Development of a Cs-free negative hydrogen ion source system using multi-pulsed plasma sources.

The Korea Atomic Energy Research Institute has recently proposed and developed a novel cesium-free negative hydrogen/deuterium ion source system based on two pulsed plasma sources for fusion and particle accelerator applications. The main feature of this ion source system is the use of both magnetic filters and plasma pulsing (also called the temporal filter). The system operates with two alternate pulsing sequences related to the respective plasma sources, thereby switching the plasmas in the after-glow state in an alternating manner. This study investigates the temporal behavior of deuterium negative ions in the system in a qualitative way by conducting a time-resolved measurement of laser photodetachment current commensurate with the negative ion density. In preliminary experiments, the current in the initial after-glow state remains higher than in the active-glow state identical to a steady-state continuous wave plasma, and the ratio reaches a maximum of about three times. This indicates that the pulsing gives highly efficient negative ion volume formation. Furthermore, it is observed that the time duration when the current is maintained at high values can be prolonged (or modulated) with the alternate dual pulsing, which is not possible with conventional single pulsing. These results provide a clue that the multi-pulsed ion source system may offer a continuous supply of negative ions at high densities and consequently become an alternative to cesium seeded ion sources.

Carbon beam extraction with 14.5 GHz electron cyclotron resonance ion source at Korea Atomic Energy Research Institute.

A 14.5 GHz Electron Cyclotron Resonance ion source (ECRIS) has been made to produce C(4+) beam for using a carbon therapy facility and recently tested at KAERI. Highly charged carbon ions have been successfully extracted. When using only CO2 gas, the beam current of C(4+) was almost 14 µA at 15 kV extraction voltage. To get higher current of the C(4+) beam, while optimizing confinement magnetic field configuration (e.g., axial strengths at minimum and extraction side), gas-mixing (CO2/He), and biased disk were introduced. When the gas mixing ratio of the CO2/He gas is 1:8 at an operational pressure of 5 × 10(-7) mbar and the disk was biased to -150 V relative to the ion source body, the highest current of the C(4+) beam was achieved to be 50 µA, more than three times higher than previously observed only with CO2 gas. Some details on the operating conditions of the ECRIS were discussed.

Long pulse beam extraction with a prototype ion source for the KSTAR neutral beam system.

Long pulse operational characteristics of the high current ion source for the KSTAR neutral beam system are described. The beam pulse length of 300 s was successfully operated at a beam power of 1.6 MW with a beam energy of 70 keV. Beam energy, beam current, beam divergence, arc power, and several other operational parameters were measured during a pulse to analyze the long pulse properties. The increase of the cooling water temperature of the accelerator grids and plasma generator components were measured by water flow calorimetric system using thermocouples. The temperature rises of the filament electrodes of the ion source and the G1 grids (plasma grids) of the accelerator turned out to be the critical factors of the long pulse operation in the current system.