Electron Density Turbulence Research Articles

Morphology of Solar Type II Bursts Caused by Shock Propagation through Turbulent and Inhomogeneous Coronal Plasma

Type II solar bursts are radio signatures of shock waves in the solar corona driven by solar flares or coronal mass ejections (CMEs). Therefore, these bursts present complex spectral morphologies in solar dynamic spectra. Here, we report meter–decameter radio observations of a type II burst on 2014 July 25 made with the Ukrainian radio telescopes UTR-2 (8.25–33 MHz) and GURT (8.25–78 MHz). The burst demonstrates fundamental and harmonic components, band splitting, a herringbone structure, and a spectral break. These specific spectral features, observed jointly in a single type II burst, are rarely detected. To contribute to our understanding of such puzzling type II events, we carried out a detailed analysis of the recorded type II dynamic spectrum. In particular, the herringbone pattern has been exploited to study electron density turbulence in the solar corona. We calculated the power spectral densities of the flux variations in selected herringbones. The spectral index is in the range of α = −1.69 to −2.00 with an average value of −1.897, which is slightly higher than the Kolmogorov spectral index of −5/3 for fully developed turbulence. We also recognized that the second type II burst consists of three drifting lanes. The lane onset times coincide with the spectral break in the first type II burst. We regard that the CME/shock passage through a streamer caused the spectral break and triggered the multilane type II radio emission. Thus, we support one of the proposed scenarios for type II burst occurrence as being the result of CME/shock–streamer interaction.

Ku-band multichannel frequency comb Doppler reflectometer on the GAMMA 10/potential control and divertor simulating experiment (PDX) tandem mirror.

A Ku-band (12-18GHz) multichannel Doppler reflectometer (DR) has been developed in the GAMMA 10/potential control and divertor simulating experiment (PDX) tandem mirror device to improve the applicability of DR measurement for simultaneous monitoring of velocity of electron density turbulence at different locations. Our previous single-channel DR circuit has been replaced by the multichannel microwave system using a nonlinear transmission line based comb generator with heterodyne technique. The multichannel DR system has been installed in the central cell of GAMMA 10/PDX. Initial results of application to GAMMA 10/PDX plasma are presented, showing Doppler frequency shifts during an additional ion cyclotron resonance frequency heating and gas-puffing experiment.

Development of a synthetic phase contrast imaging diagnostic for turbulence studies at Wendelstein 7-X

We present a synthetic phase contrast imaging (PCI) diagnostic for studying turbulence at the Wendelstein 7-X (W7-X) stellarator. We first describe the implemented instrument response model, which captures diffraction effects, detector noise, and the long-wavelength cutoff due to the phase plate of the PCI system. To verify the instrument response model, we show that it is capable of reproducing the PCI signal generated by the sound wave speaker used for calibration at W7-X. Next, we discuss the calculation of synthetic PCI signals based on the global, nonlinear gyrokinetic codes GENE-3D and EUTERPE, including results from some of the first stellarator simulations of this type with kinetic electrons (KEs) in GENE-3D. While the simulations used in this work lack a neoclassical radial electric field, which is crucial for reproducing experimental PCI signals, they do indicate that the dominant rotation direction and velocities of the turbulent fluctuations can be inferred from the wave number-frequency spectra of the PCI signals, as expected. The synthetic PCI wave number spectra are further shown to be similar to those of the line-integrated fluctuating electron density, with distinct differences between adiabatic and KE simulations, explainable by previously published turbulence models. For example, the wave number spectra of all adiabatic electron simulations analyzed here follow a power law with an exponent close to −5 for sufficiently large wave numbers. This indicates that universal features of electron density turbulence at W7-X may be studied using the PCI system.

