Magnetic Connection Research Articles

Study and optimization of lower hybrid wave coupling in the experimental advanced superconducting (EAST) tokamak

The results presented in this paper are an extension of our recent (Kong et al 2012 Plasma Phys. Control. Fusion 54 105003) studies on lower hybrid wave (LHW) coupling. By optimizing the shape of the LH grill, the misalignment between the poloidal limiter (PL) and the LH grill is nearly eliminated and the coupling of LHW is improved, especially on the top row, although some discrepancies are still present in the case with low edge density. Density modifications both by LHW and ion cyclotron range of frequency (ICRF) power are studied in EAST. Experimental results show that the edge density modification in front of the LH grill during LHW power depends mainly on the competition between ponderomotive force (PMF) and the ionization of neutral gas, provided by gas puffing and edge recycling. However, the local edge density during ICRF power can be reduced rapidly. Furthermore, such a modification is more obvious with higher ICRF power and the relevant mechanism of density modification by ICRF power can be related to RF sheaths. In addition, another analogous effect of RF sheaths on the coupling of LHW is also investigated, i.e. the density convection induced by Er × B drift. The changes in LHW coupling associated with different ICRF antennas are discussed and it is shown that in some cases the coupling on the lower rows of the LH grill is improved possibly due to magnetic connection between ICRF antennas and the LH grill. The local coupling of LHW can be improved by gas puffing from gas introduction modules (GIM) on both sides of the launcher, but it is difficult to judge which one is more beneficial due to errors in measurements. Experimental results with gas (D2) injection during ICRF power clearly show that the coupling of LHW on the upper rows will be first improved by gas injection on the electron side and the coupling on the lower rows will be effectively improved by gas injection on the ion side. The results are consistent with the mapping of field lines.

Jovian electrons and the solar wind during the minimum of the 23rd–24th solar activity cycle

Jovian electrons in Earth orbit can be regarded as probes of the inner heliosphere’s structure. They readily penetrate into the inner heliosphere in periods of the optimum magnetic connection between Earth and Jupiter. Such a penetration is also occasionally observed at arbitrary Earth-Jupiter dispositions. This phenomenon can be explained by the occurrence of long-lived magnetic traps extending from the Sun to Jupiter and rotating along with the Sun.

Saturn's ring rain

Saturn's atmosphere bears a latent image of its icy rings, implying that electrically charged bits of water ice are being transported along magnetic-field lines of force from sources in the ring plane to the upper atmosphere. See Letter p.193 A magnetic connection between Saturn and its ring system has been suggested previously. It might explain, among other things, the unexpectedly low electron densities and high temperatures observed in the ionosphere. Now that missing link has been observed. Near-infrared spectral data from the W. M. Keck II telescope, focused on Saturn's noon meridian, are consistent with the transfer of charged water from the rings to the ionosphere, sufficient to flood a third of the planet's upper atmospheric surface. This ring 'rain' links the rings to the planet electrically and magnetically, leading to the global modulation of upper atmospheric chemistry.

The domination of Saturn’s low-latitude ionosphere by ring ‘rain’

Saturn's ionosphere is produced when the otherwise neutral atmosphere is exposed to a flow of energetic charged particles or solar radiation. At low latitudes the solar radiation should result in a weak planet-wide glow in the infrared, corresponding to the planet's uniform illumination by the Sun. The observed electron density of the low-latitude ionosphere, however, is lower and its temperature higher than predicted by models. A planet-to-ring magnetic connection has been previously suggested, in which an influx of water from the rings could explain the lower-than-expected electron densities in Saturn's atmosphere. Here we report the detection of a pattern of features, extending across a broad latitude band from 25 to 60 degrees, that is superposed on the lower-latitude background glow, with peaks in emission that map along the planet's magnetic field lines to gaps in Saturn's rings. This pattern implies the transfer of charged species derived from water from the ring-plane to the ionosphere, an influx on a global scale, flooding between 30 to 43 per cent of the surface of Saturn's upper atmosphere. This ring 'rain' is important in modulating ionospheric emissions and suppressing electron densities.

