In this article, some diagnostic systems and the preliminary results of the IR-T1**
(Iran-Tokamak 1) are presented. Different diagnostic methods, including an array of
soft X-ray detectors, visible spectrometer, electron cyclotron emission detector and
electromagnetic measurement systems have been used and the hard disruptive
instability occurring in the IR-T1 plasma during an ohmic heating discharge, under
a range of reproducible conditions for 3 q(a) 2, is studied. It is found that the
disruption activity occurs when the value of the safety factor at the plasma edge
becames less than q(a) 2.7.