Statistical study of electron density turbulence and ion-cyclotron waves in the inner heliosphere: Solar Orbiter observations

Context.The recently released spacecraft potential measured by the RPW instrument on board Solar Orbiter has been used to estimate the solar wind electron density in the inner heliosphere.Aims.The measurement of the solar wind’s electron density, taken in June 2020, has been analysed to obtain a thorough characterization of the turbulence and intermittency properties of the fluctuations. Magnetic field data have been used to describe the presence of ion-scale waves.Methods.To study and quantify the properties of turbulence, we extracted selected intervals. We used empirical mode decomposition to obtain the generalized marginal Hilbert spectrum, equivalent to the structure functions analysis, which additionally reduced issues typical of non-stationary, short time series. The presence of waves was quantitatively determined by introducing a parameter describing the time-dependent, frequency-filtered wave power.Results.A well-defined inertial range with power-law scalng was found almost everywhere in the sample studied. However, the Kolmogorov scaling and the typical intermittency effects are only present in fraction of the samples. Other intervals have shallower spectra and more irregular intermittency, which are not described by models of turbulence. These are observed predominantly during intervals of enhanced ion frequency wave activity. Comparisons with compressible magnetic field intermittency (from the MAG instrument) and with an estimate of the solar wind velocity (using electric and magnetic field) are also provided to give general context and help determine the cause of these anomalous fluctuations.

Characterization of isotope effect on ion internal transport barrier and its parameter dependence in the Large Helical Device

In this paper, the background physics of the isotope effects in the ion internal transport barrier (ITB) are discussed in detail. An heuristic criterion for the ITB strength is defined based on the nonlinear dependence of the ion thermal diffusivity on the local ion temperature in the L-mode phase. Comparing deuterium plasmas and hydrogen plasmas, two isotope effects on the ion ITB are clarified: stronger ITBs formed in the deuterium plasmas and an ITB concomitant edge confinement degradation in the hydrogen plasmas. Principal component analysis reveals that the ion ITB becomes strong when a high input power normalized by the line averaged electron density is applied and electron density profile is peaked. A gyrokinetic simulation suggests that the ITB profile is determined by the ion temperature gradient driven turbulence, while the way the profile saturates in L-mode plasmas is unknown. In the electron density turbulence behavior, a branch transition is observed, where the increasing trend in turbulence amplitude against the ITB strength is flipped to a decreasing trend across the ITB formation. The radial electric field structure is measured by the charge exchange recombination spectroscopy system. It is found that the radial electric field shear plays a minor role in determining the ITB strength.

Characterization and performance evaluation of turbulent plasma sheath channel

Radio waves are highly attenuated and distorted by turbulent plasma sheath around hypersonic vehicles in near space, leading to communication blackout. The purpose of the paper is to investigate the plasma channel characteristics and the communication performances over the channel. We treat the turbulent plasma medium as a fast fading wireless channel. The coherence time and the spectrum spread of the plasma sheath channel are obtained in terms of root-mean-square (RMS). Baseband simulation scheme is proposed based on a stratified model of the plasma flow field. Results indicate that the coherence time is on the order of milliseconds and decreases rapidly with the increasing electron density turbulence. The spectrum spread due to plasma turbulence is also significant. Extensive simulations have been carried out to make communication performance evaluations. Quantitative results show that error floor takes place for PSK and QAM, while FSK with noncoherent detection is a promising method to mitigate the blackout problem.

Characterization of the Li-BES at ASDEX Upgrade

The lithium beam emission spectroscopy (Li-BES) is a powerful diagnostic to resolve the plasma edge density with high temporal and spatial resolution. The recent upgrades of the Li-BES at ASDEX Upgrade and the resulting gain in photon flux allow the plasma edge density to be determined with an advanced level of accuracy. Furthermore, electron density fluctuations are measured using Li-BES. The Li-BES capabilities and limitations to measure electron density profiles as well as density fluctuations are presented. It is well suited to characterize electron density turbulence in the scrape off layer (SOL) with decreasing sensitivity towards the plasma core. This is demonstrated by simulations as well as by comparisons with other diagnostics. The Li-BES is an appropriate tool to study transport phenomena in the SOL over a wide range of plasma parameters due to its robustness and routine usage.

