A neutron diagnostic system was developed at the Ioffe Institute as part of the Globus-M2 tokamak to optimize NBI heating conditions and evaluate heating efficiency. The system contains two compact neutron spectrometers based on the liquid organic scintillator BC-501A and two gas-discharge counters based on a 10B isotope. The BC-501A spectrometers were calibrated by measuring neutron emission produced in a 9Be(α,n)12C nuclear reaction on the cyclotron facility at the Ioffe Institute. In addition, in situ calibrations of the system, including the neutron spectrometers and the gas-discharge counters, was carried out using an Am–Be neutron source to provide accurate measurements of the total neutron yield from the plasma of the Globus-M2 tokamak. During the plasma experiments at the Globus-M2 tokamak, a deuterium beam was injected into the deuterium plasma that causes a yield of the DD-neutrons with ∼2.45 MeV energy. The neutron spectrometry diagnostic system was used to provide neutron measurements and detect the DD-neutrons in these experiments. The neutron yield and the DD-reaction rate during plasma discharges were evaluated. The energy distributions of neutrons emitted from plasma during discharges with neutron beam injection were reconstructed from the measured neutron spectra.

The NPA based diagnostic complex in ITER consists of four diagnostics: the neutral particle analyzers, the diamond neutral particle spectrometer, the gamma-ray spectrometer, and the neutron spectrometer. The diagnostics are located in equatorial port #11 and share the same vacuum channel. The present paper considers the physical basis of the diagnostic complex and its measurement capabilities in ITER. In addition, the design of the complex and the engineering solutions implemented to meet the ITER requirements are described.

We present the measured spectra of γ and neutron radiation generated in the 9Be(3He,pγ)11B and 9Be(3He,nγ)11C nuclear reactions at an energy of 2.57 MeV of 3He ions using a BC-501A organic detector and an HPGe semiconductor spectrometer. Line shapes of 6.9-MeV γ-transitions from the 9Be(3He,nγ)11C reaction and 8.92-MeV transitions from the 9Be(3He,pγ)11B reaction, measured at angles of 0°, 30°, 60°, 90°, and 120° have been determined. The angular distribution of protons emitted when populating the 8.92-MeV level of the 11B nucleus in 9Be(3He,pγ)11B reaction, as well as the energy distribution of neutrons in 9Be(3He,nγ)11C reaction, have been reconstructed.

The results of the measurements of the neutron and gamma radiation produced in the 9 Be( 3 He,pγ) 11 B and 9 Be( 3 He,nγ) 11 C nuclear reaction at the 2.57 MeV energy of the 3 He ions are represented. The measurements were carried out with organic scintillation detector BC-501A and semiconductor HPGe spectrometers. Gamma-ray spectra were measured at 0°, 30°, 60°, 90° and 120° angles. The shapes of the gamma lines 6.9 MeV from the 9 Be( 3 He,nγ) 11 C reaction and 8.92 MeV from the 9 Be( 3 He,nγ) 11 C were obtained. The angular distribution of protons populating the 8.92 MeV energy level of the 11 B nucleus was reconstructed. The energy distribution of the neutrons produced in the 9 Be( 3 He,nγ) 11 C reaction was measured (obtained).

We present the measured spectra of γ and neutron radiation generated in the 9 Be( 3 He, p γ) 11 B and 9 Be( 3 He, n γ) 11 C nuclear reactions at an energy of 2.57 MeV of 3 He ions using a BC-501A organic detector and an HPGe semiconductor spectrometer. Line shapes of 6.9-MeV γ-transitions from the 9 Be( 3 He, n γ) 11 C reaction and 8.92-MeV transitions from the 9 Be( 3 He, p γ) 11 B reaction, measured at angles of 0°, 30°, 60°, 90°, and 120° have been determined. The angular distribution of protons emitted when populating the 8.92-MeV level of the 11 B nucleus in 9 Be( 3 He, p γ) 11 B reaction, as well as the energy distribution of neutrons in 9 Be( 3 He, n γ) 11 C reaction, have been reconstructed.

