Open Magnetic Field Configuration Research Articles

Disentangling Photoelectrons and Penetrating Solar Wind Electrons in the Dayside Martian Upper Atmosphere

AbstractIn situ produced photoelectrons and precipitating solar wind electrons are two distinct hot electron populations in the dayside Martian upper atmosphere. While each population has been known for decades, its relative contribution to the measured hot electron flux has not been adequately characterized up to now. In this study, we implement a two‐stream kinetic model to compute the hot electron flux for a open magnetic field configuration. By comparing model results to realistic data acquired by the Mars Atmosphere and Volatile Evolution mission, we show that the electron fluxes predicted by the pure photoelectron model are enormously underestimated, especially in the direction toward Mars, but the measurements can be adequately reproduced once solar wind electron precipitation is taken into account. Such a precipitation plays a crucial role above 180 km, not only for hot electrons at all energies that move toward Mars but also for electrons above 1,000 eV that move away from Mars due to the backscattering of precipitating electrons. In contrast, the hot electron population is predicted to be mostly composed of photoelectrons below 180 km. The significance of precipitating solar wind electrons is also evaluated, revealing an appreciable impact on the structure of the dayside Martian upper atmosphere at high altitudes, where electron impact ionization is enhanced by a factor of 7 and cold electron heating enhanced by a factor of 4.

Spatial characteristics of rotating magnetic field (RMF) plasma acceleration method in open magnetic field configuration under partial RMF penetration

In typical electrodeless radio frequency plasma thrusters, application of a rotating magnetic field (RMF) is expected to drive an azimuthal electron current via the non-linear Hall-term effect, resulting in an additional electromagnetic acceleration effect in the presence of a diverging magnetic field. Large increases in ion Mach number and electron density were found, comparing cases with and without the RMF, under a partial RMF penetration into a plasma. Spatial characteristics of the RMF acceleration were investigated to clarify the causes of these increments: 2D profiles of plasma parameters and time-varying RMF components were measured. Partial penetration of the RMF into plasma with a phase retardation was found, but the RMF azimuthal current was driven. Large diamagnetic current derived from the large density gradient also increased by the RMF application. Synergistic acceleration effect derived from the driven RMF current and the density gradient results in the plasma acceleration effect even under the partial penetration.

CME\u2013HSS Interaction and Characteristics Tracked from Sun to Earth

In a thorough study, we investigate the origin of a remarkable plasma and magnetic field configuration observed in situ on June 22, 2011, near L1, which appears to be a magnetic ejecta (ME) and a shock signature engulfed by a solar wind high-speed stream (HSS). We identify the signatures as an Earth-directed coronal mass ejection (CME), associated with a C7.7 flare on June 21, 2011, and its interaction with a HSS, which emanates from a coronal hole (CH) close to the launch site of the CME. The results indicate that the major interaction between the CME and the HSS starts at a height of 1.3~mbox{R}_{odot } up to 3~mbox{R}_{odot }. Over that distance range, the CME undergoes a strong north-eastward deflection of at least 30^{circ } due to the open magnetic field configuration of the CH. We perform a comprehensive analysis for the CME–HSS event using multi-viewpoint data (from the Solar TErrestrial RElations Observatories, the Solar and Heliospheric Observatory and the Solar Dynamics Observatory), and combined modeling efforts (nonlinear force-free field modeling, Graduated Cylindrical Shell CME modeling, and the Forecasting a CME’s Altered Trajectory – ForeCAT model). We aim at better understanding its early evolution and interaction process as well as its interplanetary propagation and related in situ signatures, and finally the resulting impact on the Earth’s magnetosphere.

Synergistic effect of nitrogen and hydrogen seeding gases on plasma detachment in the GAMMA 10/PDX tandem mirror

We have investigated the synergistic effect of a combination of various impurity gases and hydrogen gas on plasma detachment of high temperature plasma, equivalent to scrape-off layer plasma of tokamaks in the GAMMA 10/PDX end region, utilizing an open magnetic field configuration. A small puff of an impurity gas (N2, Ne, Ar, Kr, Xe) in combination with a puff of H2 gas is examined to evaluate their synergistic effect on the formation of detached plasma; the following results are obtained. (i) A combination of N2 and H2 puffs showed a clear decrease of electron density and ion flux; (ii) N2 and H2 puffs form a strong density gradient along the axial direction; and (iii) other noble impurity gases showed an insufficient synergistic effect. The new results indicate the possibility of achieving a reliable divertor operation scheme and the importance of a deeper understanding of the H2 and N2 assisted recombination process.