CHANNEL CHARACTERIZATION AND FINITE-STATE MARKOV CHANNEL MODELING FOR TIME-VARYING PLASMA SHEATH SURROUNDING HYPERSONIC VEHICLES

Efiects on the communication signals caused by the time-varying plasma sheath surrounding hypersonic vehicles are investigated. Using computational ∞uid dynamics (CFD) technique, Demetriades's plasma turbulence model and flnite-difierence time-domain (FDTD) algorithm, amplitude variation and phase ∞uctuation induced by plasma electron density turbulence are obtained, and their statistical properties are analyzed and characterized. Furthermore, a flnite-state Markov channel (FSMC) model is proposed, to represent the dynamical efiects on electromagnetic wave propagation through plasma sheath. With high accuracy and greatly reduced complexity, the FMSC model could be very useful to develop novel communication techniques for alleviating the radio blackout problem.

The Radial Extent and Warp of the Ionized Galactic Disk. II. A Likelihood Analysis of Radio‐Wave Scattering toward the Anticenter

We use radio-wave scattering data to constrain the distribution of ionized gas in the outer Galaxy. Like previous models, our model for the H II disk includes parameters for the radial scale length and scale height of the H II, but we allow the H II disk to warp and flare. Our model also includes the Perseus arm. We use a likelihood analysis on 11 extragalactic sources and 7 pulsars. Scattering in the Perseus arm is no more than 60% of the level contributed by spiral arms in the inner Galaxy, equivalent to a 1 GHz scattering diameter of 1.5 mas. Our analysis favors an unwarped, nonflaring disk with a 1 kpc scale height, though this may reflect the non-uniform and coarse coverage provided by the available data. The lack of a warp indicates that VLBI observations near 1 GHz with an orbiting station having baseline lengths of a few Earth diameters will not be affected by interstellar scattering at Galactic latitudes |b| ~ 15 degrees. The radial scale length is 15--20 kpc, but the data cannot distinguish between a gradual decrease in the electron density and a truncated distribution. We favor a truncated one, because we associate the scattering with massive star formation, which is also truncated near 20 kpc. The distribution of electron density turbulence decreases more rapidly with Galactocentric distance than does the hydrogen distribution. Alternate ionizing and turbulent agents---the intergalactic ionizing flux and satellite galaxies passing through the disk---do not contribute significantly to scattering. We cannot exclude the possibility that a largely ionized, but quiescent disk extends to >~ 100 kpc, similar to that for some Ly-alpha absorbers.

Measurements of short wavelength VLF bursts in the auroral ionosphere: a case for electromagnetic mode conversion?

Intense, localized bursts of VLF emissions were measured on the University of California at Berkeley Alaska '93 auroral sounding rocket. A wavelength determination for these waves was obtained using cross‐spectral analysis on high time resolution electric field measurements from dipole antennas and an onboard burst memory system. The observation of an antenna null in the cross‐spectral response reveals very short wavelength emissions with wavelengths less than 5.5 meters. The applicability of a collapse theory for these emissions is put in question since these examples are not well correlated with electron density depletions. In addition, these waves do not appear to be associated with a particular type of electron distribution which may have been responsible for their generation. The presence of electromagnetic modes in the VLF frequency range in the vicinity of many of these electrostatic bursts, along with continual electron density turbulence of 1–5%, may provide evidence for a linear mode coupling mechanism in which electrostatic VLF waves are produced by the scattering of incident electromagnetic whistlers from electron density irregularities.

