Photoelectron Flux Research Articles

Parameterization of Secondary Ionization Rates and Photoelectron Heating Rates of Venus and Mars

AbstractAs a fundamental physical process in the ionosphere, photoionization and the associated photoelectrons play vital roles in determining the ionospheric electron density and temperature for Earth and other planets with atmospheres such as Mars and Venus. The production and transport of ionospheric photoelectrons have been widely examined on Earth, but relatively less studied for other terrestrial planets, such as Mars and Venus. In this study, a two‐stream photoelectron transport model for Mars and Venus is constructed, in which the photoelectron fluxes, photoelectron heating rates, primary and secondary ionization rates are calculated. The simulated photoelectron fluxes agree with Mars Atmosphere and Volatile Evolution (MAVEN) observations at various altitudes, with the input of solar spectrum irradiance, electron density and temperature, neutral density and temperature observed by MAVEN. Moreover, by parametrically fitting the simulation results for various solar zenith angles and solar activities, we obtain empirical parameterized formulas for ionization and heating efficiencies which can potentially be adapted to planetary ionospheric models for the community.

A Missing Piece of the E‐Region Puzzle: High‐Resolution Photoionization Cross Sections and Solar Irradiances in Models

AbstractMost ionospheric models cannot sufficiently reproduce the observed electron density profiles in the E‐region ionosphere, since they usually underestimate electron densities and do not match the profile shape. Mitigation of these issues is often addressed by increasing the solar soft X‐ray flux which is ineffective for resolving data‐model discrepancies. We show that low‐resolution cross sections and solar spectral irradiances fail to preserve structure within the data, which considerably impacts radiative processes in the E‐region, and are largely responsible for the discrepancies between observations and simulations. To resolve data‐model inconsistencies, we utilize new high‐resolution (0.001 nm) atomic oxygen (O) and molecular nitrogen (N2) cross sections and solar spectral irradiances, which contain autoionization and narrow rotational lines that allow solar photons to reach lower altitudes and increase the photoelectron flux. This work improves upon Meier et al. (2007, https://doi.org/10.1029/2006gl028484) by additionally incorporating high‐resolution N2 photoionization and photoabsorption cross sections in model calculations. Model results with the new inputs show increased O+ production rates of over 500%, larger than those of Meier et al. (2007, https://doi.org/10.1029/2006gl028484) and total ion production rates of over 125%, while production rates decrease by ∼15% in the E‐region in comparison to the results obtained using the cross section compilation from Conway (1988, https://apps.dtic.mil/sti/pdfs/ADA193866.pdf). Low‐resolution molecular oxygen (O2) cross sections from the Conway compilation are utilized for all input cases and indicate that is a dominant contributor to the total ion production rate in the E‐region. Specifically, the photoionization contributed from longer wavelengths is a main contributor at ∼120 km.

Evaluate the effects of kilovoltage transmission target X-ray equipment combined with radiosensitizers for Auger electron radiotherapy

Auger electrons are well-suited for targeted radiotherapy due to their ability to transfer high energy over short distances. Auger radiotherapy can be achieved by utilizing the characteristic radiation of transmission X-ray tubes and radiosensitizers to generate numerous Auger electrons. In this study, the Monte Carlo N-Particle (MCNP6) code was employed to simulate the deposition of dose in cells when combining the transmission X-ray tube with various concentrations of radiosensitizers. The results reveal that when the transmission X-ray tube is combined with 70 mg of gold nanoparticles (GNPs), the photoelectron flux is 1.16 × 103 (particles/cm2), which is 3.86 times higher than that observed with 0 mg of GNPs. Furthermore, the Auger electron flux is 3.51 × 102 (particles/cm2), representing a 15.51-fold increase compared to 0 mg of GNPs. The corresponding dose enhancement factor (DEF) is 3.14, representing the most substantial proportional increase observed. This study suggests that the combination of a transmission X-ray tube with appropriate radiosensitizers and concentrations can generate a significant number of photoelectrons and Auger electrons, resulting in a notable radio-enhancing effect. This innovative approach holds promise for the development of Auger radiotherapy as a potential therapeutic process. Future investigations could explore the optimal combination of transmission X-ray tubes and radiosensitizers to further advance the applications of Auger radiotherapy.

Single Atoms in Photocatalysis: Low Loading Is Good Enough!

