Effect of magnetic islands on the impurity flows in NCSX geometry

A new physics idea to protect a plasma from impurity ions with the use of magnetic islands can be examined on the new National Compact Stellarator Experiment device (NCSX), which is under construction at Princeton Plasma Physics Laboratory, USA. On the basis of the MHD approach the impurity ions flows are studied in the configuration with the parameters of NCSX with the magnetic islands m / n=5/3 and m / n=6/3 , which can be excited with the trim coils in NCSX. It is shown that solving the flow trajectory equations dr × uα =0 can lead us to the conclusion that ion flow trajectories are concentrated in the region of the magnetic islands.Нову фізичну ідею захисту плазми від проникнення іонів домішки за допомогою магнітних островів можна перевірити в експериментах на новому пристрої National Compact Stellarator Experiment (NCSX), який споруджується в Princeton Plasma Physics Laboratory, USA. На основі МГД наближення потоки іонів домішки вивчаються для конфігурації з параметрами NCSX з магнітними островами з «хвильовими» числами m / n=5/3 and m / n=6/3, які можна збудити спеціальними токовыми катушками (trim coils) у NCSX. Рішення рівнянь траєкторій потоків dr × uα =0 доводить, що потоки іонів можуть концентруватися в межах магнітних островів.Новая физическая идея - защитить плазму от проникновения примесных ионов c использованием магнитных островов - может быть проверена в экспериментах на новой установке National Compact Stellarator Experiment (NCSX), строящейся в Princeton Plasma Physics Laboratory, USA. На основе МГД приближения потоки ионов примеси изучаются для конфигурации с параметрами NCSX с магнитными островами с «волновыми» числами m / n=5/3 и m / n=6/3, которые могут быть возбуждены специальными токовыми катушками (trim coils) в NCSX. В результате решения уравнений траекторий потоков dr × uα =0 показано, что потоки ионов могут концентрироваться в области магнитных островов

Optimizing Stellarators for Turbulent Transport

Up to now, the term "transport-optimized" stellarators has meant optimized to minimize neoclassical transport, while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. Here, we demonstrate that stellarators can also be designed to mitigate their turbulent transport, by making use of two powerful numerical tools not available until recently, namely gyrokinetic codes valid for 3D nonlinear simulations, and stellarator optimization codes. A first proof-of-principle configuration is obtained, reducing the level of ion temperature gradient turbulent transport from the NCSX baseline design by a factor of about 2.5

Control-matrix approach to stellarator design and control

The full space Z always equal to {l{underscore}brace}Zj=1,..Nz{r{underscore}brace} of independent variables defining a stellarator configuration is large. To find attractive design points in this space, or to understand operational flexibility about a given design point, one needs insight into the topography in Z-space of the physics figures of merit Pi which characterize the machine performance, and means of determining those directions in Z-space which give one independent control over the Pi, as well as those which affect none of them, and so are available for design flexibility. The control matrix (CM) approach described here provides a mathematical means of obtaining these. In this work, the authors describe the CM approach and use it in studying some candidate Quasi-Axisymmetric (QA) stellarator configurations the NCSX design group has been considering. In the process of the analysis, a first exploration of the topography of the configuration space in the vicinity of these candidate systems has been performed, whose character is discussed

Phase transition in the collisionless regime for wave-particle interaction

Gibbs statistical mechanics is derived for the Hamiltonian system coupling self-consistently a wave to N particles. This identifies Landau damping with a regime where a second order phase transition occurs. For nonequilibrium initial data with warm particles, a critical initial wave intensity is found: above it, thermodynamics predicts a finite wave amplitude in the limit of infinite N; below it, the equilibrium amplitude vanishes. Simulations support these predictions providing new insight on the long-time nonlinear fate of the wave due to Landau damping in plasmas.Comment: 12 pages (RevTeX), 2 figures (PostScript