A technique for debugging the software of a data acquisition and preliminary processing device with a network interface for a 2D position-sensitive thermal-neutron detector with delay-line readout is described. The original software transfers data through two ring buffers. Changes are proposed in the software code to check the possibility of ring-buffer overflow. It is shown that there is no data loss in the ring buffers at input-pulse frequencies up to 1 MHz. The corresponding dead time of recording is on the order of 1 μs.

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.

NBI-assisted plasma heating with one or two injectors of fast neutral atoms was studied at the Globus-M2 spherical tokamak at the toroidal magnetic fields of 0.8–0.9 T and plasma currents of 0.35–0.4 MA. Measurements of the spatial temperature and electron density distributions, performed using the Thomson scattering diagnostics, showed a twofold increase in heating of plasma electrons during the injection of neutral particles with energies of up to 45 keV at the beam power of 0.75 MW, as compared to the ohmic heating regime. Switching on the second additional beam with the particle energy of up to 30 keV and power of up to 0.5 MW resulted in obtaining the hot ion mode in the range of mean plasma densities of (1.6–10) × 10 19 m −3 . According to the data of active spectroscopy and neutral particle analyzer diagnostics, in the hot zone, the ion temperature reached 4 keV at the plasma density of 8 × 10 19 m −3 , which is more than 2.5 times higher than the electron temperature.

A prototype of a data acquisition and processing module with a network interface for two-dimensional multiwire proportional chamber detectors with delay-line readout is developed and tested. The device consists of a domestically produced printed circuit board with inputs including a neutron-beam chopper, a neutron-beam monitor and a spin flipper. The board contains a four-channel time-to-code converter, which digitizes the delays between pulses, and a single-board computer with a processor combined with a programmable logic integrated circuit. For this single-board computer, original software is developed that collects and transmits the raw data of the experiment in digital form (coordinates, neutron time-of-flight count, etc.) though the network to the client, and the user interface of the future detector. For data collection, the web server and web client used the firmware language, Verilog programmable logic integrated circuit, programming languages C and JavaScript, respectively. In the future, the tested scheme, implemented in a more compact form, will become an integral part of neutron detectors along with a multi-wire proportional chamber with two-coordinate delay lines and a five-channel analog-signal processing unit. Work with the module, and with the neutron detector in the future, is carried out through a local network in a web browser or an alternative client. The web client for a web browser enables the accumulation of statistics and the viewing of a 2D image from the detector during the experiment, it is also possible to navigate through 2D images of individual time channels for time-of-flight experiments and save all data in the common CSV text format, viewable in office spreadsheets.

As a part of ITER diagnostics design and development, ultrasonic and stick-slip piezoelectric motors and several types of piezoelectric ceramics were tested under severe neutron and gamma ray irradiation (-10(19) per cm(2) at E > 0.1 MeV) in a pool-type fission reactor. The fission neutron and gamma ray spectra were corrected to comply with conditions expected under ITER divertor cassettes. Taking into account possible neutron-induced amorphization of crystal structure, four types of piezoelectric ceramics were pre-selected. To restore the electronic structure of piezoelectric ceramic damaged by gamma rays, recovery polarization (i.e. heating while applying reverse bias) was suggested. The motors and piezoceramic samples were assessed for performance before and after irradiation as well as after recovery polarization. Recovery polarization was performed at 330 degrees C as it is expected close to the divertor cassettes during baking. Two most promising types of piezoelectric ceramics survived multiple cycles of depolarization/polarization at both 330 degrees C and 200 degrees C as appropriate for baking ITER divertor and vacuum vessel, respectively. All the experiments and procedures are described in detail.

The possibilities are considered of using the Thomson scattering diagnostics of core and edge plasmas in the tokamak with reactor technologies, which is under design. The problems are described that can be solved using the Thomson scattering diagnostics, including the possibility of controlling the plasma current profile. Technical requirements for the diagnostics are formulated. The possibilities are analyzed of its arrangement in the tokamak vacuum chamber. The accuracies are estimated of measuring the electron temperature and density of the plasma created in the tokamak. Particular attention is paid to ensuring the operability of the proposed diagnostics in the reactor regime of the tokamak operation.

Combined Thomson scattering (TS) and laser-induced fluorescence (LIF) diagnostics are being developed. The Thomson scattering and laser-induced fluorescence are laser diagnostics, with joint both probing and c-ollecting optical systems, which are the most complex and expensive parts of the diagnostic systems of large tokamaks, can be combined. Thomson scattering by free electrons is the use-proven diagnostic method for measuring profiles of important parameters of the plasma electron component (electron tempera-ture T e and electron density n e ), which requires a minimum of model assumptions. Almost all existing tokamaks are equipped with one or more TS systems, and by now, considerable experience has been accumulated in practical methods for implementation of these systems. The use of laser-induced fluorescence for measuring parameters of ion and neutral plasma components is less common, also because it requires knowledge of electron parameters to calculate populations of excited levels. The joint diagnostics of the Thomson scattering and laser-induced fluorescence in divertor plasma will be used to simultaneously measure the plasma parameters necessary for fundamental understanding physics of plasma detachment from divertor plates. These parameters are: the local parameters of plasma electrons ( T e , n e ), ion temperature ( T i ) measured from the data on emission of helium ions (HeII), as well as densities of helium atoms ( n a (He)) and hydrogen isotopes ( n a (H,D,T)). The measured parameters make it possible to calculate the following characteristics: (i) the ionization and recombination rates (using the data on T e , n e , T i , and n a (H, D, T)); (ii) the friction force of the plasma flow due to collisions with neutral particles (using the data on T i , n i (assuming n i = n e ), and n a (H, D, T)); and (iii) the pressure of the oncoming plasma flow (using the data on T e , n e , T i , and n i ). The article discusses advantages of combining laser diagnostics and ways of further development of the joint diagnostcs, based on the experience of creating similar diagnostics for domestic tokamaks and the similar diagnostics developed for ITER.

