Plasma confinement improvement by RHF in IR-T1 tokamak

Summary form only given. It has been known that tokamak plasma parameters and energy confinement time may be reduced by plasma impurity radiation. The plasma MHD stabilities may also be influenced by the impurities. Experiments have been performed on the IR-T1 tokamak to investigate the influence of magnetic perturbations and impurities radiation on confinement. IR-T1 is a small air core transformer tokamak with circular cross-section and without copper shell and divertor (R=45 cm, a=12.5 cm, Bt<1 T, Ip=20-40 kA, Ne=(0.7-2.5)/spl times/10/sup 1/3 cm/sup -/3, Te=150-200 eV, and safety factor q=2-4). The perturbations are either imposed, via external windings, or natural plasma fluctuations. For this purpose, L=2 and L=3 helical windings have been installed on the IR-T1 tokamak. Diagnostic signals (using magnetic probes, soft X-ray detectors, visible spectroscopy and etc) from MHD instabilities have been obtained and studied during discharges with resonant helical fields (RHFs, the magnitudes of the RHFs are normally about 0.5% of that of the poloidal field Bp around the resonant surface).