Abstract：The main efforts of HT-7 superconducting tokamak were directed to quasi-steady state discharges and their relevant physics. Significant progress in obtaning high-performance discharges under quasi-steady state in HT-7 has been realized. The long pulse discharges have been obtained with a duration up to 63.95 s. The edge recycling was studied by the ratio of H to D through OSMA(Optical Spectroscopy Multichannel Analyzer) system. During the discharge, recycling dominated the particle balance. In the steady state, when the density was controllable, the deuterium(hydrogen) recycling played an important role and the recycling coefficient R≤1. During the later time, R＞1 and the density was uncontrollable. The main contribution was from the D(H) recycling and impurity from the surfaces of the limiter and the first wall due to the increased surface temperature and radiation power, and these limited the duration of long duration discharges. The influence of wall conditioning on the edge recycling was also studied through the ratio of H to D.
Key words：Doppler effect;Zeeman effect;The ratio of H toD;Recycling coefficient
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