MEASUREMENTS OF THE ENERGY-DISTRIBUTION OF FAST TRITONS AND HELIUM-IONS ESCAPING FROM THE PLASMA IN JET

The energy distributions of tritons and helium ions escaping to the wall and limiters in JET have been measured. The tritons are produced from the D-D reaction during NBI heating and are born with an energy of 1 MeV, while the He-3 ions have been accelerated by ICRH. The tritium is collected in carbon samples placed in a probe which discriminates energy on the basis of larmor radius and the ratio of perpendicular to parallel velocity. The helium ion energy is deduced by measuring the depth distribution in a nickel collector. The average energy of the escaping tritons is not greater than 6 keV and is probably thermal. The energy distribution of the helium is very broad, most ions having energies less than 30 keV but some having energies greater than 1 MeV.