We disperse Pt single atoms (SAs) with different loading densities on anatase TiO2 thin films and evaluate the photocatalytic H2 generation as a function of the incident light intensity. We show that under common illumination intensities (such as terrestrial solar illumination), a minuscule Pt SA loading of ∼105 atoms μm–2 (surface Pt content ∼0.1 at.%) is sufficient to achieve a maximized H2 production rate. This results in a maximum turnover frequency at a single Pt atom site of ∼300 H2 molecules s–1. For a vast majority of illumination conditions and a suitable surface configuration, it is not the density of co-catalytic sites that is rate-determining (a high loading is not needed!), but the charge carrier generation (and flux of photoelectrons to the co-catalytic centers) determines the overall reaction rate. This is in stark contrast to SA catalysis of classic chemical reactions where generally a maximum loading of reactive SA delivers a maximum activity.

Influence of nano-sized horizontal inhomogeneities on surface profiling by means of XPS

Quantitative analysis of thin films surface is performed by means of X-ray electron spectroscopy (XPS) according to a calculation model assuming surface layers of the target to be homogeneous and parallel. However, almost every surface of an ultra-thin film is rough. A study of such surface using the plane-parallel layer model will lead to incorrect results. This work proposes to use the model of inhomogeneous stochastic nano-structured surface layer for ultra-thin film profiling. Surface stochastic nano-structured inhomogeneities are described by the normal Gauss distribution function. To determine these inhomogeneities, three parameters are specified: dispersion (spread of thicknesses by the layer), mean and maximal thickness of the surface layer. For the first time, the type of X-ray photoelectron spectrum of an inhomogeneous stochastic nano-structured surface is found that is determined by functions of photoelectron production and transmission through that surface layer. The designed model is based on the following assumptions: photoelectrons are produced in substance and travel straight-forward (Straight Line Approximation) along the surface, photoelectron flux density decreases in the layer according to the Bouguer–Lambert law, photoelectrons of different energies lose energy differently, photoelectron energy losses in bulk and on surface differ. Modeling of X-ray photoelectron spectra of an oxidized metal film is performed using different models: homogeneous plane-parallel layers, an island nano-structured surface layer and an inhomogeneous stochastic nano-structured surface layer. Ranges of applicability of plane-parallel layer models and simple periodical nano-structured island surface layer for inhomogeneous stochastic nano-structured surface profiling are determined. The model of homogeneous plane-parallel layers shows satisfactory profiling results by some values of parameters of an inhomogeneous stochastic surface layer. It is shown that the model of a simple periodically nano-structured island layer leads to inadequate results by profiling of an inhomogeneous stochastic surface. The investigation shows that for more accurate profiling of an inhomogeneous ultra-thin film, it is necessary to consider inhomogeneity of a real surface, otherwise the calculated results would not match the true profile.

Spatio‐Temporal Structure of Far Ultraviolet Martian Dayglow Observed by EMM‐EMUS

AbstractMars' ultraviolet dayglow has been used to study its upper atmosphere for over four decades. Identifying variations in emission features has provided information on composition, density, and temperature. The Emirates Mars Ultraviolet Spectrometer onboard the Emirates Mars Mission observes Mars' dayglow at Far and Extreme UV wavelengths. Variations in disk emission features are studied, with a focus on O I 130.4, CO Fourth Positive Group and C I 156.1 nm. All show variations with local time (LT) and emission angle as expected. Dawn‐dusk asymmetry observed is attributed to LT differences in advection. Variations in the brightness of several dayglow features, including 130.4 nm, with irregular shapes are noted in around 25% of the disk images. These display some LT and hemispheric asymmetry in their occurrence rates. Examination of their spatial structure, occurrence, and spectra suggests these are associated with variations in composition and photoelectron flux.

Ionospheric photoelectrons: A lateral thinking approach

This paper presents a personal account of developments in the solution of two related problems that limited the accuracy of ionosphere calculations in the 1980s. The first problem concerns the model-data discrepancies in the ionosphere photoelectron flux spectrum. Early comparisons between measured and modeled data revealed discrepancies in magnitude and shape. A lateral thinking approach revealed that there were problems with two key photoelectron model inputs: namely, the electron impact cross-sections and the solar extreme ultraviolet irradiance. This work led to the development of a widely used EUVAC solar irradiance model for ionosphere electron density calculations. The second problem relates to the neutral winds that are crucial for modeling variations in the ionosphere ion and electron densities. There is a lack of thermosphere neutral wind data because they are difficult to measure. The winds determine the altitude at which the electron density peaks. An accurate solution to this problem was the development of an algorithm that assimilates the altitude of the peak electron density into ionosphere models. This technique works because the altitude of the peak density is very sensitive to variations in the neutral wind.

