Radial Profile Of Magnetic Field Research Articles

Radial distributions of magnetic field strength in the solar corona as derived from data on fast halo CMEs

In recent years, information about the distance between the body of rapid coronal mass ejection (CME) and the associated shock wave has been used to measure the magnetic field in the solar corona. In all cases, this tech-nique allows us to find coronal magnetic field radial profiles B(R) applied to the directions almost perpendicular to the line of sight. We have determined radial distributions of magnetic field strength along the directions close to the Sun–Earth axis. For this purpose, using the “ice-cream cone” model and SOHO/LASCO data, we found 3D characteristics for fast halo coronal mass ejections (HCMEs) and for HCME-related shocks. With these data we managed to obtain the B(R) distributions as far as ≈43 solar radii from the Sun’s center, which is approximately twice as far as those in other studies based on LASCO data. We have concluded that to improve the accuracy of this method for finding the coronal magnetic field we should develop a technique for detecting CME sites moving in the slow and fast solar wind. We propose a technique for selecting CMEs whose central (paraxial) part actually moves in the slow wind.

Радиальные распределения величины магнитного поля в солнечной короне, полученные с использованием сведений о быстрых гало-КВМ

In recent years, information about the distance between the body of rapid coronal mass ejection (CME) and the associated shock wave has been used to measure the magnetic field in the solar corona. In all cases, this tech-nique allows us to find coronal magnetic field radial profiles B(R) applied to the directions almost perpendicular to the line of sight. We have determined radial distributions of magnetic field strength along the directions close to the Sun–Earth axis. For this purpose, using the “ice-cream cone” model and SOHO/LASCO data, we found 3D characteristics for fast halo coronal mass ejections (HCMEs) and for HCME-related shocks. With these data we managed to obtain the B(R) distributions as far as ≈43 solar radii from the Sun’s center, which is approximately twice as far as those in other studies based on LASCO data. We have concluded that to improve the accuracy of this method for finding the coronal magnetic field we should develop a technique for detecting CME sites moving in the slow and fast solar wind. We propose a technique for selecting CMEs whose central (paraxial) part actually moves in the slow wind.

Coronal magnetic field profiles from shock‐CME standoff distances

AbstractCoronagraphs observe coronal mass ejections (CMEs) and driven shocks in white light images. From these observations the shock's speed and the shock's standoff distance from the CME's leading edge can be derived. Using these quantities, theoretical relationships between the shock's Alfvénic Mach number MA and standoff distance, and empirical radial profiles for the solar wind velocity and number density, the radial magnetic field profile upstream of the shock can be calculated. These profiles cannot be measured directly. We test the accuracy of this method for estimating the radial magnetic field profile upstream of the shock by simulating a sample CME that occurred on 29 November 2013 using the three‐dimensional (3‐D) magnetohydrodynamic Block‐Adaptive‐Tree‐Solarwind‐Roe‐Upwind‐Scheme code, retrieving shock‐CME standoff distances from the simulation, and comparing the estimated and simulated radial magnetic field profiles. We find good agreement between the two profiles (within ±30%) between 1.8 and 10 R⊙. Our simulations confirm that a linear relationship exists between the standoff distance and the inverse compression ratio at the shock. We also find very good agreement between the empirical and simulated radial profiles of the number density and speed of the solar wind and inner corona.

Inference of magnetic field in the coronal streamer invoking kink wave motions generated by multiple EUV waves

