Cluster Observation of Eelectrostatic Solitary Waves around Magnetic Null Point in Thin Current Sheet

Electrostatic solitary waves （ESWs） are observed in the vicinity of the magnetic null of the widely studied magnetic reconnection taking place at the near-earth tail when current sheet becomes dramatic thinning during substorm time on 1 October 2001. We use the Imada method for the 2-D reconnection model and study the characteristics of ESWs near the X-line region and the magnetic null points. The result shows that the amplitude of the observed ESWs in the vicinity of X-line region ranges from 0.1mV/m to 5mV/m, and the amplitude is larger near the magnetic null points. The generation mechanism and the role of ESWs associated with magnetic reconnection are also discussed.     

Dynamic Processes of Cross-Tail Current in the Near-Earth Magnetotail

Current dynamic processes in realistic magnetotail geometry simulations under various driven conditions and Hall effects. are studied by Hall magnetohydrodynamic （MHD） Associated with the external driving force, a thin current sheet with a broad extent is built up in the near-Earth magnetotail. The time evolution for the formation of the current sheet comprises two phases： slow growth and a fast impulsive phase before the near-Earth disruption of the current sheet resulting from the fast magnetic reconnection. The simulation results indicate that as the external driving force increases, the site and the tailward speed of the near-Earth current disruption region are closer to the Earth and faster, respectively. Whether the near-Earth disruption of the current sheet takes place or not is mainly controlled by Hall effects. It is found that there is no sudden disruption of the current sheet in the near-Earth region if the ion inertial length is below di= 0.04.     

Storm-Time Strong Field-Aligned Ion Upflow in Region of the SED Plume

We report the observations from the GPS TEC and DMSP F-13 satellites showing that very strong upward field-aligned （FA） ion velocity and flux in the outer region of the storm-enhanced density （SED） occurred in the event of the geomagnetic storm on 29-31 May 2003. By a method of coordinate transformation, upward FA ion velocities in excess of 25Orals are obtained from the observations of the DMSP F-13 satellite. Further, an FA ion flux is estimated to be about 4.5 x 1013 ions/m2 s in the dusk sector. The estimated FA ion velocity and flux provide a powerful direct proof to support the scenario that there is a strong coupling of particles between the ionosphere and plasmasphere in the region of the SED plume. In the process, FA ion flux transports from the ionosphere to the plasmasphere in the region of the SED plume. Therefore, the plume of SED in the ionosphere provides an important source to the enhanced density of O^＋ in the storm-time plasmasphere.     

Alfven Waves in a Plasma Sheet Boundary Layer Associated with Near-Tail Magnetic Reconnection

We report observations from Geotail satellite showing that large Poynting fluxes associated with Alfven waves in the plasma sheet boundary layer （PSBL） occur in the vicinity of the near-tail reconnection region on 10 December 1996. During the period of large Poynting fluxes, Geotail also observed strong tailward plasma flows. These observations demonstrate the importance of near-tail reconnection process as the energy source of Alfven waves in the PSBL. Strong tailward （Earthward） plasma flows ought to be an important candidate in generating Alfven waves. Furthermore, the strong perturbations not only of the magnetic field but also of the electric field observed in the PSBL indicate that the PSBL plays an important role in the generation and propagation of the energy flux associated with Alfven waves.     

Properties of Field Aligned Current in Plasma Sheet Boundary Layers in Magnetotail: Cluster Observation

Field aligned current （FAC） distribution in the plasma sheet boundary layers （PSBLs） in the magnetotail is studied statistically by analysing magnetic field data from the Cluster 4-point measurements. The results show that the FAC distribution on the dusk side is not the same as that on the dawn side in the magnetotail. On the each side earthward and tailward, FA C occurrences are different; occurrence and average current density of FA Cs in the northern hemisphere are different from those in the southern hemisphere. This implies that the FACs have dusk-dawn side asymmetry, polarity asymmetry and inter hemisphere difference in the magnetotail. The present results give a good observation evidence for study on the FAC mechanism.     

Modelling Energetic Electrons by a Kappa-Loss-Cone Distribution at Geostationary Orbit

We adopt a recently developed relativistic kappa-loss-cone （KLC） distribution to model energetic electrons energy spectra observed at the geostatlonary orbit in the storm of 3-4 November 1993. The KLU distribution is found to fit well with the observed data from four satellites during different universal times. This suggests that the electron flux obeys the power-law not only at the lower energies but also at the relativistic energies, and the KLU distribution may provide a better understanding of environments in those space plasmas where relativistic electrons are present.     

Out-of-plane bipolar and quadrupolar magnetic fields generated by shear flows in two-dimensional resistive reconnection

Shear flows perpendicular to the anti-parallel reconnecting magnetic field are often observed in magnetosphere and interplanetary plasmas, and in laboratory plasmas toroidal differential rotations can also be generated in magnetic confinement devices. Our study finds that such shear flows can generate bipolar or quadrupolar out-of-plane magnetic field perturbations in a two-dimensional resistive MHD reconnection without the Hall effects. The quadrupolar structure has otherwise been thought a typical Hall MHD reconnection feature caused by the in-plane electron convection. The results will challenge the conventional understanding and satellite observations of the signature of reconnection evidences in space plasmas.     

