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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Turbulence statistical analysis of the L-H transition and RMPs in KSTAR

Here, we investigate the turbulence statistics associated with low-to-high confinement (L-H) transitions and externally applied resonant magnetic perturbations (RMPs) in KSTAR. Time-series fluctuations of electron density n e , electron temperature T e , and the time derivative of the poloidal magnetic field dB θ /dt (Mirnov coils) are analysed using information-geometric measures (information rate Γ and information length $\mathcal{L}$ = ∫ Γ dt), together with kurtosis κ and variance σ 2 . In low-density upper single-null plasmas (n e ~ 1.2 x 10 19 m -3 ), a ~80 kHz magnetic mode coupling n e , T e , dB θ /dt and emerges prior to the L-H transition and persists into the edge-localised modes H-mode. Edge-localised RMPs (ERMPs) suppress this coherent mode but enhance intermittency, producing frequent bursts that abruptly reshape the time-dependent probability density functions (PDFs) and generate large spikes in Γ (with smaller changes in κ), signalling ERMP-driven departures from quasi-stationarity. The impact of ERMPs on background fluctuation levels depends on density, radial location, and the fluctuating variable itself ($\tilde{n}$, $\tilde{T}$, $\dot{B}$ θ ), whereas $\mathcal{L}$ provides a robust, regime-agnostic measure of cumulative statistical reorganisation and spatial decorrelation. In particular, at low density we observe weaker coupling between $\tilde{n}$ and $\tilde{T}$, along with a tendency toward decreased radial correlation-most clearly for $\tilde{T}$-under ERMPs. Overall, information geometry cleanly captures intermittent events, quantifies non-equilibrium PDF evolution, and offers a compact, cross-diagnostic metric for assessing resonant magnetic perturbation effects on edge transport and correlation across densities, radial locations, and confinement states.

Kim, Eun-jin [Coventry Univ. (United Kingdom); Seo↗
NASA NTRS1978

Temperate zone sporadic-E maps /f/0/E/s/ greater than 7 MHz/

Three maps are presented of f(0) sporadic-E greater than 7 MHz for temperate zones. During map preparation it was assumed that: (1) the geographical area would be between plus and minus 60 deg geomagnetic latitude, excluding the equatorial zone, (2) the maps would be for f(0) sporadic-E greater than 7 MHz, (3) sunspot cycle variation would be ignored, (4) one map would represent the peak sporadic-E period with a discontinuity at the geographic equator, (5) one map would represent non-peak periods with a discontinuity at the geographic equator, (6) one map would represent all twelve months with no equatorial discontinuity, and (7) previously determined coefficients for median and upper decile f(0) sporadic-E would be extrapolated to 7 MHz.

Smith, E. K.↗
NASA NTRS2020

Mass Determinations of the Three Mini-Neptunes Transiting TOI-125

The Transiting Exoplanet Survey Satellite, TESS, is currently carrying out an all-sky search for small planets transiting bright stars. In the first year of the TESS survey, a steady progress was made in achieving the mission’s primary science goal of establishing bulk densities for 50 planets smaller than Neptune. During that year, the TESS’s observations were focused on the southern ecliptic hemisphere, resulting in the discovery of three mini-Neptunes orbiting the star TOI-125, a V = 11.0 K0 dwarf. We present intensive HARPS radial velocity observations, yielding precise mass measurements for TOI-125b, TOI-125c, and TOI-125d. TOI-125b has an orbital period of 4.65 d, a radius of 2.726 ± 0.075 R(E), a mass of 9.50 ± 0.88 M(E), and is near the 2:1 mean motion resonance with TOI-125c at 9.15 d. TOI-125c has a similar radius of 2.759 ± 0.10 R(E) and a mass of 6.63 ± 0.99 M(E), being the puffiest of the three planets. TOI-125d has an orbital period of 19.98 d and a radius of 2.93 ± 0.17 R(E) and mass 13.6 ± 1.2 M(E). For TOI-125b and d, we find unusual high eccentricities of 0.19 ± 0.04 and 0.17(sup +0.08, sub −0.06), respectively. Our analysis also provides upper mass limits for the two low-SNR planet candidates in the system; for TOI-125.04 (R(P) = 1.36 R(E), P = 0.53 d), we find a 2σ upper mass limit of 1.6 M(E), whereas TOI-125.05 (R(P) = 4.2(sup +2.4, sub −1.4 R(E), P = 13.28 d) is unlikely a viable planet candidate with an upper mass limit of 2.7 M(E). We discuss the internal structure of the three confirmed planets, as well as dynamical stability and system architecture for this intriguing exoplanet system.