Verification of azimuthal current generation employing a rotating magnetic field plasma acceleration method in an open magnetic field configuration

Time-varying, azimuthal electron current is obtained from measured two-dimensional profiles of excited magnetic fields, using the Rotating Magnetic Field (RMF) plasma acceleration method in an open magnetic field configuration. The RMF is applied orthogonally to cylindrical plasma, leading to the azimuthal current drive via the Hall effect. Here, dc azimuthal current, whose magnitude is equivalent to that of ac azimuthal current with twice the RMF frequency, is verified for the first time. In addition, an expected current reversal is found, with the RMF rotation direction changing by 180°.

Origin and Evolution of Spontaneous Rotation in Plasma Under Different Magnetic Field Geometries in Tokamak QUEST

Spontaneous toroidal rotation of the plasma is observed in the spherical tokamak QUEST with the help of electron cyclotron resonance (ECR) heating and without the use of any externally injected momentum. Several vertical magnetic field ( $B_{z}$ ) configurations with varying mirror ratio ( $M$ ) (a measure of field curvature) are applied and evolution of rotation is studied with the help of Doppler spectroscopy of bulk and impurity ions. Significant toroidal rotation ( $V_{\phi } \sim 6$ km/s) is initiated in the open magnetic field configuration during the initial plasma breakdown phase, which is later sustained ( $V_{\phi } \sim 20$ km/s) in a closed magnetic field configuration in steady state. Rotational velocity is primarily along the cocurrent direction and is found to be proportional to the $B_{z}$ strength and the resulting plasma current. High $M$ and $B_{z}$ are demonstrated to be the two specific external controls by which rotation can be initiated in the plasma. The rotation in open field lines is found to be initiated at the ECR layer in the slablike plasma, which is evolved to produce a sustained rotation in the natural divertor inboard poloidal field null equilibrium in QUEST.

Development of microwave interferometer system for divertor simulation experiments in GAMMA 10/PDX

Microwave interferometer has newly been installed on GAMMA 10/PDX for divertor simulation study. A divertor simulation experimental module (D-module) is used to investigate the physics of divertor in the end-cell of GAMMA 10/PDX where an open magnetic field configuration is formed. D-module has a rectangular chamber with an inlet aperture. Two tungsten target plates are mounted in V-shape inside the chamber. In order to develop understandings of divertor simulation experiments the microwave interferometer using heterodyne scheme and a 1D horn-antenna mixer array (HMA) is applied to obtain electron density and density distribution inside the V-shaped target plates. Line-averaged electron density distributions inside D-module are first observed in H2 gas injection experiments.

Hubble Space Telescope scale 3D simulations of MHD disc winds: a rotating two-component jet structure

We present the results of large scale, three-dimensional magnetohydrodynamics simulations of disc winds for different initial magnetic field configurations. The jets are followed from the source to 90 au scale, which covers several pixels of Hubble Space Telescope images of nearby protostellar jets. Our simulations show that jets are heated along their length by many shocks. We compute the emission lines that are produced, and find excellent agreement with observations. The jet width is found to be between 20 and 30 au while the maximum velocities perpendicular to the jet are found to be up to above 100 km s−1. The initially less open magnetic field configuration simulations result in a wider, two-component jet; a cylindrically shaped outer jet surrounding a narrow and much faster, inner jet. These simulations preserve the underlying Keplerian rotation profile of the inner jet to large distances from the source. However, for the initially most open magnetic field configuration the kink mode creates a narrow corkscrew-like jet without a clear Keplerian rotation profile and even regions where we observe rotation opposite to the disc (counter-rotating). The RW Aur jet is narrow, indicating that the disc field in that case is very open meaning the jet can contain a counter-rotating component that we suggest explains why observations of rotation in this jet have given confusing results. Thus magnetized disc winds from underlying Keplerian discs can develop rotation profiles far down the jet that is not Keplerian.

