Measurements of ion temperature at ASDEX with improved fusion proton and triton diagnostics

Recently a new diagnostic method was developed on ASDEX to measure the charged fusion products from the reactions d(d,p)t and d(d,n)3He, respectively, with semi-conductor detectors. The protons as well as the tritons could be detected and it was possible to determine the ion-temperature Ti from both of the species using the Doppler contribution to the width of the spectrum of protons and tritons. These measurements and the results, however, are influenced by three different mechanisms: Hard X-rays emitted from the plasma give rise to background counts at a rate which drops about exponentially with the energy. Energy loss of the charged fusion products occurs in thin foils, which are applied to protect the detector from visible light, resulting in energy straggling and profile broadening, especially for too low energy fusion products. Magnetic field changes lead to uncontrolled shifts of the spectra on energy axis, resulting in a statistical spectral broadening. To improve these points, a new shielding was developed, thinner foils to lower energy loss and straggling and a double detector arrangement to subtract the magnetic field effects were applied. Measurements of proton and triton spectra and more accurate determinations of ion-temperatures were possible over a wider range of different ASDEX-discharges. During NI(D0→D+)-heated plasmas spectra were found, belonging to non-maxwellian ion-distributions. The described improvements also resulted in first measurements of 3He seen in a tokamak. (orig.)