Electron Temperature Enhancements Research Articles

Effect of a novel nonlinearity, viz., electron temperature dependence of electron-ion recombination on electromagnetic wave. Plasma interaction: Nonlinear propagation in the E-layer

In this paper, we consider the nonlinearity in the propagation of electromagnetic (e.m.) waves in a plasma caused by the electron temperature dependence of the coefficient of recombination of electrons with ions; specifically, the ionospheric E layer has been investigated. The enhancement in electron temperature by an intense electromagnetic wave causes reduction of the electron-ion recombination coefficient and thereby enhancement of electron density, the electron collision frequency also gets enhanced. The equations for number and energy balance of electrons and the wave equation have been used to predict the dependence of electron density/collision frequency and the nonlinear refractive index and absorption coefficient on αE02 (proportional to wave irradiance). The dependence of the propagation parameters on αE02 has been used to investigate the nonlinear electromagnetic wave propagation in the ionosphere. The study concludes that the electron temperature dependence of the recombination coefficient should be considered in all analyses of nonlinear plasma-e.m. wave interaction.

Two‐dimensional numerical simulation of O‐mode to Z‐mode conversion in the ionosphere

AbstractExperiments in the illumination of the F region of the ionosphere via radio frequency waves polarized in the ordinary mode (O‐mode) have revealed that the magnitude of artificial heating‐induced effects depends strongly on the inclination angle of the pump beam, with a greater modification to the plasma observed when the heating beam is directed close to or along the magnetic zenith direction. Numerical simulations performed using a recently developed finite‐difference time‐domain (FDTD) code are used to investigate the contribution of the O‐mode to Z‐mode conversion process to this effect. The aspect angle dependence and angular size of the radio window for which conversion of an O‐mode pump wave to the Z‐mode occurs is simulated for a variety of plasma density profiles including 2‐D linear gradients representative of large‐scale plasma depletions, density‐depleted plasma ducts, and periodic field‐aligned irregularities. The angular shape of the conversion window is found to be strongly influenced by the background plasma profile. If the Z‐mode wave is reflected, it can propagate back toward the O‐mode reflection region leading to resonant enhancement of the electric field in this region. Simulation results presented in this paper demonstrate that this process can make a significant contribution to the magnitude of electron density depletion and temperature enhancement around the resonance height and contributes to a strong dependence of the magnitude of plasma perturbation with the direction of the pump wave.

A numerical study of large‐scale ionospheric modulation due to the thermal process by powerful wave heating

AbstractWe present a three‐dimensional numerical model of large‐scale ionospheric electron density and temperature modulation by powerful electromagnetic waves by incorporating the transport equations and the three‐dimensional ray‐tracing algorithm. Based on this numerical model, the changes of ionospheric electron density and temperature at nighttime are investigated. The simulation results present (1) the ionospheric electron temperature enhancement due to the energy absorption; (2) the ionospheric electron density depletion at the reflection region and enhancement at the upper/lower region along the field line due to the thermal pressure; and (3) large‐scale field‐aligned irregularities (FAIs) due to the thermal self‐focusing instability with transverse scale of ~10 km. The results are quantitatively consistent with the previous theoretical predictions and experimental observations, which indicate that the thermal processes play an important role in the ionospheric electron density/temperature modulation and large‐scale FAI generation.

Electron cyclotron resonance heating by magnetic filter field in a negative hydrogen ion source

The influence of magnetic filter field on plasma properties in the heating region has been investigated in a planar-type inductively coupled radio-frequency (RF) H(-) ion source. Besides filtering high energy electrons near the extraction region, the magnetic filter field is clearly observed to increase the electron temperature in the heating region at low pressure discharge. With increasing the operating pressure, enhancement of electron temperature in the heating region is reduced. The possibility of electron cyclotron resonance (ECR) heating in the heating region due to stray magnetic field generated by a filter magnet located at the extraction region is examined. It is found that ECR heating by RF wave field in the discharge region, where the strength of an axial magnetic field is approximately ∼4.8 G, can effectively heat low energy electrons. Depletion of low energy electrons in the electron energy distribution function measured at the heating region supports the occurrence of ECR heating. The present study suggests that addition of axial magnetic field as small as several G by an external electromagnet or permanent magnets can greatly increase the generation of highly ro-vibrationally excited hydrogen molecules in the heating region, thus improving the performance of H(-) ion generation in volume-produced negative hydrogen ion sources.

