Neutron spectroscopy at JET

Measurement of the energy spectra of fusion neutrons is accorded a prominent position in the neutron diagnostics program at JET. The nature of the information on plasma properties which it is hoped will be obtained is discussed, as is the availability of suitable instruments and techniques for spectroscopy on thermonuclear plasmas. Of these instruments, only the 3He ionization chamber has so far been successfully exploited; the lessons learned regarding its performance are outlined and the results obtained for ohmically and ICRF heated plasmas are presented. It is shown that the deuterium ion energy distributions appear to be Maxwellian for all plasmas studied, that central ion temperatures have been obtained on a shot-by-shot basis which agree well with corresponding values obtained by neutral particle analysis and that the deuteron to electron density ratio in the plasma is approximately 0.5