Thermal Parametric Instability Research Articles

Simultaneous Action of X- and O-Mode HF Pump Waves on the High-Latitude Upper (F-Region) Ionosphere at EISCAT

We report experimental results from multi-instrument diagnostic tools related to phenomena in the high latitude ionosphere F-region, induced by the simultaneous action of powerful extraordinary (X-mode) and ordinary (O-mode) polarized HF radio waves at EISCAT (European Incoherent SCATter) during magnetically quiet background geophysical conditions. HF pump waves were injected towards the magnetic zenith at a frequency of 5.423 MHz, which was just below the critical frequency of the F2 layer when the excitation of X- and O-mode phenomena was possible. In the course of the experiment, the effective radiated power (ERP) of the X-mode wave was 130.5 MW, while the portion of the O-mode ERP was 29.9 MW (about 20% of the full ERP). It was found that simultaneous action of the X- and O-mode pump waves lead to the excitation of effects typical for both X- and O-mode HF pump waves. Namely, the excitation of small-scale field-aligned irregularities due to the thermal parametric (resonance) instability and a downshifted maximum (DM) component in the wideband stimulated electromagnetic emission (WSEE) spectra, typical for the O-mode HF pumping, was observed, together with multiple ion gyro-harmonic structures in the narrowband stimulated electromagnetic emission (NSEE) spectra. These latter results were recorded at a large (more than 1000 km) distance from the EISCAT/heating facility, typical only for an X-mode HF pumping. The results obtained are compared with “pure” O-mode heating and discussed in detail.

Simulating cosmological supercooling with a cold atom system. II. Thermal damping and parametric instability

We perform an analysis of the supercooled state in an analog of an early universe phase transition based on a one-dimensional, two-component Bose gas with time-dependent interactions. We demonstrate that the system behaves in the same way as a thermal, relativistic Bose gas undergoing a first-order phase transition. We propose a way to prepare the state of the system in the metastable phase as an analog to supercooling in the early universe. We show that parametric resonances in the system can be suppressed by thermal damping if the damping rate is similar to some of the higher rates previously used for modeling nonequilibrium experiments. However, the theoretically predicted damping rate for equilibrium systems within our model is too weak to suppress the resonances.

Evidence of X-mode heating suppressing O-mode heating

In this study, we present three experiments carried out at the EISCAT (European Incoherent Scatter Scientific Association) heating facility on October 29 and 30, 2015. The results from the first experiment showed overshoot during the O-mode heating period. The second experiment, which used cold-start X-mode heating, showed the generation of parametric decay instability, whereas overshoot was not observed. The third experiment used power-stepped X-mode heating with noticeable O-mode wave leakage. Parametric decay instability and oscillating two-stream instability were generated at the O-mode reflection height without the overshoot effect, which implies suppression of the thermal parametric instability with X-mode heating. We propose that the electron temperature increased because X-mode heating below the upper hybrid height decreased the growth rate of the thermal parametric instability.

Investigating Transport and Dissipation in the Subauroral E Region With Ionospheric Modification Experiments and Very High Frequency Radar Backscatter

AbstractIonospheric modification experiments have been performed at the High‐Frequency Active Auroral Research Program (HAARP) facility in Gakona, Alaska, using a Very High Frequency (VHF) coherent scatter radar in Homer, Alaska, for experimental diagnostics. The experiments were intended to determine the threshold pump electric field required to initiate thermal parametric instability in the E region. The pump power level was ramped systematically to determine the threshold, and the experiment was repeated at four closely spaced pump frequencies. This provided threshold estimates at four E region altitudes. The theory for thermal parametric instability based on the work of Dysthe et al. (1983, https://doi.org/10.1063/1.863993) has been modified for application in the E region. The theory considers magneto‐ionic effects on the pump mode, linear mode conversion theory for upper hybrid wave generation, wave heating, and the effects of transport and dissipation based on fluid theory. The theory amounts to an eigenvalue problem where the eigenvalue is the threshold pump electric field for instability. The theory shows how the threshold depends on ionospheric transport coefficients and on the fractional cooling rate for inelastic electron‐neutral collisions. The theoretical predictions for threshold are roughly consistent with experimental values although the latter are probably affected by excess ionospheric absorption.

VHF Radar Images of Artificial Field‐Aligned Ionospheric Irregularities in the Subauroral E Region

AbstractArtificial E region field‐aligned plasma density irregularities (AFAIs) have been generated using the High‐frequency Active Auroral Research Program (HAARP) ionospheric modification facility in Gakona and observed with a 30 MHz coherent scatter radar imager in Homer, Alaska. The AFAIs were generated using a distinctive, twisted‐beam antenna pattern that illuminated a particularly broad volume overhead. The broad beam facilitates studies of natural sporadic E layer patches when they are present. The center of the pattern was pointed at different angles between zenith and magnetic zenith to examine the effects on the AFAI morphology. Radar images of AFAIs generally resemble the radiation pattern of the high‐frequency source, but the irregularities are strongest within a narrow range of zenith angles bounded approximately by the Spitze angle. A number of factors which might influence AFAI generation and detection are examined. The most important is most likely the requirement for the pump mode to have a standing‐wave component for thermal parametric instability to operate.

