A simple method of impurity injection into tokamak plasmas

Hildebrandt, D.; Bakos, J. S.; Petravich, G.; Badalec, H.; Jakubka, K.
April 1989
Review of Scientific Instruments;Apr89, Vol. 60 Issue 4, p547
Academic Journal
Injection of test impurities into the edge plasma of tokamak discharges by erosion probes containing these impurities is described. By applying a short bias pulse to the probe inserted into the sol-plasma, the plasma density and temperature at the probe location can be deduced and the time of injection during the discharge can be controlled. By locating the probe at an appropriate position it is possible to release defined quantities of the material and to influence the fraction which penetrates into the core plasma. The injection of Li into hydrogen discharges of the smallsized tokamaks Castor and MT-1 is demonstrated. The nature of the main erosion process (ion sputtering or arcing) has been found to depend on the radial position of the probe and the probe potential. The lithium amount released by sputtering is determined, while in the case of arcing only an estimate can be given. The temporal evolution and the radial penetration of the Li influx into the plasma have been observed by monitoring the neutral emission line using a grating spectrometer and a CCD camera. In addition, Li transported through the plasma was collected on solid samples. An estimate is given on the fraction of the impurity efflux from the core plasma which is collected on the samples.


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