A summary of extreme scattering events and a descriptive model

view Abstract Citations (109) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Summary of Extreme Scattering Events and a Descriptive Model Fiedler, R. ; Dennison, B. ; Johnston, K. J. ; Waltman, E. B. ; Simon, R. S. Abstract An ongoing monitoring program of compact extragalactic radio sources over the past 11 years has revealed many instances of unusual variations that cannot be explained using the standard models for intrinsic variability or normal refractive interstellar scintillation. The observations included simultaneous daily measurements at 2.695 and 8.085 GHz of 40 to 150 sources using the Green Bank interferometer over the period 1979-1989. Approximately 330 sources were also monitored with the NRAO 300 foot radio telescope at 3.25 and 4.675 GHz over the 6 month period 1987 December to 1988 May. In total, 594 source-years of observations have been obtained, of which 4.8 yr constitutes the total time span of unusual variability. The unusual variations, denoted as extreme scattering events (ESEs), are summarized here. The most striking property of ESEs is their frequency dependence, in which departures from the quiescent flux density (by as much as 50% at 2.7 GHz) have no counterpart at 8.1 GHz. The single exception occurred in the 8.1 GHz light curve of 0954+658, which showed spiky variations during the 2.7 GHz event. To date, 10 ESEs have been tentatively identified in the 2.7 GHz light curves of nine quasars. These ESEs appear to occur preferentially near loops in the Galactic foreground brightness distribution. A simple model based on diffraction or refraction through Galactic regions of unusually high electron density turbulence is presented. Publication: The Astrophysical Journal Pub Date: August 1994 DOI: 10.1086/174432 Bibcode: 1994ApJ...430..581F Keywords: Electron Density (Concentration); Electron Scattering; Extragalactic Radio Sources; Galactic Structure; Interstellar Matter; Plasma Turbulence; Refraction; Astronomical Models; Brightness Distribution; Cosmology; Light Curve; Quasars; Astrophysics; ISM: STRUCTURE; RADIO CONTINUUM: GALAXIES; TURBULENCE full text sources ADS | data products SIMBAD (15) NED (9)

Rotation measures of low-latitude extragalactic sources and the magnetoionic structure of the Galaxy

view Abstract Citations (99) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Rotation Measures of Low-Latitude Extragalactic Sources and the Magnetoionic Structure of the Galaxy Clegg, Andrew W. ; Cordes, James M. ; Simonetti, John M. ; Kulkarni, Shrinivas R. Abstract We have obtained Faraday rotation measurements of 56 extragalactic sources predominantly in the range 45^deg^ < l < 93^deg^, |b| < 5^deg^. The data complement the few rotation measures (RMs) that have been published for low-latitude extragalactic sources, and are used to probe the Galactic magnetic field and electron density to great distances. Within the longitude range sampled here, we find RM(l) = 1600 sin (l_0_ - l) rad m^2^, with a null in RM occurring at l_0_ = 62^deg^. Under the assumption of a uniform circular geometry for the magnetic field lines, the magnetoionic medium must exist to a Galactocentric radius R_m_ ~ 25 kpc to produce the observed magnitudes of the RMs, where we have assumed that n_e_ and |B| equal their local values of 0.03 cm^-3^ and 2.1 microG out to R_m_. The medium must exist to an even greater radius if n_e_ and/or |B| decrease with R, as is likely. The null in RM at l_0_ confirms that a field reversal occurs interior to R_0_ (the radius of the solar orbit about the Galactic center) and requires that the product quantity n_e_|B| be greater inside the field-reversed region than in the local ISM. Comparison of extragalactic and pulsar RMs along nearly coincident lines of sight is consistent with at least one field reversal exterior to R_0_. An anomalous RM contribution of >~1000 rad m^2^ is found at l = 92^deg^, b = 0^deg^, with an angular size of ~1^deg^-8^deg^. The phenomenon is akin to enhanced RMs observed behind the Cygnus region. The majority of our sources are components of double- lobed objects with lobe separations of 30"-200". This allows us to study variations in Galactic Faraday rotation over small angular scales. The differences exceed those expected from a large-scale ordered field by more than two orders of magnitude. The implied linear scales for fluctuations in the magnetoionic medium are ~0.1-10 pc. We are able to explain the small-scale variations in RM solely in terms of previously observed electron density turbulence in the interstellar medium. Publication: The Astrophysical Journal Pub Date: February 1992 DOI: 10.1086/171000 Bibcode: 1992ApJ...386..143C Keywords: Extragalactic Radio Sources; Faraday Effect; Interstellar Magnetic Fields; Magnetoionics; Pulsars; Astronomical Models; Galactic Rotation; Milky Way Galaxy; Astrophysics; GALAXY: GENERAL; ISM: MAGNETIC FIELDS; POLARIZATION; RADIO CONTINUUM: GALAXIES full text sources ADS | data products NED (76) SIMBAD (75)

Scattering of Pulsar Radiation and Electron Density Turbulence in the Interstellar Medium

