Helical Magnetic Field Lines Research Articles

In-depth experimental search for a coupling between gravity and electromagnetism with steady fields

Any means to control gravity like electromagnetism is currently out of reach by many orders of magnitude even under extreme laboratory conditions. Some often poorly executed experiments or pseudoscience theories appear from time to time claiming for example anomalous forces from capacitors that suggest a connection between the two fields. We developed novel and high resolution horizontal-, vertical- and rotation-balances that allow to test electric devices completely shielded and remotely controlled under high vacuum conditions to perform the first in-depth search for such a coupling using steady fields. Our testing included a variety of capacitors of different shapes and compositions as well as for the first-time solenoids and tunneling currents from Zener diodes and varistors. A comprehensive coupling-scheme table was used to test almost all combinations including capacitors and solenoids with permittivity and permeability gradients as well as capacitors and varistors within crossed magnetic fields. We also tested a crossed-coil producing helical magnetic field lines as well as interactions between a pair of shielded toroidal coils to look for proposed extensions to Maxwell’s equations. No anomalous forces or torques down to the nano-Newton or nano-Newton-Meter range were found providing new limits many orders of magnitude below previous assessments ruling out claims or theories and providing a basis for future research on the topic.

Triggering of tearing instability by impurity radiation through resistive interchange reversal in a tokamak

Recent MHD simulations find that the reversal of the local resistive interchange parameter from negative to positive due to impurity radiation cooling is able to linearly destabilize the resistive tearing mode (TM) growth in a tokamak above a threshold in impurity level. A layer of perturbed Pfirsch–Schlüter current density and resistivity are also induced by the impurity radiation, which further govern the TM growth and saturation in the nonlinear stage. The impurity threshold and the TM growth strongly depend on the parallel thermal conductivity, and such a dependence derives from the impact on of the fast parallel thermal equilibration along the helical magnetic field lines.

Small-scale Magnetic Flux Ropes with Field-aligned Flows via the PSP In Situ Observations

Abstract Magnetic flux rope, formed by the helical magnetic field lines, can sometimes maintain its shape while carrying significant plasma flow that is aligned with the local magnetic field. We report the existence of such structures and static flux ropes by applying the Grad-Shafranov-based algorithm to the Parker Solar Probe in situ measurements in the first five encounters. These structures are detected at heliocentric distances, ranging from 0.13 to 0.66 au, in a 4-month time period. We find that flux ropes with field-aligned flows, although they occur more frequently, have certain properties similar to those of static flux ropes, such as the decaying relations of the magnetic fields within structures with respect to heliocentric distances. Moreover, these events are more likely with magnetic pressure dominating over the thermal pressure. About one-third of events are detected in the relatively fast solar wind. Taking into account the high Alfvénicity, we also compare with switchback spikes identified during three encounters and interpret their interrelations. We find that some switchbacks can be detected when the spacecraft traverses flux-rope-like structures. The cross-section maps for selected events are presented via the new Grad-Shafranov-type reconstruction. Finally, the possible evolution of the magnetic flux rope structures in the inner heliosphere is discussed.

On the fast waves in a cylindrical current-carrying plasma

The influence of a stationary Ohmic current on the radial structure of fast waves in a cylindrical current-carrying plasma is discussed. To evaluate the dispersion equation for fast waves, they used the dielectric tensor taking into account the radial current structure and geometry of a confining helical magnetic field by the plasma safety factor. It is shown that the dispersion characteristics of fast waves in a current-carrying plasma differ from those for an equilibrium plasma column in a homogeneous magnetic field nearby the cutoffs and resonances due to the rotational transformation (including shear-effects) of the helical magnetic field lines.

ION-CYCLOTRON ABSORPTION OF FAST WAVES IN A CYLINDRICAL CURRENT-CARRYING PLASMA

Influence of a longitudinal stationary current on the absorption and the radial structure of fast waves in a cylindrical current-carrying plasma is discussed. To evaluate the dispersion equation for fast waves, there was used the dielectric tensor taking into account the radial current structure and geometry of the confining helical magnetic field by the plasma safety factor. It is shown that the damping rate of fast waves in a non-equilibrium current-carrying plasma differ from those for an equilibrium plasma column in a homogeneous magnetic field nearby the cutoffs and resonances due to the rotational transformation (including shear-effects) of the helical magnetic field lines.

