Hiroshi Horiike

IFMIF/EVEDA lithium test loop: design and fabrication technology of target assembly as a key component

The engineering validation and engineering design activity (EVEDA) for the International Fusion Materials Irradiation Facility (IFMIF) is proceeding as one of the ITER broader approach activities. In the concept of the IFMIF, two 40 MeV deuteron beams are injected into a liquid Li stream (Li target) flowing at a velocity of 15 m s−1. The EVEDA Li test loop (ELTL) is aimed at validating the hydraulic stability of the Li target at a velocity up to 20 m s−1 under a vacuum condition of 10−3 Pa as the most important issue. Construction of the ELTL, which is the largest liquid metal loop possessing 5.0 m3 Li for the fusion research ever, was completed in the O-arai Research & Development Center in the Japan Atomic Energy Agency on 22 November 2010. This paper presents the design and fabrication technology of a target assembly called integrated target assembly, in which the Li target is produced by a contraction nozzle along a concave channel. There are two concepts regarding the target assembly: the integrated target assembly and the bayonet target assembly. Both target assemblies are outlined in this paper, and then the newly proposed design of the integrated target assembly for the ELTL and its fabrication technology are given. The integrated target assembly was processed by a five-axis milling machine and the processing accuracy was measured by 3D measurement tools. Finally, methods applied for the validation of the stability of the Li target are introduced in this paper.

Objectives and design of the JT-60 superconducting tokamak

A fully superconducting tokamak named JT-60SC is designed for the modification programme of JT-60 to enhance economical and environmental attractiveness in tokamak fusion reactors. JT-60SC aims at realizing high-β steady-state operation in the use of low radio-activation ferritic steel in a low ν* and ρ* regime relevant to the reactor plasmas. Objectives, research issues, plasma control schemes and a conceptual design for JT-60SC are presented.

Forced Convection Heat Transfer and Temperature Fluctuations of Lithium under Transverse Magnetic Fields

The MHD effects on a heat transfer of liquid lithium flowing in an annular channel were studied, using a newly constructed comparatively large-scale lithium loop. The data on the heat transfer characteristics were arranged in Nu-St diagrams where St=Ha2/Re. The diagrams indicate that Nu decreases as St increases as a whole trend. However, singular peaks of Nu were observed at about St=13, corresponding to the singular increments of temperature fluctuations, whereas the peaks occurred at St=1.5 in the previous experiment with a smaller channel. In considering a predominant MHD effect due to conductive wall duct, the current load factor KP for external circuit was taken into account. And Miyazaki number Mi=KPSt, which means the effective electromagnetic interaction, was adopted in substitution for St and the heater pin diameter was taken as the characteristic length in place of the conventional hydraulic equivalent diameter. Thus, an appreciably good agreement was obtained concerning the peaks at Mi=0.13 in the previous and at Mi=0.14 in the present experiments. Generation of vortex series in the singular phenomena was suggested from both the periodicity of temperature fluctuations in their PSD analysis and the proportionality between peak frequency and mean flow velocity, resulting in a 32 mm interval length of series.

Measurements of strongly localized potential well profiles in an inertial electrostatic fusion neutron source

Direct measurements of localized electric fields have been made by the laser induced fluorescence (LIF) method using the Stark effect in the central cathode core region of an inertial electrostatic confinement fusion (IECF) neutron (proton) source. These are expected to have various applications, such as luggage security inspection, non-destructive testing, land mine detection and positron emitter production for cancer detection, currently producing continuously about 107 n/s D-D neutrons. Since 1967, when the first fusion reaction was successfully proved to have taken place in a very compact IECF device, potential well formation due to the space charge associated with spherically converging ion beams has been a central key issue remaining to be clarified in beam-beam collision fusion, which is the major mechanism of the IECF neutron source. Many experiments, although indirect, have been done so far to clarify the nature of the potential well, but none of them has produced definitive evidence. The results found by the present LIF method show a double well potential profile with a slight dip for ion beams with relatively larger angular momenta, whereas for ions with smaller angular momenta, a much steeper potential peak develops.

Design study of National Centralized Tokamak facility for the demonstration of steady state high-β plasma operation

Design studies are shown on the National Centralized Tokamak facility, formerly called JT-60SC. The machine design is carried out to investigate the capability for flexibility in aspect ratio and shape controllability for the demonstration of the high-β steady state operation with nation-wide collaboration, in parallel with ITER towards DEMO. Two designs are proposed and assessed with respect to the physics requirements such as confinement, stability, current drive, divertor and energetic particle confinement. The operation range in the aspect ratio and the plasma shape is widely enhanced consistent with sufficient divertor pumping. Evaluations of the plasma performance towards the determination of the machine design are presented.

Heat transfer enhancement in lithium annular flow under transverse magnetic field

Magnetohydrodynamic (MHD) effect on heat transfer in liquid lithium annular flow was investigated with an emphasis on heat transfer enhancement and local turbulence. A test section was made of 10 mm heater pin and 2 in. B pipe of 304SS. The experiment covers ranges of U = 0.1-3 m/s (Re = 4 x 10 3 -1.4 x 10 5 ), B = 0-0.8 T (Ha = 0-3 x 10 3 ). The heat transfer was observed to increase over a region of St from unity to 100, and the peak value was 5-10% higher than that for B = 0 T. This was explained as a result of local turbulence enhancement in the vicinity of the heating wall. A new concept of heat transfer diagram was proposed with considering a current load factor of the test channel.

Overview of the National Centralized Tokamak programme

An overview is given of the National Centralized Tokamak (NCT) programme as a research programme for advanced tokamak research to succeed JT-60U. The mission of NCT is to establish high beta steady-state operation for DEMO and to contribute to ITER. The machine flexibility is pursued in aspect ratio and shape controllability for the demonstration of the high-β steady-state, feedback control of resistive wall modes, wide current and pressure profile control capability and also very long pulse steady-state operation. Existing JT-60 infrastructure such as the heating and current drive system, power supplies and cooling systems will be best utilized for this modification.

Lithium free surface flow experiment for IFMIF

Abstract High-speed lithium flow was demonstrated in free surface condition by using the lithium loop facility at Osaka University. The project aims at the verification of hydrodynamic stability of free surface lithium flow of up to 15 m/s. A horizontally aligned test channel was installed in the existing loop. Preliminary results show that the design of the nozzle and of the test channel is considered to be successful in order to realize a high-speed free surface flow of lithium in vacuum.

Status of the Institute of Free-Electron Laser, Osaka University

Institute of Free-Electron Laser is one of the FEL supplying facilities for 2000 hours in a year. The FEL system consists of two RF-linacs and five wigglers, and covers the wavelength range from 0.28 to 100 µm. In the operational period from April 2001 to March 2002, the mid-infrared light of 5 to 20 µm was supplied for over 40 cooperative research programs on fields of semiconductor, bio-medical and environmental chemistry. An effort is still carrying on to improve the property of the light.

Performance Characteristics of an Inertial Electrostatic Confinement Fusion Device with a Triple-Grid System

Abstract Performance characteristics of an inertial electrostatic confinement fusion triple-grid system are experimentally studied to provide an ample fusion reaction rate under a lower-gas-pressure region to make the operation free from glow discharge restrictions between the discharge voltage, current, and gas pressure. With a filament to provide sufficient electrons, the operating gas pressure is found to reduce down to 1/5 for the same discharge current and voltage. Although the gas pressure region that was achieved still remains the region where the fusion reaction between the ion beam and background gas is dominant, the neutron yield normalized by the gas pressure in the triple-grid system shows higher value than the conventional single-grid system.