Upward Electric Field Research Articles

Adhesive strength distribution of charged particles on metal substrate in external electric field

An improved airflow method to measure the distribution of adhesive strength between charged particles and a metal substrate in an external electric field is presented. In this study, toner particles were negatively charged with a corona charger and deposited on the substrate. The substrate with the particles on the surface was mounted in a rectangular air channel with parallel electrodes. Air velocity was increased at a constant rate, and entrained particles were detected by a laser particle monitor. By studying the relationships between particle entrainment efficiency and air velocity, the particle–substrate adhesion was analyzed in detail. It was found that particle adhesion increased with the increase in the initial charge of particles. It was also found that the particle adhesion increased in a vertically downward electric field but decreased in the upward electric field. These experimental results cannot be explained by the Coulomb force in the electric field. Therefore, a theoretical model based on charge transfer in the external electric field was proposed. This model explains the variation of the particle–substrate adhesion by considering the image force arising due to the transferred charges.

Direction-regulated electric field implanted in multilayer Mo–TiO2 films and its contribution to photocatalytic property

Multilayer Mo-doped TiO2 thin films were prepared by In-situ RF magnetron co-sputtering. Surface morphology, crystallite parameters, valence states and absorption band were investigated with atomic force microscopy, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy and ultraviolet–visible spectroscopy. AC impedance spectroscopy and photocatalytic capability of different layer-assemble modes were examined on an electrochemical workstation under visible light. The result indicates the electric fields resulted from Fermi level drops could remarkably accelerate the separation of photogenerated carriers. The double-layer film, which was prepared by covering the uniformly Mo doped layer with an undoped surface layer, has the smallest impedance. The strongest catalytic capability is demonstrated by the three-layer film, which has an undoped surface layer, a uniformly doped middle layer and an ultrathin, heavy doped bottom layer. Although different layer modes have little influence on absorption edge, our observations suggest that by manipulating doping content in each layer, we can implant upward electric field arrays, which has considerable potential to enhance the photocatalytic property, into multilayer Mo-doped TiO2 films.

Incoherent scatter radar observation of E-region vertical electric field at Arecibo

[1] We report the first spatially and temporally continuous observations of the upward electric field in the E-region using the Arecibo incoherent scatter radar. This is achieved by employing the dual beam incoherent scatter radar measurements of ion velocity and using a theoretical ion-neutral collision model. The derived daytime vertical electric field, from ∼105 km to 145 km, shows large height variation, as in previous nighttime rocket measurements. Assuming that the electric field along the field line is negligible, the height variation is the same as the horizontal variation at Arecibo. Although the height variation has been attributed to gravity waves in previous studies, this explanation is not consistent with the temporal characteristics in our observation. We further discuss the error sources that affect the measurement of the electric field.

Plasma boundary variability at Mars as observed by Mars Global Surveyor and Mars Express

Abstract. We have used Mars Express (MEX) and Mars Global Surveyor (MGS) simultaneous and non-simultaneous measurements to study the Martian plasma environment. In particular, we have derived quantitative expressions for the altitude of the terminator bow shock (BS) and magnetic pileup boundary (MPB) as functions of solar wind dynamic pressure, crustal magnetic fields and solar EUV flux. We have also studied the influence of the interplanetary magnetic field (IMF) direction. Through simultaneous two-spacecraft case studies we have shown that the dynamic pressure has a strong influence on the location and shape of these boundaries, which is also confirmed through a large statistical study. A higher dynamic pressure pushes the boundaries downward. The IMF direction has a weaker but still significant influence on both boundaries and causes them to move outward in the hemisphere of locally upward electric field. However, the MPB in the Southern Hemisphere is found to actually move inward when the electric field is directed locally upward. The crustal magnetic fields in the Southern Hemisphere have a strong influence on the MPB and cause it to move to higher altitudes over strong crustal magnetic fields. The influence of the crustal magnetic fields on the BS is more ambiguous since there are few crossings over the strongest crustal fields, but there appears to be at least a small trend of a higher BS for stronger crustal fields. An increased solar EUV flux has been found to cause the BS to move outward and the MPB to move inward.

