First Results of Movable Limiter Experiments and its Effects on the IR-T1 Tokamak Plasma Confinement

Tokamak limiter plays a number of roles in its operation. It serves primarily to protect the wall from the plasma when there are disruptions, runaway electrons, or other instabilities. For this reason it is commonly made of a refractory material, such as carbon, molybdenum or tungsten, capable of withstanding high heat loads. Secondly, the limiter localizes the plasma-surface interaction. The high power and particle density at the limiter surface causes rapid removal of adsorbed gas, oxide layers and other easily desorbed impurities. When only the clean substrate remains it is possible to maintain plasmas with lower impurity levels. Plasma-surface interaction in tokamaks is important in plasma conditions such as impurities, plasma parameters, and plasma confinement. Thirdly, the limiter localizes the particle recycling. A higher neutral density and more radiation are observed in the region near the limiter, than at other positions around the torus . Movable limiter was designed, constructed, and has been used on IR-T1 tokamak to investigate the possibility of modifying the plasma confinement. In this research work we present the first results of a movable limiter experiments and its effects on the tokamak plasma confinement. For this purpose we firstly designed, constructed, and installed a movable localized poloidal limiter, and then measured the effects of limiter position on the time intervals of plasma parameters such as: plasma density, temperature, and energy confinement time. The results compared in different movable limiter positions and discussed. (author)