Stimulated Brillouin scattering during electron gyro-harmonic heating at EISCAT

Abstract. Observations of secondary radiation, stimulated electromagnetic emission (SEE), produced during ionospheric modification experiments using ground-based, high-power, high-frequency (HF) radio waves are considered. The High Frequency Active Auroral Research Program (HAARP) facility is capable of generating narrowband SEE in the form of stimulated Brillouin scatter (SBS) and stimulated ion Bernstein scatter (SIBS) in the SEE spectrum. Such narrowband SEE spectral lines have not been reported using the European Incoherent Scatter (EISCAT) heater facility before. This work reports the first EISCAT results of narrowband SEE spectra and compares them to SEE previously observed at HAARP during electron gyro-harmonic heating. An analysis of experimental SEE data shows observations of emission lines within 100 Hz of the pump frequency, interpreted as SBS, during the 2012 July EISCAT campaign. Experimental results indicate that SBS strengthens as the pump frequency approaches the third electron gyro-harmonic. Also, for different heater antenna beam angles, the CUTLASS radar backscatter induced by HF radio pumping is suppressed near electron gyro-harmonics, whereas electron temperature enhancement weakens as measured by EISCAT/UHF radar. The main features of these new narrowband EISCAT observations are generally consistent with previous SBS measurements at HAARP.

Relationship between auroral substorm and ion upflow in the nightside polar ionosphere

We investigated ionospheric ion upflow during an auroral substorm using simultaneous European Incoherent Scatter radar and IMAGE satellite data. Approximately 6 min after an initial brightening identified with data from the IMAGE wideband imaging camera instrument, ion upflow was seen and the electron temperature became enhanced, too. The ion upflow, with a velocity of about 150 m/s, and the electron temperature enhancement lasted for about 25 min. During the poleward expansion phase, surges of large upward ion velocity and flux, and high ion and electron temperatures occurred over Longyearbyen. The upward ion flux reached 2 × 1014 m−2s−1. Naturally enhanced ion‐acoustic lines (NEIALs) were seen near the poleward edge of the expanded auroral oval both near the end of expansion phase 17 min after onset and also later in the recovery phase. The NEIALs seemed to be accompanied by another type of enhanced echoes, obliquely to the local geomagnetic field. Data from the Low Energy Neutral Atom instrument on the IMAGE satellite show that energetic neutral oxygen reaches the IMAGE satellite about 40 min after the initial brightening, and oxygen continues to get detected during the recovery phase. We propose that ion upflow at the poleward edge of the auroral oval during the expansion phase is related to ion/neutral outflow with energy below 18–27 eV, whereas during the recovery phase of a substorm upward ions are accelerated up to about 60 eV and flow out in the entire polar region.

Non-local approach to kinetic effects on parallel transport in fluid models of the scrape-off layer

Using a non-local model, fluid simulations can capture kinetic effects in the parallel electron heat-flux better than is possible using flux limiters in the usual diffusive models. Non-local and diffusive models are compared using a test case representative of an edge-localized mode crash in the JET scrape-off layer (SOL), simulated in one dimension. The non-local model shows substantially enhanced electron temperature gradients, which cannot be achieved using a flux limiter. The performance of the implementation, in the BOUT++ framework, is also analysed to demonstrate its suitability for application in three-dimensional simulations of turbulent transport in the SOL.

Electron temperature enhancements in nighttime equatorial ionosphere under the occurrence of plasma bubbles

Simultaneous in-situ measurements of electron density and temperature in the nighttime equatorial region were performed by a rocket experiment launched under solar minimum and geomagnetic quiet conditions from the station of Alcântara (2.24°S; 44.24°W), Brazil, on Dec. 18, 1995, 21:17 LT. These measurements detected during the upleg flight a large overheated area around the base of density profile. The presence of plasma bubbles was revealed during the downleg phase, as well as temperature enhancements detected preferentially at altitudes where plasma depletions are found. It was assumed that the region traversed by the rocket during the downleg was preceded before the bubble's onset by a large overheating as observed during the upleg flight. Analyzing this framework under the light of the Global Self-Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP), as well as a 2D numerical code that simulate the growth of an instability and the evolution of thermal energy inside a bubble, we found that despite an overheated area in the F-region bottomside can disturb the electron density profile around the altitude interval where such heat is deposited, it seems not have a direct influence over parameters responsible for the bubble onset. Additionally, the phenomenon of the intra-bubble thermal enhancement could be formed due to the convection of hot-electron fluid transported from the overheated region surrounding the base of the F-region to upper altitudes by the underlying mechanism of bubble generation.

