M. Emoto

Data acquisition system for steady-state experiments at multiple sites

A high-performance data acquisition (DAQ) system has been developed for steady-state fusion experiments at the Large Helical Device (LHD). Its significant characteristics are 110u2009MBu2009s−1 continuous DAQ capability and the performance scalability using an unlimited number of DAQ units. Incoming data streams are first transferred temporarily onto the shared random access memory, and then cut into definite time chunks to be stored. They are also thinned out to 1/N to be served for the real-time monitoring clients. In LHD steady-state experiment, the DAQ cluster has established the world record for acquiring 90u2009GB/shot. The established technology of this steady-state acquisition and store can contribute to the ITER experiments whose data amount is estimated in the range 100 or 1000u2009GB/shot. This system also acquires experimental data from multiple remote sites through the fusion-dedicated virtual private network in Japan. The speed lowering problem in long-distance TCP/IP data transfer has been improved by the packet pacing optimization. The demonstrated collaboration scheme will be analogous to that of ITER and the supporting machines.

Data Acquisition and Management System of LHD

Abstract The data acquisition (DAQ) and management system of the Large Helical Device (LHD), named the LABCOM system, has been in development since 1995. The recently acquired data have grown to 7 gigabytes per shot, 10 times bigger than estimated before the experiment. In 2006 during 1-h pulse experiments, 90 gigabytes of data was acquired, a new world record. This data explosion has been enabled by the massively distributed processing architecture and the newly developed capability of real-time streaming acquisition. The former provides linear expandability since increasing the number of parallel DAQs avoids I/O bottlenecks. The latter improves the unit performance from 0.7 megabytes/s in conventional CAMAC digitizers to nonstop 110 megabytes/s in CompactPCI. The technical goal of this system is to be able to handle one hundred 100 megabytes/s concurrent DAQs even for steady-state plasma diagnostics. This is similar to the data production rate of the next-generation experiments, such as ITER. The LABCOM storage has several hundred terabytes of storage in double-tier structure: The first consists of tens of hard drive arrays, and the second some Blu-ray Disc libraries. Multiplex and redundant storage servers are mandatory for higher availability and throughputs. They together serve sharable volumes on Red Hat GFS2 cluster file systems. The LABCOM system is used not only for LHD but also for the QUEST and GAMMA10 experiments, creating a new Fusion Virtual Laboratory remote participation environment that others can access regardless of their location.

Object-oriented data handling and OODB operation of LHD mass data acquisition system

Abstract The new data acquisition system of large helical device (LHD) diagnostics, i.e. LABCOM system, has successfully started its operation in March 1998. It has a simple but massive parallel-processing (MPP) structure by means of multiple PC/Windows NT environment, and the most significant methodology adopted for it is the object-oriented (OO) data handling through the whole system. The functions and data substances of the acquisition system are described in autonomous objects with the corresponding C++ class definitions. The object-oriented database management system (ODBMS) will be the only solution to provide a vast and virtual storage space for storing an enormous number of archiving data objects. Commercial ODBMS product ‘O2’ are installed on each diagnostic acquisition computer. Practical O2 investigations showed 300–400 kB/s as the data storing rate, whereas the data transfer rate from CAMAC digitizers to the computer is up to 700 kB/s in this system. Applying the GNU projects ‘zlib’ compression library for the data size reduction compensates this rate gap. Through the first and second (∼#7132) LHD experimental campaigns, the LABCOM system acquired about 400 GB raw data, with maximum 120 MB per shot. These experiences proved that OO technology has great promise for the next generation of the data acquisition and storage system in fusion research experiments.

Double Peltier Current Lead for Heat Leak Reduction at the Terminals for Superconducting Direct Current Applications

For superconducting direct current applications, heat leak reduction at the terminal is a key issue for high performance systems and especially for small ones such as the distribution in internet data centers. We propose a double Peltier current lead (PCL), where the suitable combination of two Peltier modules can enhance the performance of PCL. Using the model parameters of actual thermoelectric materials, we estimated the heat leak on PCL using a thermal balance equation. At the double PCL, the large temperature difference on the current lead can be split to two thermoelectric materials and then the performance of PCL can be enhanced. As each of the thermoelectric materials has better working temperature range, an optimized combination of shape factors can be used for the high performance current lead at the terminals for superconducting application systems.

Development of a flexible visualization tool

Abstract User-friendly visualization tools are indispensable for quick recognition of experimental data. One such tool, the dwscope component of the MDS-Plus system, is widely used to visualize the data that MDS-Plus acquires. However, the National Institute for Fusion Science does not use MDS-Plus, so our researchers on the Large Helical Device (LHD) project cannot use dwscope without modification. Therefore, we developed a new visualization tool, NIFScope. The user interface of NIFScope is based on JavaScope, which is a Java version of dwscope, but NIFScope has its own unique characteristics, including the following: (1) the GUI toolkit is GTK+; (2) Ruby is the equation evaluator; and (3) data loaders are provided as Ruby modules. With these features, NIFScope becomes a multi-purpose and flexible visualization tool. For example, because GTK+ is a multi-platform open source GUI toolkit, NIFScope can run on both MS-Windows and UNIX, and it can be delivered freely. The second characteristic enables users to plot various equations besides experimental data. Furthermore, Ruby is an object-oriented script language and is widely used on the Internet, allowing it to serve not only as an equation evaluator but also as an ordinal programming language. This means users can easily add new data loaders for their own data formats.