Simulation of photoelectron flux, electron density, emission rate and limb intensity of CO(a3π) Cameron bands in the Martian thermosphere: Comparisons with (1) SPICAM and IUVS observations and (2) other model calculations

Simulation of photoelectron flux, electron density, emission rate and limb intensity of CO(a3π) Cameron bands in the Martian thermosphere: Comparisons with (1) SPICAM and IUVS observations and (2) other model calculations

Photodetachment microscopy with double pulse in time-dependent fields

We present the photodetachment microscopy of the singly charged negative ions using the double pulse with a frequency near the ionization threshold in the presence of the time-dependent external electric field. In the presence of time-dependent electric field, the number of photoelectron trajectories contributing to the electron flux at a space–time point at the detector may be more than two. We demonstrate that the relative flight times of the classical trajectories, to reach a point at the detector plane can be calculated by observing the photoelectron flux at a particular time at the detector and scanning the second pulse by varying the time delay between the two coherent laser pulses. Moreover, investigating the photoelectron flux, we have found that the flux distribution can be controlled by the relative phase difference between the two coherent pulses separated by a short time delay, at spatial and temporal points where the classical trajectories associated with photoelectron emerging at different pulses arrive at the detector simultaneously and exhibit interference. The temporal and spatial photoelectron flux distribution oscillates as a function of the relative phase difference between the pulses. The time-dependent quantum propagator approach with stationary phase approximation is linked analytically with the time-dependent closed orbit theory.

System Engineering Enhances Photoelectrochemical CO2 Reduction

The photoelectrochemical carbon dioxide reduction reaction (PEC-CO2RR) allows us to convert solar power to chemical energy with photosensitive materials. Semiconductor-based, plasmon-assisted, and dye-sensitized systems have been extensively investigated in the PEC-CO2RR. Beyond the remarkable progress in materials science, it is expected to realize new systems for satisfying the needs of both research discoveries and industry applications. In this Perspective, we summarize the latest progress in the field of the PEC-CO2RR, focusing on enhancing efficiencies via matching photoelectron flux, charge transfer rate, and mass transport rate. Based on the principles for the state-of-the-art PEC-CO2RR, new designs of the system engineering strategies on photoelectrode fabrication, reactor design, electrolyte optimization, and membrane selection are proposed to enhance selectivity and stability of the PEC-CO2RR.

Conjugate Photoelectron Energy Spectra Derived From Coincident FUV and Radio Measurements

AbstractWe present a method for estimating incident photoelectrons' energy spectra as a function of altitude by combining global scale far‐ultraviolet (FUV) and radio‐occultation (RO) measurements. This characterization provides timely insights important for accurate interpretation of ionospheric parameters inferred from the recently launched Ionospheric Connection Explorer (ICON) observations. Quantification of photoelectron impact is enabled by the fact that conjugate photoelectrons (CPEs) directly affect FUV airglow emissions but not RO measurements. We demonstrate a technique for estimation of photoelectron fluxes and their spectra by combining coincident ICON and COSMIC2 measurements and show that a significant fraction of ICON‐FUV measurements is affected by CPEs during the winter solstice. A comparison of estimated photoelectron fluxes with measured photoelectron spectra is used to gain further insights into the estimation method and reveals consistent values within 10–60 eV.

Simultaneous ionosonde investigations of the ionospheric F2 layer critical frequency and peak height at both ends of the geomagnetic tube