Experiments on dust transport in plasma to investigate the origin of the lunar horizon glow

Dust grains on the lunar surface are exposed to UV radiation and solar wind plasma and can collect electrical charges, leading to their possible lift‐off and transport in the presence of near‐surface electric fields. Motivated by the long‐standing open questions about the physics of electrostatic lunar dust transport, we investigated the dynamics of dust grains on a conducting surface in a laboratory plasma. The dust used in these experiments was a nonconducting JSC‐Mars‐1 sample with particle size of less than 25 microns. We found that dust grains placed on a conducting surface, which is biased more negatively than its floating potential, charge positively, and an initial pile spreads to form a dust ring. Dust particles were observed to land on insulating blocks, indicating the height of their hopping motion. The measured electrostatic potential distribution above the dust pile shows that an outward pointing electric field near the edge of the pile is responsible for spreading the positively charged grains. A nonmonotonic potential dip was measured in the sheath above an insulating patch, indicating a localized upward electric field causing the dust lift‐off from the surface. Faraday cup measurements showed that the grains near the boundary of the dust pile collect more charge than those closer to the center of the dust pile and can be more readily lifted and moved in the radial direction, leading to the formation of a spreading ring.

The prereversal enhancement in the vertical drift for Fortaleza and the sporadic E layer

Using ionogram-recorded data for the location of Fortaleza ( 3 . 8 ∘ S, 38 . 0 ∘ W; magnetic latitude = - 6 ∘ ), the relation between the evening prereversal enhancement in the vertical F region plasma drift ( E × B ) and the diurnal variation of the sporadic E layer ( Es ) is examined. The database examined corresponds to the period of June 2001. The F region vertical drifts obtained as dh ′ F / dt for quiet days reveal that when the amplitudes of the evening prereversal enhancement (PRE) are higher, an interruption of an ongoing sporadic E layer is observed. A recent investigation by Abdu et al. [2003. Journal of Geophysical Research 108(A6), 1254. doi: 10.1029/2002JA009285.], showed that an upward electric field, intensified during the PRE, can be responsible for the inhibition of the sporadic E layer. In this work, we investigate the possible influence of a modified conductivity on the PRE development. The model developed by Batista et al. [1986. Journal of Geophysical Research 91(A11), 12055–12064.], based on the work of Heelis et al. [1974. Planetary and Space Science 22, 743–756.], was used to test the response of the PRE (its amplitude, time of occurrence and time of inversion) when the electrical conductivity of the E region is modified, specifically around sunset. The real cause of this modified conductivity is not investigated here, but the presence of a sporadic E layer could partially contribute to that. The causes of the agreement or disagreement between the computed and the observed value of vertical drift are discussed.

Electrostatic potentials in the downward auroral current region

Assuming a fixed ion density, adiabatic electron motion, and quasi‐neutrality, we use the stationary Vlasov equation to derive the self‐consistent potential in an auroral flux tube that carries downward current. Our model predicts downward electric fields ∼5 mV/m at an altitude near 2000 km, and around 4000 km the potential reaches ∼2.5 kV. A weak upward electric field at high altitudes reduces the potential, and the potential difference between the ionosphere and magnetosphere is much smaller.

Effects of treatment parameters in electric-field-enhanced postexposure bake

This article demonstrates the improved lithographic performance of Shipley UVIIHS with an electric-field treatment during postexposure bake (PEB) for KrF optical exposures. Linewidth trends with treatment are given and explained through simulation of the acid motion. An upward electric field of approximately 10 V/μm was applied during the first 7 s of PEB to crack the surface inhibition, and thereafter the field polarity was altered every 7 s to enhance the acid-catalyzed reactions. Compared with standard PEB, the electric-field treatment resulted in deeper trenches, wider openings and significant compensation for underexposure. In some cases, electric-field-enhanced PEB led to more profile tapering, indicating that a larger downward direct electric field is needed to enhance the deprotection reactions in the lower half of the resist.

Factors controlling the location of the Bow Shock at Mars

During the first year of the Mars Global Surveyor (MGS) mission, 553 shock crossings have been identified from a total of 363 orbits. The shape of the shock has been determined by examining the MGS spacecraft Magnetometer/Electron Reflectometer (MAG/ER) data. The location of the shock was found highly variable. The present study shows that the high crustal magnetic sources, found in the southern hemisphere, do not seem responsible for the Bow Shock (BS) variability. The present study shows that contrary to many expectations there is no obvious strong one to one correlation between the location of the highest crustal sources and the variability of the shock position. On the other hand, the shock appears farthest from Mars in the hemisphere of locally upward interplanetary electric field consistent with the idea that mass loading play a role in controlling the BS location, which confirms previous results.