Pitch Angle Distribution Evolution of Energetic Electrons by Whistler-Mode Chorus

We develop a two-dimensional momentum and pitch angle code to solve the typical Fokker-Planck equation which governs wave-particle interaction in space plasmas. We carry out detailed calculations of momentum and pitch angle diffusion coefficients, and temporal evolution of pitch angle distribution for a band of chorus frequency distributed over a standard Gaussian spectrum particularly in the heart of the Earth＇s radiation belt L = 4.5, where peaks of the electron phase space density are observed. We find that the Whistler-mode chorus can produce significant acceleration of electrons at large pitch angles, and can enhance the phase space density for energies of 0.5 - 1 MeV by a factor of 10 or above after about 24h. This result can account for observation of significant enhancement in flux of energetic electrons during the recovery phase of a geomagnetic storm.     

Analysis of the Interaction between Low-Frequency Waves and Ions in the High-Altitude Cusp Region Observed by Satellite Cluster

The energy transfer between ions （protons） and low frequency waves （LFWs） in the frequency range f1 from 0.3 to 10 Hz is observed by Cluster crossing the high-altitude polar cusp. The energy transfer between low frequency waves and ions has two means. One is that the energy is transferred from low frequency waves to ions and ions energy increases, The other is that the energy is transferred from ions to low frequency waves and the ion energy decreases. lon gyratory motion plays an important role in the energy transfer processes. The electromagnetic field of f1 LFWs can accelerate or decelerate protons along the direction of ambient magnetic field and warm or refrigerate protons in the parallel and perpendicular directions of ambient magnetic field, The peak values of proton number densities have the corresponding peak values of electromagnetic energy of low-frequency waves. This implies that the kinetic Alfven waves and solitary kinetic Alfven waves possibly exist in the high-altitude cusp region.     

Simulation of Resonant Interaction between Energetic Electrons and Whistler-Mode Chorus in the Outer Radiation Belt

We construct a realistic model to evaluate the chorus wave-particle interaction in the outer radiation belt L = 4.5. This model incorporates a plasmatrough number density model, a field-aligned density model and a realistic wave power and frequency model. We solve the 2D bounce-averaged momentum-pitch-angle Fokker-Planck equation and show that the Whistler-mode chorus can be effective in the acceleration of electrons, and enhance the phase space density for energies of -1 MeV by a factor from 10 to 10^3 in about two days, consistent with the observation. We also demonstrate that ignorance of the electron number density variation along field line and magnetic local time in the previous work yields an overestimate of energetic electron phase space density by a factor 5-10 at large pitch-angle after two days, suggesting that a realistic plasma density model is very important to evaluate the evolution of energetic electrons in the outer radiation belt.     

Identification of Radial Distance of Plasma Dispersionless Injection Boundary from the Injection Source

Measurements of energetic particles obtained by the two geosynchronous satellites （1991-080 and LANL-97A） are performed to investigate the plasma injection boundary and source region during the magnetospheric substorms. The measurement method is developed to allow remote sensing of the plasma injection time and the radial distance of injection boundaries by using measured energy dispersion and modelling particle drifts within the Volland-Stern electric field and the dipole magnetic field model. The radial distance of the injection boundary deduced from a dispersion event observed by the LANL-97A satellite on 14 June 1998 is 7.1RE, and the injection time agrees well with the substorm onset time identified by the Polar Ultraviolet Imager. The method has been applied to an event happened at 22.9 UT on 11 March 1998, when both the satellites （1991-080 and LANL-97A） observed the dispersionless character. The results indicate that the radial distance of injection source locates at 8.1RE at magnetotail, and particles move earthward from magnetotail into inner magnetosphere at 22.5 UT.     

Bounce-Averaged Acceleration of Energetic Electrons by Whistler Mode Chorus in the Magnetosphere

We construct the bounce-averaged diffusion coefficients and study the bounce-averaged acceleration for energetic electrons in gyroresonance with whistler mode chorus. Numerical calculations have been performed for a band of chorus frequency distributed over a standard Gaussian spectrum specifically in the region near L = 4.5, where peaks of the electron phase space density occur. It is found that whistler mode chorus can efficiently accelerate electrons and can increase the phase space density at energies of about 1 MeV by more than one order of magnitude about one day, in agreement with the satellite observations during the recovery phase of magnetic storms.     

