In improved confinement (in H-mode) in the Globus-M2 tokamak, the development of edge-localized modes (ELMs) is accompanied by the appearance of filament structures. The use of the Doppler backscattering (DBS) method allowed to determine filament parameters both during ELMs triggered by sawtooth crashes and during independent ELMs. It is shown that the number of filaments observed during synchronized ELMs is greater and their area of observation is wider. The velocity of the filaments during all types of ELMs observed on Globus-M2 ELM is higher than on the previous tokamak Globus-M. Filaments developing immediately before an ELM burst are characterized by smaller amplitudes and velocities. Comparing the results of two diagnostic techniques, DBS and poloidal correlation Doppler reflectometry, to determine the velocity of such filaments, shows a similarity of the measured values, which may indicate linear scattering off these filaments.

The paper presents the improved FCDI plasma equilibrium reconstruction algorithm implemented at the Globus-M2 tokamak. The algorithm has been improved to be able to operate in real time. The FCDI-FF (Fixed Filaments) operation mode was added, in which the plasma is modeled by current filaments at fixed positions. New user interface for the algorithm displays reconstructed plasma separatrix and contours of the internal magnetic surfaces, the poloidal flux distribution, and graphs of the reconstructed plasma parameters, including profiles of plasma pressure, poloidal current and safety factor q, plasma energy, poloidal beta and internal inductance, which can be exported in *.mat, *.json and G-eqdsk formats.

Cреди наблюдаемых на Глобус-М2 периферийных неустойчивостей выделяют краевые неустойчивости двух типов: синхронизированные и десинхронизированные с пилообразными колебаниями. Десинхронизированные срывы появляются в режимах, характеризующихся высокими значениями давления в пьедестале p ped > 3 кПа, и наблюдаются в разрядах с тороидальным магнитным полем B T > 0.6 Т и током по плазме I P > 0.3 МА. Десинхронизированные срывы краевой неустойчивости относятся к типу 3/5 с доминирующим влиянием пилинг-моды. Синхронизированные срывы наблюдались в более широком диапазоне параметров разряда, в том числе при B T < 0.6 Т и I P < 0.3 МА. Расчеты устойчивости пилинг-баллонной (ПБ) моды показали, что при ширине пьедестала ψ norm = = 0.09 и p ped > 3.5 кПа возможна дестабилизация ПБ-моды без дополнительного воздействия. Экспериментальные данные указывают на доминирующую роль микротиринговой неустойчивости в пьедестале. Микротиринговая мода не позволяет пьедесталу Глобуса-М2 достичь состояния неустойчивой кинетической баллонной моды, что объясняет низкую предиктивную силу модели EPED в токамаке Глобус-М2.

Исследован нагрев плазмы одним и двумя инжекторами быстрых нейтральных атомов в сферическом токамаке Глобус-М2 при тороидальном магнитном поле 0.8–0.9 Тл и токе плазмы 0.35–0.4 МА. Измерение пространственных распределений температуры и концентрации электронов, выполненные диагностикой томсоновского рассеяния лазерного излучения, показало двукратный нагрев электронов плазмы при инжекции нейтральных частиц с энергией до 45 кэВ при мощности пучка 0.75 МВт по сравнению с омическим режимом. Дополнительное включение второго пучка с энергией частиц до 30 кэВ и мощностью до 0.5 МВт позволило получить режим с горячими ионами в диапазоне значений средней плотности плазмы 1.6–10 × 10 19 м –3 . По данным активной спектроскопии и корпускулярной диагностики температура ионов достигла величины 4 кэВ при плотности плазмы 8 × 10 19 м –3 в горячей зоне, превысив температуру электронов более чем в 2.5 раза.

This work describes the real-time application of the Thomson scattering diagnostics. The upgraded data acquisition system of the Globus-M2 spherical tokamak provides real-time data processing with the delay <2.4 ms for 128 scattering signals from 11 spatial points. The achieved processing performance meets the requirements for Thomson scattering diagnostics of modern thermonuclear facilities and ITER in particular. The paper demonstrates the possibility of plasma electron density control, using Thomson scattering data in the feedback loop.

Diagnostics of the plasma electron component by the method of Thomson scattering (TS) of laser radiation makes it possible to reliably measure the spatial distributions of the electron temperature and density. One of the obstacles to the implementation of TS diagnostics in thermonuclear reactors is the distortion of the spectral characteristics of the optical system due to radiation-induced absorption and contamination of optical elements with erosion products of the first wall. As a consequence, the reliability of measurements by the TS method will decrease over time. The paper describes the method of multi-laser Thomson scattering, which will solve this problem. The results of the first experiments on the Globus-M2 tokamak are also presented.

The paper presents the first ion temperature profile measurements results in the new spherical tokamak Globus-M2, which were obtained in discharges with neutral beam injection using the Charge eXchange Recombination Spectroscopy (CXRS) and the Neutral Particle Analyzer (NPA). Ion heat transport modeling using ASTRA code was carried out based on the obtained experimental ion temperature. The results of the modelling indicate the predominantly neoclassical ion heat transport.

