886 research outputs found
Source of the Bursty Bulk Flow Diffuse Aurora: Electrostatic Cyclotron Harmonic and Whistler Waves in the Coupling of Bursty Bulk Flows to Auroral Precipitation
Electron cyclotron harmonic (ECH) and whistler chorus waves are recognized as the two mechanisms responsible for the resonant waveparticle interactions necessary to precipitate plasma sheet electrons into the ionosphere, producing the diffuse Aurora. Previous work has demonstrated ECH waves dominate electron scattering at L shells >8, while whistler chorus dominates scattering at L shells L 1, consistent with electron betatron acceleration. Here, however, we nd whistler chorus emissions throughout an interval of fast ows where Te,/Te,||< 1. Parallel electron beams account for the enhanced parallel electron temperature and serve as the instability mechanism for the whistler chorus. The parallel electron beams and associated cigarshaped distributions are consistent with Fermi acceleration at dipolarizations in fast ows. We demonstrate that the scattering efciency of the whistler chorus exceeds that of ECH waves, which THEMIS also detects during the fast ows. The obliquity of the whistler waves permits efcient scattering of lowerenergy electrons into the diffuse aurora. We conclude that Fermi acceleration of electrons provides one important freeenergy source for the waveparticle interactions responsible for coupling plasma sheet electrons into the diffuse aurora during substorm conditions
Single Cycle Thin Film Compressor Opening the door to Zeptosecond-Exawatt Physics
This article demonstrates a new compression scheme that has the potential to
compress a high energy pulse as high as a few hundred Joules in a pulse as
short as one optical cycle at 0.8{\mu}m making a true ultra-relativistic
{\lambda}^3 pulse. This pulse could have a focused intensity of 10^24W/cm2 or
a0 of 1000. It could form an efficient, 10%, relativistic mirror that could
compress the pulse to the atto-zeptosecond regime, with an upshifted wavelength
of 1-10keV. This technique could be a watershed making the entry of petawatt
pulses into the exawatt and zeptosecond regime possible.Comment: 6 pages, 6 figure
Parametric excitation of high‐frequency electromagnetic waves by the lower‐frequency dipole pumping
The possibility of parametric excitation of high‐frequency electromagnetic waves by lower‐frequency dipole pumping is studied. It is shown that the obtained general dispersive equation may be reduced to the Mathieu equation, provided the case of the flux instability is neglected. In the framework of the developed approach, the excitation of magnetohydrodynamic waves and whistler oscillations is examined.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70436/2/PFBPEI-5-1-92-1.pd
The nonlinear coupling of electromagnetic ion cyclotron and lower hybrid waves in the ring current region: the magnetic storm 1-7May 1998
International audienceThe excitation of lower hybrid waves (LHWs) is a widely discussed mechanism of interaction between plasma species in space, and is one of the unresolved questions of magnetospheric multi-ion plasmas. In this paper we present the morphology, dynamics, and level of LHW activity generated by electromagnetic ion cyclotron (EMIC) waves during the 2-7 May 1998 storm period on the global scale. The LHWs were calculated based on a newly developed self-consistent model (Khazanov et. al., 2002) that couples the system of two kinetic equations: one equation describes the ring current (RC) ion dynamic, and another equation describes the evolution of EMIC waves. It is found that the LHWs are excited by helium ions due to their mass dependent drift in the electric field of EMIC waves. The level of LHW activity is calculated assuming that the induced scattering process is the main saturation mechanism for these waves. The calculated LHWs electric fields are consistent with the observational data
Characterization of thermal effects in the Enhanced LIGO Input Optics
We present the design and performance of the LIGO Input Optics subsystem as
implemented for the sixth science run of the LIGO interferometers. The Initial
LIGO Input Optics experienced thermal side effects when operating with 7 W
input power. We designed, built, and implemented improved versions of the Input
Optics for Enhanced LIGO, an incremental upgrade to the Initial LIGO
interferometers, designed to run with 30 W input power. At four times the power
of Initial LIGO, the Enhanced LIGO Input Optics demonstrated improved
performance including better optical isolation, less thermal drift, minimal
thermal lensing and higher optical efficiency. The success of the Input Optics
design fosters confidence for its ability to perform well in Advanced LIGO
Impact of Precipitating Electrons and Magnetosphere-Ionosphere Coupling Processes on Ionospheric Conductance