A compact neutron spectrometer based on the BC-501A liquid organic scintillator was applied to neutron measurements at the TUMAN-3M tokamak. The spectrometer was calibrated using measurements from the ion beam of the cyclotron accelerator. Neutron spectra were measured during discharges using a neutral deuterium beam injection into the TUMAN-3M D-plasma. An energy distribution of the neutrons from the plasma that hit the spectrometer was obtained from the measured BC-501A instrumental spectra by the DeGaSum code using detector response functions obtained in the course of the calibration. This allowed for the estimation of the 2.45 MeV neutron yield and the evaluation of both the time evolution of the DD fusion rate and the characteristic time of the injected deuterium slowing down in discharges with neutral beam injection heating.

Gamma ray spectrometry measurements at high detector counting rates (on the order of 10(7) s(-1) and higher) are relevant for high-temperature plasma diagnostics for existing tokamaks and during the development of gamma ray diagnostic systems for the ITER tokamak under construction. At high loads, to obtain spectra without distortion and with a small amount of dead time, it is necessary to use advanced scintillation detector signal processing methods, which can resolve superimposed pulses. Two algorithms that can be used for digital signal processing of scintillation gamma ray detectors with many piled-up pulses are considered in this article, the fitting and deconvolution methods. These algorithms are compared with both one another and two less sophisticated pulse-height analysis algorithms (maximum height and total sum under the peak) in applications that process model and measured signals. Baseline detection algorithms are also considered, which are necessary when processing signals from detectors. The algorithms are applied to LaBr3(Ce) detector signal processing. For the modeled signals, the best results in terms of the number of resolved events and energy resolution at counting rates up to 2 x 10(7) s-1 of the LaBr3(Ce) detector are demonstrated by the fitting method. In the real gamma ray measurements at a loading of 5.1 10(6) s(-1), the deconvolution method demonstrated the best energy resolution.

Two neutron spectrometers based on a BC-501A liquid organic scintillator were calibrated. The calibration procedure included obtaining the spectrometers' response functions to monoenergetic neutron emissions and estimating the detectors' efficiency and is described in this paper. A Be-9(alpha, n gamma)C-12 nuclear reaction was used as the neutron source. Simultaneous registration of neutrons and gamma quanta with 4.44 MeV energy enabled the extraction of monoenergetic neutrons corresponding to the first excited state of a C-12 nucleus. This process is the basis of the neutron-gamma coincidence method, which was applied in the present experiments. The experiments were conducted using the cyclotron at Ioffe Institute, where a particles were accelerated to energies of 2.06, 5.35, 6.05, and 10.08 MeV. The angular dependence of the energy of produced neutrons provided a wide energy range of monoenergetic neutron emission at the same energy of the incident alpha particle. The response functions of the BC-501A spectrometers on the monoenergetic neutrons were obtained at energies of 1.9 to 10.4 MeV. The neutron registration efficiency of both detectors was estimated in the same energy range as the responses.

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.

Studies of the super-thermal and runaway electron behavior in ohmic and lower hybrid current drive FT-2 tokamak plasmas have been carried out using information obtained from measurements of hard x-ray spectra and non-thermal microwave radiation intensity at the frequency of 10 GHz and in the range of (53 divided by 78) GHz. A gamma-ray spectrometer based on a scintillation detector with a LaBr3(Ce) crystal was used, which provides measurements at counting rates up to 10(7) s(-1). Reconstruction of the energy distribution of RE interacting with the poloidal limiter of the tokamak chamber was made with application of the DeGaSum code. Super-thermal electrons accelerated up to 2 MeV by the LH waves at the high-frequency pumping of the plasma with low density < n(e)> similar to 2 x 10(13) cm(-3) and then up to 7 MeV by vortex electric field have been found. Experimental analysis of the runaway electron beam generation and evolution of their energy distribution in the FT-2 plasmas is presented in the article and compared with the numerical calculation of the maximum energy gained by runaway electrons for given plasma parameters. In addition, possible mechanisms for limiting the maximum energy gained by the runaway electrons are also calculated and described for a FT-2 plasma discharge.