Bounce-averaged Pitch-angle Diffusion by Electromagnetic Ion Cyclotron Waves in Multi-ion Plasmas

We present a study on the gyroresonant interaction particles in multi-ion （H^＋, He^＋, and O^＋） plasmas between electromagnetic ion cyclotron waves and ring current We provide a first evaluation of the bounce-averaged pitch angle diffusion coefficient 〈Dαα〉 for three typical energies of 50, 100 and 150keV at L ≈ 3.5, the heart of the symmetrical ring current. We show that in the H^＋-band and He^＋-band, 〈Dαα〉 can approach - 10^-4 s^-1 for ion H^＋, and - 5 × 10^-5 s^-1 /or ion He^＋; meanwhile, in the O^＋-band, 〈Dαα〉 can reach - 10^-5 s^-1 for ions He^＋ and O^＋. The results above show that the EMIC wave can efficiently produce precipitation loss of energetic （- 100 keV） ions （H^＋, He^＋ and even O^＋）, and such a wave tends to be a serious candidate responsible for the ring current decay.     

Optical necklaces generated by the diffraction on a stack of dielectric wedges

We demonstrate that the regular ring-shaped arrays of Gaussian beams, or optical necklaces, can be generated using diffraction on a stack of dielectric wedges. A condition for self-similarity and structural stability of the beams has been derived and shows good comparison with experimental data.     

Anomalous behavior of optogalvanic signal in a miniature neon discharge lamp

A strong optogalvanic effect has been observed in a negative glow of a miniature neon discharge lamp using tunable pulse dye laser pumped by a copper vapor laser. A comparative study on temporal evolution of optogalvanic signal in a positive and negative dynamic resistance region of the discharge is described. Dye laser beam was tuned to various neon transitions 1s_i → 2p_j (Paschen notations) within 570-617 nm wavelength range. Anomalous behavior of optogalvanic signal was observed at 588.2 nm for (1s₅ → 2p₂) neon transition at low discharge current (<220 μA). This anomalous behavior is the attributes of damped oscillations of optogalvanic signal that correlate with negative dynamic resistance (dV/di < 0) of the discharge. Penning ionization at low discharge current and small energy mismatch is assumed to be the main cause of the negative dynamic resistance. Penning ionization process has been explained by resonantly ionizing energy transfer via collisions between neon buffer gas atoms in the lowest metastable state (1s₅) and electrode sputtered atoms in ground state using their partial energy level diagram.     

Trapping State in a System of Single Three-level Trapped Ion Driven by External Fields

We investigate the interaction of a single three-level trapped ion with two laser beams. By applying a unitary transformation and a small rotating transformation, an exact solution to this quantum system is obtained without performing the Lamb-Dicke approximation, and the trapping state is observed.     

High-rate pulse-train generation by phase-only filtering of an electrooptic frequency comb: Analysis and optimization

We investigate the generation of high-rate optical pulse trains by spectral phase-only filtering of a frequency comb derived from an electrooptically phase-modulated continuous-wave laser. The technique is initially analyzed as a two-step filtering process. First, a fundamental pulse-train with repetition-rate equal to the modulation frequency is obtained by line-by-line phase-cancellation of the electrooptic frequency comb. Second, the temporal Talbot-effect is considered so that the output pulse repetition-rate is an integer multiple of the electrooptic modulation frequency. Nonidealities found in the fundamental train lead, in general, to multiplied trains with important degradations. We numerically analyze optimum modulation conditions for generation of output pulse trains with minimum peak-to-peak variations and/or maximum extinction level. On the other hand, a genetic algorithm is considered to numerically find optimum line-by-line phase-only filters that generate output multiplied trains with minimized degradations. Numerical simulations show that, in general, this second approach allows for improvement in the quality of the resultant multiplied trains, in terms of the uniformity degree and/or noise-level, compared with the pulse trains resulting from the Talbot-effect-based approach.     

Photoacoustic analysis of stimulated emission in pulsed dye lasers

Stimulated emission in pulsed dye lasers was characterized in several experimental conditions by analyzing the changes in the acoustic signals generated in a dye solution, with the dye laser cavity either active or inhibited (i.e., by blocking the optical path or misaligning of the optical components). Pump energy threshold, optimum dye concentration, tuning range and maximum-emission wavelength of a rhodamine 6G dye laser were measured by this method. An approximate model for the photoacoustic signal generation consistent with the experiments is presented.Member of CONICET     

Superhydrophobic properties of silver-coated films on copper surface by galvanic exchange reaction

Hydrophobic properties of thin nanostructured silver films produced by galvanic exchange reaction on a copper surface were studied after passivation with stearic acid. The morphology of the silver films was controlled by varying the concentration of silver nitrate in the solution. Water contact angle as high as 156° and contact angle hysteresis as low as 5° were achieved for samples obtained with initial silver ion concentration of 24.75 mM in the solution. However, a strong dependence of contact angle and contact angle hysteresis on the fractal-like morphology of the silver films was observed with the variation of silver ion concentration.     

Analytical analysis of the “collapse-revival” effect in the Jaynes-Cummings model

The evolution of the atomic state population in a two-level system coupled to a single-mode quantum field is calculated in the analytical form. Essential characteristics of the “collapse-revival” effect are expressed in terms of the physical parameters of the system by means of simple formulas in both the resonant and the non-resonant cases. The obtained results are of great importance for the qualitative analysis of the phenomenon.