Motion Of Current Sheet Research Articles

Current Sheet Axial Dynamics of 2.5-kJ KSU-DPF Under High-Pressure Regime

In dense plasma focus (DPF) machines, the high-pressure (HP) regime of operation can be used as alternative technique to short-circuit (SC) test as the current sheet motion is minimal. The SC test was performed to get the right values for the static parameters of the machine. HP shots of more than 30 mbar were performed on the 2.5-kJ Kansas State University DPF machine to determine the deviation of HP values from SC values in computed static inductance and resistance. The test was performed using various gases over a wide range of molecular/atomic mass, starting from hydrogen as the lightest gas up to argon. It was found that the deviation in static inductance and resistance computed from HP method is inversely proportional to gas molecular mass at a certain pressure. The heavy gases like neon and argon were found to give the most accurate results. At 60 mbar of argon, the inductance deviation was 6.5%, and the resistance deviation was 14%. It was found also that increasing gas pressure over 30 mbar using heavy gases like Ar or Ne gives no effective improvement on the computed static impedance. Snowplow model was used to predict the axial position and the axial speed of the current sheet during the HP regime. The model showed that the average axial speed in heavy gases like argon was 0.8 cm/ μs, whereas in hydrogen, it was 1.6 cm/μs.

Storm and substorm effects on magnetotail current sheet motion

Passes through the mid‐region of the magnetotail by the Cluster spacecraft from 2001 to 2007 have been examined to study the dynamics of the cross‐tail current sheet. Cluster is ideally placed to study this region due to the orientation of the orbit in the magnetotail, such that the current sheet is sampled at distances downtail from about 8–19 RE. Multiple fluctuations of the X component of the magnetic field (BX) from positive to negative and vice versa, measured by Cluster as it crosses the nominal location of the current sheet, indicate that the current sheet is in motion. In this study we use the number of crossings of the current sheet by the Cluster 3 spacecraft as a measure of the dynamics of the magnetotail. The effects of substorm and magnetic storm activity on the dynamics during these orbits have been investigated using the AE and SYM‐H indices. Our results indicate that the current sheet is more often in motion during orbits when there is greater than average substorm activity and a quiet ring current. Results suggest that internal processes within the tail that initiate substorms may also initiate the flapping motion of the current sheet. In addition the more dipolar field that results from an enhanced ring current during magnetic storms may inhibit tail dynamics during substorm events.

Resistive magnetohydrodynamic simulations of X-line retreat during magnetic reconnection

To investigate the impact of current sheet motion on the reconnection process, we perform resistive magnetohydrodynamic simulations of two closely located reconnection sites that move apart from each other as reconnection develops. This simulation develops less quickly than an otherwise equivalent single perturbation simulation but eventually exhibits a higher reconnection rate. The unobstructed outflow jets are faster and longer than the outflow jets directed toward the magnetic island that forms between the two current sheets. The X-line and flow stagnation point are located near the trailing end of each current sheet very close to the obstructed exit. The speed of X-line retreat ranges from ∼0.02–0.06, while the speed of stagnation point retreat ranges from ∼0.03–0.07 in units of the initial upstream Alfvén velocity. Early in time, the flow stagnation point is located closer to the center of the current sheet than the X-line, but later on the relative positions of these two points switch. Consequently, late in time, there is significant plasma flow across the X-line in the opposite direction of X-line retreat. Throughout the simulation, the velocity at the X-line does not equal the velocity of the X-line. Motivated by these results, an expression for the rate of X-line retreat is derived in terms of local parameters evaluated at the X-line. This expression shows that X-line retreat is due to both advection by the bulk plasma flow and diffusion of the normal component of the magnetic field.

Statistical research on the motion properties of the magnetotail current sheet: Cluster observations

The origin of the flapping motion of the earth’s magnetotail current sheet is one of the most important problems in the magnetotail dynamics. Using Cluster data, we make a statistical research on the motion properties of the magnetotail current sheet of 2001 and 2003. We calculate the velocities of the magnetotail current sheet using new methods and obtain the distribution of the magnetotail current sheet velocities in the X-Y plane in GSE coordinate system. Our results show that although most of the current sheets were propagating toward the tail flanks and those of the exceptions lay in dusk side, which is consistent with previous studies, the proportions of the current sheet which were propagating toward midnight (where |YGSE|=0) were higher than those in previous studies. Motions of the current sheet in the middle area (|YGSE|<8 Re) of the magnetotail are investigated. Relatively high value of the Z component of the velocity further confirms that the middle area of the magnetotail might be a source region for the motion of the current sheets which were propagating towards the tail flanks. According to our case studies, the way the current sheets propagated toward midnight area differs significantly from that toward dusk and dawn side, from which we infer that there might be two different kinds of current sheet motions originated from different sources. The statistical results of this paper may give some clues for further studies on the origin of the flapping motion of the magnetotail current sheet.