L D Nielsen↗
NASA NTRS1977

Reflection of radio waves by sporadic-E layers

A full-wave analysis of the reflection coefficient is developed and applied to electron-density profiles of midlatitude sporadic-E layers observed by rocket-borne probes. It is shown that partial reflection from the large electron-density gradients at the upper and lower boundaries of sporadic-E layers does not account for the partial transparency observed by ionosondes.

Miller, K. L.↗
NASA NTRS2004

CHANDRA Observations of RX J1914.4+ 2456: Spin-up of a White Dwarf?

RX 51914.4+2456 is a candidate double-degenerate binary with a putative 1.756 mHz orbital frequency. In a previous timing study using archival ROSAT and ASCA data we reported evidence for an increase of the putative orbital frequency at a rate consistent with expectations for gravitational radiation from the system. Here we report the results of new Chandra timing observations which confirm the previous indications of spin-up of the X-ray frequency, and provide much tighter constraints on the frequency derivative, u. We obtained with Chandra a total of 75 ksec of exposure in two epochs separated in time by 10.3 months. The total time span of the archival ROSAT, ASCA and new Chandra data is now 10.2 years. This more than doubles the interval spanned by the ROSAT and ASCA data alone, providing much greater sensitivity to a frequency derivative. With the addition of the Chandra data an increasing frequency is unavoidable, and the mean i/ is 5.9f0.9 x 10-l' Hz s-'. Interestingly, power spectra of the longest Chandra pointing show evidence for a sideband structure to the 1.756 mHz frequency. The fundamental and first harmonic show evidence for upper sidebands with a frequency separation of E 0.5 mHz from their parent peaks. Additionally, the first and second harmonics show evidence for lower sidebands with approximately half the frequency separation of the upper sidebands. Similar sideband structure is a common feature of Intermediate Polars (Ips)-although it is usually observed in the optical-and suggests the presence of a longer period in the system, perhaps the previously unseen orbital period. If this is correct the sideband structure indicates an orbital period close to 1 hr, and the observed u likely represents the accretion-induced spin-up of a white dwarf. We discuss the implications of these findings for the nature of RX J1914.4+2456.

Strohmayer, Tod E.↗
NASA NTRS2000

Latitudinal Density Dependence of Magnetic Field Lines Inferred from Polar Plasma Wave Data

Using observations of the electron density, n(sub e), based on measurement of the upper hybrid resonance frequency by the Polar spacecraft Plasma Wave Instrument, we have examined the radial density dependence along field lines in the outer plasmasphere and the near plasmatrough. Sampled L values range from 2.5 to 6.6. Our technique depends on the fact that Polar crosses particular L values at two different points with different radial distance R. In our plasmaspheric data set (n(sub e) > 100/cm3), we find that on average n(sub e) is flat along field lines from the equator up to the latitudes sampled by Polar (R approximately equal to or > 2.0). In the plasmatrough data set (n(sub e) < 100/cm-3), there is on average a mild radial dependence n(sub e) varies as R(exp -1.7).

