Taylor relaxation and lambda decay of unbounded, freely expanding spheromaks

A magnetized coaxial gun is discharged into a much larger vacuum chamber and the subsequent evolution of the plasma is observed using high speed cameras and a magnetic probe array. Photographic results indicate four distinct regimes of operation, labeled I–IV, each possessing qualitatively different dynamics, with the parameter lambdagun = µ0Igun/Phibias determining the operative regime. Plasmas produced in Regime II are identified as detached spheromak configurations. Images depict a donut-like shape, while magnetic data demonstrate that a closed toroidal flux-surface topology is present. Poloidal flux amplification shows that Taylor relaxation mechanisms are at work. The spatial and temporal variation of plasma lambda= µ0Jphi/Bphi indicate that the spheromak is decaying and expanding in a manner analogous to a self-similar expansion model proposed for interplanetary magnetic clouds. In Regime III, the plasma is unable to detach from the gun due to excess bias flux. Analysis of toroidal and poloidal flux as well as the lambda profile shows that magnetic flux and helicity are confined within the gun for this regime

Effects of CT injector acceleration electrode configuration on tokamak penetration

Through compact toroid (CT) injection experiments on the TEXT-U tokamak (with BT simeq 10 kG and IP simeq 100 kA), it has been shown that the acceleration electrode configuration, particularly in the vicinity of the toroidal field (TF) coils of the tokamak, has a strong effect on penetration performance. In initial experiments, premature stopping of CTs within the injector was seen at anomalously low TF strengths. Two modifications were found to greatly improve performance: (a) removal of a section of the inner electrode and (b) increased diameter of the 'drift tube' (which guides the CT into the tokamak after acceleration). It is proposed that the primary drag mechanism slowing CTs is toroidal flux trapping, which occurs when a CT displaces transverse TF trapped within the flux conserving walls of the acceleration electrodes (or drift tube). For a simple two dimensional (2-D) geometry, a magnetostatic analysis produces a CT kinetic energy requirement of 1/2ρv2 ≥ α(B02/2μ0), with α = 2/(1-a2/R2) a dimensionless number that is dependent on the CT radius a normalized by the drift tube radius R. For a typical CT, this can greatly increase the required energies. A numerical analysis in 3-D confirms the analytical result for long CTs (with length L such that L/a gtrsim 10). In addition to flux trapping, the CT shape is also shown to affect the energy criterion. These findings indicate that a realistic assessment of the kinetic energy required for a CT to penetrate a particular tokamak TF must take into account the interaction of the magnetic field with the electrode walls of the injector

A quick-retrieval high-speed digital framing camera

A new high-speed digital framing camera is described. The design is built around a rotating polygon mirror that provides a framing rate of 24 000 frames/s. The camera electronics digitizes an image into a 32×104 grid of pixels, where the second dimension of the grid can be varied and is determined by the 8 bit computer-aided measurement and control digitizer sampling rate. Available digitizer memory provides for 314 frames at this horizontal resolution. The advantages over other available high-speed framing cameras are (1) low cost of the system provided the digitizers are available, (2) rapid retrieval of a recorded event, and (3) the ease with which the system can be used. Sample results from an application in high-power arc photography are given to illustrate the system's spatial and temporal resolution

The Atmosphere Explorer and the shuttle glow

Recent analyses of the Atmosphere Explorer data are discussed in which it is demonstrated that the satellite glows have two components, one at high altitudes which is consistent with excitation in single collisions of atmospheric oxygen atoms with the vehicle surface and the other at low altitudes which is consistent with double collisions of nitrogen molecules. Contrary to an earlier suggestion, the low-altitude data are not consistent with collisions of oxygen molecules. The separation of the two components strengthens the conclusion that the high-altitude glow arises from vibrationally excited OH molecules produced by a formation mechanism that is different from that leading to the normal atmospheric OH airglow. The spectrum is consistent with association of oxygen and hydrogen atoms at sites on the surface into the vibrational levels of OH. The low-altitude glow is consistent with the green mechanism but there are difficulties with it. The shuttle glows are different and have the spectral appearance of emission from NO2. The characteristics of the shuttle glows and the satellite glows will be contrasted and a tentative resolution of the differences in the Atmosphere Explorer and shuttle glows will be offered

Holographic Estimate of Oblique Corrections for Technicolor

We study the oblique corrections to the electroweak interaction in the holographic model of technicolor theories. The oblique S parameter is expressed in terms of a solution to the equations of motion for the AdS bulk gauge fields. By analyzing the solution, we establish a rigorous proof that the S parameter is positive and is reduced by walking. We also present the precise numerical values for the S parameter of various technicolor models by solving the equations numerically.Comment: 10 pages, 1 figure, RevTeX 4.0: published version. references adde

Duality Symmetry in Kaluza-Klein n+D+dn+D+d Dimensional Cosmological Model

It is shown that, with the only exception of $n=2$, the Einstein-Hilbert action in $n+D+d$ dimensions, with $n$ times, is invariant under the duality transformation $a\to \frac{1}{a}$ and $b\to \frac{1}{b}$, where $a$ is a Friedmann-Robertson-Walker scale factor in $D$ dimensions and $b$ a Brans-Dicke scalar field in $d$ dimensions respectively. We investigate the $2+D+d$ dimensional cosmological model in some detail.Comment: 23 pages, Late

Another integrable case in the Lorenz model

A scaling invariance in the Lorenz model allows one to consider the usually discarded case sigma=0. We integrate it with the third Painlev\'e function.Comment: 3 pages, no figure, to appear in J. Phys.