In situ determination of the static inductance and resistance of a plasma focus capacitor bank

The static (unloaded) electrical parameters of a capacitor bank are of utmost importance for the purpose of modeling the system as a whole when the capacitor bank is discharged into its dynamic electromagnetic load. Using a physical short circuit across the electromagnetic load is usually technically difficult and is unnecessary. The discharge can be operated at the highest pressure permissible in order to minimize current sheet motion, thus simulating zero dynamic load, to enable bank parameters, static inductance L(0), and resistance r(0) to be obtained using lightly damped sinusoid equations given the bank capacitance C(0). However, for a plasma focus, even at the highest permissible pressure it is found that there is significant residual motion, so that the assumption of a zero dynamic load introduces unacceptable errors into the determination of the circuit parameters. To overcome this problem, the Lee model code is used to fit the computed current trace to the measured current waveform. Hence the dynamics is incorporated into the solution and the capacitor bank parameters are computed using the Lee model code, and more accurate static bank parameters are obtained.

Space Technology 5 measurements of auroral field-aligned current sheet motion

[1] During the 90-day Space Technology 5 (ST-5) mission, a total of 2535 auroral field-aligned current (FAC) signatures were identified. Of these 1030 were suitable to be modeled as semi-infinite current sheets aligned with L-shells and moving with constant speed in the north or south directions (hereafter called FAC speed). FAC speeds were found to range from −1 to 1 km/s with larger mean magnitude during intervals of higher geomagnetic activity. At ST-5 altitudes, ∼300 to 4500 km, the median relative errors in FAC thickness and current density, when stationary FAC is assumed, are 4%. When the ST-5 FAC speed determinations are extrapolated along the IGRF-10 magnetic field lines, these errors increase to 23% and 24% at 4 RE, and 65% and 124% at 8 RE, respectively.

Space Technology 5 multi‐point measurements of near‐Earth magnetic fields: Initial results

The Space Technology 5 (ST‐5) mission successfully placed three micro‐satellites in a 300 × 4500 km dawn‐dusk orbit on 22 March 2006. Each spacecraft carried a boom‐mounted vector fluxgate magnetometer that returned highly sensitive and accurate measurements of the geomagnetic field. These data allow, for the first time, the separation of temporal and spatial variations in field‐aligned current (FAC) perturbations measured in low‐Earth orbit on time scales of ∼10 sec to 10 min. The constellation measurements are used to directly determine field‐aligned current sheet motion, thickness, and current density. In doing so, we demonstrate two multi‐point methods for the inference of FAC current density that have not previously been possible in low‐Earth orbit: 1) the “standard method,” based upon s/c velocity, but corrected for FAC current sheet motion, and 2) the “gradiometer method” which uses simultaneous magnetic field measurements at two points with known separation. Future studies will apply these methods to the entire ST‐5 data set and expand to include geomagnetic field gradient analyses as well as field‐aligned and ionospheric currents.

Stochastic particle acceleration by the forced interaction of relativistic current sheets

We address the problem of interacting relativistic current sheets in self-consistent kinetic plasma simulations within the framework of the Particle-In-Cell model. The interaction is enforced in head-on collisions of up to 10 current sheets at relativistic bulk speeds. The simulations are motivated by the general problem of Poynting flux dissipation in ‘striped wind’ configurations presumably governing the relativistic outflows pervasive in pulsar winds and gamma-ray bursts. We identify the generation of non-thermal particles and formation of a stable power-law shape in the particle energy distributions f( γ) d γ ∝ γ − s d γ. In 1D, a spectral index s ∼ 2 is observed and attributed to a stochastic Fermi-type acceleration mechanism. In 2D, the generic index of s ∼ 3–4 is retained as in previous simulations of individual current sheets. Whereas in 2D the high energy cut-off is constrained by the limited dissipation of magnetic energy, in 1D the process converts the bulk motion of current sheets towards directed particle momentum of an exclusive class of non-thermal particles.

Magnetotail particle distributions associated with pitch angle isotropization

We present modeled ion distributions in the near-Earth magnetotail expected to be associated with high latitude pitch angle isotropization. The model consists of a magnetic field reversal and a plasma source such that particles have a ratio of the minimum field line curvature radius to maximum gyroradius near unity, a nonadiabatic regime. For precipitating particles observed at the edge of the field reversal, we find structuring in the ion distribution consisting of peaks and valleys in the pitch angle distribution, particularly for intermediate values of field line curvature, which is consistent with the near-Earth tail region. The structures are non-Maxwellian and not gyrotropic. They are resolvable by instruments such as the GEOTAIL spacecraft CPI detector and can be used as a remote sensing method for fields in this regime between adiabatic motion and current sheet motion.

