V. I. Afanasyev

Neutral particle analyzer/isotope separator for measurement of hydrogen isotope composition of JET plasmas

This article describes a neutral particle analyzer/isotope separator (ISEP) developed for measurement of the relative hydrogen isotope composition of Joint European Torus (JET) plasmas. The ISEP deployed on the JET can be regarded as a prototype of an instrument proposed for measurement of the spatial profile of the ratio of the density of deuterium and tritium ions in the plasma, nD(r)/nT(r), in the International Thermonuclear Experimental Reactor (ITER). The ISEP makes simultaneous measurements of the energy distribution of efflux of hydrogen isotope atoms (H, D, and T) from the plasma. From such measurements it is possible to deduce the radial profile of the relative hydrogen isotope ion composition of the plasma and radial transport of ions of one isotope across the plasma of another isotope species. The main elements of the ISEP are (a) use of a thin carbon foil for reionization of the incident atoms, thereby eliminating gas stripping cells and gas sources of conventional neutral particle analyzers (...

Study of fast-ion losses in experiments on neutral beam injection on the Globus-M spherical tokamak

The paper presents a review of the main results on the heating of plasma ions and behavior of fast ions in experiments on neutral beam injection (NBI) carried out in 2003–2010 on the Globus-M spherical tokamak. It is noticed that, along with significant success achieved in NBI plasma heating, there is experimental evidence indicating significant losses of the power injected into the plasma. Most probably, the power is lost due to so-called first-orbit losses, i.e., losses of fast ions that are produced in plasma after ionization of beam atoms and occur in unconfined trajectories. Until recently, the absence of appropriate diagnostic equipment did not allow one to verify this hypothesis. The use of the ACORD-M charge-exchange analyzer directed tangentially to the plasma column made it possible to measure the spectra of fast ions slowed down in plasma and confirm the assumption on the presence of substantial orbit losses of fast particles (∼25–50% of the beam power). In addition to the review of the experimental results, the paper presents analysis of orbit losses on the basis of 3D simulations of fast-ion trajectories in plasma. The results of experiments on studying the influence of the magnitude of the tokamak magnetic field on the confinement of fast ions are also presented. Along with computer simulations, these experiments made it possible to formulate recommendations on the reduction of orbit losses in the Globus-M tokamak.

A comparative analysis of the sensitivity of CsI (Tl), ZnO(Ga), and YAG(Ce) scintillators to the plasma background radiation under operating conditions of the ITER tokamak reactor

Problems related to neutral particle flux measurements on the ITER tokamak reactor under intense plasma background radiation conditions are considered. The results of measuring a background sensitivity with respect to neutron and γ-radiation for the scintillation detector, which is based on three different crystals (CsI (Tl), ZnO(Ga), and YAG(Ce)), are presented. The scintillators are compared and conclusions about the possibility of their applications in detectors of neutral particle analyzers currently created at the Ioffe Institute for the ITER tokamak reactor, are drawn.

Neutral Particle Analysis on ITER and requirements for DEMO

The use of the neutral particle analysis (NPA) to study the ion component of plasma on ITER has been reviewed. Both thermal (10–200 keV) and supra‐thermal (0.2–4 MeV) energy ranges of neutral fluxes are studied in respect to feasibility of the fusion fuel isotopic composition measurements. Influence of heating neutral beams and diagnostic neutral beam on the measurements is also shown. Possible application of the NPA to measure the energy distribution function of fusion alpha particles is discussed. Low‐ and high‐energy NPA monitors have been proposed for DEMO machine to control the DT fuel isotope ratio.

Use of neutralized knock-on ion fluxes for alpha-particle confinement studies

One of the objectives of neutral particle diagnostics on large tokamaks exploring DT plasma is to measure the distribution functions of fast deuterium (D) and tritium (T) ions in a suprathermal energy range. High energy tails in D,T-ion energy distributions (so-called knock-on ions) appear as a result of close elastic collisions between thermal fuel ions and fusion α-particles. The knock-on ion density depends directly on the density and energy distribution of the α-particles. Therefore measurements of the neutralized knock-on D,T-ion fluxes escaping from the plasma volume can provide information on the α-particle confinement in DT plasma. This paper presents the results of a numerical simulation for the neutralized fast D,T-ion fluxes in the case of ITER fusion plasma. Feasible experimental measurements of the fluxes are considered with respect to the neutral particle diagnostics. We will show that the diagnostics can provide information on the confinement properties of fast ions in DT fusion plasma.