Origin and geometry of upward parallel electric fields in the auroral acceleration region

Electric fields, magnetic fields, and plasmas measured on the Polar satellite are studied to determine the altitude extent of the upward field‐aligned current portion of the auroral acceleration region and the physical processes that populate it with parallel electric fields. This region extends upward to a geocentric altitude of 3 or 3.5 Earth radii at premidnight local times during the spring and fall. In a model for this region a necessary but not sufficient condition for the appearance of parallel electric fields is an upward field‐aligned current. Parallel electric fields will exist where the plasma density is insufficient to carry this imposed field‐aligned current through the converging magnetic field. These parallel fields are associated with (1) high‐altitude electron acceleration required to carry the imposed current through the low‐density region; (2) a low‐altitude sheath required to inject compensating positive charge into the region and to restrict entry of secondary electrons from below; and (3) the midaltitude maintenance of local charge neutrality. The parallel electric field in the low‐altitude sheath is directly measured to be as large as several hundred mV m−1, while the higher‐altitude fields appear to have magnitudes of a few mV m−1. The low‐altitude sheath is corrugated in a manner that does not depend on striations of the field‐aligned current but that may depend on density variations.

The connection between auroral acceleration and auroral morphology

Auroral acceleration is usually conceived in terms of measured electron energy-spectra and pitch-angle distributions. But another historical thread draws upon studies of auroral morphology. By 1970 it had been discovered that the rays in active rayed arcs are actually arrays of vortices similar to those observed in fluid shear and in laboratory experiments involving magnetized sheet electron beams (Kelvin-Helmholtz instability). The apparent shear flow implied that rays drift at the E X B velocity in a convergent electric field of the order of 1 v/m. But ionospheric electric fields rarely exceeded 100 mV/m. A suggested solution, that the electric fields existed in the source region but did not map down to the lower ionosphere, required that there be an upward electric field in the center of the arc. This field would accelerate electrons downward into the ionosphere. To compare electric fields inferred from inverted V energy with those inferred from ray motions requires a fortunate conjunction of a rocket or satellite passing through an overhead rayed arc. The AMICIST payload provided such an opportunity and the inferred fields were consistent. Morphology studies also show that clockwise spirals, associated with upward currents and counter-clockwise curls, associated with charge sheets, have scale-sizes differing by two orders of magnitude. This suggests that current sheets have thickness of order 50 km (multiple arc) while negative charge tends to be concentrated in thin layers of order 500m (arc elements). This difference needs to be considered in relating parallel fields to Birkeland currents. Finally, conjugate studies of auroras suggest that the potential contours close somewhere above the acceleration region rather than in the conjugate ionosphere. This raises the question of how electrons are forced into the regions of high negative potential.

Results from the DC electric field experiment on the Freja satellite

Observations by Freja were the first to show that positive potential structures associated with downward field-aligned electric fields exist in the downward field-aligned current region sometimes connected with black aurora. They form a counterpart to the negative potential structures with upward parallel electric fields observed on auroral field lines. Different mechanisms are likely to contribute to the downward parallel electric fields at different altitude regimes, resulting in an altitude distribution which at present is unknown. Downward parallel electric fields at low altitudes may be generated as a consequence of exceptionally low plasma densities caused by the erosion of ionospheric electrons and perpendicular transport of ions in a diverging electric field. High-resolution data from a satellite crossing through the head of a Westward Travelling Surge reveal a very inhomogenous and complicated picture of the surge, such as narrowly structured, intense (up to 700 mV/m) converging electric fields, intense electron precipitation and balanced field-aligned currents (up to 30 μA/m 2) embedded within an extended region of intense, high-energy electron precipitation, weak electric fields and field-aligned currents. The data suggest that a significant part of the upward surge current is closed by downward currents in the near surroundings. No evidence is found of a pronounced westward electric field with a southward polarization field, which according to some surge models is expected to be found within the high-conductivity surge region. Finally some data regarding subauroral electric fields are presented.

Flare loops heating by the 0.1?1.0 MeV proton beams

The fast heating of coronal loops at the very beginning of solar flares is discussed as a first observable signature of downstreaming 0.1–1 MeV proton beams. We place emphasis on the produced by proton beams large-scale upward electric field, supporting beam-driven instability of the kinetic Alfven waves (KAW). The considerable part of a beam kinetic energy may be converted into heat via intermediate KAW with heated region initially spreading from the top downward to footpoints of the loop-like coronal structures with velocity of about a few thousands km/s.