Jovian electrons and the structure of interplanetary space during solar activity minimum 2007-2008

The presence of Jovian electrons at the Earth orbit allows considering them as test particles probing of the structure of the inner heliosphere. The penetration of Jovian electrons into the inner heliosphere during periods of optimal magnetic connection between Jupiter and Earth is trivial phenomenon, while a special magnetic configuration is necessary for periods when such a connection is absent. The possibility of the formation of long-living CIR-like magnetic traps filled by low-energy electrons (~ 1 MeV) during their passage by Jupiter and their subsequent arrival at the Earth is considered.According to the SOHO > 0.25 MeV Jovian electron data during solar activity minimum in 2007–2008 the structure of the solar wind and its steady-state allowed the formation of such traps, existing for about a year (14 solar rotations).

RF sheath-enhanced beryllium sources at JET’s ICRH antennas

Local beryllium (Be) I and Be II line intensities were measured in the plasma–wall interaction region near an ICRH antenna in JET. The intent was to use these intensities as a measure of the formation of local Radio Frequency (RF) sheath potentials, through RF sheath rectification and potential build up at the end of field lines passing in front of the antenna. Experimentally, it was found that the Be I and Be II emission increase when using the antenna local to the spectroscopic measurement, and increase even more when using a remote antenna that is magnetically connected to the observation point. Magnetic field mapping indicates a magnetic connection between the observation location and the top corner region of the remote antenna and/or its protection limiter. These measurements can be used in support of RF sheath modeling that is an important part of the optimization of antenna design for next generation fusion energy devices, including ITER.

MAST-upgrade divertor facility and assessing performance of long-legged divertors

A potentially important feature in a divertor design for a high-power tokamak is an extended and expanded divertor leg. The upgrade to MAST will allow a wide range of such divertor leg geometries to be produced, and hence will allow the roles of greatly increased connection length and flux expansion to be experimentally tested. This will include testing the potential of the Super-X configuration [1]. The design process for the upgrade has required analysis of producing and controlling the magnetic configurations, and has included consideration of the roles that divertor closure and increasing magnetic connection length will play.

Solar Energetic Particle Events in the 23rd Solar Cycle: Interplanetary Magnetic Field Configuration and Statistical Relationship with Flares and CMEs

We study the influence of the large-scale interplanetary magnetic field configuration on the solar energetic particles (SEPs) as detected at different satellites near Earth and on the correlation of their peak intensities with the parent solar activity. We selected SEP events associated with X and M-class flares at western longitudes, in order to ensure good magnetic connection to Earth. These events were classified into two categories according to the global interplanetary magnetic field (IMF) configuration present during the SEP propagation to 1AU: standard solar wind or interplanetary coronal mass ejections (ICMEs). Our analysis shows that around 20% of all particle events are detected when the spacecraft is immersed in an ICME. The correlation of the peak particle intensity with the projected speed of the SEP-associated coronal mass ejection is similar in the two IMF categories of proton and electron events, $\approx 0.6$. The SEP events within ICMEs show stronger correlation between the peak proton intensity and the soft X-ray flux of the associated solar flare, with correlation coefficient $r=\,$0.67$\pm$0.13, compared to the SEP events propagating in the standard solar wind, $r=\,$0.36$\pm$0.13. The difference is more pronounced for near-relativistic electrons. The main reason for the different correlation behavior seems to be the larger spread of the flare longitude in the SEP sample detected in the solar wind as compared to SEP events within ICMEs. We discuss to which extent observational bias, different physical processes (particle injection, transport, etc.), and the IMF configuration can influence the relationship between SEPs and coronal activity.

Study of Local Heliospheric Current Sheet Variations from Multi-Spacecraft Observations