Modification of the High-Latitude Ionospheric F Region By High-Power HF Radio Waves at Frequencies Near the fifth and Sixth Electron Gyroharmonics

We study the modification effects of the high-latitude ionospheric F region induced by a highpower O-mode HF radio wave injected towards the magnetic zenith, at frequencies near the fifth and sixth electron gyroharmonics using the EISCAT/Heating facility. Multi-instrument diagnostics with the EISCAT incoherent scatter radar (930 MHz) at Tromso, Norway, the CUTLASS coherent radar at Hankasalmi, Finland, and stimulated electromagnetic emission (SEE) receiver at Tromso, has been used for analysis of the observed phenomena. The behavior of the ionospheric plasma parameters (electron’s density and temperature), small-scale artificial field-aligned irregularities, plasma and ion-line spectra, and ionospheric SEE are analyzed in detail. Modification effects near the fifth and sixth electron gyroharmonics have been compared. The coexistence of the thermal (resonance) parametric instability, parametric decay (striction) instability, and/or oscillating two-stream instability was found at these frequencies. The excitation of instabilities occurred at altitudes close to the reflection altitude of the HF pump wave and at the altitudes of the upper-hybrid resonance.

Phenomena in the High-Latitude Ionospheric F Region Induced by a HF Heater Wave at Frequencies Near the Fourth Electron Gyroharmonic

We present the results of multi-instrument studies of the phenomena in the high-latitude ionospheric F region stimulated by high-power HF O-mode radio waves injected towards the magnetic zenith when the ratio of the heater frequency to the cutoff frequency of the F2 layer is near the fourth electron gyroharmonic. Based on the stimulated electromagnetic emission (SEE), spectral observations in the kilohertz and hertz frequency bands of detunings relative to the heater wave frequency, the behaviors of different parameters of the ionospheric plasma and small-scale artificial field-aligned irregularities are compared and analyzed. The coexistence of the thermal (resonance) parametric instability (TPI) and parametric decay (striction) instability (PDI) was found in the vicinity of the fourth gyroresonance harmonic.

The thresholds of ionospheric plasma instabilities pumped by high‐frequency radio waves at EISCAT

We test the existing theories regarding the thresholds for the parametric decay instability (PDI), the oscillating two‐steam instability (OTSI), and the thermal parametric instability (TPI) using the European Incoherent Scatter (EISCAT) facility's ionospheric heater. In these processes, the pump wave can couple to various electrostatic waves in the F layer ionosphere, which can be observed using the EISCAT UHF radar (PDI and OTSI) or by HF radar (TPI). On 19 October 2012, the heater power was stepped from ∼0.5 MW to ∼100 MW effective radiated power in seven steps using a 1 min on, 1 min off cycle. We use an electric field model, taking into account D region absorption, to compare theory with our observations. In all three cases, we find good agreement. In addition, the growth of striations formed during the TPI causes anomalous absorption of the heater wave, which we observe as decreased UHF ion line and plasma line backscatter power. We show evidence that heating for a prolonged period of time reduces the UHF ion line intensity throughout the experiment.

Reexamining X‐mode suppression and fine structure in artificial E region field‐aligned plasma density irregularities

Artificial field‐aligned plasma density irregularities (FAIs) were generated in the E region of the ionosphere above the High Frequency Active Auroral Research Program facility during campaigns in May and August of 2012 and observed using a 30 MHz coherent scatter radar imager in Homer, Alaska. The purpose of this ionospheric modification experiment was to measure the threshold pump power required to excite thermal parametric instabilities by O‐mode heating and to investigate the suppression of the FAIs by simultaneous X‐mode heating. We find that the threshold pump power for irregularity excitation was consistent with theoretical predictions and increased by approximately a factor of 2 when X‐mode heating was present. A modified version of the Another Model of the Ionosphere (SAMI2) ionospheric model was used to simulate the threshold experiments and suggested that the increase was entirely due to enhanced D region absorption associated with X‐mode heating. Additionally, a remarkable degree of fine structure possibly caused by natural gradient drift instability in the heater‐modified volume was observed in experiments performed during geomagnetically active conditions.

