Fusion product measurements planned for ITER are reviewed from the viewpoint of alpha particle-related physics studies. Recent advances in fusion plasma physics have extended the desirable measurement requirements to the megahertz region for neutron emission rate, better resolution of neutron profiles for the study of internal transport barriers (ITBs), etc. Employing threshold counters and/or scintillation detectors confers megahertz capability on neutron emission rate measurement. The changes in the neutron/alpha particle birth profile due to the formation of ITB and its deviation from uniformity on the magnetic flux surface can be measured by addition of eight viewing chords in an equatorial port plug and seven viewing chords from the divertor to the original radial neutron camera. On the other hand, it is still difficult to measure the distributions of confined and escaping alpha particles. Several proposals to resolve these difficulties are currently under investigation.

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Due to the high neutron yield and the large plasma size many ITER plasma parameters such as fusion power, power density, ion temperature, fast ion energy and their spatial distributions in the plasma core can be measured well by various neutron diagnostics. Neutron diagnostic systems under consideration and development for ITER include radial and vertical neutron cameras (RNC and VNC), internal and external neutron flux monitors (NFMs), neutron activation systems and neutron spectrometers. The two-dimensional neutron source strength and spectral measurements can be provided by the combined RNC and VNC. The NFMs need to meet the ITER requirement of time-resolved measurements of the neutron source strength and can provide the signals necessary for real-time control of the ITER fusion power. Compact and high throughput neutron spectrometers are under development. A concept for the absolute calibration of neutron diagnostic systems is proposed. The development, testing in existing experiments and the engineering integration of all neutron diagnostic systems into ITER are in progress and the main results are presented.

Radio frequency heating of majority ions is of prime importance for understanding the basic role of auxiliary heating in the activated D-T phase of ITER. Majority Deuterium Ion-Cyclotron Resonance Heating (ICRH) experiments at the fundamental cyclotron frequency were performed in JET. In spite of the poor antenna coupling at the lowest possible commissioned RF frequency (25MHz), this heating scheme proved promising when adopted in combination with D Neutral Beam Injection (NBI). The experiments were performed in a ~90% D, 5% H plasma with some pulses including traces of Be and Ar. Up to 2MW of ICRH power was applied with dipole phasing in conjunction tõ 6MW of NBI power, either using 80keV "normal" beam or 130keV "tangential" beam injection. The toroidal magnetic field strength was typically B 0 = 3.3T, providing core ICRH of the bulk D ions. The effect of fundamental D ICRH was clearly demonstrated in these experiments: By adding 25% of heating power (P ICRH = 1.7MW / P NBI+OH = 7MW) the fusion power was increased up to 30-50%, depending on the type of NBI adopted. At this power level, the ion and electron temperatures increased from T i ~ 4.0keV and T e ~ 4.5keV (NBI-only phase) to T i ~ 5.5keV and T e ~ 5.2keV (ICRH+NBI phase), respectively. The increase in the neutron yield was stronger when 80keV rather than 130keV Deuterons were injected in the plasma. It is shown that the neutron rate, the diamagnetic energy and the electron as well as ion temperature scale roughly linearly with the applied RF power. A synergistic effect of the combined use of ICRF and NBI heating was observed: (i) The number of neutron counts measured by the neutron camera during the combined ICRF+NBI phases of the discharges exceeded the sum of the individual counts of the NBI-only and ICRF-only phases; (ii) A substantial increase in the number of slowing-down beam ions was detected by the TOFOR spectrometer when ICRF power was switched-on; (iii) A small D subpopulation with energies slightly above the NBI launch energy were detected by the neutral particle analyzer and gray spectroscopy.

This article describes a diagnostic for measuring neutron emission profile in JT-60U. The Stilbene neutron detector, developed by TRINITI laboratory in Russia, has been installed on the JT-60U Tokamak to measure the neutron emission profile for the first time. The Stilbene neutron detector is a detector which combines a Stilbene crystal scintillator with a neutron-gamma pulse shape discrimination circuit, with a very compact size. Performance tests were carried out using neutron and gamma-ray source prior to installation on JT-60U. Good gamma suppression of the Stilbene neutron detector was verified. Though the neutron emission profile obtained by Stilbene neutron detectors has error of 30% in innermost channel with a calculation using measured plasma parameters, there is an agreement within 10% error in the other channels.

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A digital pulse shape discrimination system (DPSD) has been used in conjunction with collimated NE213 scintillators for neutron spectroscopic measurements at high count rates (MHz range) in Joint European Torus discharges (DD and DT fueled, neutral beam injection and rf heated). The system, developed at ENEA-Frascati, is based on a commercial 200 MHz 12-bit analog to digital transient recorder card, which digitizes the direct output signal from the anode of a photomultiplier. Among the unique features of this DPSD system are the possibility of postexperiment data reprocessing, high count rate operation, and simultaneous neutron and gamma (γ) spectroscopy. Separation between γ and neutron (n) events is performed by means of dedicated software exploiting the charge comparison method; separate n and γ pulse height distributions are obtained and an example of neutron spectrum unfolding is shown. Implications of the DPSD in future neutron diagnostic systems on large and next step tokamaks are discussed.

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