The local magnetic structure of the heliospheric current sheet (HCS) is observed as a boundary through which the magnetic field inverts its direction toward or away from Sun. The local variability of the HCS has been studied by means of a comparison of its local orientation estimated from data of different spacecraft. With the aim of determining possible variations in the local orientation, the selected events have been grouped according to their magnetic connection. A rough estimate of the magnetic connection (C) between two observation points has been found by considering the absolute value of the difference between the elapsed and expected times (C=|Δt el – Δt ex|/Δt ex). Lower values of C imply better connections, and smaller variation in the HCS orientation is expected if variations, temporal or spatial, in the HCS shape are negligible. Two periods have been analyzed: the ascending phase of Solar Cycle 23 and the minimum of the cycle in 2007 – 2008. It has been observed that, during the ascending phase, changes in the local HCS shape are mainly due to spatial variations. During minimum, the results show an increasing trend of the variation of the HCS local inclination with distance between spacecraft up to 5000 Earth radii (R E). For larger distances the results show a downward tendency. This inversion could be related to a continuous interaction of the HCS with the solar wind and with a poor magnetic connection, which could lead to changes in the local HCS shape making it unrecognizable to analyze the evolution of the structure from one observation point to another.

DISCONNECTION FROM THE TERMINATION SHOCK: THE END OF THEVOYAGERPARADOX

The most recent Voyager 1 observations show rapidly increasing galactic cosmic ray fluxes with simultaneously decreasing anomalous cosmic ray fluxes. While this has been suggested to somehow herald the imminent crossing of the heliopause, which bounds the heliosphere, we show that such observations should naturally arise from the heliosphere's global magnetic topology. For a blunt termination shock, there must be a region of magnetic flux, still inside the heliopause, but beyond the last magnetic connection point to the termination shock, with poorer access for the shock-accelerated anomalous cosmic rays and better access for the galactic cosmic rays entering the heliosphere.

The role of power and magnetic connection to the active antenna in the suppression of intermittent structures by ion cyclotron resonance heating

The effect of the ion cyclotron resonance heating (ICRH) on the scrape-off layer (SOL) is still an open issue, where, lately it was shown on the ASDEX-Upgrade tokamak that turbulence large-scale structures, known as blobs or avaloids, are suppressed by ICRH (Antar et al 2010 Phys. Rev. Lett. 105 165001). Furthermore, it was shown that the edge localized mode-induced turbulent transport is also reduced significantly. However, the reasons behind this interaction remain unknown. On the Tore Supra tokamak, we confirm that the ICRH suppresses large-scale structures while small-scale structures are enhanced; overall, the turbulence level of fluctuations is reported to drop from about 40% to 25%. This confirms that the effects on turbulence are independent of the type of plasma confinement, L-mode on Tore Supra versus H-mode on ASDEX-Upgrade. The dependence on the ICRH power showed that if a threshold existed it would be below 500 kW and that above this power, no additional effects on the SOL turbulence are reported. The other study reported in this paper deals with the importance of the magnetic field line connections or, in other words, whether the interaction between ICRH and turbulence is global, affecting the whole plasma, or local, affecting regions that are magnetically connected to the active antenna. We found that the toroidal connection to the active antenna is not critical in the sense that turbulence in regions close to the antenna but not necessarily connected are affected. For regions that are not connected and far from the active antenna, turbulence does not change much when applying ICRH.

Covariant form of the ideal magnetohydrodynamic “connection theorem” in a relativistic plasma

The magnetic connection theorem of ideal magnetohydrodynamics by Newcomb (Newcomb W. A., Ann. Phys. (N.Y.), 3 (1958) 347) and its covariant formulation are rederived and reinterpreted in terms of a “time resetting” projection that accounts for the loss of simultaneity in different reference frames between spatially separated events.

Cassini in Titan's tail: CAPS observations of plasma escape

We present observations of CAPS electron and ion spectra during Titan distant tail crossings at 5,000–10,000 km altitude by the Cassini spacecraft. In common with closer tail encounters, we identify ionospheric plasma in the tail. Some of the electron spectra indicate a direct magnetic connection to Titan's dayside ionosphere due to the presence of ionospheric photoelectrons. Ion observations reveal heavy (m/q∼ 16 and 28) and light (m/q = 1–2) ion populations streaming into the tail. Using the distant tail encounters T9, T75 and T63, we estimate total plasma loss rates from Titan via this process of (4.2, 0.96 and 2.3) × 1024 ions s−1 respectively for the three encounters, values which are in agreement with some simulations but slightly lower than earlier estimates based on non‐differential techniques. Using the mass‐separated data, this corresponds to mass loss rates of (8.9, 1.6, 4.0) × 1025 amu s−1 for T9, T75 and T63 respectively, an average loss rate of ∼7 tonnes per Earth day. Remarkably, all of the tail encounters studied here indicate a split tail feature, indicating that this may be a common feature in Titan's interaction with Saturn's magnetosphere.

