Toroidal ripple transport of beam ions in the mega-ampère spherical tokamak

The transport of injected beam ions due to toroidalmagnetic field ripple in the mega-ampère spherical tokamak (MAST) is quantified using a full orbit particle tracking code, with collisional slowing-down and pitch-angle scattering by electrons and bulk ions taken into account. It is shown that the level of ripple losses is generally rather low, although it depends sensitively on the major radius of the outer midplane plasma edge; for typical values of this parameter in MAST plasmas, the reduction in beam heating power due specifically to ripple transport is less than 1%, and the ripple contribution to beam ion diffusivity is of the order of 0.1 m² s⁻¹ or less. It is concluded that ripple effects make only a small contribution to anomalous transport rates that have been invoked to account for measured neutron rates and plasma stored energies in some MAST discharges. Delayed (non-prompt) losses are shown to occur close to the outer midplane, suggesting that banana-drift diffusion is the most likely cause of the ripple-induced losses.This work was funded by the RCUK Energy Programme under Grant EP/I501045, by the Australian Research Council, and by the European Communities under the Contract of Association between EURATOM and CCFE

On steady poloidal and toroidal flows in tokamak plasmas

The effects of poloidal and toroidalflows on tokamakplasma equilibria are examined in the magnetohydrodynamic limit. “Transonic” poloidal flows of the order of the sound speed multiplied by the ratio of poloidal magnetic field to total field B₀/B can cause the (normally elliptic) Grad–Shafranov (GS) equation to become hyperbolic in part of the solution domain. It is pointed out that the range of poloidal flows for which the GS equation is hyperbolic increases with plasma beta and B₀/B, thereby complicating the problem of determining spherical tokamakplasma equilibria with transonic poloidal flows. It is demonstrated that the calculation of the hyperbolicity criterion can be easily modified when the assumption of isentropic flux surfaces is replaced with the more tokamak-relevant one of isothermal flux surfaces. On the basis of the latter assumption, a simple expression is obtained for the variation of density on a flux surface when poloidal and toroidalflows are simultaneously present. Combined with Thomson scattering measurements of density and temperature, this expression could be used to infer information on poloidal and toroidalflows on the high field side of a tokamakplasma, where direct measurements of flows are not generally possible. It is demonstrated that there are four possible solutions of the Bernoulli relation for the plasma density when the flux surfaces are assumed to be isothermal, corresponding to four distinct poloidal flow regimes. Finally, observations and first principles-based theoretical modeling of poloidal flows in tokamakplasmas are briefly reviewed and it is concluded that there is no clear evidence for the occurrence of supersonic poloidal flows.This work was jointly funded by the Australian Government through International Science Linkages Grant No. CG130047, the Australian National University, the United Kingdom Engineering and Physical Sciences Research Council, and by the European Communities under the contract of Association between EURATOM and CCFE

An X-ray Study of Two B+B Binaries: AH Cep and CW Cep

AH Cep and CW Cep are both early B-type binaries with short orbital periods of 1.8~d and 2.7~d, respectively. All four components are B0.5V types. The binaries are also double-lined spectroscopic and eclipsing. Consequently, solutions for orbital and stellar parameters make the pair of binaries ideal targets for a study of the colliding winds between two B~stars. {\em Chandra} ACIS-I observations were obtained to determine X-ray luminosities. AH~Cep was detected with an unabsorbed X-ray luminosity at a 90\% confidence interval of $(9-33)\times 10^{30}$ erg s$^{-1}$, or $(0.5-1.7)\times 10^{-7} L_{\rm Bol}$, relative to the combined Bolometric luminosities of the two components. While formally consistent with expectations for embedded wind shocks, or binary wind collision, the near-twin system of CW~Cep was a surprising non-detection. For CW~Cep, an upper limit was determined with $L_X/L_{\rm Bol} < 10^{-8}$, again for the combined components. One difference between these two systems is that AH~Cep is part of a multiple system. The X-rays from AH~Cep may not arise from standard wind shocks nor wind collision, but perhaps instead from magnetism in any one of the four components of the system. The possibility could be tested by searching for cyclic X-ray variability in AH~Cep on the short orbital period of the inner B~stars.Comment: Astrophysical Journal, accepte

Impairment of chloroplast development and sink strength by blockade of light in chloroembryos of Cyamopsis Tetragonoloba (L.) Taub.

