Texas Experimental Tokamak impurity injection system

Summary investigation of impurity transport and measurements of ion temperature are facilitated by injecting controlled quantities of selected impurities into tokamaks as diagnostic probes. The impurity injector now in use on the Texas Experimental Tokamak (TEXT) was designed for reliable, automatic operation. In this system, a thin film of the desired impurity is placed near the edge of the plasma. The light pulse from a Q-switched ruby laser is directed to a preselected point on the target. A small part of the impurity film evaporates and drifts into the plasma. The laser beam may be scanned to many points on the target so that enough impurity pulses can be obtained from a single target to allow a full day's operation. The scanning assembly and associated electronics are designed to operate with minimum intervention and to facilitate rapid repair and modification. The system is fully automatic but also incorporates both remote and local manual control capabilities to permit system calibration and troubleshooting. In the event of component failure, its self-diagnostic capability can indicate the area for repair. The system is demonstrating its effectiveness and reliability in the support of three different experimental programs. Engineering aspects of the system are discussed in this paper