scholarly journals Runaway electron flows in magnetized coaxial gas diodes

2021 ◽  
Vol 2064 (1) ◽  
pp. 012006
Author(s):  
G A Mesyats ◽  
K A Sharypov ◽  
V G Shpak ◽  
S A Shunailov ◽  
M I Yalandin ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electron Beam ◽  
Strong Magnetic Field ◽  
Current Density ◽  
Runaway Electron ◽  
Electron Flow ◽  
Transverse Size ◽  
Longitudinal Field ◽  
Field Lines ◽  
A Current

Abstract This paper presents the experimental results on applying a strong magnetic field (B) to increase the uniformity and density of a picosecond runaway electron flow (RAEF) formed in an air coaxial diode with a tubular cathode. A uniform longitudinal field Bz allows to confine RAEF similarly to the electron beam in a magnetically insulated coaxial vacuum diode. Dependence of the spatial discreteness of RAEF emission and the transverse size of the emitting plasma regions on Bz has been demonstrated. For the cathode diameter of 8 mm, a current density was significantly increased from 40 A/cm2 (at Bz = const) to 100 A/cm2 by applying B-field with converging field lines. In the region of B maximum (5 T) the RAEF diameter was squeezed by ≈ 4 times.

scholarly journals Analysis of Injected Electron Beam Propagation in a Planar Crossed-Field Gap

2021 ◽  
Vol 11 (6) ◽  
pp. 2540
Author(s):  
Ranajoy Bhattacharya ◽  
Adam M. Darr ◽  
Allen L. Garner ◽  
Jim Browning
Keyword(s):  
Magnetic Field ◽  
Electron Beam ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Three Dimensional ◽  
One Dimensional ◽  
Field Device ◽  
The Magnetic Field ◽  
A Current

This paper examines basic crossed-field device physics in a planar configuration, specifically electron beam perturbation and instability as a function of variation in magnetic field, and angle between magnetic and electric field. We perform a three-dimensional (3-D) simulation of electron perturbation in a planar crossed-field system using the full 3-D particle trajectory solver in CST Particle Studio (CST-PS). The structure has a length, height, width and anode-sole gap of 15 cm, 2 cm, 10 cm, and 2 cm, respectively. The anode to sole voltage is fixed at 3 kV, and the magnetic field and injected current varied from 0.01 T to 0.05 T and 1.5 mA to 1 A, respectively. The simulations show that applying a magnetic field of 0.05 T makes the beam stable for a critical current density of 94 mA/cm2 for an anode-sole gap of 20 mm. Above this current density, the beam was unstable, as predicted. Introducing a 1° tilt in the magnetic field destabilizes the beam at a current density of 23 mA/cm2, which is lower than the critical current density for no tilt, as predicted by our theory. The simulation results also agree well with prior one-dimensional (1-D) theory and simulations that predict stable bands of current density for a 5° tilt where the beam is stable at low current density (<13.3 mA/cm2), unstable above this threshold, and then stable again at higher current density, (>33 mA/cm2).

scholarly journals Magnetic nulls in interacting dipolar fields

2021 ◽  
Vol 87 (2) ◽  
Author(s):  
Todd Elder ◽  
Allen H. Boozer
Keyword(s):  
Magnetic Field ◽  
Current Density ◽  
Magnetic Flux Tube ◽  
Electron Inertia ◽  
Characteristic Spatial Scale ◽  
Field Lines ◽  
Dipolar Fields ◽  
Time Required ◽  
Magnetic Null ◽  
The Magnetic Field

The prominence of nulls in reconnection theory is due to the expected singular current density and the indeterminacy of field lines at a magnetic null. Electron inertia changes the implications of both features. Magnetic field lines are distinguishable only when their distance of closest approach exceeds a distance $\varDelta _d$ . Electron inertia ensures $\varDelta _d\gtrsim c/\omega _{pe}$ . The lines that lie within a magnetic flux tube of radius $\varDelta _d$ at the place where the field strength $B$ is strongest are fundamentally indistinguishable. If the tube, somewhere along its length, encloses a point where $B=0$ vanishes, then distinguishable lines come no closer to the null than $\approx (a^2c/\omega _{pe})^{1/3}$ , where $a$ is a characteristic spatial scale of the magnetic field. The behaviour of the magnetic field lines in the presence of nulls is studied for a dipole embedded in a spatially constant magnetic field. In addition to the implications of distinguishability, a constraint on the current density at a null is obtained, and the time required for thin current sheets to arise is derived.

scholarly journals Discovery of a strong magnetic field in the rapidly rotating B2Vn star HR 7355

2010 ◽  
Vol 6 (S272) ◽  
pp. 204-205
Author(s):  
Mary E. Oksala ◽  
Gregg A. Wade ◽  
Wagner L. F. Marcolino ◽  
Jason H. Grunhut ◽  
David Bohlender ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Least Squares ◽  
Strong Magnetic Field ◽  
Type Star ◽  
Longitudinal Field ◽  
Rotational Period ◽  
V Band ◽  
Large Program ◽  
Differential Photometry

AbstractWe report on the detection of a strong, organized magnetic field in the helium-variable early B-type star HR 7355 using spectropolarimetric data obtained with ESPaDOnS on CFHT by the MiMeS large program. We also present results from new V-band differential photometry obtained with the CTIO 0.9m telescope. We investigate the longitudinal field, using a technique called Least-Squares Deconvolution (LSD), and the rotational period of HR 7355. These new observations strongly support the proposal that HR 7355 harbors a structured magnetosphere similar to that in the prototypical helium-strong star, σ Ori E.

