Hajime Hiratsuka

Initial Boronization of JT-60U Tokamak Using Decaborane

A decaborane-based boronization system has been installed in the JT-60U tokamak in order to reduce the influx of impurities during plasma discharges. Boronization has been performed under a glow discharge using a helium-decaborane gas mixture. The properties of the boron films deposited through boronization and the effects of boronization on the tokamak discharges were investigated. It was found that the deposition of a boron layer with high purity was achieved with few impurities other than hydrogen through boronization, and that the present boronization deposited toroidally nonuniform boron film. It was also found that the decaborane-based boronization resulted in good plasma performance similar to that of conventional boronization.

A boronization system in the JT-60U tokamak: Application of a new method using a less hazardous substance

Abstract A new type of boronization system has been installed in the JT-60U tokamak. Decaborane B10H14, a material less hazardous than diborane B2H6 for boronization, has been used to deposit a pure boron film on the first wall. The purpose of the boron film is to reduce the levels of impurity contamination in the JT-60U plasmas. The first results indicate that the film produced from decaborane shows a good performance similar to that of layers produced in the conventional way. The new technique thus offers an easier and more convenient way for boronization of the tokamak first wall.

The JT-60 tokamak machine

The paper gives an historical overview of the design and construction of the JT-60 tokamak machine starting with its conceptual design in 1973 through to its completion in March 1985. Further the different components of the JT-60 tokamak are described (vacuum vessel, field coils, support structures, etc.).

Development of a compact W-shaped pumped divertor in JT-60U

In JT-60U, the modification to a W-shaped pumped divertor will be completed in May 1997, aiming to realize sufficient reduction in heat flux to the targets and good H-mode confinement simultaneously. W-shaped geometry is optimized not only for forming radiative divertor plasmas and reducing the back flow of neutral particles but also for allowing various experimental configurations. Toroidally and poloidally segmented divertor plates, dome and baffles are arranged in a W-shaped poloidal configuration. The pumping speed can be changed during a shot by variable shutter valves in the three pumping ports under the outer baffle. The net throughput is enough for particle control in the steady radiative operations with high power NBI heating. Carbon fiber composite (CFC) tiles are used for the divertor targets and the divertor throat where large heat flux is expected. Gaps between two adjacent segments are carefully sealed to suppress the leak of neutral gas from the exhaust duct below the divertor and baffles. The strength of the whole structure is confirmed by an electromagnetic force analysis and structural analysis carried out for disruptions of 3 MA discharges with a halo current.

DEVELOPMENT OF PELLET INJECTOR FOR JT-60

The pneumatic 4-shot pellet injector has been installed and operated for JT-60 (JAERI Tokamak-60). The performance tests have proved that the device provides high speed hydrogen pellets just as planned. The maximum pellet velocity obtained in the hydrogen pellet tests is greater than 1.6 km/sec at 50 bar propellant gas. The device is now in use for JT-60 contributing to plasma study. In this paper the outline of features and performance of the device is presented.

A four-pellet pneumatic injection system in the JT-60

Abstract A four-pellet pneumatic injection system has been developed for plasma fueling of the JT-60. The JT-60 pellet injector is capable of accelerating separately four cylindrical pellets 3.0 mm in diameter × 3.0 mm long for two pellets and 4.0 mm in diameter × 4.0 mm long for the remaining two. The JT-60 pellet injector was installed on the JT-60 tokamak machine at the end of 1988. Obtained pellet velocity was higher than 2300 m/s by propellant gases of up to 100 bar and the pellet fueling efficiency achieved was around 70% for both dimensions of pellets. This paper describes the design, injection operation and performance test results of the JT-60 pellet injector.

Development of fast opening magnetic valve for JT-60 pellet injector

A pneumatic four-pellet injector (JT-60 pellet injector) has been constructed for JT-60 in May, 1988 . A fast opening magnetically driven propellent gas injection valve has been developed for JT-60 pellet injector . This valve can accelerate four cylindrical pellets, two 3.8 mm diameter by 3.8 mm and two 2.7 mm diameter by 2.7 mm, to greater than 1.6 km/s with propellent gas of up to 50 bar . It is now successfuly in use in JT-60, contributing to plasma studies . In this paper the outline of a newly developed fast opening magnetic valve and the results of performance tests are presented.

Effects of plasma behavior on in-vessel components in JT-60 operation

Damage of in-vessel component tiles such as divertor and first wall tiles have been investigated from the view point of the effects of plasma behavior under the JT-60 operation.

Installation of the W-shaped divertor in JT-60U

In JT-60U, the modification from the open divertor to the W-shaped divertor with pumps was conducted from February to May in 1997. To install a new divertor in the vessel, pre-inspection of the vacuum vessel, test of installation procedure with mock-ups of the divertor components being designed were carried out, and information obtained from these procedures was taken into the installation procedure as well as the design. The actual installation works such as determination of datum lines, adjustment of new divertor components and the preparations concerning with working environment are described. The status of initial operations is also shown.

JT-60 operation results after its modification for higher plasma current with single null open divertor

The hardware performance of the JT-60U (JAERI Tokamak-60 Upgrade) tokamak machine was investigated in several aspects. The experimental operation has advanced to record D-D fusion power as high as 17 kW. The displacement of the toroidal field coil was measured, and the effect of reinforcement was confirmed. The dynamic displacement of the vessel was found to be a vibration with amplitude within 0.3 mm and relatively slow dumping. Regarding the first wall, the divertor suffered from the heat flow with the width of 4 to 5 cm that was close to the design value. The divertor armor was found to rise 500 degrees C at most for the neutral-beam heating of 20 MW for 2 s, and it is still operated with nitrogen gas circulation cooling. The power flow to the divertor is low due to large radiations of the main and divertor plasmas, while the purity of plasma was largely improved by introduction of glow discharge cleaning of 300 V*1 A.<<ETX>>