Using MHD seismology by observed kink waves, the magnetic field profile of a coronal streamer has been investigated. STEREO-B/EUVI temporal image data on 7 March 2012 shows an evolution of two consecutive EUV waves that interact with the footpoint of a coronal streamer evident in the co-spatial and co-temporal STEREO-B/COR-I observations. The evolution of EUV waves is clearly evident in STEREO-B/EUVI, and its energy exchange with coronal streamer generates kink oscillations. We estimate the phase velocities of the kink wave perturbations by tracking it at different heights of the coronal streamer. We also estimate the electron densities inside and outside the streamer using SSI of polarized brightness images in STEREO-B/COR-1 observations. Taking into account the MHD theory of kink waves in a cylindrical waveguide, their observed properties at various heights, and density contrast of the streamer, we estimate the radial profile of magnetic field within this magnetic structure. Both the kink waves diagnose the exponentially decaying radial profiles of the magnetic field in coronal steamer upto 3 solar radii. Within the limit of uncertainties in the measurements, it is indicated that coronal magnetic field of the streamer varies slowly in time at various heights, although its nature always remains exponentially decaying. It is seen that during the evolution of second kink motion in the streamer, it increases in brightness, and also in areal extent slightly, which may be associated with the decreased photospheric magnetic flux at its footpoint. As a result, the magnetic field profile produced by the second kink wave is reduced within the streamer compared to the one diagnosed by the first one. The precisely estimated magnetic field profiles with the uncertainty less than 10% match well with the empirical profile and various observational estimations of the outer coronal magnetic field.

Design and Magnetic Field Analyses of Spiral Sector Magnet in an FFAG Accelerator for Carbon Cancer Therapy

We designed a coil-dominated magnet wound with coated conductors for a spiral sector fixed-field alternating-gradient (FFAG) accelerator for carbon cancer therapy. The magnet consisted of deformed pancake coils with negative bends. Coils were arranged similar to a ladder to generate the required radial profile of magnetic field. The positions and the number of turns of the coils were iteratively adjusted to reduce the magnetic field error. We carried out numerical electromagnetic field analyses of the designed magnet to evaluate the influence of coated-conductor magnetization (screening or shielding current) on its field quality.

Determination of coronal magnetic fields from 10 to 26R ⊙ using the density compression ratios of CME-driven shocks

Recently, the estimation of coronal magnetic field using new methods, such as standoff distance method or density compression ratio method has been reported. In the present work, we utilized the density compression ratio of CME-driven shocks for 10 events at 29 different locations in the upper solar corona (10–26R ⊙) and determined the coronal magnetic field for two different adiabatic indices (γ=4/3 and 5/3). In addition, radial dependence of shock parameters in the corona is studied. It is found that the magnetic field estimated in the above range agree with the general trend. In addition, we obtained a radial profile of magnetic field [B(R)=623R −1.4] in the entire upper corona (3–30R ⊙) by combining the magnetic field estimated by Kim et al. (Astrophys. J. 746:118, 2012) in the range 3–15R ⊙ and that estimated in the present study in the range (10–26R ⊙). The power-law indices are nearly in agreement with recent results of CME-driven shocks reported in the literature. The results are discussed with the comparison of newly reported coronal magnetic field values obtained by different techniques and found that the power-law relation closely follow the literature values.

Power Deposition into the Discharge Channel of a Hall Effect Thruster

The deposition of energy into the discharge channel of a 4.5 kW Hall effect thruster from the discharge plasma is investigated. An array of 35 thermocouples is placed along the inner and outer walls of the discharge channel at a spatial resolution sufficient to enable multiple temperature measurement locations within the positive gradient portion of the radial magnetic field profile. Temperature profiles of the inner and outer discharge channels are measured at Hall effect thruster discharge power levels ranging from 0.63 to 2.83 kW, which correspond to peak wall temperatures of 578–813 K. The peak in the wall temperature profile occurs at nearly the same axial location as the peak in the wall radial magnetic field profile. The energy flux from the plasma to the channel walls varies between 0.1 and for Hall effect thruster operating conditions from 0.63 to 2.83 kW. Approximately of the discharge power is deposited into the discharge channel wall at all Hall effect thruster operating conditions. The average power radiated from the boron nitride discharge channel to the surroundings is approximately of the discharge power at all operating conditions.

