Workshop on the Development of Charge Exchange Diagnostics and Pellet Injection at W7-X, May 24-26, 2000, IPP Sub-Institute, Greifswald
G. Bracco
Abstract
This presentation describes the experimental set-up and the main physical results of the two generations of neutral particle analyzers built in ENEA Frascati and installed on JET. The first version has operated in the years from 1984 to 1989 and consisted in an array of 5 E // B analyzers for radially resolved measurements. The main task of the diagnostics has been the measurement of the ion temperature and the details of the ion energy distribution. Results from ohmic and additional heated plasma (NBI, ICRH) are presented. A severe problem for the operation of the diagnostics has been the sensitivity of the detectors (channeltrons) to neutrons produced in the high performance plasma pulse at JET. To overcome this problem a second version of analyzer was developed. The rejection of the random background noise produced by neutrons is obtained by using the coincidence technique in a time-of-flight scheme, that provides also the mass selection capability of the analyzer. This version of the analyzer has operated from 1991 to 1998. Results from various plasma scenarios are presented (ohmic, NBI and ICRH heating) with a particular stress to the measurement of the species composition of the plasma, that have played an important role in the deuterium-tritium experiment on JET. A summary of the effective neutron sensitivity of channeltrons in the various experimental configurations is also provided.