7 research outputs found
Optimization of a helicon plasma source for maximum density with minimal ion heating
Measurements of electron density and perpendicular ion temperatures in an argon helicon plasma are presented for five different antennas: A Nagoya type III antenna, a double-saddle antenna, a 19 cm long m = +1 helical antenna, a 30 cm long m = +1 helical antenna and a 19 cm m = +1 helical antenna with wide straps. Electromagnetic wave measurements in the range from 100 kHz to 50 MHz are also presented for a wide range of plasma parameters. The data show a clear transition between RF power coupling to the plasma to create density and coupling to heat ions. The transition from plasma production to ion heating indicates that the mechanism responsible for heating the ions is distinct from the mechanism responsible for ionizing the plasma in a helicon source. The primary objective of the experiments described here is to identify the operational conditions for a helicon source such that the intrinsic ion heating is minimized without sacrificing density production. Secondary objectives of this project include: identifying the optimal antenna configuration for density production and/or ion heating, investigating the mechanism responsible for ion heating through measurements of the fluctuating magnetic field at the edge of the source, and determining if downstream density measurements can be used as a quantitative measure of the electron density in the helicon source
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RAGE simulations of single-mode Richtmyer-Meshkov growth in a convergent geometry
The Richtmyer-Meshkov (RM) instability is initiated by a shock accelerating an interface between two materials. Small perturbations of the interface grow into bubble and spike structures causing mixing of the materials that lie on either side of the interface. Recent Los Alamos National Laboratory experiments have focused on RM initiated mix in a compressible, miscible, convergent geometry. Motivated by the lack of a generally accepted model for this physical regime, cylindrical implosion experiments of single-mode, nonlinear RM growth and saturation are undeway at the OMEGA laser facility. Initial targets consist of an m=28 perturbation with an initial amplitude of 2.5 microns machined onto an aluminum marker layer embedded 55 {micro}m from the target surface. Initial perturbations of varying amplitudes and wavelengths are being studied using the RAGE code
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Convergent, compressible Richtmyer-Meshkov experiment-zero order hydrodynamics
Cylindrical experiments were performed on the OMEGA laser at the University of Rochester to study unstable interfaces in single and double shells. For single shells a marker layer of more opaque and higher density material is placed between foam and an outside ablator. The marker is either smooth or with a well defined surface roughness. For double shells an inner cylinder is placed along the outer cylinder axis. The outer cylinder is irradiated directly with 50 laser beams which produces a strong shock (mach number 5-15) that passes through the unstable marker interf'ace creating a Richtmyer-Meshkov (RM) instability. For double shells this shock bounces off the inner cylinder back to the incoming marker layer causing it to decelerate. We present comparisons of the measured smooth marker layer hydrodynamics with computer simulations using both Lagrangian and Eulerian codes
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Ion dynamics in helicon sources.
Recent experiments have demonstrated that ion dominated phenomena, such as the lower hybrid resonance, can play an important role in helicon source operation. In this work, we review recent ion heating measurements and the role of the slow wave in heating ions at the edge of helicon. sources. We also discuss the relationship between parametrically driven waves and ion heating near the rf antenna in helicon sources. Recent measurements of parallel and rotational ion flows in helicon sources have important implications for particle confinement, instability growth, and helicon source operation. In this work we present new measurements of ion flows and summarize the important features of the flows