High-latitude ionospheric response to the solar eclipse of 1 August 2008: EISCAT observations and TRANSCAR simulation

On 1 August 2008, a total solar eclipse occurred and the footprint of its umbra passed North–East of the Svalbard archipelago, where the EISCAT Svalbard Radars (ESR) are installed. This eclipse is peculiar because it was seen at high-latitude, thus with large solar zenith angles and it was the first time that incoherent scatter radars were able to sound the ionospheric response at such a high latitude. The ESR data, after correction, show the typical signatures of a solar eclipse: depletion in electron density in the E- and F-regions, a decrease in electron temperature in the F-region, and a downflow of ions. Also, the UHF dish of the mainland EISCAT system measured a decrease in the same parameters, showing the influence of the penumbra (partial eclipse) on the ionosphere. We have modelled the response of the high-latitude ionosphere to this solar eclipse with the TRANSCAR code. Our simulations reproduce rather well the observations above the UHF radar in Tromsø and the ESR on Svalbard. In particular, we show the influence of particle precipitation above the ESR and we suspect an effect above Tromsø of the photoelectrons coming from the opposite hemisphere. Another interesting and quite unusual feature is the observation of the summer ionospheric cusp undergoing the eclipse. Radar data show structures of enhanced electron temperature, due to soft particle precipitation through the polar cusp.

Plasma modifications induced by an X-mode HF heater wave in the high latitude F region of the ionosphere

We presented experimental results of strong plasma modifications induced by X-mode powerful HF radio waves injected towards the magnetic zenith into the high latitude F region of the ionosphere. The experiments were conducted in 2009–2011 using the EISCAT Heating facility, UHF incoherent scatter radar and the EISCAT ionosonde at Tromsø, Norway; and the CUTLASS SuperDARN HF coherent radar at Hankasalmi, Finland. The results showed that the X-mode HF pump wave can generate strong small-scale artificial field aligned irregularities (AFAIs) in the F region of the high-latitude ionosphere. These irregularities, with spatial scales across the geomagnetic field of the order of 9–15m, were excited when the heater frequency (fH) was above the ordinary-mode critical frequency (foF2) by 0.1–1.2MHz. It was found that the X-mode AFAIs appeared between 10s and 4min after the heater is turned on. Their decay time varied over a wide range between 3min and 30min. The excitation of X-mode AFAIs was accompanied by electron temperature (Te) enhancements and an increase in the electron density (Ne) depending on the effective radiated power (ERP). Under ERPs of about 75–180MW the Te enhances up to 50% above the background level and an increase in Ne of up to 30% were observed. Dramatic changes in the Te and Ne behavior occurred at effective radiated powers of about 370–840MW, when the Ne and Te values increased up to 100% above the background ones. It was found that AFAIs, Ne and Te enhancements occurred, when the extraordinary-mode critical frequency (fxF2) lied in the frequency range fH–fce/2≤fxF2≤fH+fce/2, where fce is the electron gyrofrequency. The strong Ne enhancements were observed only in the magnetic field-aligned direction in a wide altitude range up to the upper limit of the UHF radar measurements. In addition, the maximum value of Ne is about 50km higher than the Te enhancement peak. Such electron density enhancements (artificial ducts) cannot be explained by temperature-dependent reaction rates. They can be attributed to HF-induced ionization production by accelerated electrons. The possible mechanisms for plasma modifications induced by powerful X-mode HF radio waves were discussed.

EISCAT observations of pump‐enhanced plasma temperature and optical emission excitation rate as a function of power flux

We analyze optical emissions and enhanced electron temperatures induced by high power HF radio waves as a function of power flux using the EISCAT heater with a range of effective radiated powers. The UHF radar was used to measure the electron temperatures and densities. The Digital All Sky Imager was used to record the 630.0 nm optical emission intensities. We quantify the HF flux loss due to self‐absorption in the D‐region (typically 3–11 dB) and refraction in the F‐region to determine the flux which reaches the upper‐hybrid resonance height. We find a quasi‐linear relationship between the HF flux and both the temperature enhancement and the optical emission excitation rate with a threshold at ∼37.5 μWm−2. On average ∼70% of the HF flux at the upper‐hybrid resonance height goes in to heating the electrons for fluxes above the threshold compared to ∼40% for fluxes below the threshold.

