[en] A method is presented for designing coils for compact stellarators. In contrast to methods that select a finite number of coils from an optimal continuous surface current distribution, the COILOPT code solves for the optimal parameters in an explicit representation of modular coils on a toroidal winding surface that is well separated from the plasma boundary, together with the coefficients of the winding surface. The problem is posed as a balance between approximating a prescribed magnetic configuration and satisfying certain critical engineering requirements. Results are presented for quasi-axisymmetric and quasi-poloidal compact stellarator designs

[en] The rf-SciDAC collaboration is developing computer simulations to predict the damping of radio frequency (rf) waves in fusion plasmas. Here we extend self-consistent quasi-linear calculations of ion cyclotron resonant heating to include the finite drift of ions from magnetic flux surfaces and rf induced spatial transport. The all-orders spectral wave solver AORSA is iteratively coupled with a particle based update of the plasma distribution function.

[en] An ion kinetic equation is solved by expansion in a parameter corresponding to the small parameter of neoclassical transport theory and the small parameter of geometrical optics. A slab model with perpendicular stratification of the magnetic field is assumed, and a given RF field is present with a frequency corresponding to a modest multiple of the ion cyclotron frequency. The RF induced ion flow perpendicular to the magnetic field is calculated. The parallel flow may be large, but it cannot be calculated without an analysis of the electron transport

[en] The rf-SciDAC collaboration is developing computer simulations to predict the damping of radio frequency (rf) waves in fusion plasmas. Here we extend self-consistent quasi-linear calculations of ion cyclotron resonant heating to include the finite drift of ions from magnetic flux surfaces and rf induced spatial transport. The all-orders spectral wave solver AORSA is iteratively coupled with a particle based update of the plasma distribution function using a quasi-linear diffusion tersor representative of the (k) over right arrow spectrum. Initial results are presented for a high power minority heating scenario on the Alcator C-Mod tokamak and a high harmonic beam heating scenario on DIII-D. Finite orbit effects are shown to give a less peaked perpendicular energy profile and rf induced transport.

[en] Fusion Successful simulation of the complex physics that affect magnetically confined fusion plasma remains an important target milestone towards the development of viable fusion energy. Major advances in the underlying physics formulations, mathematical modeling, and computational tools and techniques are needed to enable a complete fusion simulation on the emerging class of large scale capability parallel computers that are coming on-line in the next few years. Several pilot projects are currently being undertaken to explore different (partial) code integration and coupling problems, and possible solutions that may guide the larger integration endeavor. In this paper, we present the design and implementation details of one such project, a component based approach to couple existing codes to model the interaction between high power radio frequency (RF) electromagnetic waves, and magnetohydrodynamics (MHD) aspects of the burning plasma. The framework and component design utilize a light coupling approach based on high level view of constituent codes that facilitates rapid incorporation of new components into the integrated simulation framework. The work illustrates the viability of the light coupling approach to better understand physics and stand-alone computer code dependencies and interactions, as a precursor to a more tightly coupled integrated simulation environment.

[en] An ion kinetic equation is solved by expansion in a parameter corresponding to the small parameter of neoclassical transport theory and the small parameter of geometrical optics. A slab model with perpendicular stratification of the magnetic field is assumed, and a given rf (radio frequency) field is present with a frequency corresponding to a modest multiple of the ion cyclotron frequency. The rf induced ion flow perpendicular to the magnetic field is calculated. The parallel flow may be large, but it cannot be calculated without an analysis of the electron transport. (c) 2000 American Institute of Physics

[en] Plasma momentum transport within magnetic surfaces plays a fundamental role in a number of toroidal plasma physics issues, such as turbulence suppression, impurity transport, bootstrap current generation and the shielding of resonant magnetic error field perturbations. Stellarators provide opportunities for improved understanding of plasma flow effects because (a) new forms of quasi-symmetry (e.g. helical, poloidal) can be produced that differ significantly from the tokamak and (b) symmetry-breaking effects (always present to some degree) reduce the close coupling between parallel and cross-field transport characteristics of symmetric systems. External control coils can also be used to further enhance or suppress such effects. A method has been developed to evaluate the variation of neoclassical self-generated plasma flows in stellarators both within and across magnetic surfaces. This introduces a new dimension into both the optimization of stellarators and to the improved understanding of the existing confinement database. Application of this model to a range of configurations indicates that flow directionality and shearing rates are significantly influenced by the magnetic structure. In addition, it is demonstrated that flows in stellarators are sensitive to profile effects and the presence of external momentum sources, such as neutral beams

[en] An ion kinetic equation is solved by expansion in a parameter corresponding to the small parameter of neoclassical transport theory and the small parameter of geometrical optics. A slab model with perpendicular stratification of the magnetic field is assumed, and a given RF field is present with a frequency corresponding to a modest multiple of the ion cyclotron frequency. The RF induced ion flow perpendicular to the magnetic field is calculated. The parallel flow may be large, but it cannot be calculated without an analysis of the electron transport. (c) 1999 American Institute of Physics

[en] An important goal for a stellarator design is to incorporate enough flexibility to experimentally test a range of physics issues. The proposed Quasi-Poloidal Stellarator device achieves this by allowing independently variable currents in the modular, vertical field, and toroidal coil sets. Numerical optimizations and modeling show that this can allow significant tests of neoclassical cross-field transport rates, reduced poloidal flow damping (relative to the tokamak), and magnetic island width control. This flexibility is achieved in a unique, very low aspect ratio (R₀/< a> = 2.7) two-field period (racetrack-shaped) configuration that generates rotational transform from a combination of internal plasma currents and external shaping

[en] Energetic particle physics issues are of significant interest in stellarators and rippled tokamaks. The existence and stability of shear Alfven (SA) modes in stellarators have been examined computationally through a sequence of continuum, discrete eigenmode and (delta)f calculations. Although 3D couplings greatly increase the number of available SA modes, many of these are continuum damped. By identifying the more viable modes good contact has been made with experimental observations of TAE instabilities on LHD. Sound-wave or parallel compressibility couplings can modify the Alfven spectrum at low frequencies and have been incorporated into the STELLGAP code. Regions with coupled SA-sound continua are found in frequency ranges on the HSX experiment where coherent mode activity is observed. Finally, symmetry breaking effects are studied in ITER, taking into account TF ripple, ferritic inserts and tritium blanket modules. Finite β 3D equilibria are obtained, indicating that ripple is amplified within the plasma by the self-consistent currents over vacuum levels.