Investigation of electron temperature profile details during plasma column displacement and ECRH power up to 1.5 MW in the T-10 tokamak

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Abstract

The question of the existence of internal transport barriers (ITBs) around low-rational number values of the stability factor q = 1, 2, … in the usual L-mode of tokamaks with central additional heating and positive magnetic shear remains open. To clarify the existence of such ITBs, experiments were carried out with a programmed linear time shift of the plasma column, in which the positions of the electron temperature measurements Te of the emission at the second electron cyclotron harmonic are shifted relative to the plasma column, which allows one to study the Te profile details. A series of experiments with perpendicular input of EC radiation with a power of 0.4 and 0.85 MW at a central ECRH and a fast (60 ms) shift of the column by 0.13a (minor plasma radius a) were carried out on the T-10 tokamak in plasma with a carbon limiter. In both cases, outside the q = 1 surface narrow (about 0.03a wide) and weak (a decrease in the coefficient of electron thermal conductivity χe by approximately two times) ITBs detected, which disappeared when the discharge parameters changed. These ITBs are 2–3 times narrower and an order of magnitude weaker than the ITBs near the surface q = 1, which was previously proposed to explain the RTP tokamak results. ITBs were not detected in the L-mode in experiments with simultaneous generation of a co-current and counter-current in the plasma center by two gyrotrons with a total power of 1.5 MW in a plasma with a tungsten limiter (column shift by 0.1a in 30 ms). This article appears to be the first journal publication on the study of Te profile details with rapid movement of the plasma column.

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S. V. Neudachin

National Research Centre “Kurchatov Institute”

Author for correspondence.
Email: sneudat@yandex.ru
Russian Federation, Moscow, 123098

A. A. Borschegovskii

National Research Centre “Kurchatov Institute”

Email: nrcki@nrcki.ru
Russian Federation, Moscow, 123098

I. S. Pimenov

National Research Centre “Kurchatov Institute”

Email: sneudat@yandex.ru
Russian Federation, Moscow, 123098

I. N. Roy

National Research Centre “Kurchatov Institute”

Email: nrcki@nrcki.ru
Russian Federation, Moscow, 123098

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Supplementary files

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2. Fig. 1. Schematic influence of the width of the U-shaped spatial instrumental function of the EC radiation receivers δECE on the “measured” gradient Te: conventional VTB (a), VTB when moving from a flat Te profile in the central part of the cord inside q = 1 to the gradient region (b).

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3. Fig. 2. Schematic change of Te during the transition from the slightly increasing flat part of the cord to the VTB zone in the plasma of the JT-60U tokamak with a reverse shear during the inward shift of the cord.

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4. Fig. 3. Evolution of raw uncalibrated 2nd harmonic EC signals in pulse 64488 at r = 14.6 cm and PECRH = 0.4 MW compared to pulse 64494 at r = 14.9 cm and PECRH = 0.85 MW. The intervals of the 4 cm outward shift are shown by arrows (a); the change in the plasma column center shift DR in pulses 64488 and 64494 (later shift) (b).

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5. Fig. 4. Evolution of raw uncalibrated signals with a resolution of 1 μs on two EC channels during a 4 cm outward shift at PECRH = 0.4 MW in pulse 64487 with Ip = 225 kA (a); evolution of the same but calibrated signals (averaging over 100 μs) in the same pulse along the radius (b). The upper curve is shifted upward to avoid overlapping.

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6. Fig. 5. Evolution of calibrated signals (averaging over 100 μs) on two EC channels during the shift at PECRH = 0.4 MW in pulse 64488 with Ip = 250 kA. VTB is not visible.

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7. Fig. 6. Evolution of the uncalibrated signal with a resolution of 1 μs on the EC channel with r = 17.5 cm during a 4 cm outward shift at PECRH = 0.85 MW in pulse 64493 with Ip = 285 kA.

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8. Fig. 7. Evolution of calibrated signals (averaging over 100 μs) on two EC channels in pulse 64493. The zone of increased gradient is visible at the beginning of the shift at r = 14.7 cm and at the end of it at r = 17.5 cm.

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9. Fig. 8. Evolution of calibrated signals (averaging over 100 μs) on two EC channels during a 4 cm outward shift at PECRH = 0.85 MW in pulse 64494 with Ip = 290 kA. VTB is not visible.

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10. Fig. 9. Changes in calibrated EC signals (averaging over 100 μs) at different radii during a 3 cm outward shift at PECRH = 1.5 MW in a 73 120 s pulse with Ip = 220 kA from the side of the weak magnetic field (a); the same from the side of the strong magnetic field (b).

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11. Fig. 10. Evolution of raw EC signals of the same channel in pulse 73 120 and in the same pulse 73 121 with a toroidal field 0.8% larger. The shift time is shown by the horizontal arrow.

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