Taisei Uede

dc voltage holding experiments of vacuum gap for high‐energy ion sources

dc voltage holding characteristics were investigated to obtain a data base for designing high‐energy and high‐power ion sources of neutral beam injectors. We confirmed that the voltage holding characteristics almost obey the clump theory in the experimental gap length of up to 50 mm. The magnetic field in the gap lowered the breakdown voltage in a gas discharge region higher than a pressure of 10−3 Torr. The breakdown voltage of 30% was reduced by seeding cesium on the electrode with one order higher density than that of actual ion source at the pressure region of lower than several mTorr.

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.

MONTE CARLO SIMULATION OF TRANSMISSION PROBABILITY IN CRYOPUMPS FOR NEUTRAL BEAM INJECTORS

Neutral Beam Injector (NBI) with negative ion source is under development as one of the most promising heating devices for achieving the objective plasma parameters in the Large Helical Device (LHD) at NIFS. This paper considers the development of high speed cryopumps for the NBI in the LHD. A new type of louvre blind cryopump having parallel 80 K louvre blinds and 3.7K cryopanels, located parallel to the 80 K louvre blinds, is proposed. At the ratios of B/C = 0.92 and D/B = 1.2, the transmission probability of this advanced type is calculated to be 0.72 which means the cryopump system with this louvre blind type can theoretically attain a high pumping speed.

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.

Geometrical Injection Efficiency of a Neutral Beam Having a Circular Cross Section

A normalized equation that gives the geometrical injection efficiency E in a neutral beam injector (NBI) having a circular cross-sectional beam is shown. The efficiency E is defined as the ratio of the fast neutral beam intensity into the exit port of the NBI to the total beam intensity which arrives near the port. The solution of the equation is represented as a special diagram which is available for the design of a NBI. Analyzed results are as follows: (1) The efficiency E is a function of five parameters: a, beam radius on the extraction electrode; l, target distance; f, beam focal length; w, divergent angle of a beam element; and b, exit port radius. And E can be represented by a normalized equation using two normalized parameters. (2) The efficiency E is a maximum when the focus point of the ion source is in the port.

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.

Pumping Speed of Parallel-Louvre-Blind-Type Cryopump. Transmission Probability of Cryopump with Multiple Parallel-Mounted Panels.

As a new type of louvre blind cryopump, a parallel-louvre-blind cryopump with a rectangular chamber with opening distance B, louvre width C and depth D, is proposed. The influence of louvre size ratio Rc(=B/C) and pump depth size ratio Rd(=D/B) on the transmission probability Pbc is calculated by the Monte Carlo simulation and measured in model experiments. The following results are obtained. (1) The transmission probability of a cryopump designed with a dimensional ratio of Rd=1.28, is calculated as 0.7 at ratios of RC=0.7∼0.9, which means that this type of cryopump can theoretically atttain a high pumping speed of more than 300 m3·s-1/m2 per opening area. (2) The transmission probability of the cryopump strongly depends on Rd and decreases rapidly for Rd less than 1.0 in the case of Rc=0.92.