Negative ion sources based on plasma‐surface interactions (BLAKE ion source) have been developed at KEK for producing negative heavy ions. The first negative heavy ion source (BLAKE‐II) was developed by modifying the ordinary negative hydrogen ion source with converter (BLAKE‐I) placed into the plasma. It generates various species of negative heavy ions with intense beam currents. For example, a more than 10 mA Au− ion beam was obtained from the ion source. Recently, the large scaled negative heavy ion source (BLAKE‐III) has been developed and in the preliminary test experiment, more than 100 mA Cu‐ ion beam has been stably obtained with a 10% duty factor in pulsed operation. The BLAKE‐II ion source was attached to the BNL 15 MV and Tsukuba University TANDEM accelerators and large current negative heavy ion beams were successfully accelerated in pulsed mode operation. Also, it was found that the space charge effect should be carefully considered for such a large current acceleration in a tandem accelerato...