Modeling of electrodynamic coupling between the magnetosphere and ionosphere depends on accurate specification of ionospheric conductances produced by auroral electron precipitation. Magnetospheric models determine the plasma properties on magnetic field lines connected to the auroral ionosphere, but the precipitation of energetic particles into the ionosphere is the result of a two step process. The first step is the initiation of electron precipitation into both magnetic conjugate points from Earths plasma sheet via wave-particle interactions. The second step consists of the multiple atmospheric reflections of electrons at the two magnetic conjugate points, which produces secondary superthermal electron fluxes. The steady state solution for the precipitating particle fluxes into the ionosphere differs significantly from that calculated based on the originating magnetospheric population predicted by MHD and ring current kinetic models. Thus, standard techniques for calculating conductances from the mean energy and energy flux of precipitating electrons in model simulations must be modified to account for these additional processes. Here we offer simple parametric relations for calculating Pedersen and Hall height-integrated conductances that include the contributions from superthermal electrons produced by magnetosphere-ionosphere-atmosphere coupling in the auroral regions
A bounce‐averaged kinetic model of the ring current ion population
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94668/1/grl7966.pd
Kinetic-scale magnetic turbulence and finite Larmor radius effects at Mercury
We use a nonstationary generalization of the higher-order structure function
technique to investigate statistical properties of the magnetic field
fluctuations recorded by MESSENGER spacecraft during its first flyby
(01/14/2008) through the near Mercury's space environment, with the emphasis on
key boundary regions participating in the solar wind -- magnetosphere
interaction. Our analysis shows, for the first time, that kinetic-scale
fluctuations play a significant role in the Mercury's magnetosphere up to the
largest resolvable time scale ~20 s imposed by the signal nonstationarity,
suggesting that turbulence at this planet is largely controlled by finite
Larmor radius effects. In particular, we report the presence of a highly
turbulent and extended foreshock system filled with packets of ULF
oscillations, broad-band intermittent fluctuations in the magnetosheath,
ion-kinetic turbulence in the central plasma sheet of Mercury's magnetotail,
and kinetic-scale fluctuations in the inner current sheet encountered at the
outbound (dawn-side) magnetopause. Overall, our measurements indicate that the
Hermean magnetosphere, as well as the surrounding region, are strongly affected
by non-MHD effects introduced by finite sizes of cyclotron orbits of the
constituting ion species. Physical mechanisms of these effects and their
potentially critical impact on the structure and dynamics of Mercury's magnetic
field remain to be understood.Comment: 46 pages, 5 figures, 2 table
Saturation of Alfven oscillations in the ring current region due to generation of lower hybrid waves
The possibility of flux generation of lower hybrid oscillations in the ring current region of the Earth's magnetosphere is suggested in this paper. The energy level of lower hybrid oscillations can exceed the modulational instability threshold, which leads to the formation of caverns. The consequences of this are qualitatively analysed. Also, an assumption is made that the flux instability of lower hybrid oscillations may limit the level of Alfven oscillations in the ring current region.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30137/1/0000514.pd
A theoretical model for the ring current interaction with the earth's plasmasphere
This paper reports on a theoretical study of the magnetospheric ring current effect on the topside plasmasphere and ionosphere. MHD waves generated by energetic anisotropic protons of the ring current are used as the mechanism for energy transfer to plasmaspheric electrons and ions. Plasmaspheric parameters are calculated in a numerical model for ionospherelasmasphere coupling using a complete system of modelling equations in the 13-moment approximation of the Grad method. The calculations made have shown that the wave mechanism for energy transfer to the thermal plasma ensures its heating in the equatorial plasmasphere to experimentally observed temperatures. The resulting heat flux is able to considerably heat the plasma in the region of the topside ionosphere. It is also shown that the MHD waves present in the plasmasphere substantially influence the height profile of the electron density. The results obtained in this paper lend support to the existence of the experimentally discovered "hot" (or "warm") zone and to its influence on the underlying ionosphere.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30027/1/0000395.pd
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