Based on the results of simultaneous ionosonde observations during low solar and weak magnetic activities, a coupling was found between diurnal and quasi-periodic variations in ionospheric parameters over magnetically conjugated regions, where the Ukrainian Antarctic Station (UAS) and Millstone Hill Observatory are located. A significant impact of the summer hemisphere on the nighttime variations of the F2 layer critical frequency foF2 in the magnetically conjugated region in the winter hemisphere was found. The most characteristic manifestation of this impact is the control of foF2 variations over the UAS not by the local sunset (sunrise), but by the sunset (sunrise) over Millstone Hill. It was found that the sunset over Millstone Hill leads to an increase in foF2 over the UAS, while the sunrise leads to a decrease in foF2 with a subsequent sharp increase. Both phenomena are associated with changes in the photoelectron flux from the northern hemisphere, corresponding changes in the electron temperature in the ionosphere above the UAS and the effect of these changes on the compression or rarefaction of the ionospheric plasma and changes in the plasmaspheric fluxes of H + ions. It was shown that the transition from nighttime to daytime conditions over both observation points was characterized by a significant decrease in the F2 layer peak height, and the difference in the values of this ionospheric parameter over Millstone Hill and UAS at night is due to seasonal differences in the thermospheric circulation and the difference in the behavior of the ionospheric parameters in the Northern and Southern hemispheres. Manifestations of atmospheric gravity waves, caused by the passage of local sunrise terminators, as traveling ionospheric disturbances with periods of about 90 and 75 – 120 mins over Millstone Hill and UAS, respectively, were found. These waves were most likely generated in the region located between the ionospheric F1 and F2 layers, where the sharp gradients in the electron and ion densities occur during changes in the intensity of solar radiation. It is confirmed that wave disturbances in atmospheric and ionospheric parameters can be transferred between magnetically conjugated regions by slow magnetohydrodynamic waves generated both at the heights of the ionospheric dynamo region due to the modulation of atmospheric and ionospheric parameters by atmospheric waves and the occurrence of external currents, and at the top of the plasmaspheric tube, where sharp plasma compression and heating or rarefaction and cooling occur during the passage of the solar terminator. Keywords: the ionosphere, F2 region, ionosonde measurements, geomagnetic field tube, magnetoconjugate region coupling, atmospheric gravity waves, traveling ionospheric disturbances, generation of slow magnetohydrodynamic waves

Spin-Polarized Photoelectron Fluxes from Fullerene Anions

Initial insights into spin-polarized photoelectron fluxes from fullerene anions are presented here. Both the angle-dependent and angle-integrated degrees of spin polarization of said photoelectron fluxes are discussed. Empty C60−(2p) and endohedral H@C60−(2p) and He@C60−(2p) anions, where the attached electron resides in a 2p state, are chosen as case studies. We uncover the characteristics of the phenomenon in the framework of a semi-empirical methodology where the C60 cage is modeled by a spherical annular potential, rather than aiming at a rigorous study. It is found that the spin-polarization degree of photoelectron fluxes from fullerene anions can reach large values, including a nearly complete polarization, at/in specific values/domains of the photoelectron momentum. This is shown to correlate with an inherent feature of photoionization of fullerenes, the abundance of resonances, known as confinement resonances, in their photodetachment spectra owing to a large empty space inside fullerenes. Moreover, the results obtained can serve as a touchstone for future studies of the phenomenon by more rigorous theories and/or experiments to reveal the significance of interactions omitted in the present study.

Розвиток дослідницьких здібностей учнів при вивченні оптики в умовах дистанційної освіти

An important aspect of the application of information and communication technologies (ICT) in the study of physics is the organization of a virtual experiment using appropriate software modeling tools (SMT). Such programs allow both monitor the progress of the experiment, and easily change its parameters. This is especially true when working with real equipment in the school physics classroom becomes impossible due to quarantine measures and the corresponding transition of domestic education to distance learning. The article considers the peculiarities of the use of the virtual laboratory Wolfram Demonstration Project in the study of optics by high school students in distance education. Examples of research of the phenomena of wave, geometric and quantum optics are given. The program allows students to more clearly present the studied phenomena and objects, in a matter of minutes to trace the processes that take place over a big duration in real life, or their demonstration requires complex and expensive equipment. The relevance of the development of PMZ in optics is also caused by the fact that light waves and objects with which these waves interact due to their small size (wavelength, elementary particles, the periodicity of the diffraction grating) can not be directly observed. We learn about their properties indirectly: interference and diffraction pattern, inelastic light scattering on microparticles, Photoeffect, etc.) Conducting appropriate virtual demonstrations and experiments, the teacher by increasing the component of research activities and visibility increases the activity and interest of students, improves understanding of educational material, which is especially important in distance education. The use of the virtual laboratory Wolfram Demonstration Project can significantly help the teacher in studying the optics of students in the mode of distance education, in particular, conducting laboratory work in physics. Each student, if connected to the Internet, has the opportunity to conduct their own research, following the instructions of the teacher. The described PMZ makes it possible not only to record the results of the experiment (interference and diffraction patterns, instrument readings), but also to visually observe the dynamics of motion of objects inaccessible to real observations (wave front motion, photoelectron flux, etc.). The proposed virtual demonstrations and experiments promote the development of research abilities of students, increase their activity and interest in acquiring knowledge, improve the understanding of educational material.