Control and plasma data acquisition system for LHD experiment

The large helical device (LHD) is a superconducting magnet system, created for the performance of plasma-fusion experiments, with an operation time of over a half-year for one cycle and long discharge being one of its main missions. We have developed a new monitoring system for data acquisition dedicated to the special characteristics of the LHD. Here, we describe the systems design and configuration, its current performance regarding real-time monitoring and future plans for the systems improvement.

Development of a Peltier Current Lead for the 200-m-Class Superconducting Direct Current Transmission and Distribution System

Reducing cryogenic heat leaks is critical for superconducting applications. Reduction of heat leak at the terminals is essential for uses with short-length applications, where cryogenic losses at the terminals dominate. We are developing a 200-m-class superconducting direct current (DC) transmission and distribution system (CASER-2), and have used a Peltier current lead (PCL) for heat insulation at the terminals. The PCL consists of thermoelectric elements and copper leads, which enhance the performance of superconducting systems. As DC flows through the current lead, thermoelectric elements on opposite terminations of a superconducting line can be used to decrease the heat ingress to the cryogenic environment (n-type on one end, p-type on the opposite end). During the current feeding and cooling test, a large temperature difference was observed across thermoelectric elements in the PCL. This demonstrates that we have successfully insulated the heat leak at the current lead. During the fourth cooling test, we established a new PCL design with p-type elements at terminalxa0B, and then compared the performance of the terminals. Several improvements were implemented, including balancing the resistances of the PCL to enhance the stability of the superconducting systems.

Refrigeration Process to Realize a Multistage and Gas-Cooled Current Lead

Heat leak from the current lead is the major source of power loss for superconducting (SC) magnets, motors and generators, and short distance SC power transmission lines. Therefore, reducing the heat leak from the current lead can improve the economy of the SC system and allow the use of SC systems commercially. The Peltier current lead was proposed and developed at Chubu University to reduce the electrical power consumption of the refrigerator. The heat leakage of the Peltier current lead saves almost 40%, but the power requirement of the refrigerator is still high. In order to realize greater power savings, the multistage current lead (MCL) and the gas-cooled MCL are proposed. The heat leakage reduction of the gas-cooled MCL depends on the characteristics of the cryogen and its pressure and the realization of high cost of performance and a high-temperature refrigerator. Here, we show the calculation results of the high-pressure effect of cryogen and discuss the performance of nitrogen trifluoride as cryogen.

Cryogenic Fluid Dynamics for DC Superconducting Power Transmission Line

Distributions of the velocity, the temperature and the pressure of a liquid nitrogen (LN2) flow are analyzed at hydraulic cross-sections on two types of superconducting power transmission lines (SC PT). One is on a DC-SC PT, the other is on a three phase AC-SC PT. Inflow heat from the pipe wall and the cables to LN2 are evaluated, however the heat flux from the DC cable is zero. The channels are straight, and hydraulic cross-sections are 3.77 times 10-3 m2 and 4.27 times 10-3 m2 on the DC and AC-SC PT lines, respectively. The increased temperature and the pressure drops on the DC-SC PT lines are lower than those of the AC-SC PT. The fluid velocity dependence on the distance between two cooling stations and on the pump power are estimated. When cooling stations are installed every 10 km, the flow velocity of the DC and AC system are 0.10 and 0.25 m/s, respectively. The pump power of the DC system is dramatically lower compared with the AC system. Therefore, minimizing the SC PT by using DC systems is much more practical.

LHD diagnostics toward steady-state operation

The large helical device (LHD) is the world largest helical system having all superconducting coils. After completion of LHD in 1998, six experimental campaigns have been carried out successfully. The maximum stored energy, central electron temperature, and volume averaged beta value are 1.16 MJ, 10 keV, and 3.2%, respectively. The confinement time of the LHD plasma appears to be equivalent to that of tokamaks. One of the most important missions for LHD is to prove steady-state operation, which is also significant to international thermonuclear experimental reactor (ITER) and to future fusion reactors. LHD is quite appropriate for this purpose based upon the beneficial feature of a helical system, that is, no necessity of the plasma current. So far, the plasma discharge duration was achieved up to 150 s. The plasma density was kept constant by feedback control of gas puffing with real time information of the line density. The issue for demonstrating steady-state operation is whether divertor function to control particle and heat flux is effective enough. Relevant to this, LHD diagnostics should be consistent with the following: 1) continuous operation of main diagnostics during long-pulse operation for feedback control and physics understanding; 2) measurement of fraction of H, He, and impurities in the plasma; 3) heat removal and measure against possible damage or surface erosion of diagnostic components inside of the vacuum chamber; 4) data acquisition system for handling real time data display and a huge amount of data. Although there are already some achievements on the above subjects, there remain still several issues to be resolved. On the other hand, the long-pulse operation of the plasma gives benefits to the diagnostics. For example, the polarizing angle of ECE emission can be changed during the discharge, and the intensity dependence on the polarizing angle has been obtained. The spatial scanning of the neutral particle analyzer and the spectrometer can supply the spatial profiles of the fast neutral particle flux and the specific impurity lines. In this paper, the present status of these issues and future plans are described.