Longitudinal Electric Field in the Ohmic and Electron Cyclotron Resonance Regimes of Plasma Heating at the L-2M Stellara
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RAL EXPERIMENTAL TECHNIQUES
Longitudinal Electric Field in the Ohmic and Electron Cyclotron Resonance Regimes of Plasma Heating at the L-2M Stellarator1 A. I. Meshcheryakova, *, I. Yu. Vafina, and I. A. Grishinaa a Prokhorov
General Physics Institute, Russian Academy of Sciences, Moscow, 119991 Russia *e-mail: [email protected]
Received April 6, 2020; revised April 15, 2020; accepted April 16, 2020
Abstract—A method for determining the longitudinal electric field from the spectrum of soft X-ray radiation is used to measure the radial distribution of the longitudinal electric field. In the ohmic heating regime, statistically reliable spectra of soft X-ray radiation were measured at the L-2M stellarator. It was obtained that the longitudinal field is distributed approximately uniformly over the radius. Comparison of the measured soft X-ray radiation (SXR) spectra with the model bremsstrahlung spectrum of magnetized plasma in the longitudinal electric field has shown that at energies W > 3 keV, the measured spectrum deviates markedly not only from the Maxwellian one but also from the model spectrum of magnetized plasma in an electric field. Using SXR spectra that were measured in the regime of electron cyclotron resonance (ECR) plasma heating (without the ohmic-heating current), estimates are made of the longitudinal electric field that may occur in plasma due to drag currents, which are created during ECR heating. The dependence of the electric field on the plasma density was measured and it was shown that it agrees with the dependence of the difference current flowing through the plasma on the density. DOI: 10.1134/S002044122005019X
1. INTRODUCTION This paper describes experiments on determination of the longitudinal electric field and its radial distribution in plasma of the L-2M stellarator. The longitudinal electric field is an important characteristic of plasma. It is measured at any facility with magnetic confinement of plasma. The electric field strength must be known when solving some problems, e.g., when calculating the effective charge of plasma from its conductivity. It is also important to know the distribution of the longitudinal electric field over the minor radius of plasma [1]. However, at present, the longitudinal electric field is calculated from the measured loop voltage. It is assumed that the electric field is distributed uniformly over the minor radius of the torus, and for all magnetic surfaces, the tubes of current have the same length that is equal to 2πR (where R is the major radius of the torus). As will be shown below, these conditions are generally not met in toroidal magnetic traps. Therefore, the electric field strength obtained in this way is only an estimate that provides some average characteristic. This paper describes a method for measuring the radial distribution of the longitudinal electric field that 1 Materials
of the XVIII All-Russian Conference “Diagnostics of High-Temperature Plasma” (September 11–13, 2019, Krasnoe village, Krasnopakhorskoe settlement, Moscow, Russia).
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