A Compact Plasma System for Experimental Study

A compact plasma system is set up at Ravenshaw University, India. The plasma system consists of a curved vacuum chamber which is nothing but a part of a toroid (θ=700) having minor radius, r= 0.3 m and major radius, R= 0.5 m, vacuum system, electromagnet, gas injected washer stacked plasma gun to produce plasma blobs/filaments, pulse forming network to energise plasma gun, diagnostic tools like electric probes, magnetic probes, spectrometer, high speed CCD camera, digital pulse/delay generator to synchronise the diagnostic tools. A pair of copper coil is wound over the chamber and capacitive pulse is fed to the coil to produce non-uniform magnetic field inside the chamber. The gas injected washer stacked plasma gun is a mono-anode - multi cathode system having five cathodes made up of brass and an anode made up of copper. The gun impedance is ~ 15 Ω. The pulse forming network (PFN) is Guillemin E type which consists of capacitors having equal capacitance 5.5 μF and inductors having equal inductances 1.5 μH. The pulse width of the PFN is ~ 7.6 μs for a seven stage network, as tested with known resistive circuit. Magnetic probes are designed and calibrated using a Helmholtz coil to map the radial magnetic field profile of the plasma chamber. Electric probes like Langmuir triple probe, velocity probes are designed to measure plasma parameters like blob velocity, density, temperature etc. Emission spectroscopy method is used to identify charged species inside the plasma. High speed CCD camera is used to interpret the structure of the plasma. A digital pulse/trigger generator is used to synchronise the CCD, spectrometer and switching thyristor etc. Preliminary results are also reported.

CONSTRAINTS ON COSMIC RAYS, MAGNETIC FIELDS, AND DARK MATTER FROM GAMMA-RAY OBSERVATIONS OF THE COMA CLUSTER OF GALAXIES WITH VERITAS ANDFERMI

Observations of radio halos and relics in galaxy clusters indicate efficient electron acceleration. Protons should likewise be accelerated, suggesting that clusters may also be sources of very high-energy (VHE; E>100 GeV) gamma-ray emission. We report here on VHE gamma-ray observations of the Coma galaxy cluster with the VERITAS array of imaging Cherenkov telescopes, with complementing Fermi-LAT observations at GeV energies. No significant gamma-ray emission from the Coma cluster was detected. Integral flux upper limits at the 99% confidence level were measured to be on the order of (2-5)*10^-8\ ph. m^-2 s^-1 (VERITAS, >220 GeV} and ~2*10^-6 ph. m^-2 s^-1 (Fermi, 1-3 GeV), respectively. We use the gamma-ray upper limits to constrain CRs and magnetic fields in Coma. Using an analytical approach, the CR-to-thermal pressure ratio is constrained to be < 16% from VERITAS data and < 1.7% from Fermi data (averaged within the virial radius). These upper limits are starting to constrain the CR physics in self-consistent cosmological cluster simulations and cap the maximum CR acceleration efficiency at structure formation shocks to be <50%. Assuming that the radio-emitting electrons of the Coma halo result from hadronic CR interactions, the observations imply a lower limit on the central magnetic field in Coma of (2 - 5.5) muG, depending on the radial magnetic-field profile and on the gamma-ray spectral index. Since these values are below those inferred by Faraday rotation measurements in Coma (for most of the parameter space), this {renders} the hadronic model a very plausible explanation of the Coma radio halo. Finally, since galaxy clusters are dark-matter (DM) dominated, the VERITAS upper limits have been used to place constraints on the thermally-averaged product of the total self-annihilation cross section and the relative velocity of the DM particles, <\sigma v>. (abr.)

Measurements of the radial profile of magnetic field in the Gas-Dynamic Trap using a motional Stark effect diagnostic

We have implemented a spectral motional Stark effect diagnostic for spatially localized measurements of magnetic field on the Gas-Dynamic Trap (GDT) magnetic mirror device. A 7 A, 40 keV diagnostic neutral hydrogen beam was focused to a current density of 0.25 A/cm2 in the measurement volume, allowing achievement of a radial resolution of 4.5 cm by viewing the beam at 45° with a well-defined light collection chord. The entire Stark spectrum was recorded by a spectrometer with a charge-coupled device detector. Analysis of the splitting of the components of the Stark spectrum directly results in a measurement of local |B|. When operated with deuterium heating neutral beam injection into a hydrogen target plasma, the GDT axial magnetic field is strongly perturbed by plasma diamagnetic effects. Thus, measurement of the radial profile of the perturbed magnetic field, combined with equilibrium modeling, will yield an estimate of the plasma beta.