This paper presents the measurement results of the radiated power Prad and the effective ion charge Zeff in a toroidal magnetic field of up to 0.7 T and a plasma current of up to 300 kA for a wide range of electron density, which were first obtained on the Globus-M2 tokamak. An analysis of the results demonstrated that the content of radiation losses relative to the input power decreased in the Globus-M2 tokamak compared to the Globus-M tokamak, and the measured profiles of Prad had a strong dip in the central region. In addition, a decrease of the effective ion charge Zeff with increasing electron density was observed.

Массив из десяти встроенных диверторных зондов был установлен на нижний купол сферического токамака Глобус-М. С его помощью проведены измерения профилей плавающего потенциала, электронной температуры, ионного тока насыщения и плотности потока тепла на дивертор. Продемонстрировано резкое изменение плавающих потенциалов зондов, находящихся вблизи внешней ветви сепаратрисы, при развитии периферийной неустойчивости. Ключевые слова: токамак, дивертор, пристеночная плазма, ленгмюровские зонды.

In Globus-M2 ohmic discharges with low density, by means of Mirnov coils array, magnetic field oscillations with frequencies in 1 MHz range were detected. Frequency range of these oscillations significantly exceed the range of TAE and RSAE frequencies, which were previously observed on Globus-M and Globus-M2 tokamaks, and their amplitude, contrary, turned out to be up to an order of magnitude lower. It was found that high frequency oscillations are interrelated with suprathermal electron fraction. At the same time the observed instability seems to have Alfvenic nature, since its frequency correlates well with Alfven frequency scaling. It was also found that magnetic perturbation always forms standing wave with predominantly low toroidal wavenumbers, including n = 0 structure, which makes gap (e.g. TAE) mode excitation impossible. Frequency chirping during single bursts with δω ~ √t is consistent with hole-clump model predictions.

Представлены результаты исследования переноса тепла и частиц в сферическом токамаке Глобус-М2 в разрядах с нейтральной инжекцией на стадии роста тока. Пучок атомов инжектировался в плазму токамака при фиксированном тороидальном магнитном поле 0.7 T. Значение тока плазмы на плато варьировалось в диапазоне 0.2-0.3 MA. На основании пространственных распределений температуры и концентрации электронов, измеренных методом томсоновского рассеяния, было проведено моделирование переноса тепла и частиц в плазме с помощью кода ASTRA. Определено время удержания тепловой энергии плазмы, а также выполнены оценки коэффициентов температуропроводности и диффузии. Ключевые слова: термоядерный синтез, транспортный анализ, нагрев плазмы с помощью нейтральной инжекции, внутренние транспортные барьеры.

New information on the development of Alfvén modes in the Globus-M2 spherical tokamak is presented. The data were obtained using a V-band Doppler reflectometer with probing radiation frequencies from 50 to 75 GHz. A microwave harmonic synthesizer was used as a multifrequency probing source. As a result of using a new reflectometer, the localization of the toroidal Alfvén eigenmode has been determined at a magnetic field of 0.5 T. The spectral components of the Alfvén mode with Doppler frequency shifts due to toroidal plasma rotation have been recorded. The so-called Alfvén cascades have been investigated in the central regions of the discharge.

With an increase of magnetic field up to 0.8 T and plasma current to 400 kA, fast ion losses rate in the discharges with toroidal Alfven eigenmodes decreased in tokamak Globus-M2 comparing with Globus-M tokamak discharges. Taking into account the data on the discharges with increased magnetic field and plasma current, the regression fit of neutral particle analyzer flux drop in energy channel close to neutral beam energy on relative eigenmode magnitude, the value of magnetic field and plasma current was analyzed. The power of flux drop dependence on TAE magnitude was found to be ~0.5 and inverse proportional on the value of product of magnetic field and plasma current, which is highly likely is determined only by plasma current due to weak dependence on magnetic field. The result obtained indicates that fast ion losses in Globus-M2, stimulated by toroidal Alfven eigenmodes are mostly determined by the shift of passing orbits to the plasma edge. With the increase of plasma current and magnetic field, neutron flux drops arising in the moments of toroidal mode bursts have also decreased.

On the spherical tokamak Globus-M2 in discharges with toroidal magnetic field B= 0.7 T by means of magnetic probes and a number of other diagnostics during neutral beam injection at the current ramp up stage, magnetic field oscillations in the range of 100-300 kHz having their frequency increasing in time, had been observed. Eigenmodes with wavenumbers $n = 1-3$ (toroidal number) and $m = 2-4$ (poloidal number) were being registered. These oscillations were identified as Alfven cascades. By means of multi-channel fluctuation reflectometer, observed eigenmodes were found to be localized near magnetic shear reversal radius. Application of MHD-spectroscopy technique allowed us to determine safety factor $q_{min}$ temporal evolution and experimental values are in well agreement with modelling results, provided by ASTRA transport code.

The results of the study of toroidal Alfven modes (TAE) using the multi-frequency Doppler backscattering (DBS) in the Globus-M tokamak are presented. The article is focused on the presentation of the Alfven mode registration method for multichannel probing. The possible causes of the observed oscillations of the poloidal plasma rotation velocity at the Alfvén oscillation frequencies are discussed in detail. The data on the spatial distribution of Alfvén modes revealed by multi-frequency DBS are given. The recommendations for the further development of the DBS with the aim of a more detailed study of TAE in tokamaks were determined.