Model calculation of ionization efficiency in the Martian dayside ionosphere using MAVEN observations

ABSTRACT The ionization efficiency (η), which is defined as the ratio of the electron impact to the photon impact ionization rates, is calculated for the dayside Martian ionosphere using Mars Atmosphere Volatile EvolutioN (MAVEN) observations of neutral density and solar flux as input to the model. To calculate the secondary (electron impact) ionization rates, the photoelectron flux is computed using the Analytical Yield Spectrum (AYS) approach. Model calculations suggest that η should increase consistently as altitude decreases in the lower ionosphere. However, when the secondary ionization rates are calculated using the SWEA/MAVEN measured photoelectron flux, the ionization efficiency remains constant in the region 160–250 km. This behaviour is not in agreement with the theory of the altitude variation of ionization efficiency. The reason for this discrepancy is examined in detail. It is suggested that this disagreement is caused by the altitude-independent nature of MAVEN measured photoelectron flux. In two MAVEN deep dip orbits SWEA measured flux showed an altitudinal variation and the η curve estimated using these observations showed the variation in agreement with the theory. This suggests that the ionization efficiency calculated using SWEA/MAVEN measured photoelectron flux will show an altitude-dependent behaviour only when the instrument can resolve the altitudinal variation in the electron flux. We also calculated the ionization efficiency for two MAVEN dayside deep dip campaigns. The efficiency of CO2 and O showed an increase of 30 per cent and 60 per cent, respectively, at 130 km as compared to its value at 200 km.

MEANS OF IMPROVING THE QUALITY OF SERVICE OF THE COMPUTER NETWORK OF THE FORENSIC INFORMATION SYSTEM

The relevance of research. In modern forensic practice, computer networks (CN) are an integral part of computer-technical examination, therefore, ensuring their normal functioning becomes a vitally important task. In this regard, the theory of the construction, modification and operation of digital telecommunication systems raises a fairly general problem of digital signal processing, network synchronization and its stability. A solution to this problem was devoted to research, which analyzed the characteristics of the stability of the network and proposed methods for measuring the physical parameters that determine it. Many of the studies conducted were based on the use of frequency measurements in communication channels of computer networks for transmitting information. Acousto-optic spectrum analyzers (AOSAs) are widely used in forensic information system networks improving the QoS of forensic computer networks. The subject of the research: resolution of acousto-optical spectrum analyzers. The purpose of the research to improve the quality of diagnostics of parameters of computer information transmission networks based on the use of the developed signal processing technique in acousto-optic spectrum analyzers, which allows increasing the resolution of AOSA by increasing the frequency resolution of two non-simultaneous long-duration radio pulses. The results of the research. The research presents analysis of the influence of the frequency parameters of the computer network on the implementation of the relevant requirements for quality of service. Studies have been carried out on possible ways to increase the resolution of AOAC in frequency. The nonlinear characteristics of AOSA were studied, which made it possible to modernize methods for increasing the frequency resolution. The classical method of processing radar signals is used, which allows determining the delay time of arrival of a sufficiently long pulse with an accuracy significantly exceeding the pulse size. When analyzing the operation of AOSA, it is taken into account that the signal photoelectron flux in the acousto-optical spectrum analyzer is known to be described by the Poisson distribution. But one of the main properties of random variables distributed according to Poisson's law is the lack of cross-correlation of the components of the Poisson stream. This assumption can significantly increase the frequency resolution of AOSA. Conclusions. The research ascertains analytical relationship for the dispersion of the signal frequency measurement. The research proposes a technique for processing signals in AOSA, allowing to increase the resolution of AOSA by increasing the frequency resolution of two non-simultaneous radio pulses of long duration.