Recent ICRF Heating Experiments for a Divertor Simulation Study on GAMMA 10

In GAMMA 10, a divertor simulation study has been started with open magnetic field configuration in the end region. High heat and particle fluxes are required along the magnetic field line to the end region. Plasmas with high ion-temperature of several keV and strong temperature anisotropy of more than 10 have been produced by using ion-cyclotron range of frequency (ICRF) heating in the central cell. Direct anchor heating experiments with new anchor antennas have been performed and the enhancement of the MHD stabilization has been observed. High energy ions whose energy is more than 50 keV have been observed in the end-loss ions. The axial transport of high-energy ions due to loss processes other than the classical Coulomb scattering has been discussed. Alfvén-ion-cyclotron (AIC) waves are spontaneously excited owing to such the strong temperature anisotropy and considerable energy transport along the magnetic field line due to the AIC waves is expected. In this review, recent ICRF heating experiments for the divertor simulation study are described.

Research plan for divertor simulation making use of a large tandem mirror device

We are planning to start a study of divertor simulation under the closely resemble to actual fusion plasma environment making use of the advantage of open magnetic field configuration and to contribute the solution for realizing the divertor in ITER as a future research plan of Plasma Research Center of the University of Tsukuba. In the research plan, the concepts of two divertor devices are introduced. One has an axi-symmetric divertor configuration with the separatrix which is similar to toroidal divertor of torus systems and the other is a high heat flux divertor simulator by using an end-mirror exit of the existing tandem mirror device. Development of magnetic field configuration for ensuring the MHD stability is under way and a designed example is investigated under the optimal condition for plasma production. Consideration of plasma heating scheme using Fokker–Planck simulation code was successfully performed at both axi-symmetric divertor and end-mirror regions. Preparative experiments using calorimeter, Mach probe and high-speed camera have been started at the end-mirror region and the heat flux density of the level in 1–10 MW m −2 was achieved in standard hot-ion mode plasma-confining experiments, which gives a clear prospect of generating the required heat flux density for divertor studies.

Numerical Analysis on Generation of High Density Plasmas in the Toroidal Device NAGDIS-T for SOL and Divertor Simulation Studies

Toroidal simulator for boundary plasma studies may have a substantial potential in plasma and impurity transport under an open magnetic field configuration and plasma-surface interactions under a grazing incident magnetic field line to the wall of the plasma-facing component in fusion devices. NAGDIS-T is the toroidal version in NAGDIS-series plasma simulator with RF Joule heating for toroidal plasma generation. A simple numerical analysis was employed to predict the plasma parameters in this new machine, considering the particle and energy balance equations. It was found that the gas pressure dependence of the plasma density is very similar to that obtained in the preliminary experiment with moderate RF power. The analysis predicts a plasma density exceeding 1019 m–3 by injecting the RF power of more than 10 kW which will be available soon. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Chromospheric evolution and the flare activity of super-active region NOAA 6555

Super-active region NOAA 6555 was highly flare productive during the period March 21st–27th, 1991 of its disk passage. We have st udied its chromospheric activity using high spatial resolution Hα filtergrams taken at Udaipur along with MSFC vector magnetograms. A possible relationship of flare productivity and the variation in shear has been explored. Flares were generally seen in those subareas of the active region which possessed closed magnetic field configuration, whereas only minor flares and/or surges occurred in subareas showing open magnetic field configuration. Physical mechanisms responsible for the observed surges are also discussed.

Contribution of Yushmanov-trapped electrons to a thermal dike

A substantial amount of Yushmanov-trapped electrons are generated as a result of electron cyclotron resonance heating employed for generating a thermal dike in an open magnetic field configuration. The production rate and the energy spectrum of the trapped electrons are calculated by using a heating response function. The calculated energy spectrum of the end-loss electrons driven from the Yushmanov-trapped region indicates a reduction in power efficiency of the thermal dike. The potential profile modified by the Yushmanov-trapped particles tends to reduce their production rate, leading to a stationary state. Their significance to a thermal dike basic experiment in the end region of the GAMMA 10 tandem mirror [Plasma Physics and Controlled Nuclear Fusion Research 1992 (International Atomic Energy Agency, Vienna, 1993), Vol. 2, p. 651] is discussed.