PERTURBATION THEORY FOR THE ALFVÉN WAVE

1995 ◽  
Vol 09 (22) ◽  
pp. 2857-2898 ◽  
Author(s):  
Z. YOSHIDA ◽  
S.M. MAHAJAN
Keyword(s):  
Magnetic Field ◽  
Perturbation Theory ◽  
Electron Beam ◽  
Continuous Spectrum ◽  
Point Spectrum ◽  
Alfven Wave ◽  
Wave Number ◽  
Ambient Magnetic Field ◽  
Field Lines ◽  
The Magnetic Field

The Alfvén wave is the dominant low frequency transverse mode of a magnetized plasma. The Alfvén wave propagates along the magnetic field, and displays a continuous spectrum even in a bounded plasma. This is essentially due to the degeneracy of the wave characteristics, i.e. the frequency (ω) is primarily determined by the wave number in the direction parallel to the ambient magnetic field (k||) and is independent of the perpendicular wavenumbers. The characteristics, that are the direction along which the wave energy propagates, are identical to the ambient magnetic field lines. Therefore, the spectral structure of the Alfvén wave has a close relationship with the geometric structure of the magnetic field lines. In an inhomogeneous plasma, the Alfvén resonance (ω−cAk||=0; cA is the phase velocity of the Alfvén wave) constitutes a singularity for the defining wave equation; this results in a singular eigenfunction corresponding to the continuous spectrum. The aim of this review is to present an overview of the perturbation theory for the Alfvén wave. Emphasis is placed on those perturbations of the continuous spectrum which lead to the creation of point spectra. Such qualitative changes in the spectrum are relevant to many plasma phenomena. The first category of perturbations consists of nonideal effects such as the finite conductivity, kinetic effects arising from the finite electron inertia, and finite gyroradius. These effects add singular perturbations to the mode equation, and modify the spectrum dramatically. These modification, viz. the conversion of the continuous to the point spectrum, can lead to interesting physical phenomenon. A case in point is that of an electron beam propagating in a plasma which Cherenkov emits a left-hand circularly polarized Alfvén wave. The helicity of the ambient magnetic field imparts a frequency shift to the eigenmodes changing the critical velocity for Cherenkov emission. It, then, becomes possible for a sub-Alfvénic electron beam to excite a nonsingular Alfvén wave corresponding to a point spectrum. The second category comprises of geometric perturbations associated with higher dimensional inhomogeneity of the ambient field. Forbidden bands occur when a periodic modulation is applied. In a chaotic magnetic field, the weak localization of the wave occurs, resulting in a point spectrum.

scholarly journals Time behavior of an electron beam current pulse in the axial and peripheral zones of an anode in vacuum and gas-filled diodes

2021 ◽  
Vol 2064 (1) ◽  
pp. 012031
Author(s):  
D A Sorokin ◽  
M I Lomaev ◽  
A V Dyatlov ◽  
V F Tarasenko
Keyword(s):  
Electron Beam ◽  
Current Pulse ◽  
Current Density ◽  
Beam Current ◽  
Beam Current Density ◽  
Electron Beam Current ◽  
Time Behavior ◽  
Beam Current Pulse ◽  
Axial Part ◽  
A Current

Abstract The study of the time behavior of a current pulse of an electron beam generated during a high-voltage nanosecond discharge in gas-filled and vacuum diodes has been carried out. As follows from the experimental results, in both cases, the distribution of the beam current density in the plane of a grounded anode is non-uniform. The highest beam current density is recorded in the axial part of the anode. It was established that in the case of a gas-filled diode, ~ 2 ns after the onset of the beam current pulse, its shape in the axial anode zone changes relative to that in the peripheral one. It is assumed that the most probable reason for this is the effect of compensation of the charge of the beam electrons by the positive charge of ions arising in the ionization process in the paraxial zone.

Prototypes of a Field Disruption Energy Harvester

2012 ◽  
Author(s):  
Karim El-Rayes ◽  
Ahmed Abdel-Aziz ◽  
Eihab M. Abdel-Rahman ◽  
Raafat Mansour ◽  
Ehab El-Saadany
Keyword(s):  
Magnetic Field ◽  
Energy Source ◽  
Energy Harvesting ◽  
Energy Harvester ◽  
Low Frequency ◽  
Center Frequency ◽  
Field Source ◽  
Field Lines ◽  
The Magnetic Field ◽  
A Current

Energy harvesting from vibrations offers a prevailing non-traditional energy source. We introduce a novel electromagnetic transduction mechanism that can be used to harvest low-frequency vibrations. The mechanism induces a current in a coil by disrupting the electromagnetic field around the coil. The harvester is composed of a coil wound around track and surrounded by a magnetic field. The coil and magnetic field source remain stationary while a ferromagnetic ball material moves freely along the track cutting the field lines, disrupting the magnetic field, and inducing current in the coil. We present a prototype and experiments validating our energy harvesting mechanism as well as a model for the energy harvester. We find that our harvester can generate as much as 2mV and 21 μW from base vibrations of 0.9g amplitude. Our harvester demonstrates low-frequency harvesting with a center frequency as low as 9.4 Hz and a 3db harvesting bandwidth as wide as 5.8 Hz.

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