Trapping of deuterium implanted in carbon and silicon: A calibration for particle-energy measurements in the plasma boundary of tokamaks

Abstract

Measurements have been made of the number of deuterons retained in carbon and silicon as a function of fluence, for incident energies between 50 eV and 1 keV. Three independent techniques were used for measuring the retained D: (1) by probing the trapped deuterons with 790 kV 3He +, and counting the total proton yield from the D( 3He, H) 4He nuclear reaction, (2) by measuring the re-emitted deuterium during and after implantation using mass spectrometry, (3) by thermal desorption mass spectrometry. Initially, the amount of trapped hydrogen increases proportionally to the fluence, while at high doses a saturation value is reached. The quantity of hydrogen trapped at saturation as a function of particle energy follows a power law. The data have particular significance in the estimate of the mean energy of particles to the near-wall region in tokamaks by observing the build-up of trapped hydrogen in a carbon probe during cumulative discharges. As an aid to the interpretation of such data, a multi-energy implant simulating a Maxwellian energy distribution has been made, and the trapping characteristics have been investigated as a function of incident ion fluence.