Intense negative hydrogen ion source for neutral injection into tokamaks

In this scheme negative ions are extracted from a plasma source, accelerated to the required energy and then neutralized by stripping in a gas, metal vapor or plasma jet. One of the most promising direct extraction sources is the magnetron source, operating in the mixed hydrogen-cesium mode. In the present source cathode current densities are up to 20 A/cm$sup 2$ at arc voltages between 100 V and 150 V. In order to utilize the discharge more efficiently multislit extraction geometry was adopted. Highest currents were obtained by using six slits, with a total extraction area of 1.35 cm$sup 2$. At an extraction voltage of 18 kV negative hydrogen ion currents close to 1 A were obtained, which corresponds to current densities of about 0.7 A/cm$sup 2$ at the extraction aperture. Pulse length was 10-20 ms and the repetition rate 0.1 Hz. The total extracted current was usually 2-3 times the H$sup -$ current. (auth