The dayside ionosphere of Mars: Comparing a one-dimensional photochemical model with MAVEN Deep Dip campaign observations

A one dimensional photochemical model for the dayside ionosphere of Mars has been developed for calculating the density profiles of ions and electrons under steady state photochemical equilibrium condition. The study focuses on the Deep Dip campaigns of the Mars Atmosphere and Volatile EvolutioN mission (MAVEN) and used the in-situ measurements of neutral density profiles, solar flux and electron temperatures from instruments onboard MAVEN as input to the model. An energy deposition model is employed for calculating the attenuated photon flux and photoelectron flux at different altitudes in the ionosphere. The Analytical Yield Spectrum approach is used for calculating the photoelectron fluxes. Volume production rates of major primary ions, CO2+, CO+, O+, C+, N2+, and N+, due to photon and photoelectron impact are calculated and used as input to the model in which ion-neutral chemistry in the dayside ionosphere is simulated. The modeled ion profiles are compared with the ion mode observations of Neutral Gas Ion Mass Spectrometer (NGIMS) and electron density estimates from Langmuir Probe and Waves (LPW). The model could reproduce the observed structure of the major ion profiles O2+, CO2+, and electron density reasonably well. However, when the magnitudes are compared, the modeled values are roughly a factor of 2 larger than observation. By reducing the neutral CO2 density, the model outputs and the observed ion profiles and electron density profile can become closer. The model also calculated the densities of 11 other ions, viz. N+, C+, O+, NO+, N2H+, HCO+, N2+, CO+, OCOH+, HNO+, and OH+. Profiles of each of these ions are compared with the NGIMS observations during the respective orbits and are discussed in detail. Such a comparison for the deep dip periods is reported for the first time, which showcases the level of the current understanding of the ion chemistry in the Martian ionosphere.

Photoelectron Sheath on Lunar Sunlit Regolith and Dust Levitation

Abstract Photoelectron sheath formation and subsequent fine dust levitation over the sunlit lunar regolith have been investigated by consistently accounting for the continuous interaction of the solar wind and solar radiation with the Moon. In deriving the photoelectron sheath, the Poisson equation is coupled with the latitude-dependent population density of the Fermionic photoelectrons. The altitude and latitude profiles of the electric potential, electric field, and electron density within the photoelectron sheath have been derived. A larger sheath is predicted near the terminator compared to the subsolar point. Accounting for the sheath features, the charging of levitating particles under the kinetic balance of anisotropic photoelectron flux, solar radiation, and solar wind plasma has been calculated. The dust charge is coupled with a characteristic sheath field to evaluate the altitude profile of the particle size, displaying levitation under its electrostatic equilibrium with the lunar gravity. Our analysis suggests that in equilibrium, the submicron particles may levitate up to a couple of meters above the lunar surface; for instance, at the subsolar point (0° latitude) 200 and 50 nm particles may float up to an altitude of ∼64 and ∼194 cm, respectively, while at 70° latitude near the terminator these particles are estimated to levitate at an altitude of ∼18 and ∼227 cm, respectively. The floating charged submicron dust may electrostatically interact with the functioning of experiments and can significantly affect the instrument operation.

Sensors for Photoemission Temperature Measurements

The characteristics of four different photomultiplier tubes (PMTs) that can be used for photoemission spectroscopy analysis of radiation and, in particular, for temperature measurements, are presented. The integral color temperature is determined by the ratio of two responses of a photoemissive device, which correspond to the entire photoelectron flux from the spectral sensitivity region of the photocathode, and by the current limited by the decelerating field or separated by the energy in the field of an electrostatic lens. The modulation of the electron beam instead of the light beam with a frequency of up to 1 MHz makes it possible to obtain a time resolution of 1 μs in a temperature measurement. The method error due to emissive capacity is ~0.3% for most materials in the temperature range of 1200–3300 K, which is much smaller than the error in measuring the brightness or color temperature. The instrumental error depends on the design of the electron-optical system of the entrance chamber in a PMT and on the layout of data acquisition and processing and may be 2–6%. The conversion parameter is (2–15) × 10–3 K–1. The described PMTs can be used to measure the temperature dynamics in fast high-temperature processes.

Formation of the Potential Jump Over the Geomagnetically Quiet Sunlit Polar Cap Region

AbstractWe consider the formation of a potential drop over the Earth's polar cap during geomagnetically quiet daytime. The observed potential drop is primarily defined by the hydrogen, photoelectron, and polar rain fluxes ratios and depends strongly on the energy distribution of the photoelectron flux. Polar rain is an essential component of the model required for plasma quasi‐neutrality. The potential distribution along the magnetic field line has two regions, with a small, gradual, potential drop of 3–4 V and a potential jump. The value of the potential jump depends on the hydrogen ion to photoelectron flux ratio and is also controlled by polar rain electrons. With quasi‐neutrality required at its upper boundary, the jump only occurs in the presence of polar rain and its location depends on the polar rain flux. Model predictions compare well with FAST observations presented by Kitamura et al. (2012, https://doi.org/10.1029/2011JA017459).