Small-scale Magnetic Flux Ropes in the First Two Parker Solar Probe Encounters

Abstract Small-scale magnetic flux ropes (SFRs) are a type of structure in the solar wind that possess helical magnetic field lines. In a recent report we presented the radial variations of the properties of SFRs from 0.29 to 8 au using in situ measurements from the Helios, Advanced Composition Explorer/WIND (ACE/Wind), Ulysses, and Voyager spacecrafts. With the launch of the Parker Solar Probe (PSP), we extend our previous investigation further into the inner heliosphere. We apply a Grad–Shafranov-based algorithm to identify SFRs during the first two PSP encounters. We find that the number of SFRs detected near the Sun is much less than at larger radial distances, where magnetohydrodynamic (MHD) turbulence may act as the local source to produce these structures. The prevalence of Alfvénic structures significantly suppresses the detection of SFRs at closer distances. We compare the SFR event list with other event identification methods, yielding a dozen well-matched events. The cross-section maps of two selected events confirm the cylindrical magnetic flux-rope configuration. The power-law relation between the SFR magnetic field and heliocentric distances seems to hold down to 0.16 au.

Identifying Flux Rope Signatures Using a Deep Neural Network

Among the current challenges in Space Weather, one of the main ones is to forecast the internal magnetic configuration within Interplanetary Coronal Mass Ejections (ICMEs). Currently, a monotonic and coherent magnetic configuration observed is associated with the result of a spacecraft crossing a large flux rope with helical magnetic field lines topology. The classification of such an arrangement is essential to predict geomagnetic disturbance. Thus, the classification relies on the assumption that the ICME's internal structure is a well organized magnetic flux rope. This paper applies machine learning and a current physical flux rope analytical model to identify and further understand the internal structures of ICMEs. We trained an image recognition artificial neural network with analytical flux rope data, generated from the range of many possible trajectories within a cylindrical (circular and elliptical cross-section) model. The trained network was then evaluated against the observed ICMEs from WIND during 1995-2015. The methodology developed in this paper can classify 84% of simple real cases correctly and has a 76% success rate when extended to a broader set with 5% noise applied, although it does exhibit a bias in favor of positive flux rope classification. As a first step towards a generalizable classification and parameterization tool, these results show promise. With further tuning and refinement, our model presents a strong potential to evolve into a robust tool for identifying flux rope configurations from in situ data.

About the cyclotron resonance conditions in magnetized current-carrying plasmas

The resonant cyclotron wave-particle interactions in a cylindrical current-carrying plasma and in two-dimensional axisymmetric toroidal plasma models for tokamaks with D-shaped, elliptic and circular magnetic surfaces are discussed. The corresponding phase resonance conditions are derived by solving the linearized Vlasov equations as a boundary-value problem for perturbed plasma particle distribution functions, accounting for the geometry of a confinement magnetic field in the zero-order over magnetization parameters. It is shown that the Doppler shifts under the cyclotron resonance conditions in the current-carrying plasmas differ from those for a plasma in a uniform magnetic field due to the rotational transformation (including the shear-effects) of the helical magnetic field lines. As for elongated tokamaks, the cyclotron wave-particle resonance conditions in the general case, along with helicity-corrections, involve the bounce-resonances of the untrapped (circulating, passing) and two groups of so-called t-trapped and d-trapped particles.

