E. Hinnov

MEASUREMENT OF ABSOLUTE RADIATION INTENSITIES IN THE VACUUM-ULTRAVIOLET REGION

A method for calibrating vacuum-ultraviolet monochromators for measurement of absolute radiation intensities is described. It is based on calculating the brightness of an optically thin spectral line in the far ultraviolet from the brightness of a visible line originating from the same upper level. A grazing incidence monochromator and a Seya–Namioka monochromator were calibrated at a number of wavelengths between 1640 and 231 A, using line pairs of hydrogen and ionized helium. Light sources used to obtain these lines are described. Problems of measurement and sources of error, particularly in the case of hydrogenlike spectra, are discussed.

The ontogeny of a Tokamak discharge

A detailed description of the time behaviour of a hydrogen discharge in the ST-Tokamak is based on measured radial electron temperature and density profiles at 12 different times, together with measurements of the Ohmic-heating current and voltage, the temporal, spatial, and spectral distributions of hydrogen light, the ion temperatures, and impurity concentrations. Early in the discharge the electron temperature profiles show evidence of a skin effect that develops on a time-scale of several milliseconds into a peaked profile of about 2.2 keV maximum. Thereafter the peak temperature stops growing and develops into a flat plateau, the width of which appears to be determined by the Kruskal-Shafranov limit. The average particle confinement time scales with , and reaches a maximum of 13-14 ms. The power balance is dominated by electron loss and re-cycling, rather than ion loss or radiation. The recycling process at the aperture limiter appears to involve sufficiently energetic neutral atoms to provide a fairly flat radial source function for particles, and hence to influence directly the development of the radial distribution of power input and energy balance.

Plasma Diagnostics with Ionized Barium and Tunable Dye Lasers

Resonance fluorescence and optical pumping techniques using tunable dye lasers permit the measurement of density, ion temperature, electron temperature, and ion drifts, over a wide range of density in barium, or barium doped plasmas.

Spectroscopic measurements of ion temperature in ATC tokamak with RF and neutral-beam heating

Measurements of ion temperatures in the ATC tokamak by means of Doppler broadening of various ion lines are described, and typical results presented for the various auxiliary heating experiments: compression, neutral beam, lower hybrid and ion cyclotron frequency heating. Radial resolution of the temperature measurements is achieved by utilizing spectrum lines of ions of different ionization potentials: O VII λ 1623 A, C V λ 2271 A and C IV λ 1548 A, which are emitted from regions of different electron temperature. Measurement at a given radial location is performed as a function of time by repeated scanning of the line contour in times 1.5–3.0 ms. The results indicate variations of heating efficiency with location and with power input level.

Excitation and Ionization Rates of Neon Ions in a Stellarator Discharge

The intensities of various resonance multiplets of neon ions, from Ne ii to Ne viii, emitted by an ohmically heated hydrogen discharge of the C stellarator, with about 3% neon added, were measured with a calibrated grazing-incidence monochromator. The electron densities (Ne∼1013 cm−3) were determined by means of 4-mm microwave interferometers, and the electron temperature (Te∼10–50 eV from the electrical conductivity of the plasma. The neon-ion concentrations at the different states of ionization were calculated from the light intensities by means of an assumed energy dependence for the excitation cross sections, the magnitude of the cross sections being adjusted to make the sum of the calculated ion concentrations agree with the known total neon concentration. Atomic oscillator strengths deduced from the excitation-rate coefficients thus obtained, were found to be in reasonable agreement with various calculations. Ionization-rate coefficients were deduced from the time behavior of the ion concentrations and the known particle-confinement time in the discharge. As compared with expected values, the measured rate coefficients appear to be increasingly too large with successive states of ionization. The most likely reason for the discrepancies is a possible deviation from Maxwellian electron-energy distribution in the discharge, to which these rate coefficients would be particularly sensitive.

The 3s2 1S0-3s3p 3P1 magnesium sequence intercombination lines from ScX to MoXXXI observed in the PLT tokamak

Abstract Wavelengths of the 3s 2 1 S 0 -3s3p 3 P 1 transitions of the ScX, NiXVII, CuXVIII, GeXXI, SeXXIII, ZrXXIX and MoXXXI ions have been measured in the PLT tokamak discharges, with the appropriate elements introduced by laser blow-off injection.

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.

Description of tokamak discharges in present and future devices at Princeton PPL

Abstract The evolution in time and space of plasma temperatures and densities in typical discharges of presently operating tokamak is reviewed. The characteristics of the concomitant bombardment of vacuum walls and aperture limiters by electrons ions, neutral atoms, and photons are described together with the behavior impurities of wall and adsorbed materials in the discharge. The influence of the impurities on the plasma properties is discussed, with special consideration for cumulative effects. The discussion is extended to the extrapolated behavior of the discharges in the next generation of tokamaks at PPL.

Plasma-materials interactions during RF experiments in tokamaks

Plasma-materials interactions studied in recent ICRF heating and lower hybrid current drive experiments are reviewed. The microscopic processes responsible for impurity generation are discussed. In ICRF experiments, improvements in machine operation and in antenna and feedthrough design have allowed efficient plasma heating at RF powers up to 3 MW. No significant loss of energy from the plasma core due to impurity radiation occurs. Lower hybrid current drive results in the generation and maintenance of hundreds of kiloamperes of plasma current carried by suprathermal electrons. The loss of these electrons and their role in impurity generation are assessed. Methods to avoid this problem are evaluated.

Radiation losses in PLT during neutral-beam and ICRF heating experiments

Radiation and charge-exchange losses in the PLT tokamak are compared for discharges with Ohmic heating only (OH), and with additional heating by neutral beams (NB) or RF in the ion cyclotron frequency range (ICRF). Spectroscopic, bolometric and soft-X-ray diagnostics were used. The effects of discharge cleaning, vacuum wall gettering, and rate of gas inlet on radiation losses from OH plasmas and the correlation between radiation from plasma core and edge temperatures are discussed. – For discharges with neutral-beam injection the radiation dependence on type of injection (e.g. co-injection versus counter- and co- plus counter-injection) was investigated. Radial profiles of radiation loss were compared with profiles of power deposition. Although total radiation was in the range of 30–60% of total input power into relatively clean plasma, nevertheless only 10–20% of the total central input power to ions and electrons was radiated from the plasma core. The radiated power was increased mainly by increased influx of impurities, however, a fraction of this radiation was due to the change in charge-state distribution associated with charge-exchange recombination. – During ICRF heating radiation losses were higher than or comparable to those experienced during co- plus counter-injection at similar power levels. At these low power levels of ICRF heating the total radiated power was ~ 80% of auxiliary-heating power. Radiation losses changed somewhat less rapidly than linearly with ICRF power input up to the maximum available at the time of these measurements (0.65 MW).