ABSTRACT
A new positive ion source for the Korea Superconducting Tokamak Advanced Research neutral beam injection (KSTAR NBI-1) system was designed, fabricated, and assembled in 2011. The characteristics of the arc discharge and beam extraction were investigated using hydrogen and helium gas to find the optimum operating parameters of the arc power, filament voltage, gas pressure, extracting voltage, accelerating voltage, and decelerating voltage at the neutral beam test stand at the Korea Atomic Energy Research Institute in 2012. Based on the optimum operating condition, the new ion source was then conditioned, and performance tests were primarily finished. The accelerator system with enlarged apertures can extract a maximum 65 A ion beam with a beam energy of 100 keV. The arc efficiency and optimum beam perveance, at which the beam divergence is at a minimum, are estimated to be 1.0 A/kW and 2.5 uP, respectively. The beam extraction tests show that the design goal of delivering a 2 MW deuterium neutral beam into the KSTAR Tokamak plasma is achievable.
ABSTRACT
In this study it is found that the cusp magnetic field configuration of an anode bucket influences the primary electron behavior. An electron orbit code (ELEORBIT code) showed that an azimuthal line cusp (cusp lines run azimuthally with respect to the beam extraction direction) provides a longer primary electron confinement time than an axial line cusp configuration. Experimentally higher plasma densities were obtained under the same arc power when the azimuthal cusp chamber was used. The newly designed azimuthal cusp bucket has been investigated in an effort to increase the plasma density in its plasma generator per arc power.
ABSTRACT
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.