Proton acceleration in the solar flare

Hundred years of cosmic ray investigations have not lead to the ultimate understanding the mechanisms of particle acceleration. Most popular theoretical mechanisms of solar comic ray generation are associated with shock waves. The discovery of sources of protons with relativistic energies, generated by the Sun (solar cosmic ray), gives us hope for the opportunity to clarify the mechanism of cosmic rays generation. The important information about the mechanism of proton acceleration in the Sun has been obtained from results by GOES of measurements. The association of a proton event with a particular flare is beyond doubt. The GOES measurements indicate propagation of the high-energy protons front without collisions from the flares that appeared on the western part of the solar disk. These protons can move along the helical magnetic field lines to the Earth. The protons from flares on the back side of the Sun can also come to the Earth's magnetosphere along magnetic lines. Protons from eastern part of the solar disk can come to the GOES across the magnetic lines. The front of the proton flux from eastern flares comes to Earth with a delay of several hours. The series of 2–3 weeks long proton events produced by several proton flares are observed one - two times in the 11 year cycle of solar activity. Nature of a trigger for initiating such series of proton events is not clear.

Proton acceleration in the solar flare

100 years of cosmic ray investigations have not led to understanding the mechanism of particles acceleration. The most popular acceleration mechanisms of cosmic ray considered in the theory are associated with shock waves. The discovery of sources of protons with energies up to 20 GeV, generated by the Sun (solar cosmic ray), gives us hope for the opportunity to clarify the mechanism of cosmic rays generation. The important information about the mechanism of proton acceleration in the Sun has been obtained from results by GOES of measurements. The association of a proton event with a particular flare is beyond doubt. The GOES measurements indicate the high-energy protons propagation without collisions from the flares that appeared on the western part of the solar disk. These protons move in the interplanetary space along helical magnetic field lines. The protons from flares on the back side of the Sun can also arrive to the Earth’s magnetosphere along magnetic lines. The protons from eastern flares come to the Earth’s magnetosphere with the solar wind velocity or due to diffusion across the magnetic lines.

Density filament and helical field line structures in three dimensional Weibel-mediated collisionless shocks

Collisionless shocks mediated by Weibel instability are attracting attention for their relevance to experimental demonstrations of astrophysical shocks in high-intensity laser facilities. The three dimensional structure of Weibel-mediated shocks is investigated through a fully kinetic particle-in-cell simulation. The structures obtained are characterized by the following features: (i) helical magnetic field lines elongated in the direction upstream of the shock region, (ii) high and low density filaments inside the helical field lines. These structures originate from the interaction between counter-streaming plasma flow and magnetic vortexes caused by Weibel instability, and potentially affect the shock formation mechanism.

A MULTI-WAVELENGTH POLARIMETRIC STUDY OF THE BLAZAR CTA 102 DURING A GAMMA-RAY FLARE IN 2012

We perform a multi-wavelength polarimetric study of the quasar CTA 102 during an extraordinarily bright $\gamma$-ray outburst detected by the {\it Fermi} Large Area Telescope in September-October 2012 when the source reached a flux of F$_{>100~\mathrm{MeV}} =5.2\pm0.4\times10^{-6}$ photons cm$^{-2}$ s$^{-1}$. At the same time the source displayed an unprecedented optical and NIR outburst. We study the evolution of the parsec scale jet with ultra-high angular resolution through a sequence of 80 total and polarized intensity Very Long Baseline Array images at 43 GHz, covering the observing period from June 2007 to June 2014. We find that the $\gamma$-ray outburst is coincident with flares at all the other frequencies and is related to the passage of a new superluminal knot through the radio core. The powerful $\gamma$-ray emission is associated with a change in direction of the jet, which became oriented more closely to our line of sight ($\theta\sim$1.2$^{\circ}$) during the ejection of the knot and the $\gamma$-ray outburst. During the flare, the optical polarized emission displays intra-day variability and a clear clockwise rotation of EVPAs, which we associate with the path followed by the knot as it moves along helical magnetic field lines, although a random walk of the EVPA caused by a turbulent magnetic field cannot be ruled out. We locate the $\gamma$-ray outburst a short distance downstream of the radio core, parsecs from the black hole. This suggests that synchrotron self-Compton scattering of near-infrared to ultraviolet photons is the probable mechanism for the $\gamma$-ray production.

