The filamentary nature and dynamics of edge-localized modes (ELMs) in the KSTAR high-confinement mode plasmas have been visualized in 2D via electron cyclotron emission imaging. The ELM filaments ...rotating with a net poloidal velocity are observed to evolve in three distinctive stages: initial linear growth, interim quasisteady state, and final crash. The crash is initiated by a narrow fingerlike perturbation growing radially from a poloidally elongated filament. The filament bursts through this finger, leading to fast and collective heat convection from the edge region into the scrape-off layer, i.e., ELM crash.
The electron cyclotron emission imaging (ECEI) diagnostic is a powerful tool to study the MHD and turbulent transport in magnetically confined fusion plasmas. In this work, the optical system ...including the local oscillator (LO) coupling and radio frequency (RF) receiving optics, has been designed and analyzed for the HL-2M ECEI diagnostic. The LO optics can illuminate the antenna array and drive the mixer diode to work efficiently, with more than 36% of the beam intensity for the channels which probe the plasma edge relative to those of channels which probe the plasma core. The RF optics aims at guiding the plasma emission signal to the antenna array. To meet different physical requirements, three types of field of view have been achieved for the plasma imaging, with zoom factors of around 1, 1.5 and 2, respectively. The focal surfaces are almost flat, with a maximum off-mapping (defined as the radial distance between the beam waists of the lower-/uppermost antennas and electron cyclotron emission layer) less than 2.5 cm, which can match the electron cyclotron emission layer quite well and suppress the image distortion in the plasma edge region. The impact of possible vibrations and installation error on the focal plane has been evaluated. In addition, the predefined MHD and turbulence perturbations are well reproduced by combining the optical simulation results and synthetic ECEI modeling, which further verifies the good performance of the RF optics.
•Optical system of electron cyclotron emission imaging diagnostic.•Maximum off-mapping of image surface of RF optics from ECE layer is less than 2.5 cm.•Synthetic ECEI modeling.
In this article, a 263-GHz traveling wave tube (TWT) for electron paramagnetic resonance (EPR) spectroscopy is designed, fabricated, and tested. A periodic permanent magnet (PPM) focused pencil beam ...electron optical system is adopted. A folded waveguide (FWG) slow wave structure (SWS) with modified serpentine bends is optimized to provide high-power wideband performance and stable operation. An experiment has been performed to verify the analysis results and confirm the amplifier stability. The device provides a maximum 11.9-W saturation output power and 25.5-dB saturation gain. Although the available solid-state signal source is unable to drive the amplifier to saturation beyond 260-264 GHz, 10-W output power over 5.6-GHz bandwidth has been measured.
Composition of Titan's ionosphere Cravens, T. E.; Robertson, I. P.; Waite, J. H. ...
Geophysical research letters,
April 2006, Letnik:
33, Številka:
7
Journal Article
Recenzirano
Odprti dostop
We present Cassini Ion and Neutral Mass Spectrometer (INMS) measurements of ion densities on the nightside of Titan from April 16, 2005, and show that a substantial ionosphere exists on the nightside ...and that complex ion chemistry is operating there. The total ionospheric densities measured both by the INMS and the Cassini Radio and Plasma Wave (RPWS) experiments on Cassini suggest that precipitation from the magnetosphere into the atmosphere of electrons with energies ranging from 25 eV up to about 2 keV is taking place. The absence of ionospheric composition measurements has been a major obstacle to understanding the ionosphere. Seven “families” of ion species, separated in mass‐to‐charge ratio by 12 Daltons (i.e., the mass of carbon), were observed and establish the importance of hydrocarbon and nitrile chains in the upper atmosphere. Several of the ion species measured by the INMS were predicted by models (e.g., HCNH+ and C2H5+). But the INMS also saw high densities at mass numbers not predicted by models, including mass 18, which we suggest will be ammonium ions (NH4+) produced by reaction of other ion species with neutral ammonia.
We report on our efforts to model the ambient solar wind out to 1
AU around the time of the May 12, 1997 halo coronal mass ejection (CME) and to identify its coronal source regions. We use the simple ...physics and empirical based Wang–Sheeley–Arge (WSA) model driven by two different sets of updated photospheric field synoptic maps to accomplish this: daily updated maps from Mount Wilson Solar Observatory and updated SOHO/MDI maps constructed with the Schrijver et al. flux transport data assimilation algorithm. The results generated by the WSA model are then compared with the WIND satellite observations near Earth, as well as with each other. We find that the model describes the observed ambient solar wind stream structure around the time of the May 12, 1997 CME generally well, except for the ejecta itself. Our results suggest that the source of the high-speed stream that followed the CME is a coronal hole extension located south of the Sun's equator. We conclude that the northern active region associated with the May 12th CME did not play a role in the formation of the small southern coronal hole extension that produced the high-speed stream, which followed and eventually compressed the ICME from behind. Overall, this analysis suggests how the solar wind context of CME-related events can be analyzed and understood using coronal and solar wind models.