Temporal evolution of radar echoes associated with mesospheric dust clouds after turn‐on of radio wave heating

The initial perturbation of polar mesospheric summer echoes PMSEs during radio wave heating provides significant diagnostic information about the charged dust layer associated with the irregularity source region. Comparison between the results of computational models and the observation data can be used as a tool to estimate charged dust layer parameters. An analytical model is developed and compared to a more accurate computational model as a reference to investigate the possibilities for diagnostic information as well as insight into the physical processes after heater turn‐on. During radio wave heating of the mesosphere, which modifies the background electron temperature, various temporal evolution characteristics of irregularity amplitude may be observed which depend on the background plasma parameters and the characteristics of the dust layer. Turn‐on overshoot due to the dominant electron charging process and turn‐on undershoot resulting from the dominant ambipolar diffusion process, that can occur simultaneously at different radar frequencies, have been studied. The maximum and minimum of the electron density irregularity amplitude and the time at which this amplitude has been achieved as well as the decay time of irregularity amplitude after the maximum amplitude are unique observables that can shed light on the physical processes after the turn‐on of the pump heating and to diagnose the charged dust layer. The agreement between the computational and analytical results are good and indicate the simplified analytical model may be used to provide considerable insight into the heating process and serve as the basis for a diagnostic model after heater turn‐on. Moreover, the work proposes that conducting PMSE active experiments in the HF and VHF band simultaneously may allow estimation of the dust density altitude profile, dust charge state variation during pump heating, and ratio of electron temperature enhancement in the irregularity source region.

Ionospheric anomalies associated with the Haiti earthquake of 12 January 2010 observed by DEMETER satellite

Abstract. This paper examines the ionospheric anomalies around the time of a strong earthquake (M = 7.0) which occurred in Haiti region (18.457° N, 72.533° W) on 12 January 2010. DEMETER satellite data have been used to study the plasma parameters variation during the Haiti earthquake. One day (11 January 2010) before the earthquake there is a significant enhancement of electron density and electron temperature near the epicenter. Decrease of electron temperature is observed few days after the earthquake. Anomalous plasma parameter variations are detected both in day and nighttimes before the quake. Statistical processing of the DEMETER data demonstrates that satellite data can play an important role for the study of precursory phenomena associated with earthquakes.

Dusty space plasma diagnosis using temporal behavior of polar mesospheric summer echoes during active modification

Abstract. The objective of this paper is to study the effect of different plasma and dust parameters on Polar Mesospheric Summer Echoes (PMSE) temporal behavior after turn-on and turn-off of radio wave heating and to use these responses to diagnose the properties of the dust layer. The threshold radar frequency and dust parameters for the enhancement or suppression of radar echoes after radio wave heating turn-on are investigated for measured mesospheric plasma parameters. The effect of parameters such as the electron temperature enhancement during heating, dust density, dust charge polarity, ion-neutral collision frequency, electron density and dust radius on the temporal evolution of electron irregularities associated with PMSE are investigated. The possible diagnostic information for various charged dust and background plasma quantities using the temporal behavior of backscattered radar power in active experiments is discussed. The computational results are used to make predictions for PMSE active modification experiments at 7.9, 56, 139, 224 and 930 MHz corresponding to existing radar facilities. Data from a 2009 VHF (224 MHz) experiment at EISCAT is compared with the computational model to obtain dust parameters in the PMSE.

Temporal development of the magnetic zenith effect

[1] An experimental investigation of the temporal dynamics of the magnetic zenith (MZ) effect associated with ionospheric modification by high-power HF electromagnetic waves is presented. The observed electron temperature enhancement when the heater beam and the UHF radar are directed along the magnetic zenith is at least twice that observed when the heater and radar are both directed vertically. It is shown that the temperature enhancement reaches the stationary state within 10 s after the heater is turned on. Such times (∼5–10 s) are typical for the development of striations with transverse sizes of the order of several meters. Also, the temporal behavior of the ion line spectra is analyzed for the field-aligned and vertical directions of the UHF radar. A new theoretical explanation is suggested for the aspect sensitivity of the electron temperature enhancement that explains the fast manifestation of the MZ effect. Furthermore, it is shown that maximum electron heating is achieved at some intermediate inclination angle of the heater beam between the MZ and the Spitze angle. An estimate of the angle within which the maximum heating effect exists is presented.

