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

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

Molecular Gastronomy: A Food Fad or an Interface for Science-based Cooking?

A review is given over the field of molecular gastronomy and its relation to science and cooking. We begin with a brief history of the field of molecular gastronomy, the definition of the term itself, and the current controversy surrounding this term. We then highlight the distinction between molecular gastronomy and science-based cooking, and we discuss both the similarities and the distinctions between science and cooking. In particular, we highlight the fact that the kitchen serves as an ideal place to foster interactions between scientists and chefs that lead to benefits for the general public in the form of novel and high-quality foods. On the one hand, it can facilitate the implementation of new ideas and recipes in restaurants. On the other hand, it challenges scientists to apply their fundamental scientific understanding to the complexities of cooking, and it challenges them to expand the scientific understanding of many chemical and physical mechanisms beyond the common mass-produced food products. In addition, molecular gastronomy forms an ideal base to educate the general public about the basic principles of science and cooking and how they can be utilized to improve the awareness of the role of food and nutrition for the quality of life

The quasi-linear relaxation of thick-target electron beams in solar flares

The effects of quasi-linear interactions on thick-target electron beams in the solar corona are investigated. Coulomb collisions produce regions of positive gradient in electron distributions which are initially monotonic decreasing functions of energy. In the resulting two-stream instability, energy and momentum are transferred from electrons to Langmuir waves and the region of positive slope in the electron distribution is replaced by a plateau. In the corona, the timescale for this quasi-linear relaxation is very short compared to the collision time. It is therefore possible to model the effects of quasi-linear relaxation by replacing any region of positive slop in the distribution by a plateau at each time step, in such a way as to conserve particle number. The X-ray bremsstrahlung and collisional heating rate produced by a relaxed beam are evaluated. Although the analysis is strictly steady state, it is relevant to the theoretical interpretation of hard X-ray bursts with durations of the order of a few seconds (i.e., the majority of such bursts)

Nonlinear wave propagation and reconnection at magnetic X-points in the Hall MHD regime

The highly dynamical, complex nature of the solar atmosphere naturally implies the presence of waves in a topologically varied magnetic environment. Here, the interaction of waves with topological features such as null points is inevitable and potentially important for energetics. The low resistivity of the solar coronal plasma implies that non-MHD effects should be considered in studies of magnetic energy release in this environment. This paper investigates the role of the Hall term in the propagation and dissipation of waves, their interaction with 2D magnetic X-points and the nature of the resulting reconnection. A Lagrangian remap shock-capturing code (Lare2d) is used to study the evolution of an initial fast magnetoacoustic wave annulus for a range of values of the ion skin depth in resistive Hall MHD. A magnetic null-point finding algorithm is also used to locate and track the evolution of the multiple null-points that are formed in the system. Depending on the ratio of ion skin depth to system size, our model demonstrates that Hall effects can play a key role in the wave-null interaction. In particular, the initial fast-wave pulse now consists of whistler and ion-cyclotron components; the dispersive nature of the whistler wave leads to (i) earlier interaction with the null, (ii) the creation of multiple additional, transient nulls and, hence, an increased number of energy release sites. In the Hall regime, the relevant timescales (such as the onset of reconnection and the period of the oscillatory relaxation) of the system are reduced significantly, and the reconnection rate is enhanced.Comment: 13 pages, 10 figure

Murex medic field evaluation.

Trials: 90GE113, 90MO62, 90WH87, 90ME72, 90NO115, 90A24, 90AB17, 90AL35 Locations: Geraldton, New Norcia, Wongan Hills, Merredin, Southern Brook, Avondale, Katanning, Tenderden. The selection SEP29.1 was outstanding for both dry matter production and seed yield over a wide range of sites varying in both rainfall and soil type. On the basis of these trials, six lines have been selected for further evaluation in 1991. They are: SEP29.1 SEP26.2.7 GRC69 GRC87.1 87F01.28 87FB2.36 Trials 90A25 and 90NO116 Redlegged earthmite field experiments. Very low levels of redlegged earthmite and only minor damage to test varieties was recorded in this trial. Damage ratings were recorded at 3, 4 and 5 weeks after sowing and plant yields at 3, 5 and 7 weeks, but the trial was then abandoned due to minimal responses. 90NO116 - This trial was abandoned soon after sowing due to massive germination of contaminant clover present in the paddock and negligible levels of redlegged earthmite