No abstract

No abstract

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.

No abstract

Absolutely calibrated measurements of the neutron yield are important for the evaluation of plasma performance such as the fusion gain Q in D–D operating tokamaks. The time-resolved neutron yield is measured with 235U and 238U fission chambers and 3He proportional counters in the JT-60U tokamak. The in situ calibration was performed by moving the 252Cf neutron source toroidally through the JT-60 vacuum vessel. Detection efficiencies of three 235U and two 3He detectors were measured for 92 locations of the neutron point source in toroidal scans at two different major radii. The total detection efficiency for the torus neutron source was obtained by averaging the point efficiencies over the whole toroidal angle. The uncertainty of the resulting detection efficiency for the plasma neutrons is estimated to be ±11%.