaces which is only possible by comparison with the variable currents from the ion beams of ASPOC. The results are discussed, and plasma densities determined by this method are shown in comparison with measurements by the Fast Plasma Instrument (FPI) for some intervals of the MMS mission.

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