Goldstein, J.↗
DOE OSTI2024

Study of e + e − → ω X ( 3872 ) and γ X ( 3872 ) from 4.66 to 4.95 GeV

Using data samples with an integrated luminosity of 4.5 fb − 1 collected by the BESIII detector at center-of-mass energies ranging from 4.66 GeV to 4.95 GeV, we study the processes of e + e − → ω X ( 3872 ) and e + e − → γ X ( 3872 ) . With the e + e − → ω X ( 3872 ) process, the branching fraction ratio R ≡ B ( X ( 3872 ) → γ J / ψ ) B ( X ( 3872 ) → π + π − J / ψ ) is measured to be 0.38 ± 0.2 0 stat ± 0.0 1 syst ( R < 0.83 at 90% confidence level). In addition, we measure the ratio of the average cross section of e + e − → ω X ( 3872 ) to e + e − → ω χ c 1 ( ω χ c 2 ) to be σ ω X ( 3872 ) / σ ω χ c 1 ( σ ω X ( 3872 ) / σ ω χ c 2 ) = 5.2 ± 1.0 stat ± 1.9 syst ( 5.5 ± 1.1 stat ± 2.4 syst ) . Finally, we search for the process of e + e − → γ X ( 3872 ) , and no obvious signal is observed. The upper limit on the ratio of the average cross section of e + e − → γ X ( 3872 ) to e + e − → ω X ( 3872 ) is set as σ γ X ( 3872 ) / σ ω X ( 3872 ) < 0.23 at 90% confidence level. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
NASA NTRS1998

Observation and Modeling of the Solar Transition Region: A Quasi-Static Loops Model with Implications for Heating the Lower Transition Region - 1

We report on observations of the solar atmosphere in several extreme ultraviolet and far-ultraviolet bandpasses obtained by the Multi-Spectral Solar Telescope Array, a rocket borne spectroheliograph, on flights in 1987, 1991, and 1994, spanning the last solar maximum. Quiet sun emission observed in the 171 A - 175 A bandpass, which includes lines of 0Ov, O vi, Fe ix, and Fe x, has been analyzed to test models of the temperatures and geometries of the structures responsible for this emission. Analyses of intensity variations above the solar limb reveal scale heights consistent with a quiet sun plasma temperature of 500 000 K less than or equal to T(sub e) less than or equal to 800 000 K. Intensity modulations in the quiet sun are observed to occur on a scale comparable to the supergranular scale. The structures responsible for the quiet sun EUV emission are modeled as small quasi-static loops. We find that the emission predicted by loop models with maximum temperatures between 700 000 K and 900 000 K are consistent with our observations. We also present a preliminary comparison of the predictions of our models with observations of diagnostic spectral line ratios obtained from previous observers. We discuss the implications a distribution of loops of the type we model here would have for heating the lower transition region. Finally, in fight of the models we calculate here, we briefly review the current state of knowledge concerning the contributions thermal conduction from coronal (T(sub e) greater than or equal to 10(exp 6) K) and upper transition region (10(exp 5) K less than T(sub e) less than 10(esp 6) K) structures make to lower transition region emission. We argue that the evidence which has lead many authors to conclude that the interface of hotter and cooler plasmas makes a negligible contribution to lower transition region emission is much less compelling in light of recent observations and analyses. We further argue that it is the interface of chromospheric material with structures such as loops that have sub-coronal peak temperatures (i.e. less than 900 000 K) that makes the dominant contribution to lower transition region emission in the quiet sun.

Oluseyi, Hakeem M.↗
NASA NTRS1981

Natural variability of tropical upper stratospheric ozone inferred from the Atmosphere Explorer backscatter ultraviolet experiment

Analysis of backscattered ultraviolet radiances observed at tropical latitudes by the Atmosphere Explorer-E satellite reveals both annual and semiannual cycles in upper stratospheric ozone. The annual variation dominates the signal at wavelengths which sense ozone primarily above 45 km while below this, to the lowest altitude sensed, 35 km, the semiannual component has comparable amplitude. Comparison of radiance measurements taken with the same instrument at solar minimum during 1976 and solar maximum in 1979 show no significant differences. This suggests that variations in upper stratospheric ozone over the solar cycle are small, although the data presently available do not allow a definite conclusion.

Frederick, J. E.↗