Magnetic islands are frequently observed in high-performance tokamak plasmas. These islands limit the achieved plasma performance and are of concern for next-generation burning plasma experiments. Modern gyrotron sources have been used to stabilize these islands using Electron Cyclotron Current Drive (ECCD). The ITER device is currently planning on using this technique to stabilize the magnetic islands; however, uncertainties exist regarding the amount of power needed for island stabilization. Computational modeling of ECCD-stabilization of islands would allow better extrapolation of current experiments to ITER, but quantitative prediction requires accurate modeling of the current drive and of island dynamics. The Simulation of Wave Interactions with MHD (SWIM) SciDAC project is a collaboration of different groups to enable this modeling. In this talk, we present the development of the mathematical formalism for simulating RF-stabilized tearing modes, and initial simulations of feedback stabilization.
The Colorado FRC is a local experiment designed to study turbulence, flow, and stability in a field-reversed configuration (FRC). The FRC is a self-organized, high-beta plasma that provides a unique laboratory for basic plasma physics as well as fusion energy research. In this introduction to our ongoing research here in CIPS, I will provide a brief overview of the physics of compact toroids, describe the Colorado FRC machine and diagnostics, discuss current and planned experiments, and present recent results.
I'll talk about some recent progress in the simulations and observational studies of magnetic reconnection. With full kinetic particle-in-cell simulations, the work is to address two issues: how does fast reconnection initially grow, and what decides the evolution of the reconnection rate. The fast reconnection onset is discovered to be an nonlinear electron self-reinforcing process. Accelerated by the reconnection electric field, the small portion of energetic electrons in the vicinity of the X point could enhance the reconnection rate. During the later stage, the reconnection rate was thought to be throttled by the elongation of the electron diffusion region (EDR). Yet a new satellite observation found that the EDR could be verfy long and the reconnection rate remains fast. Here we find the change of reconnection rate is not controlled by the length of the EDR, but rather by the availability of plasma inflows from upstream. These results may give us some new insights to the macro-micro coupling process of reconnection.
I will discuss RF ion traps used at NIST in quantum information experiments. In these traps linear crystals (or strings) of beryllium ion qubits (two-level quantum systems) are confined in segmented multi-zone electrode structures. The harmonic motion of the trapped ions is laser cooled to the quantum mechanical ground state. Strong Coulomb coupling between ions provides the basis for quantum gates mediated by phonon exchange. Quantum information processing with many qubits requires trapping and transport of many ions in structures with many trapping zones. I will describe current efforts at NIST toward achieving this goal thru the construction of microfabricated RF ion trap arrays.
We have compiled a cross section set for H+, H2+, H3+, H and H2 collisions with H2 that is consistent with collision theory and experiment and with our measured absolute Halpha emission, Halpha Doppler profiles, near-UV molecular H2 continuum emission, ion energy distributions at the cathode, transient currents, and transient Halpha emission. Our measurements used a very low current, uniform electric field drift tube so that hydrogen dissociation and plasma electric fields are negligible. At the higher electric field to gas density ratios (E/N = 10 kTd and mean H+ ion energies of ~ 300 eV), the principle source of Halpha and continuum excitation is collisions of H with H2. At our lowest E/N of 350 Td (mean H+ energy ~ 40 eV) electron excitation dominates, but excitation by H atoms is still observed. Brief references will be made to the initial application of these results to glow discharges, inertial electrostatic confinement devices, edge plasmas of fusion devices, auroral Halpha emission from the outer planets, and evaluation of experimental evidence for hydrinos.
The talk will be an overview of the interdisciplinary field of dust research staring with fundamentals of dusty plasma through the interaction of cosmic dust with the upper atmosphere, the dusty surface of the Moon and ending with the recent discovery of interstellar dust within the solar system. Dust particles immersed in plasmas will acquire charge and introduce a variety of new phenomena, including dust acoustic waves and the formation of crystal-like structures. The upper atmosphere is the place where incoming meteoritic dust particle ablate and re-condense back to nanometer size smoke particles. These particles provide the seed for the nucleation of water ice in the summertime polar mesosphere that is exhibited as visible noctilucent clouds or as a layer with large radar backscatter. On the Moon, there are several in-situ and remote sensing observations that indicate that dusty plasma processes are likely to be responsible for the mobilization and transport of lunar soil. These observations remain largely unresolved up today. In 1992 the dust detector on the Ulysses spacecraft identified interstellar dust passing through the solar system. A new and exciting opportunity is now open to directly sample these fundamental building blocks of the Universe.
In an effort to increase the luminosity of Brookhaven National Lab's Relativistic Heavy Ion Collider (RHIC), a novel electron cooling system has been proposed. Although the ions and electrons are highly relativisticin the lab frame, their motion is non-relativistic in the beam frame. The dynamics shares similarities with the classical n-body problem of astrophysics. In arbitrary external fields, the dynamical friction force on ions (and, hence, the cooling rate) is difficult to estimate. We present numerical algorithms that simulate the friction force from first principles. This is a challenging regime for electron cooling due to the high energy of the ions,and the design of the cooling section has changed several times over the past few years. We will discuss design trade-offs, and numerical simulations of each design.
The spontaneous formation of electric current sheets in a magnetic-field dominated, electrically highly conducting plasma is a physically attractive process to explain the heating of the solar corona. Current sheets can reach such thinness via nonlinear ideal MHD as to dissipate with the resistive reconnection of magnetic fields despite a high but finite conductivity. Thus highly conducting plasmas are necessarily also resistively heated under astrophysical circumstances. X-ray astronomy has revealed that most solar-type stars have million-degree hot coronae. The hot corona is therefore a universal astrophysical phenomenon. The theory of this process due to E. N. Parker will be illustrated with a recent direct theoretical demonstration of current-sheet formation. The mathematics of the demonstration is remarkably simple but its physical implications seem far reaching.
The MASS (Mesospheric Aerosol Sampling Spectrometer) rocket campaign was conducted from the Andoya Rocket Range the first week of August 2007 coincident with the German-Norwegian ECOMA rocket campaign. The two MASS rockets carried electrostatic mass analyzers for the charged fraction of the aerosol particles in noctilucent clouds (NLC). The mass analyzer was mounted on the tip of the payload and pointed in the ram direction. Aerosol particles with different ranges of charge-to-mass ratio were collected within the instrument housing on two sets of four biased collector plates, with one set for positive particles and one set for negative particles. The first rocket was launched into NLC on 3 August approximately 26 minutes after an AIM (Aeronomy of Ice in the Mesosphere) satellite overpass. NLC were seen earlier in the day at 83 km by the ALOMAR RMR lidar pointed along the rocket trajectory. The data show the density of negative particles with radius greater than 3 nm rising sharply at 83 km and continuing to 89 km, collocated with PMSE (Polar Mesosphere Summer Echo) detected by the ALWIN radar. Particles with 1-2 nm radii with both signs of charge and positive particles with less than 1 nm radius were detected at 86-88 km. Initial charge-density estimates are several thousands per cubic centimeter for each of these size ranges.