We report measurements, using the Culgoora circular array at 80 and 160 MHz and the Parkes 64 m telescope at 410 MHz, of the pulse broadening due to interstellar scattering on 33 pulsars. These results are added to published data on 52 other pulsars in order to investigate the interstellar turbulence levels over 85 paths in the Galaxy. We find a significant relation between the turbulence level C~ and dispersion measure, heliocentric distance, galactocentric distance, galactic latitude and galactic longitude. Our results are consistent with a distribution of turbulence that peaks near the galactic centre and extends out to past the solar circle, with the scale height perpendicular to the plane at least equal to that of the pulsars. The magnitude of the fluctuations in electron density responsible for the scattering is not proportional to the average electron density, but increases much more rapidly than the latter as the galactic centre is approached. The apparent dependence of C~ on heliocentric distance is preferentially interpreted as due to the presence of a highly clumped distribution of turbulence along all lines of sight.

Small-scale electron density turbulence in the interstellar medium

view Abstract Citations (321) References (74) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Small-scale electron density turbulence in the interstellar medium. Cordes, J. M. ; Weisberg, J. M. ; Boriakoff, V. Abstract Diffraction phenomena associated with the scattering of pulsar radiation are used to constrain the power spectrum and galactic distribution of electron density fluctuations. The authors combine new measurements of interstellar scintillation bandwidths and pulse broadening times with those from the literature to yield information on 76 lines of sight. For individual objects, the scaling of scintillation bandwidth with frequency is in agreement with a Kolmogorov spectrum. The study of all objects, however, indicates strong disagreement with a model in which turbulence is uniformly distributed. The data suggest a two-component model for electron density turbulence: (1) a clumped medium with scale height H ⪉ 100 pc; (2) a nearly uniform medium with H ⪆ 0.5 kpc. Scattering material is ubiquitous but is preferentially located near regions of large energy input into the interstellar medium. Publication: The Astrophysical Journal Pub Date: January 1985 DOI: 10.1086/162784 Bibcode: 1985ApJ...288..221C Keywords: Electron Density (Concentration); Interstellar Matter; Pulsars; Turbulence; Cross Correlation; Line Of Sight; Radiative Transfer; Stellar Radiation; Stellar Spectra; Wave Scattering; Astrophysics full text sources ADS | data products SIMBAD (75)

Radio wave scattering in the galactic disk

Electron density turbulence in the Galaxy causes radio sources to be broadened angularly by amounts that depend strongly on the direction of the source. Recent scattering measurements using very long baseline interferometry (VLBI)1 and interplanetary scintillations (IPS)2 of extragalactic sources, and interstellar scintillations (ISS) of pulsars3 are used here to constrain the distribution of scattering material in the Galaxy. Although ubiquitous, scattering material appears to be highly concentrated in a thin disk of ∼100 pc thickness and in clumps of 1–10 pc size probably associated with H II regions, stellar wind bubbles, and/or supernova shocks. Typical transverse velocities of scattering material are much smaller than typical pulsar velocities. We predict the scattering angle as a function of galactic latitude. The results imply a maximum observable surface brightness for incoherent sources of electron synchrotron radiation.

Radio wave scattering observations of the solar corona First-order measurements of expansion velocity and turbulence spectrum using Viking and Mariner 10 spacecraft

Radio wave scattering data were collected at 3.6 and 13 cm wavelengths by means of the radio link between the Viking orbiters and the earth during the Nov. 25, 1976 solar conjunction of Mars, which occurred near the beginning of solar cycle 21; Mariner 10 solar activity observations during 1974 are also used. It is found that the temporal frequency variance spectrum of amplitude fluctuations is useful for characterizing the bulk motion of the plasma, and the spectral index of electron density turbulence is obtained. The measurements of solar wind velocity and spectral index cover 78 days for Viking and 49 days for Mariner 10 and show the combined effects of changing heliocentric distance, solar latitude, and solar longitude as well as solar activity. It is concluded that the observational velocity profile differs significantly from the theoretical profiles in two ways: (1) the theoretical profile does not show the abrupt change in velocity at about 15 solar radii, and (2) the observational profile shows acceleration at larger radial distances than the model profiles. The observational profiles indicate velocities of less than about 150 km/sec out to 15 solar radii.