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Notes: Some diagnostic components in ITER will be subject to high levels of radiation (neutrons and gammas) and changes in their physical properties can result. During the ITER EDA an extensive range of tests on relevant materials, e.g., window materials, metals, and insulators, have been carried out and the changes in their physical properties have been measured. The effects examined include radiation induced electrical damage (RIED) and radiation induced conductivity (RIC) in potential insulators; radiation induced absorption and radio luminescence in potential optical materials; and changes to the reflectivity and surface properties of bulk metal mirrors. The results give a database of information which is of use to the designers of ITER diagnostic systems. Recent and planned work is concentrating on the testing of diagnostic prototypes in relevant radiation fields. The results obtained thus far will be summarized and the planned work outlined. © 1999 American Institute of Physics.

Notes: Two natural diamond detectors (NDDs) operating at room temperature were used for Fusion Neutronics Source (FNS) deuterium–tritium (DT) neutron spectra measurements at different points around the tritium target and for different deuteron beam energies. Energy resolution of both NDDs were measured, with values 1.95% and 2.8%. Due to the higher energy resolution of one of the two NDDs studied it was possible to measure the shape of the DT neutron energy distribution and its broadening due to deuteron scattering inside the target. The influence of pulse pileup on the energy resolution of the combined system (NDD+electronics) at count rates up to 3.8×105 counts/s was investigated. A 3.58% energy resolution for the spectrometric system based on NDD and a 0.25 μs shaping time amplifier has been measured at a count rate of 5.7×105 counts/s. It is shown that special development of a fast pulse signal processor is necessary for NDD based spectrometry at count rates of approximately 106 counts/s. © 1997 American Institute of Physics.

Notes: Three natural diamond detectors (NDD) based spectrometry systems have been developed and used on TFTR to perform D–T neutron spectrum and flux measurements. DT neutrons interact with the NDD through the 12C(n, alpha)9Be reaction to produce a narrow peak in the pulse height distribution which has 2%–3% energy resolution and is well isolated from other reactions by ∼2 MeV in energy. The NDD detector is also highly radiation resistant (5×1014 n/cm2) and compact in size (diameter ∼4 mm, thickness ∼0.2 mm). Three detectors have been installed near TFTR. One, installed in a central sight line of the neutron collimator views perpendicularly from below. Two other detectors placed inside radiation shields in the TFTR test cell have tangential and perpendicular cones of view. These three spectrometers provide spectrometry of D–T neutrons escaping the tokamak with angles with respect to plasma current in the ranges close to 90°, 110°–180°, and 60°–120° correspondingly. The fastest standard electronics have been used to reduce the influence of pulse pileup during spectrometry measurements at count rates up to 3×105 counts/s. Results of the first D–T neutron spectra and flux dynamics measurements made with the three NDD based spectrometers during TFTR high power neutral beam injection are presented. © 1997 American Institute of Physics.

Notes: Neutron diagnostics will play a prominent role in the control and evaluation of thermonuclear plasmas in ignition device to test engineering concepts (ITER). As in present D-T experiments, measurements of neutron yield and of fusion power and power density are essential. In addition, the spectral width of the 14.1-MeV t(d,n)α neutron emission should be a reliable indicator of ion temperature in an ignited plasma. More detailed measurements of the neutron spectrum may allow determination of the densities of tritium, deuterium, and confined alpha particles. Although the central fusion power density in ITER will be comparable to the maximum values obtainable in TFTR and JET, neutron flux on the first wall will be ten times higher, and the neutron yield per discharge will be about five orders of magnitude greater than previously experienced. The thermal and radiation shielding necessary to protect the ITER superconducting coils from the intense flux at the first wall will restrict diagnostic access for neutron cameras and spectrometers, complicate the design of material activation systems, and limit the applicability of conventional calibration techniques for neutron source strength monitors. These considerations, together with unprecedented reliability requirements and the need for full remote handling of many components, pose demanding challenges for the design of the ITER neutron diagnostic systems. © 1997 American Institute of Physics.

Notes: In this article we present the description of compact neutron generators with gas-filled tubes that can be used for neutron detector calibration and stability control. The absolute neutron emission was measured with natural diamond detector and appeared to be in 3% agreement with a standard metrology monitor. Neutron generators design are discussed in regard to neutron emission anisotropy and stability improvement. Data illustrating the neutron spatial and energy distributions are presented. © 1999 American Institute of Physics.