Gamma detectors measures emission from nuclear reactions with fast ions, and also bremsstrahlung radiation from runaway electrons decelerating on the bulk plasma and vacuum vessel components. Diagnostic under consideration gives data on distribution functions of these particles, which play an important and often even the crucial role in many plasma phenomena: burning, energy balance, instabilities, etc. Dedicated ITER spectrometer is under development by Ioffe Institute Cyclotron Laboratory team. Design of system will accumulate most of the experience of the analogous systems currently in use and also will have to solve new technical challenges due to the requirement to operate in fusion reactor conditions of ITER. Discussion on the last stages of design preparation, including retrospective neutronic analysis and necessary mockup tests, is given below.

A gamma-ray spectrometer based on LaBr3(Ce) scintillator has been used for measurements of hard X-ray emission generated by runaway electrons in the FT-2 tokamak plasmas. Using of the fast LaBr3(Ce) has allowed extending count rate range of the spectrometer by a factor of 10. A developed digital processing algorithm of the detector signal recorded with a digitizer sampling rate of 250MHz has provided a pulse height analysis at count rates up to 107s−1. A spectrum deconvolution code DeGaSum has been applied for inferring the energy distribution of runaway electrons escaping from the plasma and interacting with materials of the FT-2 limiter in the vacuum chamber. The developed digital signal processing technique for LaBr3(Ce) spectrometer has allowed studying the evolution of runaways energy distribution in the FT-2 plasma discharges with time resolution of 1–5ms.

Gamma-ray spectrometry on ITER can provide information both on confined fusion alpha particles for optimization of plasma heating and runaway electrons, which is important for safe reactor operations. For the purpose of deconvolution of gamma-ray spectra recorded in fusion plasma experiments the DeGaSum code has been developed. The code can be applied for processing of both spectra of monoenergetic gamma rays, which are born in nuclear reactions produced by alpha particles and other fast ions, and continuous bremsstrahlung spectra generated by runaway electrons in the MeV range in the plasma and reactor structure materials. Gamma-ray spectrometer response functions and bremsstrahlung spectra generated by electrons in the MeV energy range are calculated and used in the DeGaSum code. The deconvolution of the discrete spectra allows the identification of nuclear reactions, which give rise to gamma rays, and the calculation of their intensities. By applying the code for continuous hard x-ray spectra, the runaway electron energy distribution can be inferred. It can provide the maximal energy of runaway electrons with accuracy, which satisfies the ITER project requirements. The code has been used for processing of spectra recorded in JET experiments. An application of the deconvolution technique for gamma-ray emission measurements on ITER is discussed.

The possibility of application of deconvolution methods to solving the problem of reconstruction of gamma-radiation spectra of thermonuclear plasma is demonstrated. The DEGAS code is created, which implements the modified algorithms of deconvolution. The results of the code application to the test spectra, the discrete spectra of radiation sources, and the gamma spectra measured during the experiments at the JET tokamak using methods for additional plasma heating are presented. The possibility of reconstruction of spectra with low statistics is shown.

Gamma-ray spectrometry is a diagnostic tool for fast ions in large tokamak plasmas. The information provided allows us to identify and simultaneously distinguish the presence of fast α-particles and other ions (H, D, T, 3He) to obtain information on their energy distribution and relative densities, in addition to performing a tomographic radial profile reconstruction of the γ-emission sources. The lack of vertical diagnostic ports in ITER makes the implementation of tomographic neutron and γ-ray systems more complicated. The use of a vertical divertor port for the implementation of a vertical viewpoint is currently suggested. The strong magnetic field (∼2 T) found there makes it hard to use conventional multi-dynode photomultipliers as light detectors. Instead, the use of micro-channel plate photomultipliers is suggested here. Investigations of the magnetic field impact on the performance of the γ-spectrometer with a micro-channel photomultiplier are carried out. A high-speed pulse height analysis technique, which allows us to trace gain changes in the photomultiplier tube, is developed at the Ioffe Institute. The tests demonstrate the feasibility of γ-spectrometric measurements in the divertor port provided that micro-channel photomultiplier detectors and the developed high-speed technique are used.

Results are presented from experimental studies of runaway electrons in the ohmic heating regime in the Globus-M tokamak. The periodical hard X-ray bursts observed with the help of two hard X-ray spectrometers with high time resolution are attributed to MHD oscillations in the plasma core and at the periphery.

Interpretation of the B(E2) values at energies higher the first backbending indicates that the maximum boson of IBM has to increase with energy and spin.