An experimental investigation of the internal magnetic field topography of an operating Hall thruster

Magnetic field measurements were made in the discharge channel of the 5 kW-class P5 laboratory-model Hall thruster to investigate what effect the Hall current has on the static, applied magnetic field topography. The P5 was operated at 1.6 and 3.0 kW with a discharge voltage of 300 V. A miniature inductive loop probe (B-Dot probe) was employed to measure the radial magnetic field profile inside the discharge channel of the P5 with and without the plasma discharge. These measurements are accomplished with minimal disturbance to thruster operation with the High-speed Axial Reciprocating Probe system. The results of the B-Dot probe measurements indicate a change in the magnetic field topography from that of the vacuum field measurements. The measured magnetic field profiles are then examined to determine the possible nature and source of the difference between the vacuum and plasma magnetic field profiles.

Stationary magnetospheric convection on November 24, 1981. 1. A case study of &amp;quot;pressure gradient/minimum-&amp;lt;i&amp;gt;B&amp;lt;/i&amp;gt;&amp;quot; auroral arc generation

Abstract. We present two case studies in the night and evening sides of the auroral oval, based on plasma and field measurements made at low altitudes by the AUREOL-3 satellite, during a long period of stationary magnetospheric convection (SMC) on November 24, 1981. The basic feature of both oval crossings was an evident double oval pattern, including (1) a weak arc-type structure at the equatorial edge of the oval/polar edge of the diffuse auroral band, collocated with an upward field-aligned current (FAC) sheet of \\sim1.0 µA m-2, (2) an intermediate region of weaker precipitation within the oval, (3) a more intense auroral band at the polar oval boundary, and (4) polar diffuse auroral zone near the polar cap boundary. These measurements are compared with the published magnetospheric data during this SMC period, accumulated by Yahnin et al. and Sergeev et al., including a semi-empirical radial magnetic field profile BZ in the near-Earth neutral sheet, with a minimum at about 10-14 RE. Such a radial BZ profile appears to be very similar to that assumed in the "minimum- B/cross-tail line current" model by Galperin et al. (GVZ92) as the "root of the arc", or the arc generic region. This model considers a FAC generator mechanism by Grad-Vasyliunas-Boström-Tverskoy operating in the region of a narrow magnetic field minimum in the near-Earth neutral sheet, together with the concept of ion non-adiabatic scattering in the "wall region". The generated upward FAC branch of the double sheet current structure feeds the steady auroral arc/inverted-V at the equatorial border of the oval. When the semi-empirical BZ profile is introduced in the GVZ92 model, a good agreement is found between the modelled current and the measured characteristics of the FACs associated with the equatorial arc. Thus the main predictions of the GVZ92 model concerning the "minimum-B" region are consistent with these data, while some small-scale features are not reproduced. Implications of the GVZ92 model are discussed, particularly concerning the necessary conditions for a substorm onset that were not fulfilled during the SMC period.Key words. Magnetospheric physics (auroral phenomena; magnetospheric configuration and dynamics; plasma sheet).

M = +1 mode helicon wave excitation using solenoid antenna

In most helicon wave experiments, there has been a poor agreement between the theoretical wave power deposition and the plasma density radial profiles. The characteristics of the solenoid antenna employed for the excitation of m = 1 mode helicon waves are investigated. A cylindrical high density plasma column with high intensity ArII emission is observed to be of a cylindrical shell shape. In cross section, the location of the high intensity column nearly coincides with the maximum point of wave power deposition. The wave magnetic field radial profiles agree well with computations. These results show an excellent agreement between the theory and density profile produced by the m = 1 helicon wave.

The control and data acquisition system for the ISTTOK heavy ion beam diagnostic

A heavy ion beam diagnostic for the tokamak ISTTOK has been developed with the aim of measuring the temporal evolution of the electron density, plasma potential, electron temperature and poloidal magnetic field radial profiles. The control and data acquisition system for this diagnostic is described. This system was designed in a modular and versatile approach based on locally developed VME timing, waveform generator and digitizer modules. Its integration into the ISTTOK control and data acquisition system as well as the first experimental results are also reported.