Synergistic effects of hot plasma‐driven potentials and wave‐driven ion heating on auroral ionospheric plasma transport

Transverse acceleration by waves and parallel acceleration by field‐aligned electric fields are important processes in the transport of ionospheric ions along auroral field lines. In order to study the transport of ionospheric plasma in this environment we have developed a generalized semikinetic model which combines the tracking of ionospheric ion gyrocenters with a generalized fluid treatment of ionospheric electrons. Large‐scale upward and downward directed electric fields are generated within the model by introducing magnetospheric plasma whose components have differing temperature anisotropies. We study the effects of such potentials when combined with the effect of ion heating by a distribution of waves along the flux tube. We find that the combination of wave heating and an upward electric field results in an order of magnitude increase in O+ outflow (compared to a case with an upward electric field and no wave heating). Under these conditions we observe the formation of bimodal conics. When a downward electric field is added to a case with wave heating, the energy gained by the ions from the waves increases by a factor of 2 or 3 (over the scenario with wave heating and no hot plasma‐driven electric field) owing to their slower transit of the heating region. Typically, the velocity distributions under these conditions are toroids and counterstreaming conics. We also find that the upflowing, dense, heated ionospheric plasma acts to reduce the potential set up by the anisotropies in the magnetospheric components.

On the instability of ionospheric plasma originated by charge separations in the troposphere. The «UFO» phenomenon mechanism

The troposphere is the seat of powerful processes which originate separation of electric charges. Thunder clouds give rise to a huge vertical separation of charges. But also known is a different electrification mechanism activated by wind, which allows for horizontal separation of charges. In favourable conditions, when charges are displaced at long distances, image charges appear in the ionspheric plasma and an upward electric field is originated which makes the ionosphere boundary unstable. If this occurs, recombination of displaced charges involves ionosphere conductivity and gives rise to a downward electron stream ejected from the bottom of the ionosphere. It may produce a peculiar airglow phenomenon, which consists of the emission of light in a narrow region lying at stratospheric or mesospheric altitudes. This outcome of the electrification process just mentioned shows a close connection with a special class of «UFO» sightings, that is, those referred to by J. Hynek as «nocturnal light» and which consist of bright specks of light moving in the night sky.

The effect of the electric field and neutral winds on E-region ion densities and conductivities at low latitudes

A model to calculate electron densities and electrical conductivities in the ionospheric E-region at low latitudes has been developed. Calculations have been performed under photochemical equilibrium and including plasma transport due to the electric field and neutral winds. Results have been compared with observations at Arecibo (18.15°N, 66.20°W), Thumba (8°32′N, 76°51′E) and SHAR (14.0°N, 80.0° E). Good agreement is obtained for Arecibo. For Thumba and SHAR agreement is satisfactory for altitudes above 110 km. Below 100 km, model predictions are too low in comparison with the observed data. The effect of plasma transport on electron densities and Hall and Pedersen conductivities is investigated in detail. A combination of neutral winds and a downward (or westward) electric field can compress the plasma into a thin layer. An upward electric field along with the neutral winds gives rise to a broad, multilayered profile. The ratio of height-integrated Hall to Pedersen conductivities changes from 1.2 to 2 in some cases.

Dual sounding rocket observations of low‐altitude electrostatic shocks

Two sounding rockets were launched near simultaneously into the late evening auroral zone from Poker Flat and Fort Yukon, Alaska, on February 7, 1984, placing two payloads on nearly the same magnetic field lines simultaneously. The Black Brant X payload, with an apogee of 1040 km, measured dc electric fields of ∼300 mV/m, while the lower altitude Terrier‐Malemute payload (apogee 640 km) measured only typical ionospheric electric fields under ∼100 mV/m. These measurements imply a parallel potential of several kV below the higher payload, most probably occurring between the two payloads. The exact value of the parallel potential is dependent on the motion of the potential structure with respect to the payload. There is some evidence of an ∼2‐kV potential drop between the payloads in the electron data. Nonadiabatic electron trajectories are also implied. No possible resistive mechanism to support the parallel field is observed in the 100‐Hz to 10‐kHz frequency band. The existence of resistance‐producing turbulence at other frequencies or of a type not measured by the probes, or localized parallel potentials not coincident with the payload trajectories, are thus implied. The observation of apparent “secondaries” at all altitudes implies either a potential barrier of hundreds of electron volts that trapped these electrons above the region of upward electric field or that the secondaries were actually locally accelerated electrons originating out of the cold background. The plasma conditions encountered at 1000 km are unusual for sounding rockets. During the highest electric fields and lowest densities, a 5.8‐m antenna measured significantly larger dc electric fields than a 3‐m antenna. Internal consistency checks, the near‐sinusoidal nature of the spin‐dependent waveform, and the >10 λDebye separation of the booms from the payload lead to the conclusion that the longer boom measurements were correct, the payload wake having interfered with the shorter antennas.