Model simulation for periodic double-peaked outbursts in blazar OJ 287: binary black hole plus lighthouse effect

The mechanism of formation for double-peaked optical outbursts observed in blazar OJ 287 is studied. It is shown that they could be explained in terms of a lighthouse effect for superluminal optical knots ejected from the center of the galaxy that move along helical magnetic fields. It is assumed that the orbital motion of the secondary black hole in the supermassive binary black hole system induces the 12-year quasi-periodicity in major optical outbursts by the interaction with the disk around the primary black hole. This interaction between the secondary black hole and the disk of the primary black hole (e.g. tidal effects or magnetic coupling) excites or injects plasmons (or relativistic plasmas plus magnetic field) into the jet which form superluminal knots. These knots are assumed to move along helical magnetic field lines to produce the optical double-peaked outbursts by the lighthouse effect. The four double-peaked outbursts observed in 1972, 1983, 1995 and 2005 are simulated using this model. It is shown that such lighthouse models are quite plausible and feasible for fitting the double-flaring behavior of the outbursts. The main requirement may be that in OJ 287 there exists a rather long (~40–60 pc) highly collimated zone, where the lighthouse effect occurs.

The new TORPEX in-vessel toroidal conductor for the generation of a poloidal magnetic field

TORoidal Plasma EXperiment (TORPEX) is a Simple Magnetized Torus featuring open helical magnetic field lines obtained from the superposition of a small vertical component on the main toroidal field. This work introduces the experimental setup developed to include a poloidal magnetic field. The toroidal and poloidal fields generate a rotational transform, making the magnetic geometry of TORPEX closer to that of a tokamak. This upgrade opens the possibility to deal with closed and open flux surfaces, as well as with the transition region across the last closed flux surface. The main technical solutions are discussed together with the physical considerations at the basis of the system design. Selected examples of the magnetic configurations accessible with the set of magnetic field coils available on TORPEX are discussed, ranging from single-null X-points to magnetic snowflakes. The simplest magnetic configuration of quasi-circular concentric flux surfaces is tested experimentally. Measurements of the two-dimensional electron plasma density profiles and the particle confinement time are presented, together with the first steps towards the understanding of plasma production mechanisms.

Magnetic helicity transported by flux emergence and shuffling motions

AbstractMagnetic helicity can be transported from sub-photosphere into corona by the emergence of helical magnetic field lines and the shuffling motions of foot-points of pre-existing coronal field lines. Active region NOAA 10930 was observed by SP and NFI of SOT on board Hinode when it pass through the solar meridian. Based on these observations, we calculate magnetic helicity flow of both terms, by regarding Doppler velocity as normal velocity. The results are compared with which calculated by method proposed by Zhang et. al. (2012). Our results show that helicity injection maps calculated by both methods have similar distribution and the integration values have the same magnitude.

MAGNETIC HELICITY TRANSPORTED BY FLUX EMERGENCE AND SHUFFLING MOTIONS IN SOLAR ACTIVE REGION NOAA 10930

We present a new methodology which can determine magnetic helicity transport by the passage of helical magnetic field lines from sub-photosphere and the shuffling motions of foot-points of preexisting coronal field lines separately. It is well known that only the velocity component which is perpendicular to the magnetic field ($\upsilon_{\perp B}$) has contribution to the helicity accumulation. Here, we demonstrate that $\upsilon_{\perp B}$ can be deduced from horizontal motion and vector magnetograms, under a simple relation of $\upsilon_t = \mu_t + \frac{\upsilon_n}{B_n} B_t$ as suggested by D$\acute{e}$moulin & Berger (2003). Then after dividing $\upsilon_{\perp B}$ into two components, as one is tangential and the other is normal to the solar surface, we can determine both terms of helicity transport. Active region (AR) NOAA 10930 is analyzed as an example during its solar disk center passage by using data obtained by the Spectro-Polarimeter and the Narrowband Filter Imager of Solar Optical Telescope on board Hinode. We find that in our calculation, the helicity injection by flux emergence and shuffling motions have the same sign. During the period we studied, the main contribution of helicity accumulation comes from the flux emergence effect, while the dynamic transient evolution comes from the shuffling motions effect. Our observational results further indicate that for this AR, the apparent rotational motion in the following sunspot is the real shuffling motions on solar surface.