Reconnection at the magnetopause of Saturn: Perspective from FTE occurrence and magnetosphere size

Flux transfer events observed at Mercury, Earth, and Jupiter are attributed to spatially and temporally limited events in which the magnetosheath and magnetospheric magnetic field become interconnected and magnetic flux is transported from the dayside to the lobes of the magnetotail. Examination of the Saturnian magnetopause at local times from 1000 to 1400 shows no evidence for this phenomenon. Nevertheless, we do find brief intervals during which the normal component of the magnetic field across the magnetopause becomes significantly enhanced for typically one to ten minutes. Magnetosheath electrons appear during these episodes of enhanced magnetic field normal components indicating that indeed the magnetosphere is connected to the magnetosheath by these magnetic bridges. To determine if this magnetic connection leads to a measurable transfer of magnetic flux from the dayside, we check the location of the magnetopause standoff distance for both northward and southward magnetosheath fields. In 71 crossings, we find no obvious dependence of the distance on the direction of the magnetosheath field, indicating that the direction of the interplanetary magnetic field is not a major factor in the determination of the location of the Saturnian magnetopause. This is unlike the position of the terrestrial magnetosphere that undergoes significant motion through reconnection with the interplanetary magnetic field.

What Are Special About Ground-Level Events?

Ground level events (GLEs) occupy the high-energy end of gradual solar energetic particle (SEP) events. They are associated with coronal mass ejections (CMEs) and solar flares, but we still do not clearly understand the special conditions that produce these rare events. During Solar Cycle 23, a total of 16 GLEs were registered, using ground-based neutron monitor data. We first ask if these GLEs are clearly distinguishable from other SEP events observed from space. Setting aside possible difficulties in identifying all GLEs consistently, we then try to find observables which may unmistakably isolate these GLEs by studying the basic properties of the associated eruptions and the active regions (ARs) that produced them. It is found that neither the magnitudes of the CMEs and flares nor the complexities of the ARs give sufficient conditions for GLEs. It is possible to find CMEs, flares or ARs that are not associated with GLEs but that have more extreme properties than those associated with GLEs. We also try to evaluate the importance of magnetic field connection of the AR with Earth on the detection of GLEs and their onset times. Using the potential field source surface (PFSS) model, a half of the GLEs are found to be well-connected. However, the GLE onset time with respect to the onset of the associated flare and CME does not strongly depend on how well-connected the AR is. The GLE onset behavior may be largely determined by when and where the CME-driven shock develops. We could not relate the shocks responsible for the onsets of past GLEs with features in solar images, but the combined data from the Solar TErrestrial RElations Observatory (STEREO) and the Solar Dynamics Observatory (SDO) have the potential to change this for GLEs that may occur in the rising phase of Solar Cycle 24.

Cassini observations of ionospheric photoelectrons at large distances from Titan: Implications for Titan's exospheric environment and magnetic tail

Discrete peaks near 24.1 eV are seen in electron spectra measured in Titan's ionosphere by the ELS (Electron Spectrometer), part of the Cassini Plasma Spectrometer (CAPS), and are interpreted as photoelectrons. These photoelectrons are generated as a result of ionization of N2 by the strong solar He II (30.4 nm) line. They are generally observed in the dayside ionosphere, because this is where neutral N2 particles can be ionized by solar radiation. Coates et al. (2007) discussed initial observations of photoelectrons in Titan's distant tail during the T9 encounter. Here, we describe additional photoelectron peak observations at large distances from Titan, where they are unlikely to have originated because of low neutral N2 densities. We consider the tail structures during the encounters T15, T17, and T40. We infer that the distant photoelectrons may have traveled to the observation sites by means of a magnetic connection from lower altitudes in the dayside ionosphere, where they could have been produced. This idea is supported by results of hybrid modeling. Thus photoelectrons may be used as tracers of magnetic field lines and further improve our understanding of Titan's complex plasma environment.