Background and radiation resistance tests of neutral particle analyzer detectors for ITER by using a fast neutron beam

The radiation resistance and background sensitivity of scintillation (Hamamatsu H8500D photo-multiplier) and semiconductor (ORTEC BF-018-100-60 and BU-012-050-100) detectors to neutron and gamma radiation were investigated. Conclusions are drawn concerning the possibility of using such detectors in neutral particle analyzers that are being developed for ITER at the Ioffe Institute.

The effect of sawtooth oscillations on the alpha particle distribution and energy balance in the ITER plasma

The mixing of toroidal plasma under the conditions of sawtooth oscillations is considered using the Kadomtsev model. A new mixing formula for the averaged distribution function of fast transit and trapped particles is proposed in the methodology of a kinetic equation averaged over drift trajectories. The proposed formula generalizes the known results for the case of non-circular magnetic surfaces, an arbitrary aspect ratio, and charged particle drift trajectories significantly deviating from the magnetic surfaces. The formula is applicable for a sufficiently wide class of instabilities. The 3D kinetic equation is numerically solved using the FPP- 3D computation code for parameters close to the ITER inductive scenario. The alpha particle distribution function and the power introduced by alpha particles in plasma when sawtooth oscillations occur are calculated. It is shown that such oscillations may change the energy input of a thermonuclear reaction in certain areas by several times.

The Sawtooth Oscillation Effect on Fast-Ion Energy Spectra in ITER Plasma and Neutral Particle Analyzer Measurements

ITER plasma with parameters close to those with the inductive scenario is considered. The distribution functions of fast ions of deuterium D and tritium T are calculated while taking into account the elastic nuclear collisions with alpha particles 4He using the code FPP-3D. The D and T energy spectra detected by the neutral-particle analyzer (NPA) are determined. The plasma mixing effect on these spectra during sawtooth oscillations is studied. It is shown that the NPA makes it possible to detect sawtooth plasma oscillations in ITER and determine the percentage composition of the D‒T mixture in it both with the presence of instabilities and without them. A conclusion is drawn on the prospects of using NPA data in automatic controllers of thermonuclear fuel isotopic composition control and plasma oscillation regulation in ITER.

DESIGN FEATURES OF NEUTRAL PARTICLE DIAGNOSTIC SYSTEM FOR ITER

ОСОБЕННОСТИ КОНСТРУКЦИИ СИСТЕМЫ ДИАГНОСТИКИ ПО ПОТОКАМ АТОМОВ ИЗОТОПОВ ВОДОРОДА ДЛЯ МЕЖДУНАРОДНОГО ТЕРМОЯДЕРНОГО РЕАКТОРА ИТЭР С.Я. Петров, В.И. Афанасьев, А.Д. Мельник, М.И. Миронов, А.С. Наволоцкий, В.Г. Несеневич, М.П. Петров, Ф.В. Чернышев, И.В. Кедров, Е.Г. Кузьмин, Б.В. Люблин, С.С. Козловский, А.Н. Мокеев Физико-технический институт им. А.Ф. Иоффе, Санкт-Петербург, Россия АО «Научно-исследовательский институт электрофизической аппаратуры им. Д.В. Ефремова», Санкт-Петербург, Россия Санкт-Петербургский политехнический университет Петра Великого, Санкт-Петербург, Россия Частное учреждение «ИТЭР-Центр», Москва, Россия

Specific features of measuring the isotopic composition of hydrogen ions in ITER plasma by using neutral particle diagnostics under neutral beam injection conditions

Results of numerical simulation of signals from neutral particle analyzers under injection of the heating and diagnostic neutral beams in different operating modes of the ITER tokamak are presented. The distribution functions of fast ions in plasma are simulated, and the corresponding neutral particle fluxes escaping from the plasma along the line of sight of the analyzers are calculated. It is shown that the injection of heating deuterium (D0) beams results in the appearance of an intense background signal hampering measurements of the ratio between the densities of deuterium and tritium fuel ions in plasma in the thermal energy range. The injection of a diagnostic hydrogen (H0) beam does not affect measurements owing to the high mass resolution of the analyzers.