The distribution of spacecraft in the inner heliosphere during 2019 March enabled comprehensive observations of an interplanetary coronal mass ejection (ICME) that encountered Parker Solar Probe ...(PSP) at 0.547 au from the Sun. This ICME originated as a slow (∼311 km s−1) streamer blowout (SBO) on the Sun as measured by the white-light coronagraphs on board the Solar TErrestrial RElations Observatory-A and the Solar and Heliospheric Observatory. Despite its low initial speed, the passage of the ICME at PSP was preceded by an anisotropic, energetic ( 100 keV/n) ion enhancement and by two interplanetary shocks. The ICME was embedded between slow (∼300 km s−1) solar wind and a following, relatively high-speed (∼500 km s−1), stream that most likely was responsible for the unexpectedly short (based on the SBO speed) ICME transit time of less than ∼56 hr between the Sun and PSP, and for the formation of the preceding shocks. By assuming a graduated cylindrical shell (GCS) model for the SBO that expands self-similarly with time, we estimate the propagation direction and morphology of the SBO near the Sun. We reconstruct the flux-rope structure of the in situ ICME assuming an elliptic-cylindrical topology and compare it with the portion of the 3D flux-rope GCS morphology intercepted by PSP. ADAPT-WSA-ENLIL-Cone magnetohydrodynamic simulations are used to illustrate the ICME propagation in a structured background solar wind and estimate the time when PSP established magnetic connection with the compressed region that formed in front of the ICME. This time is consistent with the arrival at PSP of energetic particles accelerated upstream of the ICME.
Various upstream spacecraft have now observed the solar wind conditions affecting the Earth since the 1970s, covering over four solar activity cycles. These measurements provide a long term picture ...of the related patterns in large scale incident plasma and magnetic field parameters of interest for both interpreting cycles in geospace effects, and understanding how the Sun controls our space environment. This paper focuses on the latter, in part to provide context at the start of the new solar cycle 25, and toward establishing connections between the 1 AU ecliptic solar wind behavior and the unprecedented near‐Sun measurements of heliospheric features on Parker Solar Probe and Solar Orbiter. Magnetograph data‐based potential field source surface models provide a basic picture of how the solar wind sources, including those that give rise to corotating high speed streams in the ecliptic, have changed since the beginning of the record of regular solar wind measurements. In particular, they suggest the contributions from low to mid latitude coronal holes dominate the observed cycles (21–24), especially the weaker cycles (23 and 24), impacting upstream measurement interpretations, modeling, and forecasting considerations. For example, recurring features are affected by differential rotation of the Sun's surface field, which through its effects on the corona, can produce solar wind streams reappearing at ∼25–30 days intervals instead of at the canonical 27.3 days Carrington rotation rate. In addition, the conditions that lead to the corotating stream structure that can dominate periods of low solar activity are seen to be more complicated than suggested by the simple concepts of early studies. The overall results illustrate where in the cycles well‐defined, long‐lived large scale structures can be expected, and the advantages of synoptic displays of 1 AU solar wind parameters for anticipating timings of recurring features.
Plain Language Summary
The solar wind is generally composed of a complex set of plasma (ionized gas) streams that flow out of regions where the coronal magnetic field is “open” to interplanetary space. These “coronal holes,” or solar wind sources, have locations and shapes that depend on the solar magnetic field and so evolve with the solar cycle. Models have been developed that can describe the solar wind structure at any time, based on the solar field observations. These are useful for understanding the Earth's space environment, but we now wish to use them to make forecasts. The work described here suggests that by examining the long‐term behavior of both the solar wind observations and the models, we can provide better forecasts by identifying and making projections based on solar cycle‐dependent trends. This is particularly relevant to forecasting the times of return of so‐called “corotating” structures: large spatial scale, “high speed” streams, and their related density compressions, that seem to reappear roughly every month‐producing significant responses in near‐Earth space.
Key Points
The solar wind in the ecliptic varies with the solar cycle as coronal field topology changes with the surface magnetic field
Potential field source surface models present a picture of this evolution as global coronal hole distributions and low‐latitude locations where the open fields map
Low latitude coronal holes dominate the local solar wind for much of the cycle, including long periods of recurring high speed streams
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