Thermonuclear fusion product diagnostics by nuclear track detectors

Abstract

The nuclear track detector materials CR-39 and PM-355 are capable of proton and alpha particle track recording and thus well suited to charged particle diagnostics in thermonuclear fusion devices. In a study to determine the respective absolute recording efficiencies and energy resolutions for protons and alpha particles in real diagnostics situations, a series of experiments with monoenergetic particles of known energies and angles of incidence were performed. Alpha particles could be quantitatively detected for angles of incidence of up to 70°, and their etch pit depth rather than the diameter for defined etching conditions gave satisfying information on the alpha particle energy. Contrary to other investigators, however, we found a monotonically decreasing detection probability for protons already above 3 MeV and no proton track could be developed above incident energies of 7 to 8 MeV. The proton detection depends more strongly on the angle of incidence; only tracks of protons with angles of incidence smaller than 30° could be made visible by etching. The proton energy could be derived from track diameter measurements better than from etch pit depths.