The heavy ion beam probe (HIBP) diagnostics at the TUMAN-3M tokamak was updated to provide measurements in the regime with neutral beam injection co-directed with plasma current (co-NBI). By means of HIBP, plasma potential measurements in the center of plasma were carried out. Plasma potential evolution in the discharge with the LH transition (transition to the improved confinement mode) is in good agreement with the concept of negative radial electric field generation during formation of the transport barrier.

Heavy ion beam probe (HIBP) diagnostics on TUMAN-3M tokamak was updated to provide measurements in the regime with neutral beam injection co-directed with plasma current (co-NBI). By means of HIBP plasma potential measurements in the center of plasma were carried out. Plasma potential evolution in the discharge with L-H transition (transition to improved confinement mode) is in good agreement with the concept of negative radial electric field generation during the formation of transport barrier.

Paper reports a physical model of the beam transportation through the duct with realistic geometry. The beam losses are explained by interaction of the energetic particles of the beam with the duct walls resulting in strong influx of neutral gas, which interact with beam particles and cause their reionizaton. Using the model new design of the beam duct was developed. Ratio of the neutron fluxes values obtained under similar experimental conditions with the new transition duct and the old one fitted well with the model predictions.

The results of experiments on determining the polarization of two types of Alfvén oscillations observed with magnetic probes in the TUMAN-3M tokamak are presented. The difference in the polarization of short and long bursts of Alfvén oscillations, arising both in ohmic regime and during neutral beam injection, is found. The role of high-energy electrons in the excitation of Alfvén oscillations is discussed.

A study of the spectral properties of electromagnetic radiation in the ion-cyclotron range from the plasma of the TUMAN-3M tokamak in the NBI heating mode has been carried out. The spectrum of this radiation consists of several (up to four) narrow lines corresponding to different harmonics of the ion-cyclotron resonance frequency of injected fast ions in the center of the plasma. Wave vectors corresponding to individual spectral lines are determined from the signal delays between spatially separated probes. It is shown that under the assumption that all the measured frequencies and wave vectors follow the same dispersion relation, the observed radiation can be explained by the appearance in the plasma of an unstable fast magneto-acoustic wave propagating almost normally to the direction of the magnetic field.

The results of an analysis of the mechanisms of losses of a high-energy atomic beam in the connecting duct of the TUMAN-3M tokamak are presented. A numerical model is developed describing the effect of reduction of the duct transmission coefficient and allows reducing the power losses of the beam injection. Based on the model, a new duct with an increased cross section was constructed and installed on the tokamak. It was found that the replacement of the duct with the new one led to a 1.5- to 2-fold increase in the integral rate of the neutrons originated from dd-reactions of energetic deuterons with the target plasma.

In TUMAN-3M tokamak ohmic hydrogen and deuterium discharges oscillations with ion cyclotron (IC) frequency were detected. Fast magnetic probes poloidal array in TUMAN-3M is capable of detecting several harmonics of IC frequency of main plasma isotope. Fuel pellet injection significantly reduces IC oscillations intensity, though after complete pellet evaporation returns to initial level. IC oscillations localization and excitation conditions are of certain interest. Based on drift-cyclotron instability excitation theory and numerical modeling of scenarios with ohmic LH-transition and pellet-injection plasma parameters (density gradient primarily) effect on IC oscillations excitation was studied.

Geodesic acoustic mode (GAM) observations in TUMAN-3M tokamak show that in ohmic discharges with low plasma density GAM have intermittent character; transition to high confinement regime (LH-transition) is usually preceded by a short (up to 5 ms) GAM burst series with distinctive frequency drop, or there exists long (up to 30 ms) GAM burst series evolution with several characteristic timescales and varying amplitude. To determinate the effect of GAM temporal parameters on the possibility of LH-transition initiation numerical modeling of plasma density profile evolution under the effect of GAM burst sequence with varying frequency and amplitude was carried out.

In TUMAN-3M tokamak ohmic hydrogen and deuterium discharges oscillations with ion cyclotron (IC) frequency were detected. Fast magnetic probes poloidal array in TUMAN-3M is capable of detecting several harmonics of IC frequency of main plasma isotope. Fuel pellet injection significantly reduces IC oscillations intensity, though after complete pellet evaporation returns to initial level. IC oscillations localization and excitation conditions are of certain interest. Based on drift-cyclotron instability excitation theory and numerical modeling of scenarios with ohmic LH-transition and pellet-injection plasma parameters (density gradient primarily) effect on IC oscillations excitation was studied.

Radiation at the ion cyclotron resonance frequencies in both the ohmic mode and the injection heating mode—ion cyclotron emission (ICE)—is observed on the TUMAN-3M tokamak (minor radius a = 0.25 m, major radius R0 = 0.5 m, toroidal field BT = 1 T, plasma current Ip ≤ 180 kA, and average plasma electron density ne ≤ 5 × 1019 m–3). Usually, the ICE is associated with the presence of high-energy ions in the plasma. Such ions may be products of a thermonuclear reaction or arise as a result of additional plasma heating, e.g., by means of electromagnetic waves or by injection of beams of high-energy atoms (neutral beam injection, NBI). The properties of the ICE in the TUMAN-3M tokamak in the NBI-heating mode and their possible connection with the features of fast ion trajectories and their energy spectrum are considered.