Physical model of dynamic phenomena in impulse plasma coaxial accelerator

Impulse plasma is used in surface engineering (Impulse Plasma Deposition 1) as an efficient source of mass and energy in the synthesis and deposition of various materials in the form of layers. The plasma is generated and accelerated in a coaxial accelerator. 2,3 In the present work, on the basis of previous studies 4 and a snow plow model of the current sheet motion, we propose and discuss a physical model of dynamic phenomena in such device.

Numerical simulation of the current sheet above solar spots

Current sheet (CS) creation in a region with anX-type zero magnetic field line in plasma was simulated by numerically solving the 3D MHD equations for conditions which were close to the solar corona: the disturbance propagated from the photosphere boundary under which the magnetic field sources were situated. Some of values (B,ρ,V) were set on the photosphere boundary, while others were determined from the conditions inside the region. Several Alfven times after its creation, the CS motion practically ceased, and the plasma velocity changed its direction above the sheet, so that the plasma flow was directed into the CS from both sides.

Verification of quantitative relationship among Birkeland current sheet motion, intensity, and convective velocity, and also of criterion for expansion onset

In this paper, 14 substorms are used to verify the conclusions of an earlier paper on current sheet motions. These conclusions can be summarized as follows: (1) The quantitative relationship VN = VCN − kvI∥ is valid when applied to the upward current sheet in the premidnight quadrant except during the expansion and early recovery phases of substorms (VN and VCN are the components, normal to the sheet, of the sheet velocity and the convection velocity, kv is a constant, and I∥ is the current sheet intensity). (2) At the time of local northward expansion of the auroras there appears to be a decrease by 1 order of magnitude of the amount of plasma on flux tubes. (3) The time of initiation of local northward expansion occurs when VCN = kvI∥. A few additional points emerge from this study: The above relationships are not valid at stations east of the location of initial onset of expansion, and the amount of plasma on flux tubes tends to return to its preexpansion value after a substorm. Further conclusions are (1) that the physical mechanism responsible for the northward expansion in a westward traveling surge is the same as in the initial near‐midnight expansion, (2) that the triggering of expansion occurs just as the tail begins to recede away from the earth, and (3) that the apparent decrease in plasma content is consistent with the formation of a near‐earth neutral line; however, it could also result from the breakdown of the sheet approximation for the currents.

Characteristics of Plasma Compression in Z-Pinch Discharge

The motion of current sheet in linear Z-pinch is analyzed by Leontovich-Osovets' equation combined with the circuit equation, and two characteristic phenomena observed so for are successfully explained. According to the calculation for higher circuit inductance, the value ρ0M of initial mass density of gas in the discharge tube, at which a maximum appears in the heavy particle density at maximum compression time of plasma, is given by ξρ0M1/4≃0.85 for any kind of gas, where ξ is a parameter determined by experimental condition. This relation gives a good agreement with the experimental results. Further, the abrupt voltage change at discharge gap and corresponding kink in current, obsereved by Kurchatov near the maximum compression time, are explained in relation to the trajectory of current sheet calculated with lower circulit inductadce.

On the Motion of Current Sheets, and the Radio, Optical, and X-Ray Emission from Pulsars. III. The Independent-Particle Picture and Radiation

On the Motion of Current Sheets, and the Radio, Optical, and X-Ray Emission from Pulsars. III. The Independent-Particle Picture and Radiation

On the Motion of Current Sheets, and the Radio, Optical, and X-Ray Emission from Pulsars. II. Pulse Structure, Polarization, Time-Varying Features, and Tight-Beam Emission

On the Motion of Current Sheets, and the Radio, Optical, and X-Ray Emission from Pulsars. II. Pulse Structure, Polarization, Time-Varying Features, and Tight-Beam Emission

On the Motion of Current Sheets, and the Radio, Optical, and X-Ray Emission from Pulsars

view Abstract Citations (21) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Motion of Current Sheets, and the Radio, Optical, and X-Ray Emission from Pulsars Lerche, I. Abstract We suggest that an oscillating current sheet is the source of pulsar radiation produced over a broad band of high frequencies ( 108-10' c/s). The differential spectrum of the emitted radiation varies as f-2/3, where j is the frequency. The radiation extends through the radio, optical, and X-ray regions. The efficiency of the radiation mechnnism is so high that the oscillation energy goes mainly into radiation in each cycle of the oscillation. Applications to pulsars suggest that this parametric conversion mechanism may be responsible for the broad-band spectrum observed in, say, pulsar NP 0532. Publication: The Astrophysical Journal Pub Date: January 1970 DOI: 10.1086/150305 Bibcode: 1970ApJ...159..229L full text sources ADS | Related Materials (2) Part 2: 1970ApJ...160.1003L Part 3: 1970ApJ...162..153L