Measurement of the D-D fusion neutron energy spectrum and variation of the peak width with plasma ion temperature

We report a set of neutron spectrum measurements made at the Alcator-$C$ tokamak under Ohmic-heating conditions. It has been found that the width of the D-D fusion neutron peak increases with the plasma ion temperature consistent with the theoretical prediction. In particular, the neutron spectra resulting from the sum of many plasma discharges with ion temperatures of 780 and 1050 eV have been obtained. The width for the 780-eV case is ${64}_{-11\mathrm{}}^{+ 9}$ keV and that of the 1050-eV case, ${81}_{-14\mathrm{}}^{+10\mathrm{}}$ keV (full width at half maximum), corresponding to ion temperatures of 740 and 1190 eV, respectively.