Method for Measuring the Plasma Temperature at the GOL-NB Facility

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Abstract

A new method is proposed for measuring the electron plasma temperature at the GOL-NB facility.The method is based on measuring the ratio between the intensities of the spectral lines emitted by the fastatoms injected into the plasma. The beams of fast hydrogen atoms used for heating the plasma at the GOLNBfacility contain not only atoms with a full energy (E) but also atoms with fractional energies (E/2, E/3,E/18) that appear as a result of the dissociation of the H2+, H3+, and H2O+ molecular ions. The spectral linesof the beam components with these energies (and, in particular, the hydrogen Hα line) can be resolved dueto the Doppler shift caused by the difference between the atom speeds. For atoms with low energy, the excitationthat leads to the photon emission occurs only due to their collisions with thermal electrons, while foratoms with high energy, a sufficient deposition into their excitation is given by their collisions with the plasmaions. This is why the ratio between the intensities of the lines of different beam components depends on theplasma electron temperature, and thus, it can be used to measure this temperature. At the beam energy of24 keV, the proposed method can be used to measure the electron temperature in the range of up to 40 eV,which is of interest for the current experiments conducted at the GOL-NB facility. Note that measurementof the electron temperature higher than 20 eV requires that the ratio between the spectral line intensities bemeasured with an accuracy of the order of one percent, and that the attenuation of the neutral beam thatpasses through the plasma be measured with the same accuracy. The proposed method can be used at otherfusion facilities that use fast hydrogen atom injection to measure the temperature of the edge plasma.

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About the authors

S. V. Polosatkin

Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences; Novosibirsk State Technical University; Novosibirsk State University

Author for correspondence.
Email: s.v.polosatkin@inp.nsk.su
Russian Federation, Novosibirsk, 630090; Novosibirsk, 630073; Novosibirsk, 630090

G. S. Pavlova

Private Institution Project Сenter ITER

Email: G.Pavlova@iterrf.ru
Russian Federation, Moscow, 123098

References

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2. Fig. 1. GOL-NB setup: 1 – central section, 2 – strong field solenoids, 3 – fast hydrogen atom injectors, 4 – plasma gun, 5 – fast atom beam spectrum measurement point. Below – magnetic field distribution along the setup axis. Configurations with uniform and corrugated fields are shown.

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3. Fig. 2. Location of diagnostics on the GOL-NB installation: 1 – neutral beam, 2 – plasma, 3 – fast atom radiation observation line, 4 – beam profilometer, 5 – secondary emission sensor.

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4. Fig. 3. Emission ability on the Hα line for fast atoms in plasma with a concentration of 1012 cm–3 (a), 1013 cm–3 (b) and 1014 cm–3 (c): 1 – energy of 24 keV atoms, 2 – energy of 12 keV atoms, 3 – energy of 8 keV atoms, 4 – energy of 1.33 keV atoms.

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5. Fig. 4. The ratio of normalized intensities of Doppler-shifted Hα lines at a plasma density of 1013 cm–3 (a); the relative error in measuring the line intensities to determine the electron temperature with an accuracy of 10% at a plasma density of 1013 cm–3 (b); the absolute error in the plasma density value to determine the electron temperature with an accuracy of 10% at a plasma density of 1013 cm–3 (c): 1 – the ratio of the intensities of the lines of atoms with energies of 12 and 24 keV, 2 – the ratio of the intensities of the lines of atoms with energies of 8 and 24 keV, 3 – the ratio of the intensities of the lines of atoms with energies of 1.33 and 24 keV.

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6. Fig. 5. Required errors of the experimental parameters needed to measure the electron temperature at the GOL-NB facility with an accuracy of 10% (the experimental parameters are given in the text); relative error in measuring the normalized intensities of spectral lines (a), relative error in the attenuation coefficient of the beam of fast atoms in plasma (b), relative error in measuring the plasma radius (c), relative error in measuring the radius of the beam of fast atoms (d). The line designations coincide with the designations in Fig. 3.

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