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  • 1.
    Appelgren, Patrik
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Skoglund, Melker
    Lundberg, Patrik
    Westerling, Lars
    Larsson, Anders
    Hurtig, Tomas
    Experimental Study of Electromagnetic Effects on Solid Copper Jets2010In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 77, no 1, p. 011010-Article in journal (Refereed)
    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]

  • 2.
    Elfsberg, Mattias
    et al.
    FOI.
    Hurtig, Tomas
    FOI.
    Möller, Cecilia
    FOI.
    Nyholm, Sten E.
    FOI.
    Experimental studies on a coaxial vircator, designed for operation in TE11 mode2011In: Proc. of Pulse Power Conference (PPC 2011), 2011, Vol. 38, no 1, p. 811-814Conference paper (Refereed)
    Abstract [en]

    Experiments on a coaxial vircator have been performed. A vircator is a narrow band high power microwave source without any external generated magnetic field [1]. A coaxial vircator is an advantageous design of a microwave radiation source for a compact HPM-system. With a limited size and outer diameter it is possible to use a larger emitting area compared to an axial design. A conventional coaxial vircator will generate the radiation in TM01 mode, due to its geometrical properties. For a compact HPM-system, radiation in TE11 mode is preferred when the radiated energy needs to be focused on a specific target. For operation in TE11 mode a sectioned emitter can be used rather than a circumcircular. The efficiency of the vircator can be greatly improved by optimizing the geometry of the vircator housing. The impedance of the pulsed power supply driving the vircator and the impedance of the vircator, depending on the A-K gap and amount of emitting material, is also important for maximizing the vircator efficiency. For the experiments reported on, the vircator was driven by a 500 kV/500 J compact Marx generator that can be operated repetitively at 10 Hz. For these experiments, the Marx generator was operating in single shot mode. During the experiments presented here, a couple of geometrical features were varied as well as the applied voltage. Their influence on the radiated field strength, dominating frequency and bandwidth are reported on and discussed.

  • 3.
    Elfsberg, Mattias
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Möller, Cecilia
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Hurtig, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    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 Vircator2008In: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 36, p. 688-693Article in journal (Refereed)
    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.

  • 4.
    Hurtig, Tomas
    KTH, Superseded Departments, Alfvén Laboratory.
    Plasma cloud penetration across magnetic boundaries2004Doctoral thesis, comprehensive summary (Other scientific)
  • 5.
    Hurtig, Tomas
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Brenning, Nils
    KTH, Superseded Departments, Alfvén Laboratory.
    Raadu, Michael A.
    KTH, Superseded Departments, Alfvén Laboratory.
    The penetration of plasma clouds across magnetic boundaries: The role of high frequency oscillations2004In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 11, no 7, p. L33-L36Article in journal (Refereed)
    Abstract [en]

    Experiments are reported where a collision-free plasma cloud penetrates a magnetic barrier by self-polarization. Two closely related effects, both fundamental for the penetration mechanism, are studied quantitatively: anomalous fast magnetic field penetration (two orders of magnitude faster than classical), and anomalous fast electron transport (three orders of magnitude faster than classical and two orders of magnitude faster than Bohm diffusion). It is concluded that they are both mediated by highly nonlinear oscillations in the lower hybrid range, driven by a strong diamagnetic current loop which is set up in the plasma in the penetration process.

  • 6.
    Hurtig, Tomas
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Wistedt, J.
    Probes for High Frequency Measurements in a Plasma Gun2003In: Rev. Sci. Instr. (AIP), ISSN 0034-6748, Vol. 74, p. 1153-1155Article in journal (Refereed)
    Abstract [en]

    High-frequency correlation measurements of plasma density, and electric and magnetic fields in a plasma gun have been performed. In this article, we give a description of the probes developed for this purpose. The probes described are characterized by a large bandwidth (>15 MHz) and very low susceptibility to electrostatic noise.

  • 7.
    Möller, Cecilia
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Bieth, F.
    Delmote, P.
    Elfsberg, Mattias
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Hurtig, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Nyholm, Sten
    Experimental study of a vircator with premodulated electron beam2011In: Proc. of Pulse Power Conference (PPC 2011)”, Chicago,USA, June 2011., 2011, p. 815-818Conference paper (Refereed)
    Abstract [en]

    An initial experimental study of a vircator where a feedback mechanism is used to premodulate the electron beam has been performed. The anode-cathode gap distance and the applied voltage were varied and their influence on the frequency content and field strength of the generated microwave pulse are investigated and compared with particle in cell simulations. The frequency content of the microwave radiation was in good agreement between experiments and simulations. The vircator was very narrow banded at 2 GHz.

  • 8.
    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 Vircator2010In: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 38, no 1, p. 26-31Article in journal (Refereed)
    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.

  • 9.
    Möller, Cecilia
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Hurtig, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    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.
    Electron Beam Deviation due to Lorentz Force in Reflex Triode2006In: Proc. of 1stEuro-Asian Pulsed Power Conference (EAPPC), 2006Conference paper (Refereed)
  • 10.
    Möller, Cecilia
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Hurtig, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Larsson, Anders
    Nyholm, Sten
    Numerical Simulation of the TE11 Mode in a Coaxial Vircator2007In: IEEJ Transactions on Fundamentals and Materials, ISSN 0385-4205, Vol. 127, no 11, p. 687-689Article in journal (Refereed)
    Abstract [en]

    Studies of the concept of direct excitation of the TE11 mode in a coaxial vircator using three-dimensional particle-in-cell simulations is presented. The excitation of the TE11 mode is made possible by sectioning the emitting surface of the cathode, thus creating two interacting virtual cathodes. It is shown that the two virtual cathodes formed oscillate in push-pull mode as previously has been described for a planar geometry.  

  • 11. Novac, Bucur M.
    et al.
    Istenic, Marko
    Luo, Jing
    Smith, Ivor R.
    Brown, John
    Hubbard, Martin
    Appelgren, Patrik
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Elfsberg, Mattias
    Hurtig, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Möller, Cecilia
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Larsson, Anders
    Nyholm, Sten E.
    A 10-GW pulsed power supply for HPM sources2006In: IEEE TRANS PLASMA SCI, 2006, Vol. 34, no 5, p. 1814-1821Conference paper (Refereed)
    Abstract [en]

    A research activity involving the detailed consideration of novel high-voltage transformers for pulsed-power applications has recently begun at Loughborough University. Although the main goal is the demonstration of a compact and lightweight unit employing magnetic insulation under vacuum conditions, the initial stage of the work is directed toward the development of a conventional air-cored transformer as a main component in a compact power supply for high power microwave sources. In cooperation with the Swedish Defence Research Agency (FOI), the power supply has been tested with a microwave source of the vircator type. The power generator for the system uses a 70-kJ/25-kV capacitor bank and an exploding wire array to generate a 150-kV voltage pulse in the primary circuit of a transformer. A pressurized SF6 spark gap in the secondary circuit sharpens the high-voltage output so that pulses approaching 500 kV and with a rise time well below 100 ns are generated on a 20-Omega high-power resistors With the peak power in excess of 10 GW. Experimental results are presented from final testing of the system, where a reflex triode vircator replaces the 20-Omega resistor. Measurements of the microwave emission using free-field sensors are presented, and comments are made with the microwave emission from the same vircator when powered by a Marx generator at FOI.

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