The interplanetary magnetic structure that guides solar relativistic particles

Relating in situ measurements of relativistic solar particles to their parent activity in the corona requires understanding the magnetic structures that guide them from their acceleration site to the Earth. Relativistic particle events are observed at times of high solar activity, when transient magnetic structures such as Interplanetary Coronal Mass Ejections (ICMEs) often shape the interplanetary magnetic field (IMF). They may introduce interplanetary paths that are longer than nominal, and magnetic connections rooted far from the nominal Parker spiral. We present a detailed study of the IMF configurations during ten relativistic solar particle events of the 23rd activity cycle to elucidate the actual IMF configuration guiding the particles to Earth, where they are measured by neutron monitors. We use magnetic field (MAG) and plasma parameter measurements (SWEPAM) from ACE, and determine interplanetary path lengths of energetic particles through a modified version of the velocity dispersion analysis based on energetic particle measurements with SoHO/ERNE. We find that the majority (7/10) of the events is detected in the vicinity of an ICME. Their interplanetary path lengths are found to be longer (1.5-2.6 AU) than those of the two events propagating in the slow solar wind (1.3 AU). The largest apparent path length is found in an event within the fast solar wind, probably due to enhanced pitch angle scattering. The derived path lengths imply that the first energetic and relativistic protons are released at the Sun at the same time as electron beams emitting type III radio bursts. The timing of the first high-energy particle arrival at Earth is dominantly determined by the type of IMF in which the particles propagate. Initial arrival times are as expected from Parker's model in the slow solar wind, and significantly larger in or near transient structures such as ICMEs.

BEHIND-THE-EAR HEARING DEVICE WITH A MAGNETICALLY-ATTACHED EAR HOOK

An ear hook is to be able to be tightly attached to a hearing device housing in a simple fashion. To this end, provision is made for it to be possible to clip the ear hook onto the hearing device housing. One of the two parts; hearing device housing and ear hook has a sound outlet tube, which can be inserted into a corresponding opening in the other part. The two parts are detachably fastened to one another in an axial direction in respect of the sound outlet tube by means of a magnetic connection. The magnetic connection ensures that the two components are fitted tightly onto one another, though it enables said two components to rotate in respect of each other.

THE DISAPPEARING SOLAR FILAMENT OF 2003 JUNE 11: A THREE-BODY PROBLEM

The eruption of a large quiescent filament on 2003 June 11 was preceded by the birth of a nearby active region?a common scenario. In this case, however, the filament lay near a pre-existing active region and the new active region did not destabilize the filament by direct magnetic connection. Instead it appears to have done so indirectly via magnetic coupling with the established region. Restructuring between the perturbed fields of the old region and the filament then weakened the arcade overlying the midpoint of filament, where the eruption originated. The inferred rate (~11??day?1) at which the magnetic disturbance propagates from the mature region to destabilize the filament is larger than the mean speed (~5?-6??day?1) but still within the scatter obtained for Bruzek's empirical relationship between the distance from a newly formed active region to a quiescent filament and the time from active region appearance to filament disappearance. The higher propagation speed in the 2003 June 11 case may be due to the broadside (versus ''end-on) angle of attack of the (effective) new flux to the coronal magnetic fields overlying a central section of the axis of the filament.

Magnetic Actuator Group of Globular Type Capable of Free Movement in a Complex Pipe

Finding damage inside pipes is important for the inspection of complex pipes used in nuclear power plants and chemical plants. A number of studies have investigated the mechanisms of an actuator with an electric cable to provide locomotion through various devices in complex pipes. An in-pipe robot capable of movement in narrow complex pipes has not yet been developed. In the present paper, we propose a globular magnetic actuator group that exhibits a very high thrust force and is capable of free reversible motion in complex pipes. Two actuators of the same size and characteristics are coupled by the magnetic connection method, which generates almost no mechanical loss. The globular magnetic actuator group capable of reversible motion through elongation and contraction of eight shape-memory-alloy (SMA) coils was fabricated. Experimental results indicate that the prototype actuator group is able to climb at a rate of 29 mm/s in a straight pipe while pulling a load mass of 48 g.