Hiroyuki Kawakami

Development of an intense negative hydrogen ion source with an external magnetic filter

An intense negative hydrogen ion source has been developed, which has a strong external magnetic filter field in the wide area of 35 cm×62 cm produced by a pair of permanent magnet rows located at 35.4 cm separation. The filter strength is 70 G in the center and the line‐integrated filter strength is 850 G cm, which keeps the low electron temperature in the extraction region. Strong cusp magnetic field, 1.8 kG on the chamber surface, is generated for improvement of the plasma confinement. These resulted in the high arc efficiency at the low operational gas pressure. 16.2 A of H− ion current with the energy of 47 keV was obtained at the arc efficiency of 0.1 A/kW at the gas pressure of 3.8 mTorr in the cesium‐mode operation. The magnetic field in the extraction gap is also strong, 450 G, for the electron suppression. The ratio of the extraction current to the negative ion current was less than 2.2 at the gas pressure of 3 mTorr. The two‐stage acceleration was tested, and 13.6 A of H− ion beam was accelerat...

Production of high-current large-area H/sup -/ beams by a bucket-type ion source equipped with a magnetic filter

A negative-ion-based neutral beam injection (NBI) system is planned for plasma heating of the Large Helical Device (LHD). We have developed a negative ion source, which is 1/3 the scale of the source for the NBI. A magnetic filter held was generated by external permanent magnets to lower the electron temperature in a large-area bucket plasma source (35 cm/spl times/62 cm) for efficient H/sup -/ production. We investigated the magnetic field configuration and found a low electron temperature high density plasma ( 15 A: 1/3 current of LHD ion source). Based on the results, we are designing a negative ion source for the LHD.

Three-dimensional analysis of ion beam deflection by the magnetic field at H− ion sources for the negative-ion-based neutral beam injection

In negative-ion-based neutral beam injection (NBI) systems for the large helical device (LHD), beams must be transported over 13 m from the H− ion source to the injection port. In order to clarify beam deflection by the electron deflection magnets set in a beam extraction grid (EG) and to control beam transport direction, we analyzed beam trajectories. The physics of the beam deflection was studied with theoretical calculations and the deflection angle was estimated by 3D beam trajectory simulation. The evaluated deflection angle was 10 mrad in the opposite direction of the electron deflection when the maximum magnetic field on the beam axis was 480 G and the beam energy was 83.2 keV. The electrostatic lens effect on the beam deflection at the EG exit was estimated to be larger than the magnetic field effect. This deflection was reduced to 2 mrad by a 1.3 mm displacement of the grounded grid (GG) aperture, a result in agreement with experimental results of a 1/3-scale model for the LHD ion source. The max...

Development of a high-efficient negative ion source for NBI system in Large Helical Device

Present status of the hydrogen negative ion source development is reported for an NBI system in the Large Helical Device. An external-filter type negative ion source has produced a 16.2 A of H - ion beam with the energy of 47 keV at the arc efficiency of 0.1 A/kW and at the operational gas pressure of 3.8 mTorr. The H - ion beam of 13.6 A was successfully accelerated to 125 keV with two-stage acceleration. A rod-filter type negative ion source has also produced a 16 A of H - ion beam with the current density of 45 mA/cm 2 . A vacuum-immersed negative ion source has demonstrated stable operation on condition that the ion source is shielded from the beam-induced plasma. For the future long-lifetime operation, an RF-driven negative ion source has been developed, where an induction coil antenna is placed inside a metal-walled magnetic multicusp source.

DEVELOPMENT OF A PARALLEL-LOUVRE-BLIND TYPE CRYOPUMP FOR FUSION REACTORS

As a new type of actual sized cryopump with high pumping speed, a parallellouvre-blind type cryopump of a rectangular cross section with opening distance B, width C and depth D, is proposed and is produced as a trial pump unit designed to actual size. The influence of pump depth size ratio Rd(=D/B) and number of secondary cryopanels on the transmission probability Pbc of the pump unit is calculated by Monte Carlo simulation and the hydrogen pumping speed is measured by experiments. The following results are obtained: (1) The transmission probability of a cryopump designed with dimensional ratio of Rd=1.3, is calculated to be 0.66 at ratios of Rc(=B/C)=0.88, which means that hydrogen pumping speed of this sized cryopumps can attain 294m3s−1/m2per opening area. (2)The experimental hydrogen pumping speed of the trial pump unit with 29 secondary cryopanels, is measured to be 295m3s−1/m2.

Pumping Speed of Parallel-Louvre-Blind-Type Cryopumps. Hydrogen Pumping Speed of Cryopump with Multiple Parallel Mounted Panels.

As a new type of actual-sized cryopump with high pumping speed, a parallel-louvre-blind type cryopump of a rectangular cross section with opening distance B, width C and depth D, is proposed and is produced as a trial pump unit designed as actual size. The influence of pump depth size ratio Rd(=D/B) and number of secondary cryopanels on the transmission Probability Pbc of the pump unit is calculated by Monte Carlo simulation, and the hydrogen pumping speed is measured by experiments. The following results are obtained. (1) The transmission probability of a cryopump designed with dimensional ratio of Rd=1.3 is calculated to be 0.66 at ratios of Rc(=β/C)=0.88, which means that hydrogen pumping speed of cryopumps of this size can attain 294 m3·s-1/m2 per opening area. (2) The real hydrogen pumping speed of the trial pump unit with 30 secondary cryopanels is measured as 295m3·s-1/m2.