D. Eames

Fusion neutron production during deuterium neutral-beam injection into the PLT tokamak

Fusion neutron emission of 1.5 × 1014 neutrons s−1 and 2 × 1013 neutrons/pulse has been observed for PLT deuterium discharges with up to 2.5 MW of deuterium neutral-beam injection. The neutron time evolution and magnitude are consistent with theoretical calculations of the fusion reactions caused by energetic injected ions which are confined and slow down classically. The factor-of-two accuracy in the absolute neutron calibration is the major uncertainty in the comparison with theory. Neutron sawtooth oscillations ( 3%) are observed which can also be explained classically.

Soft x-ray measurements from the PDX tokamak

Temporally and spatially resolved profiles of the PDX soft x‐ray spectra have been measured during single tokamak pulses of circular divertor plasmas with a recently developed pulse‐height analyzer. This detection system incorporates an array of five vertically displaced sets of lithium‐drifted silicon detectors, each consisting of three independent channels optimized for rapid data collection in adjacent energy regions. Simultaneous measurements of x‐ray emission integrated along five chords of the plasma cross section can, thereby, be achieved. Abel inversion of these data yields temporally resolved radial profiles of the local electron temperature from the slope of the continuum, concentrations of high‐Z impurities from the characteristic line intensities, and a measure of Zeff from the continuum intensity. The techniques of x‐ray pulse‐height analysis, with illustrations featuring the results from the initial PDX circular plasma experiments, are discussed in detail. In addition, comparisons between ci...

The effect of current profile evolution on plasma-limiter interaction and the energy confinement time

Experiments conducted on the PLT tokamak have shown that both plasma-limiter interaction and the gross energy confinement time are functions of the gas influx during the discharge. By suitably controlling the gas influx, it is possible to contract the current channel, decrease impurity radiation from the core of the discharge, and increase the gross energy confinement time, whether the aperture limiters are of tungsten, stainless steel or carbon.

Conductivity and transport in neon deuterium discharges in the PLT tokamak

Introduction of large amounts of neon into Ohmically heated deuterium discharges in the PLT tokamakl results in higher central electron temperature (Te(0) 3 keV) and values of electron energy containment time that are larger than in regular discharges at the same electron density (τEe = 44 ms at e = 2 × 1019 m−3). For steady-state discharges with high effective Z (~ 5–8) the conductance is larger than that predicted by neoclassical theory by as much as a factor of two. Transport rates of hydrogen-like and helium-like ions can be fairly well approximated by assuming a diffusion constant of between 0.4 and 1 m2s−1. Within experimental uncertainties the diffusion of hydrogen-like neon is the same for co- and counter-directed high-power neutral beams.

ENERGY BALANCE OF THE PLT TOKAMAK

Abstract PLT discharges are categorized in terms of energy balance into three types: radiation dominated (RD); transport dominated (TD), and an intermediate type (TR). Control of plasma edge conditions is essential for the formation of these types. Measurements and calculations show the relative importance of radiation, transport, and electron-ion coupling in different regions of the discharge. Ion heating for neutral beam injection is found to be effective in all types. Electron heating by neutral beam injection is only consistently obtained for TD discharges.

X-Ray Radiation from Tokamaks

Tokamak discharges, which are studied for the magnetic confinement of fusion plasmas, emit soft x-ray radiation in the energy range from 1–20 keV. This radiation consists of a bremsatrahlung and recombination continuum, and characteristic line spectra of impurity ions from the plasma limiter and the walls of the vacuum vessel. The radiation represents a unique source of information and is increasingly used as a diagnostic of plasma parameters. This includes measurements of the electron and ion temperature, investigation of the ionization equilibrium and particle transport, and the study of MHD fluctuations and disruptions.

Successor oscillations of internal disruptive instabilities in the PLT tokamak

The experimentally observed persistence of the m = 1 mode following an internal disruption is described. The hot central region appears to spiral outward, being pared by interception with the radius of q = 1 (as deduced from the radial extend of the m = 1 mode). The outward motion of the axis can be arrested and the surviving helical filament can subsequently spiral inward, rather than being annihilated as expected from nonlinear resistive internal kink mode simulations.

Observations of several disruptions in PLT using soft and ultra-soft x-ray radiation

The evolution of ultra-soft x-ray radiation (USX, h..nu.. approx. > 100 eV) is compared to that of the soft x-ray radiation (SX, h..nu.. approx. > 1000 eV) during several disruptions in PLT. Spatial resolution is obtained in both cases by arrays of silicon surface barrier detectors viewing along different chords. During some disruptions the USX behaves quite differently from the SX, and a classification is made based on the USX behavior. Different interpretations of the data are discussed, along with the possibility that these measurements may distinguish between the roles of temperature and impurity density changes during disruptions.