Dayside auroral particle acceleration mechanisms derived from dynamics explorer data.

The characteristics of dayside electron acceleration regions, or inverted V's, and the nature of the field-aligned currents flowing in their vicinity are studied by using data from Dynamics Explorer hot-plasma and magnetic-field instruments. It is shown that dayside inverted-V events are common features of the mid-altitude extension of the boundary layer, which lies equatorward of the cusp. Upward-accelerated ionospheric electron beams are found to be carriers of downward region-1 currents even in regions of downward electron acceleration. It is not clear, however, how the upward-accelerated cold electron beams can exist above an apparent upward parallel electric field, since such a potential different would tend to confine the cold ionospheric electrons to low altitudes.

Average low‐latitude meridional electric fields from DE 2 during solar maximum

Electric field data from the double probe vector electric field instrument (VEFI) on the DE 2 spacecraft have been analyzed to determine the average meridional electric field (zonal ion flow) patterns in the region between ±30° magnetic latitude during solar maximum conditions. Over 300 passes were used to compile the data set. Data were projected to a constant 300‐km altitude and to the equatorial plane assuming that the electric field along the magnetic field was zero. The average data set displayed a rapid increase of the downward meridional electric field with local time near 1800 MLT with the higher latitudes seeing the change first. A secondary nighttime maximum of this electric field component was observed post midnight with the crossover to upward electric fields (westward ion flow) occurring between 0400 and 0500 MLT. A sharp return to near zero was observed between 1200 and 1300. Typical average amplitudes range between 3 and 6 mV/m. No consistent variations with magnetic activity were observed. Although the daily variation in the zonal ion flow is dominated by the diurnal term, a net superrotation is evident in the harmonic analysis. The superrotation is strongest near the equator and decreases with latitude, because of the disturbance dynamo. The higher order harmonics up through the quatrediurnal term are also of significant magnitude in the analysis of the shape of the daily variation. Close similarity is seen to the zonal neutral winds indicating that they form the principal driving force. The magnitudes of the electric field derived ion drift are somewhat higher than the average F region neutral wind values. This along with the higher order harmonic content argues for the need to develop fully coupled E and F region model depicting the ionosphere and thermosphere interactions in a self‐consistent fashion.

Plasma Processes Driven by Current Sheets and Their Relevance to the Auroral Plasma

Satellite and rocket observations have revealed a host of auroral plasma processes, including large dc perpendicular electric fields (E⊥) associated with electrostatic shocks, relatively weak parallel electric fields (E║) associated with double layers, upflowing ions in the form of beams and conics, downflowing and upflowing accelerated electron beams, several wave modes such as the electrostatic ion-cyclotron (EIC), lower hybrid (LH), very low frequency (VLF), extremely low frequency (ELF), and high-frequency waves and associated nonlinear phenomena. Recently, we have attempted to simulate the various processes using a two-dimensional particle-in-cell code in which the plasma is driven by current sheets of a finite thickness. Striking similarities between the observed auroral plasma processes and those seen in the simulations are found. In this paper we give a review of the plasma processes dealing with dc and ac electric fields, formation of ion beams and conics, and electron acceleration. Electrostatic shock-type electric fields (E┴e) occur near the current sheet edges. Such fields arise because of the contact between the high-and low-density plasmas inside and outside the sheet, respectively. Double layers having upward electric fields form inside the sheet and they are distinguishable from the large perpendicular electric fields (E⊥e) only in wide sheets with thicknesses l >> ρi, the ion Larmor radius. Double layers with a reverse polarity form outside the sheet where downward currents flow. The most energetic ions are found to have pitch angles near 90°, implying a large perpendicular acceleration of the ions.