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.

A two-dimensional thermal-neutron detector developed for a small-angle diffractometer by the Petersburg Nuclear Physics Institute is described. The detector, with a sensitive area of 600 × 600 mm2, is based on a multiwire proportional chamber. A gas mixture containing 3He is the neutron converter. A new technology for manufacturing electrodes has been developed and used to increase both the gas purity and the lifetime of the detector without refilling its working volume under the experimental conditions. Data acquisition is carried out by the readout system based on the method of cathode-strip data readout to an LC delay line, which is located inside the detector. The detector is operable in a vacuum owing to its design.

Divertor Thomson scattering (DTS) and laser-induced fluorescence (LIF) are both laser aided diagnostics well suited to combination with common probing and collecting optics that are the most sophisticated and expensive part of any ITER optical diagnostic system. The combination of DTS and LIF are used for simultaneous measurement of local electron (Te, ne), ion (Ti, nHeII) and atom (nHeI, nH(D,T)) parameters and provide basic information on rates of electron and ion processes to allow basic understanding of the physics of divertor plasma detachment. The measured parameters permit the calculation of rates of ionization and recombination using Te, ne, Ti, ni, nHeI and nH(D,T); emission intensity—Te, ne, ni, nHeI and nH(D,T); frictional force of the plasma flow due to collisions with neutrals—Ti, ni, T0, nHeI and nH(D,T) and pressure of the incoming plasma flow—Te, ne, Ti and ni. The paper discusses the benefits of DTS and LIF integration, suggests new approaches to the estimation of DTS capability, LIF implementation and possibilities for further diagnostic development.

— A description of the operation and functional units of a test time-of-flight meter for neutron spectra for a polarized neutron reflectometer that will be installed after the neutron cold source of the IR-8 reactor neutron guide is presented. The developed electronic and software support allows measurement of the neutron transit time and, accordingly, the determination of the spectral characteristics of a neutron beam, as well as controlling the exact spatial positions of a chopper disk, diaphragm, and 3 He-detector using stepper motors and controllers.

The electronics for functional units of the polarized-neutron reflectometer (PNR) is presented. The electronic system connects the reflectometer units to the PNR control computer and provides control of step motors and absolute sensors for moving the experimental equipment, specification and change of the parameters of devices during operation, and acquisition of experimental data in the graphic and digital forms. Devices developed by the Petersburg Nuclear Physics Institute are also included in the electronic system.

Recent research at three small tokamaks with different parameters located at the Ioffe Institute—the spherical tokamak Globus-M, the large aspect ratio tokamak FT-2 and the compact tokamak TUMAN-3M—are reviewed. This overview covers energy confinement (Globus-M and FT-2), L–H transition (TUMAN-3M and FT-2), Alfvén waves (Globus-M and TUMAN-3M), ion cyclotron emission (TUMAN-3M), major plasma discharge disruption (Globus-M) and scrape-off layer (Globus-M) studies. A full-f global gyrokinetic modeling benchmark using synthetic diagnostics in FT-2 is described. Anomalous absorption and emission in electron cyclotron resonance heating experiments due to the parametric excitation of localized upper hybrid waves are analyzed theoretically. Progress in the development of the neutral particle analysis, gamma-ray spectrometry and divertor Thomson scattering combined with laser-induced fluorescence diagnostics for ITER is discussed. The status of the new Globus-M2 spherical tokamak is reported.

Physical and engineering aspects of RF plasma cleaning developed for actively cooled first mirror serving as grounded DC-coupled electrode are under consideration. Feasibility of the water-cooling lines implemented as the coaxial notch filter for ITER in-vessel diagnostic mirrors was demonstrated for Capacitively Coupled Radio Frequency (CCRF) discharge in neon at 1-10 Pa. The impinging ions energy as a function of absorbed RF power was measured for both the DC-coupled and -decoupled schemes. Sputtering yield variation over rectangular surface of stainless steel mirror was studied experimentally. The measured sputtering yield profiles were found to be in qualitative agreement with the RF plasma numerical simulations. It was demonstrated that Al/Al2O3 used as Be/BeO proxy can be removed from the water cooled mirror surface by 100 eV neon ions with the use of the notch filter. The 14 h plasma exposure didn't affect the mirror reflectivity.