S. Sakata

Recent developments in the JT-60 data processing system

Abstract The JT-60 data processing system was originally a large computer complex system including a lot of micro-computers, several mini-computers, and a mainframe computer. Recently, several improvements have been made to the original system to modernize the system. Many sub-systems composed of aged mini-computers have been replaced with workstations by utilizing recent progress in computer and network technologies. The system can handle ∼300 MB of raw data per discharge, which is three times larger than the amount in the original system. These improvements have been applied to develop element technologies necessary to the remote participation in JT-60 experiments. A remote diagnostics control and monitoring system and a computer system for access to JT-60 data from the Internet are used together with video conferencing systems for a real-time communication. In 1996, the remote participation based on them was successfully demonstrated in collaboration with Japan Atomic Energy Research Institute, Los Alamos National Laboratory, and Princeton Plasma Physics Laboratory.

Feedback control of neutron emission rate in JT-60U

Abstract A real-time control function of neutron emission rate has been developed as a first step towards fusion power control. By controlling the number of neutral beam injection units, the neutron emission rate was successfully kept constant for ∼ 5 s until the feedback control was turned off. The plasma stored energy was also kept constant during the same period owing to the correlation between the stored energy and the neutron emission rate. This function is expected to be effective in extending the steady-state performance and in controlling the reactivity of a fusion reactor at Q ≤ 1.

Status of JT-60 data processing system

Abstract The JT-60 data processing system is a large computer complex and gradually modernized by utilizing progressing computer and network technology. There are two major changes in our system. A main computer of FACOM M-780 has been replaced with compatible GS8300 using state-of-art CMOS technology, which results in lower power and space usage with nearly the same performance. Now it can handle ∼500 MB of data per discharge. A gigabit ethernet switch with FDDI ports has been introduced to cope with the increase of handling data. The switch will connect a tera-byte (TB) data server at the bandwidth of a gigabit per second with the main computer and many data acquisition workstations. Other developments in our system are the realization of three workstation-based plans, the TB data server, the VME-based fast data acquisition system and a CICU. The TB data server is basically a UNIX workstation with ∼100 GB RAID disks and ∼900 GB MO auto-exchangers. The VME-based fast data acquisition system has been developed to enlarge the present TMDS. The CICU, which has a function of interfacing the main computer with the CAMAC system, has been replaced with the workstation-based system after the fine tuning.

Mass data acquisition systems in JT-60 data processing system

In the data processing system for the JT-60 tokamak, a unique mass data acquisition system with fast sampling, a transient mass data storage system (TMDS), has been used since 1988. It is composed of a minicomputer and 61 channels of 4/6 MB memory modules with a sampling rate up to 200 kHz and about 300 MB of data are transferred to a main computer by using a special LAN developed by Fujitsu Ltd. TMDS can handle a large amount of data, but cannot be enlarged in its capability, such as CPU power or the number of channels. To solve the problems of TMDS, a new fast VME data acquisition system (FDS), has been developed. It can acquire 6 MB of data per channel with a sampling rate of 200 kHz or 1 MHz and consists of a workstation with VMEbus memory modules. Up to now there are three FDSs with 24 channels. The minicomputer of TMDS has been replaced with a new system based on the technology of FDS. To cope with mass data transfer to a data server, they are connected with a gigabit ethernet switch.

Real time processor in JT-60 data processing system

Abstract Real time processor, RTP, is a basic subsystem in the JT-60 data processing system and plays an important role in JT-60 feedback control utilizing various diagnostic signals. An original mini-computer system was replaced in 1994 with a workstation. It has 2 CPUs with a real-time parallel UNIX. During the experiment, one CPU communicates with the main computer synchronized with the experimental sequence, and the other executes a real-time process with 1 ms clock. RTP has been upgraded to a compatible RISC workstation with a faster A/D converter in 1997 in response to increased requests of handling the increased signals in more complicated manners. After this upgrade, an elapsed time is reduced to ∼75% and an I/O time is now dominant. To reduce a CAMAC access time, we try to use a reflective memory for the data transfer. Now RTP handles six kinds of signals to control an electron density, a neutron emission, an electron density and a radiation in the divertor region, and a neutral pressure. RTP will handle five more kinds of signals this year and be used for an advanced control with more complicated processing.

Feedback control of radiation region in radiative divertor plasma on JT-60U tokamak

The sustainment of radiative divertor plasma in JT-60U is performed by the feedback control of the gas puffing rate into the divertor region with an actuator of the divertor radiation power. The feedback control system switches the piezoelectric gas valve every 10 ms, so that the proper amount of gas flux is fed for divertor radiation power to follow the reference waveform. The divertor radiation of 6 MW, which is about 40% of the heating power, is sustained for about 3 s by the hydrogen gas puffing with feedback control. The present logic of the feedback system, however, is not sufficient to fully control the divertor radiation which is modified by the change in heatings and plasma parameters. In order to prevent the loss of control, multi actuators for the feedback control, for example, the involvement of the heating power, and the selection of observed bolometer channels may be required.

Recent changes of JT-60 data processing system

The JT-60 data processing system is a large computer complex, gradually being modernized by utilizing progressing computer and network technologies. There were three major changes in our system recently. A VME-based fast data acquisition system (FDS) has been developed to enlarge a transient mass-data storage system (TMDS). It can acquire the data of 6 MB per channel with 1 or 5 μs sampling. Now there are three FDSs with 29 channels. The TMDS, which was composed of a mini-computer and 61 channels of 6 MB memory modules with 5-μs sampling, has been replaced with a new system based on the technology of the VME-based fast data acquisition system. One of the outdated auxiliary crate controllers with micro-processor (ACM), which controls CAMAC modules in the crate on the serial highway, acquires data from them and transfers data to the main computer, has been replaced by a workstation with a VMEbus byte-serial highway driver. The combination of a workstation and a VMEbus byte-serial highway driver has been developed and used to replace many mini-computers in our system. A workstation with a digital linear tape (DLT) library has been introduced as final data storage. The conversion of a few terabytes of raw data tapes for a cartridge tape library (CTL), which is attached to a mainframe computer, Fujitsu GS8300, will be started by using data conversion software prepared to handle mainframe data on the workstation.

Systems for remote participation in JT-60 experiments

Since 1996, the remote participation in JT-60 experiments has been successfully conducted in collaboration with JAERI, Los Alamos National Laboratory and Princeton Plasma Physics Laboratory. The remote analysis system is a computer complex consisting of an analysis server and a data server for access to JT-60 data. Collaborators of the remote participation can analyze JT-60 data by using this system through the Internet. For the remote diagnostic system, an X Window control program has been customized to communicate via the overseas line using a UNIX workstation at the remote site and one in the JT-60 control room. It has a feature of real-time remote control of diagnostic equipment and remote access to CAMAC data. Both systems are used together with the ISDN-based video-conferencing system for real-time communication between the remote laboratory and the JT-60 control room.