Cometary x-rays: Line emission cross sections for multiply charged solar wind ion charge exchange

Absolute line emission cross sections are presented for 1 keV amu -1 charge-exchange collisions of multiply charged solar wind ions with H2O. These cross sections can be used to model charge-exchange processes with cometary targets with similar binding energies such as H, O, CO2 and CO. A parameter-free model is used to successfully predict the recently observed x-ray spectra of comet Linear C/1999 S4 and McNaught-Hartley C/1999 T1. We show that the resulting spectrum is extremely sensitive to the time variations of the solar wind composition.Fil: Otranto, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Universidad Nacional del Sur. Departamento de Física; Argentina. University of Missouri; Estados UnidosFil: Olson, R.E.. University of Missouri; Estados UnidosFil: Beiersdorfer, P.. Lawrence Livermore National Laboratory; Estados Unidos. University of California at Berkeley; Estados Unido

Dielectronic recombination measurements of highly-charged heliumlike and neonlike ions using an electron beam ion trap

The electron beam ion trap (EBIT) at LLNL is a unique device designed to measure the interactions of electrons with highly-charged ions. We describe three methods used at EBIT to directly measure the dielectronic recombination (DR) process: the intensity of the stabilizing x-rays is measured as a function of electron beam energy; the ions remaining in a particular ionization state are counted after the electron beam has been held at a fixed electron energy for a fixed time; and high-resolution spectroscopy is used to resolve individual DR satellite lines. In our discussions, we concentrate on the KLL resonances of the heliumlike target ions (V{sup 21+} to Ba{sup 54+}), and the LMM resonances of the neonlike target ions (Xe{sup 44+} to Th{sup 80+}). 12 refs., 8 figs

Overview of NSTX Upgrade Initial Results and Modelling Highlights

The National Spherical Torus Experiment (NSTX) has undergone a major upgrade, and the NSTX Upgrade (NSTX-U) Project was completed in the summer of 2015. NSTX-U first plasma was subsequently achieved, diagnostic and control systems have been commissioned, H-Mode accessed, magnetic error fields identified and mitigated, and the first physics research campaign carried out. During 10 run weeks of operation, NSTX-U surpassed NSTX-record pulse-durations and toroidal fields, and high-performance ~1MA H-mode plasmas comparable to the best of NSTX have been sustained near and slightly above the n=1 no-wall stability limit and with H-mode confinement multiplier H98y2 above 1. Transport and turbulence studies in L-mode plasmas have identified the coexistence of at least two ion-gyro-scale turbulent micro-instabilities near the same radial location but propagating in opposite (i.e. ion and electron diamagnetic) directions. These modes have the characteristics of ion-temperature gradient and micro-tearing modes, respectively, and the role of these modes in contributing to thermal transport is under active investigation. The new second more tangential neutral beam injection was observed to significantly modify the stability of two types of Alfven Eigenmodes. Improvements in offline disruption forecasting were made in the areas of identification of rotating MHD modes and other macroscopic instabilities using the Disruption Event Characterization and Forecasting (DECAF) code. Lastly, the Materials Analysis and Particle Probe (MAPP) was utilized on NSTX-U for the first time and enabled assessments of the correlation between boronized wall conditions and plasma performance. These and other highlights from the first run campaign of NSTX-U are described.readme and data file