CALIBRATION OF THE TFTR LOST ALPHA-DIAGNOSTIC

We present various aspects of the calibration of the TFTR lost alpha diagnostic. The diagnostic consists of four detectors, forming a poloidal array at the bottom of TFTR inside the vacuum vessel. The detector is composed of a ZnS(Ag) scintillator and a pair of collimating apertures which permit pitch angle, energy, and time resolution of the escaping flux of high-energy ions (MeV range). The first goal of this study was to establish the absolute calibration of the diagnostic for different particle types and energies. This enables us to compare for the first time, measured losses with loss calculations based on a first-orbit model. However, the factor of 2 uncertainty in the final calibration is still too large for full, quantitative comparisons of the data with the theory based on absolute flux measurements alone. We also present some of the aspects related to the detector's resolution capabilities, its temperature dependence, and its time response.