skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Alfvenic phenomena triggered by resonant absorption of an O-mode pulse

Abstract

A simulation and modeling study is made of the nonlinear interaction of an electromagnetic pulse, in the O-mode polarization, with a magnetized plasma having a cross-field density gradient. For small amplitudes, the pulse propagates up to the cutoff layer where an Airy pattern develops. Beyond a certain power level, the ponderomotive force produced by the standing electromagnetic fields carves density cavities. The excess density piled up on the side of the cavities causes secondary, field-aligned plasma resonances to arise. Strong electron acceleration occurs due to the short scale of the secondary resonant fields. The fast electrons exiting the new resonant layers induce a return current system in the background plasma. This generates a packet of shear Alfven waves of small transverse scale and increasing frequency. The results provide insight into microscopic processes associated with a recent laboratory investigation in which large-amplitude Alfven waves have been generated upon application of high-power microwaves [B. Van Compernolle et al., Phys. Plasmas 13, 092112 (2006)].

Authors:
; ;  [1]
  1. Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States)
Publication Date:
OSTI Identifier:
20974913
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 4; Other Information: DOI: 10.1063/1.2711428; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ABSORPTION; ACCELERATION; ALFVEN WAVES; AMPLITUDES; ELECTROMAGNETIC FIELDS; ELECTROMAGNETIC PULSES; ELECTRONS; INTERACTIONS; LAYERS; MICROWAVE RADIATION; NONLINEAR PROBLEMS; PLASMA; PLASMA DENSITY; PLASMA SIMULATION; POLARIZATION; PONDEROMOTIVE FORCE

Citation Formats

Tsung, F. S., Morales, G. J., and Tonge, J.. Alfvenic phenomena triggered by resonant absorption of an O-mode pulse. United States: N. p., 2007. Web. doi:10.1063/1.2711428.
Tsung, F. S., Morales, G. J., & Tonge, J.. Alfvenic phenomena triggered by resonant absorption of an O-mode pulse. United States. doi:10.1063/1.2711428.
Tsung, F. S., Morales, G. J., and Tonge, J.. Sun . "Alfvenic phenomena triggered by resonant absorption of an O-mode pulse". United States. doi:10.1063/1.2711428.
@article{osti_20974913,
title = {Alfvenic phenomena triggered by resonant absorption of an O-mode pulse},
author = {Tsung, F. S. and Morales, G. J. and Tonge, J.},
abstractNote = {A simulation and modeling study is made of the nonlinear interaction of an electromagnetic pulse, in the O-mode polarization, with a magnetized plasma having a cross-field density gradient. For small amplitudes, the pulse propagates up to the cutoff layer where an Airy pattern develops. Beyond a certain power level, the ponderomotive force produced by the standing electromagnetic fields carves density cavities. The excess density piled up on the side of the cavities causes secondary, field-aligned plasma resonances to arise. Strong electron acceleration occurs due to the short scale of the secondary resonant fields. The fast electrons exiting the new resonant layers induce a return current system in the background plasma. This generates a packet of shear Alfven waves of small transverse scale and increasing frequency. The results provide insight into microscopic processes associated with a recent laboratory investigation in which large-amplitude Alfven waves have been generated upon application of high-power microwaves [B. Van Compernolle et al., Phys. Plasmas 13, 092112 (2006)].},
doi = {10.1063/1.2711428},
journal = {Physics of Plasmas},
number = 4,
volume = 14,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • If irreversible heating of the solar corona is a result of hydromagnetic wave dissipation, then I propose that the relevant mode responsible for heating coronal active regions is an Alfvenic surface wave. Alfvenic surface waves are supported by the elasticity afforded by nonuniformities and therefore thrive in the inhomogeneous environment which characterizes coronal active regions.An Alfvenic surface wave is easily excited by the 300 s chromospheric oscillations shaking the footpoints of a magnetic loop (such loops are now thought to comprise coronal active regions); it travels along the loop's magnetic field lines and resonantly excites ''kinetic Alfven waves'' (KAW) withinmore » a thin (about 1 km thick) ''resonant absorption sheath'' which envelops the loop. Because of their kinetic structure, the resonantly excited KAW dissipate their energy very efficiently and thus act as an intermediary through which the Alfvenic surface wave irreversibly heats the sheath. Such a heated sheath induces a global convection within the loop: hot plasma rises in a boundary layer (< or approx. =100 km thick) adjacent to the sheath and enters the loop's interior (at the top of the loop) through the action of an electrostatic Rayleigh-Taylor instability. These upflows are aided by anomalous cross-field transport which results from a temperature-gradient plasma instability within the boundary layer. Upon entering the loop's interior, this hot plasma cools by radiating in the EUV, condenses into clumps, and falls downward along the loop's field lines.If one assumes that the footpoints of a typical coronal loop (height approx. =10/sup 5/ km and poloidal radius approx. =10/sup 4/ km) are being shaken by 6 km s/sup -1/ chromospheric oscillations with a period of 300 s, energy balance results in a sheath temperature T/sub S/approx. =2.9 x 10/sup 6/ K and an interior temperature T/sub INT/approx. =1 x 10/sup 4/ K. The radiative output of such a loop is 6.8 x 10/sup 23/ ergs s/sup -1/.« less
  • This paper relates to the recovery capacities of a triggered vacuum switch after the crossing of a 25-{mu}s high-current pulse. The recovery time is less than 100 {mu}s. The authors experiment with several electrodes with different gaps, and study the influence of an axial magnetic field on the switch.
  • The concept of wave-particle interactions via resonance is well discussed in plasma physics. This paper shows that intrinsic Alfven waves can qualitatively modify the physics discussed in conventional linear plasma kinetic theories. It turns out that preexisting Alfven waves can affect particle motion along the ambient magnetic field and, moreover, the ensuing force field is periodic in time. As a result, the meaning of the usual Landau and cyclotron resonance conditions becomes questionable. It turns out that this effect leads us to find a new electromagnetic instability. In such a process intrinsic Alfven waves not only modify the unperturbed distributionmore » function but also result in a different type of cyclotron resonance which is affected by the level of turbulence. This instability might enable us to better our understanding of the observed radio emission processes in the solar atmosphere.« less
  • We report both experimental and theoretical studies on x-ray absorption measured in the resonant Auger scattering mode of gas phase carbon monoxide near the O1s{yields}2{pi} region. Both experiment and theory display a crucial difference between the x-ray absorption profiles obtained in the conventional and resonant scattering modes. Lifetime vibrational interference is the main source of the difference. It is demonstrated that such interference, which arises from a coherent excitation to overlapping intermediate levels, ruins the idea for obtaining x-ray absorption spectra in a lifetime broadening free regime.