In many members of Fabaceae synthesis of chloroplast pigments takes place even when the embryo is deep inside the fruit. Blockade of light totally etiolated the embryos of developing Cyamopsis fruits upto 16-18 days after anthesis (DAA), whereas the pigments of the mature embryos, when shaded, were not significantly affected. Upon illuminatio resynthesis of green pigments by etiolated embryos occurred both l n v i v o and in vitro more significantly during the early stages of growth of the embryos (upto 18 DAA). Shading of developing fruits at different growth stages of embryos, reduced the growth of sink. The results are discussed in relation to the importance of light on embryo greening and dry matter production

A Coordinated X-ray and Optical Campaign of the Nearby Massive Binary δ\delta Orionis Aa: II. X-ray Variability

We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral dataset of the $\delta$ Orionis Aa binary system. The four observations, obtained with Chandra ACIS HETGS, have a total exposure time of ~479 ks and provide nearly complete binary phase coverage. Variability of the total X-ray flux in the range 5-25 $\AA$ is confirmed, with maximum amplitude of about +/-15% within a single ~125 ks observation. Periods of 4.76d and 2.04d are found in the total X-ray flux, as well as an apparent overall increase in flux level throughout the 9-day observational campaign. Using 40 ks contiguous spectra derived from the original observations, we investigate variability of emission line parameters and ratios. Several emission lines are shown to be variable, including S XV, Si XIII, and Ne IX. For the first time, variations of the X-ray emission line widths as a function of the binary phase are found in a binary system, with the smallest widths at phase=0.0 when the secondary $\delta$ Orionis Aa2 is at inferior conjunction. Using 3D hydrodynamic modeling of the interacting winds, we relate the emission line width variability to the presence of a wind cavity created by a wind-wind collision, which is effectively void of embedded wind shocks and is carved out of the X-ray-producing primary wind, thus producing phase-locked X-ray variability.Comment: 36 pages, 14 Tables, 19 Figures, accepted by ApJ, one of 4 related papers to be published togethe

A Coordinated X-ray and Optical Campaign on the Nearest Massive Eclipsing Binary, Delta Ori Aa: I. Overview of the X-ray Spectrum

We present an overview of four phase-constrained Chandra HETGS X-ray observations of Delta Ori A. Delta Ori A is actually a triple system which includes the nearest massive eclipsing spectroscopic binary, Delta Ori Aa, the only such object which can be observed with little phase-smearing with the Chandra gratings. Since the fainter star, Delta Ori Aa2, has a much lower X-ray luminosity than the brighter primary, Delta Ori A provides a unique system with which to test the spatial distribution of the X-ray emitting gas around Delta Ori Aa1 via occultation by the photosphere of and wind cavity around the X-ray dark secondary. Here we discuss the X-ray spectrum and X-ray line profiles for the combined observation, having an exposure time of nearly 500 ksec and covering nearly the entire binary orbit. Companion papers discuss the X-ray variability seen in the Chandra spectra, present new space-based photometry and ground-based radial velocities simultaneous with the X-ray data to better constrain the system parameters, and model the effects of X-rays on the optical and UV spectrum. We find that the X-ray emission is dominated by embedded wind shock emission from star Aa1, with little contribution from the tertiary star Ab or the shocked gas produced by the collision of the wind of Aa1 against the surface of Aa2. We find a similar temperature distribution to previous X-ray spectrum analyses. We also show that the line half-widths are about $0.3-0.5\times$ the terminal velocity of the wind of star Aa1. We find a strong anti-correlation between line widths and the line excitation energy, which suggests that longer-wavelength, lower-temperature lines form farther out in the wind. Our analysis also indicates that the ratio of the intensities of the strong and weak lines of \ion{Fe}{17} and \ion{Ne}{10} are inconsistent with model predictions, which may be an effect of resonance scatteringComment: accepted by ApJ; revised according to ApJ proo