An investigation of hydrodynamic waves with a cylindrical microwave resonator. III. The influence of an axial magnetic field

1969 ◽  
Vol 47 (10) ◽  
pp. 1051-1055
Author(s):  
F. L. Curzon ◽  
R. L. Pike
Keyword(s):  
Magnetic Field ◽  
Surface Wave ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Axial Magnetic Field ◽  
Microwave Resonator ◽  
Hydrodynamic Waves ◽  
Vertical Magnetic Field

A microwave resonator has been employed to study the damping of a surface wave on mercury in the presence of a vertical magnetic field. The conditions of the experiment satisfy the linearity requirements of the theory and confirm the expected dependence of the damping frequency on magnetic field strength, fluid depth, and radius.

Turbulence changes from magnetic fields in a stationary plasma

2010 ◽  
Vol 77 (4) ◽  
pp. 537-545 ◽  
Author(s):  
A. B. ALEXANDER ◽  
C. T. RAYNOR ◽  
D. L. WIGGINS ◽  
M. K. ROBINSON ◽  
C. C. AKPOVO ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Axial Magnetic Field ◽  
Turbulent Energy ◽  
Dominant Mode ◽  
Dc Glow Discharge ◽  
Turbulent Fluctuations ◽  
Stationary Plasma

AbstractWhen the krypton plasma in a DC glow discharge tube is exposed to an axial magnetic field, the turbulent energy and the characteristic dominant mode in the turbulent fluctuations are systematically and unexpectedly reduced with increasing magnetic field strength. When the index measuring the rate of transfer of energy through fluctuation scales is monitored, a lambda-like dependence on turbulent energy is routinely observed in all magnetic fields. From this, a critical turbulent energy is identified, which also decreases with increasing magnetic field strength.

scholarly journals No universal connection between the vertical magnetic field and the umbra-penumbra boundary in sunspots

2020 ◽  
Vol 639 ◽  
pp. A106
Author(s):  
B. Löptien ◽  
A. Lagg ◽  
M. van Noort ◽  
S. K. Solanki
Keyword(s):  
Magnetic Field ◽  
Statistical Analysis ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Filling Factor ◽  
Spot Size ◽  
Vertical Magnetic Field ◽  
Continuum Intensity ◽  
The Mean ◽  
The Continuum

Context. It has been reported that the boundary between the umbra and the penumbra of sunspots occurs at a canonical value of the strength of the vertical magnetic field, independently of the size of the spot. This critical field strength is interpreted to be the threshold for the onset of magnetoconvection. Aims. Here we investigate the reasons why this criterion, also called the Jurčák criterion in the literature, does not always identify the boundary between the umbra and the penumbra. Methods. We performed a statistical analysis of 23 sunspots observed with Hinode/SOT. We compared the properties of the continuum intensity and the vertical magnetic field between filaments and spines and how they vary between spots of different sizes. Results. We find that the inner boundary of the penumbra is not related to a universal value of the vertical magnetic field. The properties of spines and filaments vary between spots of different sizes. Both components are darker in larger spots and the spines exhibit a stronger vertical magnetic field. These variations of the properties of filaments and spines with the spot size are also the reason for the reported invariance in the averaged vertical magnetic field at 50% of the mean continuum intensity. Conclusions. The formation of filaments and the onset of magnetoconvection are not related to a canonical value of the strength of the vertical magnetic field. The seemingly unique magnetic field strength is rather an effect of the filling factor of spines and penumbral filaments.

Experimental study of fast hydromagnetic waves in an argon plasma

1964 ◽  
Vol 278 (1373) ◽  
pp. 243-255 ◽  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Axial Magnetic Field ◽  
Argon Plasma ◽  
Wave Number ◽  
Axially Symmetric ◽  
Plasma Parameters ◽  
Quantitative Evidence ◽  
Hydromagnetic Waves

In these experiments fast hydromagnetic waves are excited by discharging a capacitor through a single turn coil surrounding a cylindrical column of magnetized argon plasma. The plasma column is 200 cm long and 22 cm in diameter, and the axial magnetic field strength is varied in the range from 1 to 6 kG. The wave amplitude is typically 10 G, and the frequency is varied between 1.2 and 6 times the ion cyclotron frequency. Measurement of the radial variation and the relative amplitudes of the three components of the wave magnetic field shows that the oscillation is the lowest axially-symmetric mode. As predicted by the theory, the wave is elliptically polarized in the rθ plane with the magnetic vector rotating in the same sense as the electron cyclotron rotation. The experimental results demonstrate the cut-off of this mode both as the frequency is decreased and as the axial magnetic field strength is increased. Measurements of the axial wave number and absorption coefficient are in good numerical agreement with theoretical dispersion curves computed from the measured plasma parameters. This work provides quantitative evidence to support the theories currently used in treating hydromagnetic oscillations, both stable and unstable, of magnetized plasmas.

