S. Ya. Petrov

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.

Upgrade of the neutral particle analyzers for the TJ-II stellaratora)

The TJ-II stellarator, a magnetically confined plasma device, is equipped with a broad range of diagnostics for plasma characterization. These include 4 neutral particle analyzers (NPAs), consisting of two Acord-12s, to perform poloidal measurements, plus a compact NPA, and an Acord-24, these in tangential viewing positions. The Acord-12s were originally equipped with two rows of 6 channels each, one for hydrogen neutrals and the other for deuterium neutrals but were changed to a single row of 12 detectors for hydrogen, the principal working gas in TJ-II. With this upgrade the resultant improved energy resolution spectrum has allowed more reliable ion temperature estimates to be obtained. Here we present the upgrades undertaken and present results to demonstrate the improved performance of this diagnostic.

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.

Engineering design of the neutral particle analyser system on ITER

Engineering aspects of a neutral particle analyser setup for International Experimental Thermonuclear Reactor (ITER) have been considered. The setup consists of two neutral particle analysers, LENPA (for energy range of 10–200 keV) and HENPA (for range of 0.1–4 MeV). LENPA is intended for control of isotope ratio of the plasma hydrogen component by measuring an intensity ratio of hydrogen/deuterium/tritium fluxes. It will be incorporated into a system controlling the plasma isotope composition. HENPA is assumed to analyse He atom fluxes to study the fusion alpha particle distribution function. The analysers are located in the protecting vacuum container and are connected with ITER plasma vessel by a beam line. A suggested design of the beam line is described, a pressure distribution along the beam line is calculated, influence of collisions of neutral atoms with the working gas molecules on spectra of atoms is estimated. The design of the analysers will be described shortly.

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.

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.

A method for monitoring the parameters of a stripping target in neutral particle analyzers for the ITER

A method is described, which will be used as a basis for designing a system for monitoring the parameters of a stripping target in neutral particle analyzers being developed for neutral particle diagnostics of the ITER plasma. This method is based on examining the target by a beam of alkali ions and measuring the energy spectrum of the beam passed through it. Results of testing of this method at the experimental facility—a model of the monitoring system—are presented. Based on analysis of the experimental data obtained in the study, conclusions are drawn on the applicability of this method to monitoring of the stripping target parameters.

The angular distribution of light ions past a thin carbon foil

The scattering angles of ions formed upon the transmission of a monoenergetic beam of hydrogen (5–230 keV), deuterium (5–25 keV), or helium-4 (52–230 keV) atoms through a thin (2.7 μg/cm2) carbon foil were measured. The experimental data are compared to the results of calculations using an SRIM-2000 numerical modeling program. For hydrogen, the isotope effect (i.e., dependence of the angular distribution on the isotope mass) is estimated.