Upgrading of the Magnetic Confinement Plasma Device KT-5E

In this article we present ideas of providing appropriate poloidal magnetic field for helimaks to help to generate toroidal magnetic plasma torus. Placing a conductive ring in the center of the cross-section to induce a suitable current, we change the helical magnetic field lines in the helimak discharge into magnetic surface. In this kind of discharge, the plasma density is greatly increased, and the corresponding density fluctuation is significantly decreased, showing a better confinement by magnetic shear. It allows more flexible and efficient experimental investigations on the toroidal magnetic confinement plasmas to be carried on in this kind of device.

Localization of MHD modes and consistency with q-profiles in JET

The measurement of the safety factor q in tokamaks, which describes the winding of the helical magnetic field lines, is very important especially for the achievement of advanced scenarios. The motional Stark effect diagnostic can provide a direct measurement of the magnetic field orientation but the derivation of the q-profiles requires a simulation of the magnetic equilibrium taking into account inputs from several other diagnostics. This analysis can be affected by large errors. In order to validate the results, q-profiles are compared with the radii of MHD modes, which can be attributed to surfaces of known q.

Electron thermal transport within magnetic islands in the reversed-field pinch

Tearing mode induced magnetic islands have a significant impact on the thermal characteristics of magnetically confined plasmas such as those in the reversed-field pinch (RFP). New Thomson scattering diagnostic capability on the Madison Symmetric Torus (MST) RFP has enabled measurement of the thermal transport characteristics of islands. Electron temperature (Te) profiles can now be acquired at 25 kHz, sufficient to measure the effect of an island on the profile as the island rotates by the measurement point. In standard MST plasmas with a spectrum of unstable tearing modes, remnant islands are present in the core between sawtoothlike reconnection events. Associated with these island remnants is flattening of the Te profile inside the island separatricies. This flattening is characteristic of rapid parallel heat conduction along helical magnetic field lines. In striking contrast, a temperature gradient within an m=1, n=5 island is observed in these same plasmas just after a sawtooth event when the m=1, n=5 mode may briefly come into resonance near the magnetic axis. This suggests local heating and relatively good confinement within the island. Local power balance calculations suggest reduced thermal transport within this island relative to the confinement properties of standard MST discharges between reconnection events. The magnetic field and island structure is modeled with three-dimensional nonlinear resistive magnetohydrodynamic simulations (DEBS code) with Lundquist numbers matching those in MST during standard discharges. During improved confinement plasmas with reduced tearing mode activity, temperature fluctuations correlated with magnetic signals are small with characteristic fluctuation amplitudes of order T̃e/Te∼2%.

The structure of an earthward propagating magnetic flux rope early in its evolution: comparison of methods

Abstract. We analyze a magnetic signature associated with the leading edge of a bursty bulk flow observed by Cluster at −19 RE downtail on 22 August 2001. A distinct rotation of the magnetic field was seen by all four spacecraft. This event was previously examined by Slavin et al. (2003b) using both linear force-free modeling as well as a curlometer technique. Extending this work, we apply here single- and multi-spacecraft Grad-Shafranov (GS) reconstruction techniques to the Cluster observations and find good evidence that the structure encountered is indeed a magnetic flux rope and contains helical magnetic field lines. We find that the flux rope has a diameter of approximately 1 RE, an axial field of 26.4 nT, a velocity of ≈650 km/s, a total axial current of 0.16 MA and magnetic fluxes of order 105 Wb. The field line twist is estimated as half a turn per RE. The invariant axis is inclined at 40° to the ecliptic plane and 10° to the GSM equatorial plane. The flux rope has a force-free core and non-force-free boundaries. When we compare and contrast our results with those obtained from minimum variance, single-spacecraft force-free fitting and curlometer techniques, we find in general fair agreement, but also clear differences such as a higher inclination of the axis to the ecliptic. We further conclude that single-spacecraft methods have limitations which should be kept in mind when applied to THEMIS observations, and that non-force-free GS and curlometer techniques are to be preferred in their analysis. Some properties we derived for this earthward– moving structure are similar to those inferred by Lui et al. (2007), using a different approach, for a tailward-moving flux rope observed during the expansion phase of the same substorm.