Negative ion yield in long pulse operation of the KAMABOKO III source

Experiments on MANTIS have shown 1000 s operation, however the current density was lower than anticipated, with transmission to the calorimeter as low as 50%. Investigations into the effect of the temperature of the plasma grid on the negative ion yield have been carried out, with increases of ≤40% observed during long pulse operation, substantially below the expected 100%, demonstrated in short pulse operation. A model of the dynamic behaviour of the Cs in the source was proposed and subsequently investigated. Results from these experiments suggest that the Cs injected into the source is rendered unusable due to its “burial” under tungsten evaporated from the filaments.