Ion cyclotron emission (ICE) in routinely registered in many tokamaks. It was recently observed in the TUMAN-3M tokamak [1, 2] in ohmically and neutral beam injection (NBI)heated regimes in D and H plasma. This paper describes some characteristic features of NBIinduced ICE observed in TUMAN-3M, with emphasis on spectral structure of the emission. Experiments presented hereafter were performed on compact tokamak TUMAN-3M [3] (R0/a = 0.55 m / 0.25 m, totoidal field BT < 1.1 T, plasma current Ip < 180 kA, central line average density ne < 6×10 19 m -3 ) in NBI-heated scenario (60%-40% D-H mix, beam energy Eb<20keV, beam power Pb<400kW). Neutral beam was injected in toroidal coplasma current, countertoroidal field direction, with tangential radius Rb=0.42 m. Details of experimental set-up and diagnostic used may be found in [3]. Typical plasma parameters evolution in a shot with NBI heating and LH-transition is shown in Fig.1a. Characteristic example of ICE spectrum registered in a typical NBI shot in deuterium target plasma is shown in Fig. 1b. The ICE with frequency around 12.8 MHz appears ~2ms after NBI power was turned on, and disappears in ~5 ms, well before the end of the NBI pulse.

AbstractRadiation at the ion cyclotron resonance frequencies in both the ohmic mode and the injection heating mode—ion cyclotron emission (ICE)—is observed on the TUMAN-3M tokamak (minor radius a = 0.25 m, major radius R _0 = 0.5 m, toroidal field B _ T = 1 T, plasma current I _ p ≤ 180 kA, and average plasma electron density n _ e ≤ 5 × 10^19 m^–3). Usually, the ICE is associated with the presence of high-energy ions in the plasma. Such ions may be products of a thermonuclear reaction or arise as a result of additional plasma heating, e.g., by means of electromagnetic waves or by injection of beams of high-energy atoms (neutral beam injection, NBI). The properties of the ICE in the TUMAN-3M tokamak in the NBI-heating mode and their possible connection with the features of fast ion trajectories and their energy spectrum are considered.

The Alfvén oscillations have been studied in ohmically heated deuterium discharges with LH-transition in the TUMAN-3M tokamak in order to clarify their location in a plasma column. The Alfvén oscillation location was determined by comparison of the oscillation frequency measured with magnetic probes and that calculated from local density assuming the typical dispersion relation for Alfvén waves f = (2π)−1k||v A , where v A is the Alfvén velocity and k|| is the the parallel wave number in the direction of the magnetic field. It was found that they are localized in central part of plasma column inside r/a < 0.5 region. Candidate sets of mode numbers have been determined.

Spatial and temporal structure of Alfvén waves was studied with array of magnetic probes in compact tokamak TUMAN-3M. Poloidal mode numbers have been determined for Alfven instabilities bursts of the two types: short and long ones. Absence of poloidal rotation of magnetic field perturbations was found for both types of bursts. Also, in both cases, no pronounced asymmetry of magnetic field perturbation in the direction of the major radius was detected.

Properties of Alfvén waves (AWs) are studied which were excited in ohmic plasma of the TUMAN-3M tokamak. By means of matching the AWs frequency calculated from electron density profile with the experimentally measured one, it was found that the waves are localized in the region of r/a < 0.5. The effect of the impurity carbon ions on AWs frequency has been studied. It has been experimentally confirmed that, in the case of fully ionized carbon ions, when mass-to-charge ratios are equal for both the dominant and impurity ions, the AWs frequency does not depend on the impurity density, and is determined by the plasma electron density and the mass of dominant ions.

A new gas-inlet system in the gas-discharge chamber of an ion source has been developed that makes it possible to adjust the arc discharge burning mode and the parameters of the plasma ion emitter. The measurements of the main electrotechnical parameters of the ion source and signals of secondary-emission probes have been performed. Based on the obtained data, the profile of power distribution in a beam has been restored. The optimum form of the control signal for the gas inlet valve of the atom injector of the spherical Globus-M tokamak has been selected.

Разработка системы напуска газа в ионный источник инжектора атомов токамака Глобус-М и оптимизация с ее помощью параметров атомного пучка

We have experimentally studied the influence of toroidal magnetic field (B T) and plasma current (I p) on the capture and confinement of energetic ions (EIs) formed upon ionization of a neutral beam injected in a tokamak. Based on the results of measurements of the flux of 2.45-MeV fusion neutrons, it is concluded that the amount of EIs significantly grows with increasing B T from 0.7 to 1.0 T and Ip from 140 to 180 kA. In addition to the classical Coulomb slowing down, a supplementary channel of EI losses is found that accounts for a 15% decrease in their confinement time.

Horizontal displacement of plasma along the major radius has been found to significantly influence the fluxes of 2.45 MeV DD neutrons and high-energy charge-exchange atoms from neutral beam injection (NBI) heated plasma of the TUMAN-3M tokamak. An inward shift by ΔR = 1 cm causes 1.2-fold increase in the neutron flux and 1.9-fold increase in the charge-exchange atom flux. The observed increase in the neutron flux is attributed to joint action of several factors-in particular, improved high-energy ion capture and confinement and, probably, decreased impurity inflow from the walls, which leads to an increase in the density of target ions. A considerable increase in the flux of charge-exchange neutrals in inward-shifted plasma is due to the increased number of captured high-energy ions and, to some extent, the increased density of the neutral target. As a result of the increase in the content of high-energy ions, the central ion temperature T i (0) increased from 250 to 350 eV. The dependence of the neutron rate on major radius R 0 should be taken into account when designing compact tokamak-based neutron sources.