Study of three-mode parametric instability

The effect of parametric instability in advanced interferometric gravitational wave detectors is a potential problem for their proper operation. Great efforts have been made to study the onset of parametric instabilities and to find ways to control them. Here we present an experimental design for studying parametric instability in a 72 m cavity with suspended high quality fused silica mirrors. With 5 W input power and 20 kW circulation power inside the cavity, it is predicted that parametric instability will occur. The resonant condition of parametric instability can be met by thermally tuning the radius of curvature of a test mass. We will present simulation results of parametric gains for different radii of curvature of a test mass. The simulation results will provide the basis for designing the thermal tuning and observation parametric instability experiments. This will provide a test bed for studying parametric instability and its control for next generation detectors.

Coordinated optical and radar observations of ionospheric pumping for a frequency pass through the second electron gyroharmonic at HAARP

On 4 February 2005, the High‐frequency Active Auroral Research Program (HAARP) facility was operated in O and X mode while pointing into the magnetic zenith to produce artificial optical emissions in the ionospheric F layer. The pump frequency was set to 2.85 MHz to ensure passing through the second electron gyroharmonic of the decaying ionosphere. Optical recordings at 557.7 and 630 nm were performed simultaneously with the side‐viewing high frequency (HF) and colocated ultra high frequency (UHF) ionospheric radars. No X‐mode effects were found. For O‐mode pumping, when passing from below to above the second gyroharmonic frequency, the optical intensity shows a distinct increase when the plasma frequency passes through the second electron gyroharmonic, while the UHF backscatter changes from persistent to overshoot in character. The optical intensity decreases when pump wave reflection ceases, dropping to zero when upper‐hybrid resonance ceases. The HF radar backscatter increases when the upper‐hybrid resonance frequency passes from below to above the second gyroharmonic frequency. These observations are consistent with the coexistence of the parametric decay and thermal parametric instabilities above the second gyroharmonic. The combined optical and radar data provide evidence that up to three electron‐acceleration mechanisms are acting, sometimes simultaneously, depending on the pump frequency relative to the second gyroharmonic. In addition, we provide the first evidence of lower‐hybrid waves in HF radar centerline data and show that the parametric decay instability producing Langmuir waves can be stimulated in the magnetic zenith at high latitudes despite the pump wave not reaching the nominal frequency‐matching height.

Gingin High Optical Power Test Facility

The Australian Consortium for Gravitational Wave Astronomy (ACIGA) in collaboration with LIGO is developing a high optical power research facility at the AIGO site, Gingin, Western Australia. Research at the facility will provide solutions to the problems that advanced gravitational wave detectors will encounter with extremely high optical power. The problems include thermal lensing and parametric instabilities. This article will present the status of the facility and the plan for the future experiments.

Competition between Langmuir and Upper-Hybrid Turbulence in a High-Frequency-Pumped Ionosphere

We show how the secondary escaping radiation, also known as stimulated electromagnetic emission (SEE), from the ionosphere irradiated by a high-intensity radio beam, can be used to study both reflection altitude ponderomotive parametric instabilities and upper-hybrid altitude thermal parametric instabilities. This has allowed us to observe the transfer of energy from smaller to higher sideband frequency offsets and to identify a new transient SEE feature.

HF‐induced airglow at magnetic zenith: Thermal and parametric instabilities near electron gyroharmonics

We analyze airglow induced by intense radio waves at the High‐frequency Active Auroral Research Program (HAARP) facility for pump frequencies f0 near the second and third electron gyroharmonic (fc). While passing through the double resonance in the weakening ionosphere during heating at f0 ∼ 2fc, airglow intensities rose abruptly and remained elevated during four consecutive pulses. During this period both the thermal and parametric instabilities coexisted. Subsequently, the thermal parametric instability was hampered. The effectiveness of heating near the second gyroharmonic is ascribed to specific dispersion characteristics near the double resonance. The observations suggest that Langmuir waves participate in cyclotron acceleration when the local plasma and second gyroharmonic frequencies match. With f0 ∼ 3fc the airglow terminated due to the suppression of cyclotron acceleration and parametric decay instability.

Properties of the thermal narrow-continuum component in the spectrum of stimulated ionospheric emission

We present the results of experimental studies of the properties of the thermal narrow-continuum component NCth of stimulated electromagnetic emission (SEE) of the ionosphere observed in a narrow region between the pump frequency and the downshifted maximum (DM). Spectral and dynamic characteristics of the NCth component are considered and the dependence of its properties on the frequency and power of the pumping wave as well as on the zenith angle of a high-power radio-wave beam in the geomagnetic-meridian plane is analyzed. It is proved that the NCth generation is determined by the thermal (resonant) parametric instability near the level of the upper-hybrid resonance for a high-power radio wave. New experimental data on the properties of the main DM thermal component in the spectrum of stimulated electromagnetic emission, which we used as the reference component in most measurements, are presented.

