Modification to the accelerator of the NBI-1B ion source for improving the injection efficiency.

Minimizing power loss of a neutral beam imposes modification of the accelerator of the ion source for further improvement of the beam optics. The beam optics can be improved by focusing beamlets. The injection efficiencies by the steering of ion beamlets are investigated numerically to find the optimum modification of the accelerator design of the NBI-1B ion source. The beam power loss was reduced by aperture displacement of three edge beamlets arrays considering power loadings on the beamline components. Successful testing and operation of the ion source at 60 keV/84% of injection efficiency led to the possibility of enhancing the system capability to a 2.4 MW power level at 100 keV/1.9 µP.

Development progresses of radio frequency ion source for neutral beam injector in fusion devices.

A large-area RF (radio frequency)-driven ion source is being developed in Germany for the heating and current drive of an ITER device. Negative hydrogen ion sources are the major components of neutral beam injection systems in future large-scale fusion experiments such as ITER and DEMO. RF ion sources for the production of positive hydrogen (deuterium) ions have been successfully developed for the neutral beam heating systems at IPP (Max-Planck-Institute for Plasma Physics) in Germany. The first long-pulse ion source has been developed successfully with a magnetic bucket plasma generator including a filament heating structure for the first NBI system of the KSTAR tokamak. There is a development plan for an RF ion source at KAERI to extract the positive ions, which can be applied for the KSTAR NBI system and to extract the negative ions for future fusion devices such as the Fusion Neutron Source and Korea-DEMO. The characteristics of RF-driven plasmas and the uniformity of the plasma parameters in the test-RF ion source were investigated initially using an electrostatic probe.

Improvement of a plasma uniformity of the 2nd ion source of KSTAR neutral beam injector.

The 2nd ion source of KSTAR (Korea Superconducting Tokamak Advanced Research) NBI (Neutral Beam Injector) had been developed and operated since last year. A calorimetric analysis revealed that the heat load of the back plate of the ion source is relatively higher than that of the 1st ion source of KSTAR NBI. The spatial plasma uniformity of the ion source is not good. Therefore, we intended to identify factors affecting the uniformity of a plasma density and improve it. We estimated the effects of a direction of filament current and a magnetic field configuration of the plasma generator on the plasma uniformity. We also verified that the operation conditions of an ion source could change a uniformity of the plasma density of an ion source.

First neutral beam injection experiments on KSTAR tokamak.

The first neutral beam (NB) injection system of the Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak was partially completed in 2010 with only 1∕3 of its full design capability, and NB heating experiments were carried out during the 2010 KSTAR operation campaign. The ion source is composed of a JAEA bucket plasma generator and a KAERI large multi-aperture accelerator assembly, which is designed to deliver a 1.5 MW, NB power of deuterium at 95 keV. Before the beam injection experiments, discharge, and beam extraction characteristics of the ion source were investigated. The ion source has good beam optics in a broad range of beam perveance. The optimum perveance is 1.1-1.3 µP, and the minimum beam divergence angle measured by the Doppler shift spectroscopy is 0.8°. The ion species ratio is D(+):D(2)(+):D(3)(+) = 75:20:5 at beam current density of 85 mA/cm(2). The arc efficiency is more than 1.0 A∕kW. In the 2010 KSTAR campaign, a deuterium NB power of 0.7-1.5 MW was successfully injected into the KSTAR plasma with a beam energy of 70-90 keV. L-H transitions were observed within a wide range of beam powers relative to a threshold value. The edge pedestal formation in the T(i) and T(e) profiles was verified through CES and electron cyclotron emission diagnostics. In every deuterium NB injection, a burst of D-D neutrons was recorded, and increases in the ion temperature and plasma stored energy were found.

Development of a plasma generator for a long pulse ion source for neutral beam injectors.

A plasma generator for a long pulse H(+)/D(+) ion source has been developed. The plasma generator was designed to produce 65 A H(+)/D(+) beams at an energy of 120 keV from an ion extraction area of 12 cm in width and 45 cm in length. Configuration of the plasma generator is a multi-cusp bucket type with SmCo permanent magnets. Dimension of a plasma chamber is 25 cm in width, 59 cm in length, and 32.5 cm in depth. The plasma generator was designed and fabricated at Japan Atomic Energy Agency. Source plasma generation and beam extraction tests for hydrogen coupling with an accelerator of the KSTAR ion source have been performed at the KSTAR neutral beam test stand under the agreement of Japan-Korea collaborative experiment. Spatial uniformity of the source plasma at the extraction region was measured using Langmuir probes and ±7% of the deviation from an averaged ion saturation current density was obtained. A long pulse test of the plasma generation up to 200 s with an arc discharge power of 70 kW has been successfully demonstrated. The arc discharge power satisfies the requirement of the beam production for the KSTAR NBI. A 70 keV, 41 A, 5 s hydrogen ion beam has been extracted with a high arc efficiency of 0.9 -1.1 A/kW at a beam extraction experiment. A deuteron yield of 77% was measured even at a low beam current density of 73 mA/cm(2).

Arc plasma simulation of the KAERI large ion source.

The KAERI large ion source, developed for the KSTAR NBI system, recently produced ion beams of 100 keV, 50 A levels in the first half campaign of 2007. These results seem to be the best performance of the present ion source at a maximum available input power of 145 kW. A slight improvement in the ion source is certainly necessary to attain the final goal of an 8 MW ion beam. Firstly, the experimental results were analyzed to differentiate the cause and effect for the insufficient beam currents. Secondly, a zero dimensional simulation was carried out on the ion source plasma to identify which factors control the arc plasma and to find out what improvements can be expected.

An ion optics study for KSTAR neutral beam injector development.

Ion optics of three accelerator geometries was studied in terms of an analytic linear optics analysis, a numerical simulation using the IGUN program, an optical multichannel measurement of Doppler-shifted H(alpha) lines, and a water-flow calorimetry on the beam absorbing target. In general, there was a reasonable agreement observed between the four analysis methods and thus the theoretical analyses can be utilized with confidence for design iteration.