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Ali, S., Davies, J. R., & Mendonca, J. T. (2010). Inverse Faraday Effect with Linearly Polarized Laser Pulses. Physical Review Letters, 105(3).
Abstract: The inverse Faraday effect is usually associated with circularly polarized radiation; here, we show that it can also occur for linearly polarized radiation. The quasistatic axial magnetic field generated by a laser propagating in plasma can be calculated by considering both the spin and the orbital angular momenta of the laser pulse. A net spin is present when the radiation is circularly polarized and a net orbital angular momentum is present if there is any deviation from perfect rotational symmetry. The orbital angular momentum gives an additional contribution to the axial magnetic field that can enhance or reduce the effect usually attributed to circular polarization and strongly depends on the intensity profile of the Laguerre-Gaussian modes involving the azimuthal and radial mode numbers.
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Ali, S., & Mendonca, J. T. (2011). Inverse Faraday effect with plasmon beams. Plasma Physics And Controlled Fusion, 53(4).
Abstract: The angular momentum conservation equation is considered for an electron gas, in the presence of Laguerre-Gaussian (LG) plasmons propagating along the z-axis. The LG plasmons carry a finite orbital angular momentum despite longitudinal nature, which can be partly transfered to the electrons. For short timescales, such that ion motion can be neglected, plasmons primarily interact with the electrons, creating an azimuthal electric field and generating an axial magnetic field. This effect can be called an inverse Faraday effect due to plasmons. Numerically, it is found that the magnitude of the magnetic field enhances with the plasmon density or with the energy of the electron plasma waves. A comparison of the magnitudes of the axial magnetic field is made for the inverse Faraday effect excited by both plasmons and transverse photons.
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Ali, S., Tercas, H., & Mendonca, J. T. (2011). Nonlocal plasmon excitation in metallic nanostructures. Physical Review B, 83(15).
Abstract: We investigate the excitation of electrostatic wake fields in metallic nanostructures (nanowires) due to the propagation of a short electron pulse. For that purpose, a dispersive (nonlocal) dielectric response of the system is considered, accounting for the conning along the transverse direction of the wire, which generalizes previous results presented in the literature. We discuss the stability conditions of wake fields and show that the underling mechanism can be useful to investigate new sources of radiation in the extreme-ultraviolet range.
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Alonso, J. A., Andrew, P., Neto, A., de Pablos, J. L., de la Cal, E., Fernandes, H., et al. (2009). Fast visible imaging of ELM-wall interactions on JET. Journal Of Nuclear Materials, 390-91, 797–800.
Abstract: We present and discuss recent measurements of the fast imaging diagnostic in JET. We focus on wide angle observations of few large ELM events (Delta W(ELM) similar to 700 kJ) in plasmas with high current, magnetic field and stored energy (similar to 3 T, 3 MA, 8 MJ). Measurements were taken at recording speeds around 30 kHz. The ELM-wall interaction shows a filamentary structure that appears together with the radiation increase in the divertor, implying similar times of flight for ELM radial and parallel transport in the SOL, tau(11) – tau(r), within a time resolution of 30 μs. Two high and low triangularity cases are compared. For high triangularity the ELM-wall interaction is seen to start in the upper dump plate reaching the outer limiters some 70 μs later. In the low triangularity cases interaction generally starts in the outer wall but clear evidence of radiation increase in the upper dump plate is seen shortly after (30 Its) or together with the first filament impact on the outer limiters. A poloidal drift of the filament strike point on the limiters is sometimes visible which allows an estimation of the perpendicular filament velocity (similar to 1 km/s). (C) 2009 Elsevier B.V. All rights reserved.
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Alonso, J. A., Hidalgo, C., Pedrosa, M. A., Van Milligen, B., Carralero, D., & Silva, C. (2012). Dynamic transport regulation by zonal flow-like structures in the TJ-II stellarator. Nuclear Fusion, 52(6), 063010.
Abstract: Floating potential structures that are correlated over a long distance are observed with a 2D probe array in the plasma edge of the TJ-II stellarator. We introduce a method based on the singular value decomposition to extract the spatio-temporal structure of the global, fluctuating, zonal-flow(ZF)-like floating potential from the combined measurements of a 2D probe array and a distant single probe. The amplitude of these global structures is seen to modulate not only the high k(theta) spectral power of the local turbulence but also particle transport into the unconfined scrape-off layer, as observed by H-alpha monitors around the device. These observations provide the first direct evidence of the global modulation of transport by ZF-like structures. The ability to identify spontaneous and collective rotation events with flux surface symmetry opens up the possibility to perform unperturbative studies of the effective viscosity in stellarators and tokamaks.
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