Artificial small-scale field-aligned irregularities in the high latitude F region of the ionosphere induced by an X-mode HF heater wave

[1] The effects on the high-latitude F region of the ionosphere by X-mode powerful HF radio waves injected towards the magnetic zenith (MZ) are analysed. The experiments were conducted using the EISCAT/Heating facility and UHF radar at Tromso, Norway, the CUTLASS (SuperDARN) radar and the EISCAT ionosonde (dynasonde). The results show that the X-mode HF pump wave, radiated into the magnetic zenith from the HF heater, can generate very strong small-scale artificial field aligned irregularities (AFAIs) in the F-region of the high-latitude ionosphere. These irregularities, with spatial scales across the geomagnetic field of the order of 8–15 m, are generated when the heater frequency is above the ordinary-mode critical frequency but comparable with the extraordinary-mode critical frequency. The generation of the X-mode AFAIs was accompanied by electron temperature (Te) enhancements up to 50% above the background level and an increase in the electron density (Ne) by up to 30%.

A statistical survey of electron temperature enhancements in heater modulated polar mesospheric summer echoes at EISCAT

A statistical analysis has been made of 26 Polar Mesospheric Summer Echoes (PMSE) active modulation experiments between 2002 and 2007. Observed with the EISCAT VHF radar the PMSE signature can be reduced by means of heating the ionosphere with powerful high frequency (HF) radio waves. However, PMSE modulation experiments sometimes fail. We use a computational model to estimate the enhanced electron temperatures due to ionospheric heating from HF radio waves in the D-region. We show that the statistical PMSE modulation for a fixed HF heater-induced electron temperature enhancement appears to be independent of altitude. In addition, for experiments where the PMSE modulation experiment failed, we show that the atmospheric attenuation of the HF heater wave was too great for the HF wave to have any effect on the PMSE layer.

Autofocused, enhanced proton acceleration from a nanometer-scale bulged foil

We report an autofocused, enhanced proton acceleration by the interaction of an intense laser pulse with a bulged target. These results are obtained from two-dimensional particle-in-cell simulations using a real Gaussian laser pulse, normally incident on a bulged/planar, 60 nm thick foil (C:H=1:1). When the laser pulse hits the precurved target, energetic protons are converged on the axis automatically. For the bulged foil, due to oblique incidence at the wing region, the efficient vacuum heating at larger incidence angles will result in more energetic hot electrons than from the flat foil. The enhancement of hot electron temperature and density will result in a larger longitudinal field, which contributes to an enhancement of proton energy. The maximum proton energy of 124 MeV is attained from a bulged target irradiated by a linear polarized laser pulse at an intensity of 1.3×1020 W/cm2, which is two times higher than from the planar target (61 MeV).

Observations of the Heating Experiments in the Polar Winter Ionosphere III–Analysis in the Low Region

AbstractUnder the condition of ionosphere heating in the low region, the theoretical incoherent scatter model with the non‐Maxwellian distribution in collisional plasma is presented, and the measured data in polar winter ionospheric modification experiments carried out in January 2008 at Tromsø are analyzed. The obvious electron temperature enhancement can be seen in this experiment, and the maximum percentage is up to 168.9%. The non‐Maxwellian index is also given, and the heating electric field is deduced from the index, which has important meaning for numerical simulation of the artificial ionospheric modification.

Metal-dielectric structures for high power electron cyclotron resonance ion source

Metal-dielectric (MD)-structures in electron cyclotron resonance ion source (ECRIS) devices (partially) restore the plasma ambipolarity and supply cold electrons to the plasma. Both effects lead to an enhancement of the plasma electron density and temperature and significantly increase the performance of this type of ion source. At the same time, MD-structures are well suited to reduce the heat load on cold masses by Bremsstrahlung radiation. Here, we report on experiments at high microwave powers to test the practical use of MD-structures for new, high performance ECRISs with their much higher power densities. The comparatively long conditioning times can be shortened by covering only those parts of the source with MD-structures, which are essential for the improvement.