Forced Convection During Liquid Encapsulated Crystal Growth With an Axial Magnetic Field

1998 ◽  
Vol 120 (4) ◽  
pp. 844-850 ◽  
Author(s):  
Nancy Ma ◽  
John Walker ◽  
David Bliss ◽  
George Bryant
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Forced Convection ◽  
Magnetic Field Strength ◽  
Axial Magnetic Field ◽  
Vertical Wall ◽  
Czochralski Growth ◽  
Centripetal Acceleration ◽  
Radial Gap ◽  
The Magnetic Field

This paper treats the forced convection, which is produced by the rotation of the crystal about its vertical centerline during the liquid-encapsulated Czochralski or Kyropoulos growth of compound semiconductor crystals, with a uniform vertical magnetic field. The model assumes that the magnetic field strength is sufficiently large that convective heat transfer and all inertial effects except the centripetal acceleration are negligible. With the liquid encapsulant in the radial gap between the outside surface of the crystal and the vertical wall of the crucible, the forced convection is fundamentally different from that with a free surface between the crystal and crucible for the Czochralski growth of silicon crystals. Again unlike the case for silicon growth, the forced convection for the actual nonzero electrical conductivity of an indium-phosphide crystal is virtually identical to that for an electrically insulating crystal. The electromagnetic damping of the forced convection is stronger than that of the buoyant convection. In order to maintain a given balance between the forced and buoyant convections, the angular velocity of the crystal must be increased as the magnetic field strength is increased.

scholarly journals The magnetic nature of umbra–penumbra boundary in sunspots

2018 ◽  
Vol 611 ◽  
pp. L4 ◽  
Author(s):  
J. Jurčák ◽  
R. Rezaei ◽  
N. Bello González ◽  
R. Schlichenmaier ◽  
J. Vomlel
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Field Component ◽  
Vertical Component ◽  
Vertical Magnetic Field ◽  
Intensity Threshold ◽  
The Magnetic Field ◽  
Magnetic Nature

Context. Sunspots are the longest-known manifestation of solar activity, and their magnetic nature has been known for more than a century. Despite this, the boundary between umbrae and penumbrae, the two fundamental sunspot regions, has hitherto been solely defined by an intensity threshold. Aim. Here, we aim at studying the magnetic nature of umbra–penumbra boundaries in sunspots of different sizes, morphologies, evolutionary stages, and phases of the solar cycle. Methods. We used a sample of 88 scans of the Hinode/SOT spectropolarimeter to infer the magnetic field properties in at the umbral boundaries. We defined these umbra–penumbra boundaries by an intensity threshold and performed a statistical analysis of the magnetic field properties on these boundaries. Results. We statistically prove that the umbra–penumbra boundary in stable sunspots is characterised by an invariant value of the vertical magnetic field component: the vertical component of the magnetic field strength does not depend on the umbra size, its morphology, and phase of the solar cycle. With the statistical Bayesian inference, we find that the strength of the vertical magnetic field component is, with a likelihood of 99%, in the range of 1849–1885 G with the most probable value of 1867 G. In contrast, the magnetic field strength and inclination averaged along individual boundaries are found to be dependent on the umbral size: the larger the umbra, the stronger and more horizontal the magnetic field at its boundary. Conclusions. The umbra and penumbra of sunspots are separated by a boundary that has hitherto been defined by an intensity threshold. We now unveil the empirical law of the magnetic nature of the umbra–penumbra boundary in stable sunspots: it is an invariant vertical component of the magnetic field.

Axial magnetic field strength needed for a 126kV single break vacuum interrupter

2010 ◽  
Author(s):  
Yingyao Zhang ◽  
Yingsan Geng ◽  
Li Yu ◽  
Jing Yan ◽  
Zhiyuan Liu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Axial Magnetic Field ◽  
Vacuum Interrupter ◽  
Single Break
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