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Title: Determination of the plasma effective charge from the soft X-ray spectrum and plasma conductivity at the L-2M stellarator after boronization of the vacuum chamber

Abstract

Boronization of the vacuum chamber wall results in a considerable change in the composition of the plasma generated in working pulses of the L-2M stellarator and, accordingly, in the plasma effective charge. The paper presents results of measurements of the plasma effective charge carried out by two methods in the ohmic heating mode: from the data on the plasma conductivity and from the soft X-ray spectrum of plasma emission. Comparison of the values of the plasma effective charge obtained by these two methods makes it possible to determine the conditions in which the two values are in good agreement. Under these conditions, the plasma effective charge can be correctly estimated from spectral measurements.

Authors:
;  [1]
  1. Russian Academy of Sciences, Prokhorov General Physics Institute (Russian Federation)
Publication Date:
OSTI Identifier:
22614101
Resource Type:
Journal Article
Resource Relation:
Journal Name: Plasma Physics Reports; Journal Volume: 42; Journal Issue: 7; Other Information: Copyright (c) 2016 Pleiades Publishing, Ltd.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; EFFECTIVE CHARGE; JOULE HEATING; PLASMA; PULSES; SOFT X RADIATION; STELLARATORS; VACUUM SYSTEMS; WALLS; X-RAY SPECTRA

Citation Formats

Meshcheryakov, A. I., E-mail: meshch@fpl.gpi.ru, and Vafin, I. Yu., E-mail: ildar@fpl.gpi.ru. Determination of the plasma effective charge from the soft X-ray spectrum and plasma conductivity at the L-2M stellarator after boronization of the vacuum chamber. United States: N. p., 2016. Web. doi:10.1134/S1063780X16070084.
Meshcheryakov, A. I., E-mail: meshch@fpl.gpi.ru, & Vafin, I. Yu., E-mail: ildar@fpl.gpi.ru. Determination of the plasma effective charge from the soft X-ray spectrum and plasma conductivity at the L-2M stellarator after boronization of the vacuum chamber. United States. doi:10.1134/S1063780X16070084.
Meshcheryakov, A. I., E-mail: meshch@fpl.gpi.ru, and Vafin, I. Yu., E-mail: ildar@fpl.gpi.ru. Fri . "Determination of the plasma effective charge from the soft X-ray spectrum and plasma conductivity at the L-2M stellarator after boronization of the vacuum chamber". United States. doi:10.1134/S1063780X16070084.
@article{osti_22614101,
title = {Determination of the plasma effective charge from the soft X-ray spectrum and plasma conductivity at the L-2M stellarator after boronization of the vacuum chamber},
author = {Meshcheryakov, A. I., E-mail: meshch@fpl.gpi.ru and Vafin, I. Yu., E-mail: ildar@fpl.gpi.ru},
abstractNote = {Boronization of the vacuum chamber wall results in a considerable change in the composition of the plasma generated in working pulses of the L-2M stellarator and, accordingly, in the plasma effective charge. The paper presents results of measurements of the plasma effective charge carried out by two methods in the ohmic heating mode: from the data on the plasma conductivity and from the soft X-ray spectrum of plasma emission. Comparison of the values of the plasma effective charge obtained by these two methods makes it possible to determine the conditions in which the two values are in good agreement. Under these conditions, the plasma effective charge can be correctly estimated from spectral measurements.},
doi = {10.1134/S1063780X16070084},
journal = {Plasma Physics Reports},
number = 7,
volume = 42,
place = {United States},
year = {Fri Jul 15 00:00:00 EDT 2016},
month = {Fri Jul 15 00:00:00 EDT 2016}
}
  • After boronization of the vacuum chamber of the L-2M stellarator, radiative losses from ohmically and ECR heated plasmas were reduced by a factor of 3-4. Under these conditions, radiative losses in the ECRH regime comprise only 10-15% of the input microwave power. Some effects have been detected that were not observed previously: a substantial increase in the gradient of the electron temperature near the separatrix, a preferentially outward-directed radial turbulent particle flux (both throughout the discharge phase and from shot to shot), and a longer (by a factor of 2-3) duration of the plasma cooling phase.
  • Results are presented from experimental studies of variations in the plasma parameters during the excitation of a multiaxis magnetic configuration by the induction current (up to 17 kA) in the basic magnetic configuration of the L-2M stellarator in the regime of ECR heating at a microwave power of {approx}200 kW ({approx}1 MW m{sup -3}) and an average plasma density of (1-2) x 10{sup 19} m{sup -3}. The current direction was chosen to reduce the net rotational transform (the so-called 'negative' current). The current was high enough for the rotational transform to change its sign inside the plasma column. Computer simulationsmore » of the L-2M magnetic structure showed that the surface with a zero rotational transform is topologically unstable and gives rise to magnetic islands, i.e., to a multiaxis magnetic configuration. Magnetic measurements showed that, at negative currents above 10 kA, intense bursts of MHD oscillations with a clearly defined toroidal mode number n = 0 were observed in the frequency range of several kilohertz. Unfortunately, the experimental data are insufficient to draw the final conclusion on the transverse structure of these oscillations. The radial temperature profiles along the stellarator major radius in the equatorial plane were studied. It is found that the electron temperature decreases by a factor of 1.3 in the plasma core (r/a {<=} 0.6) and that the temperature jump is retained near the boundary. A change in turbulent fluctuations of the plasma density during the excitation of a negative current was studied using wave scattering diagnostics. It is found that the probability density function of the increments of fluctuations in the plasma core differs from a Gaussian distribution. The measured distribution is heavy-tailed and broadens in the presence of the current. It is found that the spectrum of turbulent fluctuations and their Doppler shift near the plasma boundary are nonuniform in the radial direction. This may be attributed to the shear of the poloidal velocity. The experimental results indicate that the formation of regions with a zero rotational transform in the plasma core somewhat intensifies plasma transport.« less
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  • The L 23 emission spectrum obtained from liquld aluminium shows some resemblance to that of the solid but with the peak characteristic of the zone overlaps rather less pronounced. It is suggested that this result supports a model of local crystalline order in the liquid, with the valence electrons occupying an energy band having some resemblance to that of the solid. (auth)
  • The propagation and damping of waves excited by a poloidal antenna in a hydrogen plasma at the ion cyclotron resonance (ICR) frequency were investigated. The longitudinal wavenumber and damping length of waves excited in the ohmically heated plasma of the L-2M stellarator, the dependence of the damping length of fast magnetosonic waves on the magnetic field strength, and the dependence of the antenna load resistance on the plasma density were measured. It is the first time that such complex measurements were performed in experiments on ICR heating of a hydrogen plasma at the fundamental harmonic of the ion gyrofrequency inmore » toroidal magnetic confinement systems.« less