On the linear stage of thermal parametric instabilities in the ionosphere excited by HF pumping near electron gyroharmonics

Thresholds and growth rates of the thermal parametric instability in the ionosphere were studied taking into account the regular inhomogeneity (altitude dependence) of the plasma density and of the magnetic field strength. A noticeable decrease of the pump wave threshold power and an increase of the growth rate occurs when f 0 approaches the double resonance frequency f d = nf ce( z d) = f UH( z d), z d being the altitude for double resonance. Particularly, the threshold power decreases relative to the non-resonant case by a factor 3–7 at | f 0 − f d( z d)| ≲ 15 kHz for n = 3 and up to a factor 3 for n = 4. The instability growth rate can increase with a factor of 10 3–10 4 relative to the non-resonant case. The decrease of the threshold and increase of the growth rate occur for quite small scales of the striations, l ⊥ ∼ 1 m for n = 3 and l ⊥ ∼ 0.5 m for n = 4.

Predicted and observed characteristics of small-scale field-aligned irregularities generated in the F-region by low power HF heating

Abstract. Simultaneous HF scattering from the different regions of the heated volume is used to investigate characteristics of the small-scale field-aligned irregularities in the F-region. Time of growth, decay rate and saturation level for different pump powers are deduced from the observations and are compared with their behaviour predicted by the thermal parametric instability model. As a result, the estimates of the density and of the temperature modifications inside of the irregularities are obtained.Key words. Ionosphere (ionospheric irregularities)

Features of the broad upshifted structure in stimulated electromagnetic emission spectra

We present experimental results concerning features of the broad upshifted structure (BUS) in stimulated electromagnetic emission spectra, generated in the ionospheric F region plasma by a powerful electromagnetic wave. The BUS is observed for pump frequencies far from electron cyclotron harmonics. Modification experiments, using O‐mode HF pump waves, were conducted at the SURA heating facility (56°N, 44°E, Nizhny Novgorod, Russia). We investigated the BUS properties for pump frequencies ranging from the third to the sixth electron cyclotron harmonic, concentrating on the dependence of (1) the BUS spectral features on pump frequency and power and (2) the BUS temporal evolution under different ionospheric conditions with and without additional heating of the ionosphere by another pump wave. We find (1) that the frequency range of BUS generation depends on the gyroharmonic mode number, becoming narrower with increasing mode number, and (2) that the BUS is produced in the vicinity of the upper hybrid resonance layer, located typically a few kilometers below the pump wave reflection height. An important result is that small‐scale striations, being produced concurrently with the upper hybrid plasma waves due to the thermal parametric instability, do not play a crucial role for the BUS evolution. A possible relationship of the BUS to gyroharmonic features is discussed.

Study of large-scale irregularities generated in the ionosphericF-region by high-power HF waves

Experimental studies of the features of artificial ionospheric turbulence was performed at the “Sura” heating facility in August 1998 using numerous diagnostic tools, such as scintillation, chirp-sounding, backscattering, and stimulated electromagnetic emission (SEE) measurements, as well as sounding a HF-disturbed volume (DV) by probing waves. It has been found that generation of strong artificial large-scale irregularities (ALSIs), which manifest themselves through the F-spread on ionograms, scintillations of the satellite signal propagated through the DV, and amplitude fluctuations of the probing wave sounding the DV, is observed not only for an overdense heating, at fo≤foF2, but also at higher frequencies fo>foF2≥fuh (here fo is the pump-wave frequency, foF2 is the critical frequency of the F2-layer for O-mode electromagnetic wave, and fuh is the plasma frequency at the upper-hybrid resonance height). This means that transfer of the pump-wave energy in the plasma due to the development of thermal parametric (resonance) instability, rather than thermal self-focussing instability, plays the key role in the ALSI generation in the case where the O-mode HF wave is used for the overdense heating. This conclusion is also confirmed by the fact that the ALSI generation is suppressed in the gyroharmonic frequency range, which is similar to the well-studied quenching of the downshifted maximum (DM) in SEE spectra. In this paper, we discuss new ALSI features revealed by the measurements, as well as the limits by which one can control the ALSI spectrum using complex pumping schemes.

Ionospheric observations of F region artificial plasma turbulence, modified by powerful X‐mode radio waves

We study the influence of additional X‐mode heating of the ionospheric plasma on the features of artificial ionospheric turbulence, induced in the ionospheric F region by O‐mode waves over the “Sura” heating facility (Nizhny Novgorod, Russia). The X heating is shown to suppress the generation of HF plasma turbulence resulting from the development of both the parametric decay and thermal parametric instabilities. Typical times of variations in the turbulence intensity change from ≤0.1 s to ∼10 s, strongly depending on the heating scheme. Aftereffects of the X heating last up to 30–60 s. We distinguish at least three types of phenomena, according to the observed typical times of the processes, and discuss possible reasons for each of them.