Notes: Natural diamond detectors (NDD) developed in Russia were used for fast charge exchange H0 atom spectrometry and flux dynamic measurements during Tokamak Fusion Test Reactor (TFTR) H+ minority ion cyclotron resonance heating (ICRH) experiments in deuterium plasma. For selected NDDs, the high energy resolution (∼2%–3%) and radiation resistance (5×1014 n/cm2) and low sensitivity to neutrons and gammas enable spectrometry of fast (0.2–3 MeV) atoms in TFTR radiation conditions. The NDD compact housing (∼2 cm+3) allowed noninterfering insertion into the particle charge exchange flight tube giving both systems similar views which allows comparison of their spectra and fluxes. A small NDD was chosen to limit count rates to 7×105 s−1. A spectroscopy amplifier operating with pileup inspection at such rates was developed, enabling measurement of the dependence of fast perpendicular proton energy spectra on ICRH heating power during sawtooth-free and sawtooth-crash times. The results agree with a model developed for sawtooth redistribution of fast particles. © 1999 American Institute of Physics.

Notes: Neutron cameras with horizontal and vertical views have been designed for ITER, based on systems used on JET and TFTR. The cameras consist of fan-shaped arrays of collimated flight tubes, with suitably chosen detectors situated outside the biological shield. The sight lines view the ITER plasma through slots in the shield blanket and penetrate the vacuum vessel, cryostat, and biological shield through stainless steel windows. This article analyzes the expected performance of several neutron camera arrangements for ITER. In addition to the reference designs, we examine proposed compact cameras, in which neutron fluxes are inferred from 16N decay gammas in dedicated flowing water loops, and conventional cameras with fewer sight lines and more limited fields of view than in the reference designs. It is shown that the spatial sampling provided by the reference designs is sufficient to satisfy target measurement requirements and that some reduction in field of view may be permissible. The accuracy of measurements with 16N-based compact cameras is not yet established, and they fail to satisfy requirements for parameter range and time resolution by large margins. © 1999 American Institute of Physics.

Notes: Natural diamond detectors (NDDs) being developed for the spectrometric applications in tokamak fusion plasma experiments, have been used also for fast x-ray flux measurements and time-of-flight (TOF) electron spectrometry in laser beam-target interaction experiments on the CO2 laser installation TIR (λ=10.6 μm, E=80–95 J, τ∼14 ns). The magnetic field created in front of the detector provided separation of the signals induced by x ray and electrons. The waveform of a NDD current response has been shown to provide an information about energy spectra of the particles generated during laser beam-target interaction. Fast response time (〈1 ns), low sensitivity to visible light and x rays, high radiation resistance, and 100% charge collection efficiency of the type IIa diamond samples, make NDDs to be the optimal choice for TOF spectrometry of charged fusion products in inertial confinement fusion experiments. © 2001 American Institute of Physics.

Notes: The concept of the neutron flux measurements for International Thermonuclear Experimental Reactor ITER-FEAT is discussed. In spite of the fact that ITER-FEAT has reduced fusion power with respect to ITER-FDR, the requirements for neutron flux monitors are similar—wide dynamic range (seven orders), good temporal resolution (1 ms), and high accuracy (10%). It is clear that fission chambers are the most suitable detectors for this application. However high neutron intensity of the fusion plasma and hard requirements lead to a more sophisticated detection system than the ordinary fission chamber. Another problem is an absolute calibration of the detectors. We propose a neutron flux monitoring system, which consist of microfission chambers placed inside the ITER vacuum chamber, three wide range fission chambers placed outside the vacuum chamber, natural diamond detector based compact neutron monitors placed inside the channels of the neutron cameras, and a compact neutron generator for calibration. Microfission chambers could be installed in the standard plugs with other detectors (vacuum x-ray diode, magnetic probe). 235U could be used as well as threshold fission materials (238U, 237Np, 232Th). In the last case the fission chamber will be covered by a boron shield to reduce the changes in the sensitivity. Wide range fission chambers will operate in both pulse count mode and Campbell mode. High linearity is provided by count mode. Temporal resolution of 1 ms is provided by the count mode at low neutron flux and by the Campbell mode at high flux. The nonlinearity of the fission chamber during the switch from count mode to Campbell mode will be corrected by another fission chamber with low sensitivity operating in count mode. Compact neutron flux monitors placed inside neutron cameras will consist of up to ten natural diamond neutron counters with sensitivity to DT neutrons doubled by properly installed poliethilen radiators. Such monitors provide DT neutron flux profile measurements with dynamic range (three orders), temporal resolution (1 ms), and accuracy (10%). The full system could be calibrated by compact moveable neutron generator with neutron yield 1011 neutron/s, which operate in continuous mode. All elements of the system are commercially available, except for the neutron generator and diamond detector based monitors. The neutron generator and multidiamond detector based DT neutron monitors are now under development. An existing prototype of the neutron generator operates with a yield of one order less. Performance and major characteristics of the proposed systems of neutron flux monitoring will be discussed from the point of view of their application for neutron flux measurements and control of deuterium and deuterium–tritium phases of the ITER-FEAT operation. © 2001 American Institute of Physics.

Notes: Abstract Presence of two maxima on the DTA curves of coked catalysts is attributed to the metal-catalyzed oxidation of less polymerized coke in a higher temperature region.