Solar Mass Ejections and Coronal Holes

AbstractIn this paper we present observations of two types of solar mass ejections, which seem to be associated with the location of coronal holes. In the first type, a filament eruption was observed near a coronal hole, which gave rise to a strong interplanetary scintillations, as detected by IPS observations. In the second type, several large scale soft X-ray ‘blow-outs’ were observed in the YOHKOH SXT X-ray movies, in all the cases they erupted from or near the boundary of coronal holes and over the magnetic neutral line. It is proposed that the open magnetic field configuration of the coronal hole provides, the necessary field structure for reconnection to take place, which in turn is responsible for filament eruption, from relatively lower heights. While, in the case of X-ray ‘blow-outs’, the reconnection takes place at a greater height, resulting in high temperature soft X-ray emission visible as X-ray ‘blow-outs’.

Solar mass ejections and coronal holes

In this paper we present observations of two types of solar mass ejections, which seem to be associated with the location of coronal, holes. In the first type, a filament eruption was observed near a coronal hole, which gave rise to a strong interplanetary scintillations. as detected by IPS observations. In the second type, several large scale soft X-ray ‘blow-outs’ were observed in the YOHKOH SXT X-ray movies, in all the cases they erupted from or near the boundary of coronal holes and over the magnetic neutral line. It is proposed that the open magnetic field configuration of the coronal hole provides, the necessary field structure for reconnection to take place, which in turn is responsible for filament eruption, from relatively lower heights. While, in the case of X-ray ‘blow-outs’, the reconnection takes place at a greater height, resulting in high temperature soft X-ray emission visible as X-ray ‘blow-outs’.

Suppression of secondary electrons from an endplate of a tandem mirror by use of a biased mesh

Negative bias is applied to a mesh placed in front of an endplate of the GAMMA 10 tandem mirror [Phys. Rev. Lett. 55, 939 (1985)]. A bias voltage of around 10 V results in an increase of the potential difference by an order of kV in the end region. The increment is about two times the temperature of end-loss electrons and most of that stems from the sheath potential drop in front of the endplate. Provided that almost all the secondary electrons emitted from endplate are reflected, these results agree with the prediction of a potential model for the open magnetic field configuration [J. Phys Soc. Jpn. 61, 3153 (1992)].

Study of Potential Formation in an Open Magnetic Field Configuration

A theoretical model is developed on the electrostatic potential which is formed during fundamental electron cyclotron resonance heating in an end region of a tandem mirror. The model includes experimental conditions such as expanding magnetic flux tube, multicomponent electron temperature and secondary electrons emitted from an end plate. The axial potential profile of a collisionless plasma is analyzed with non-Maxwellian velocity distribution functions of ions and electrons. The potential profile in the plasma region, where the charge-neutrality holds, depends predominantly on the magnetic field profile. The potential drop in the sheath region in front of the end plate strongly depends on the secondary electrons and the fraction of the higher temperature component of the primary electrons.

Magnetohydrodynamics of atmospheric transients. III - Basic results of nonplane two-dimensional analysis

The dynamic response of a stratified atmosphere permeated by a magnetic field to a sudden localized energy release (e.g., the onset of a flare) is examined in a physically self-consistent manner within the approximation of axisymmetric two-dimensional magnetohydrodynamics. In contrast to the previous plane analyses, with the inclusion of out-of-plane components of magnetic and velocity fields, it is shown that the presence of transverse waves leads to spiraling material motions and formation of ring current with open (mostly radial) magnetic field configuration. In the closed (mostly azimuthal) magnetic field, the evolutionary response of a magnetic field is shown to follow the typical sequence observed with a flare, namely, the relaxations of magnetic shear toward the potential configuration. The details of the results are described with discussions on their physical significance.