Axisymmetric, High-β, Steady-State Plasma Torus: A "Wind-Tunnel" to Develop Whole Device Models
The development of experimentally-validated whole device models is a grand challenge of fusion energy science and a major goal of integrated simulation research. As explained in the 2009 Joint FES/ASCR Workshop Report [1], extreme-scale computing power will allow “improved versions” of large-scale simulations “to produce an experimentally validated integrated simulation capability for scenario modeling of the whole device.” Whole device models will integrate multi-scale physics (e.g. turbulence and transport, local and nonlocal coupling), magnetic geometry (e.g. anisotropy between parallel and perpendicular dynamics, interfaces between closed and open field lines), nonlinear and electromagnetic dynamics (e.g. instability-induced energy transfer, particle kinetics and resonances), and carefully designed validation experiments. This scientific challenge is unquestionably “grand.” Workshop participants called integrated predictive modeling both “urgent” and “one of the most difficult and least understood problems in fusion energy research” [1]. This white paper presents a cost-effective and near-term research step that makes progress towards this grand challenge by considering the simpler task of experimentally validated integrated simulation of a steady-state, high-β plasma torus confined by a simple axisymmetric current ring. Using our nation’s only toroidal confinement device with superconducting magnets, we can now make unparalleled measurements of fusion-relevant plasmas confined for several minutes and use these measurements for critical validation studies. We call this approach a “plasma wind tunnel”, because it is analogous to using low-cost instrumented objects in wind tunnels to validate CFD and turbulent hydrodynamics for various aerodynamical applications. In a manner of speaking, we want to follow in the footsteps of the Wright brothers. Just as the Wright brothers validated the means to predict lift and drag in their wind tunnel, we should build confidence in our whole-plasma capabilities by first demonstrating success with a fusion-relevant plasma torus that has the least complicated magnetic geometry and the least complicated particle kinetics. We believe the axisymmetric current ring is both the simplest magnetized plasma torus that can be used for whole-plasma modeling, and, also, the simplest plasma torus that incorporates features of any fusion device: multi-scale and boundary layer physics, nonlinear stability and turbulence phenomena, and important kinetic effects and particle resonances. Steady-state high-β plasmas have proven to be relatively easy to produce in the laboratory [2-7], and gyro-kinetic and gyro-fluid models have been successfully applied to this geometry, yielding important insights into the fundamental nonlinear turbulent transport processes [8-12]. Like a tokamak, the plasma torus confined by a current ring is sustained by sources of heat, particles, and toroidal momentum and involves turbulent transport across boundary layers, upgradient turbulent pinches [13,14], nonlinear fast particle dynamics [15], filamentary “blobs” [16], and turbulent cascades [17]. Unlike a tokamak, turbulent transport does not always lead to plasma loss. Instead turbulence causes self-organization, centrally-peaked profiles, and either an inward particle or an inward thermal pinch [11, 12] as the plasma approaches a state of minimum entropy production [18].
Operation of the Levitated Dipole Experiment Floating Coil
The Levitated Dipole Experiment (LDX) is an innovative facility to study plasma confinement in a dipole magnetic field, created by a superconducting solenoid (floating coil), which is magnetically levitated in the center of a 5 m diameter by 3 m tall vacuum chamber. This persistent mode, floating coil (F-coil) consists of a Nb3Sn magnet installed inside a high-pressure vessel filled with 12.5 MPa helium gas at room temperature. It is surrounded by a high heat capacity fiberglass-lead composite radiation shield and by a toroidal vacuum shell. The built-in tube heat exchanger serves to cool the magnet, the helium vessel, and the thermal shield. When positioned at the lower part of the vacuum chamber the F-coil is cooled by retractable cryogenic transfer lines to about 4.5 K and it is charged inductively by the charging coil installed outside of the vacuum chamber. Then the helium flow is interrupted, the heat exchanger is pumped out, retractable lines are disengaged from F-coil ports, the ports are plugged, and the F-coil is lifted to the middle of the chamber to initiate and study plasmas. After several hours and just before the F-coil warms up to about 10 K it is lowered down for the next re-cooling or for discharging. This paper describes the F-coil cooling system and inductive charging system operation and performance
The unfolded universe of elementary particles. A geometric explanation of the standard model structure
We propose a geometric explanation of the standard model of Glashow, Weinberg and Salam for the known elementary particles. Our model is a generic Quantum Field Theory in dimension four, obtained by developing along a Lorentz sub-manifold the lagrangian of Einstein and Dirac in dimension twelve. The main mechanism which gives birth to the standard model is a certain gauge fixing of triality, which permits to identify the multiplicity of fermions, as seen from the four dimensional world, with the eight unseen dimensions of the generating universe. In this way we get the known tables of particles, explaining the series of fermions and the gauge bosons. We suggest that the Higgs field dynamics could appear through a bosonization of the right handed neutrino and correspond to a displacement in the unseen dimensions. We also propose hypotheses for dark matter, and perhaps dark energy. Then we suggest predictions to go beyond the standard model.