Y. Kawamata

Response of fusion gain to density in burning plasma simulation on JT-60U

A burning plasma simulation scheme has been developed with consideration for temperature dependence of the DT fusion reaction rate in JT-60U. The heating power for the simulation of alpha particle heating was calculated using real-time measurements of density and ion temperature. The response of a simulated fusion gain to the density was investigated in this scheme where a constant heating power was used for the simulation of external heating, in order to understand burn controllability by the fuel density in a fusion reactor. When temperature dependence of the fusion reaction rate was assumed as a square of ion temperature, density dependence of the simulated fusion gain stronger than the square of density was observed. Transport analysis using a 1.5 dimension transport code indicated that the strong density dependence is induced by changes in a confinement improvement factor and changes in a pressure profile.

JT-60 Control System

The present status of the JT-60U control system is reported including its original design concept, the progress of the system, and various modifications since the JT-60 upgrade. This control system has features of a functionally distributed and hierarchical structure, using CAMAC interfaces initially, which have been replaced by versatile module Europe (VME)-bus interfaces, and a protective interlock system composed of both software and hard-wired interlock logics. Plant monitoring and control are performed by efficient data communication through CAMAC highways and Ethernet with TCP/IP protocols. Sequential control of plasma discharges is executed by a combination of a remodeled VME-bus system and a timing system. A real-time plasma control system and a human interface system have been continuously modified corresponding to the progress of JT-60U experiments.

Shape reconstruction of RF-driven divertor plasma on QUEST

In the present RF-driven plasma with a lot of high-energy electrons, there may be anisotropic plasma pressure, which makes the usual equilibrium analysis difficult, but the Cauchy condition surface method can reconstruct the plasma shape precisely regardless of the anisotropy. In addition, the plasma current effect in the open magnetic surfaces outside of the closed magnetic surfaces is considered in the RF-driven divertor plasma. In the reconstruction process, singular value (SV) decomposition is used and optimal criterion function for generalized cross validation is estimated concerning truncation or reduction of the small-SV components.

Burn control study using burning plasma simulation experiments in JT-60U

Abstract Burning plasma simulation experiments were performed for burn control study on ELMy H-/L-mode plasmas and reversed shear (RS) plasmas with an internal transport barrier in JT-60U. In a burning plasma simulation scheme, two neutral beam (NB) groups were used: one that simulates alpha-particle heating and another that simulates external heating. For the alpha-particle heating simulation, the heating power proportional to the deuterium-deuterium (D-D) neutron yield rate was injected. The behavior of the part of the NB heating simulating alpha-particle heating was varied by increasing the proportional gain relating the applied power to the measured neutron yield rate in both ELMy H-mode and RS plasmas, while the part of the NB power in the role of external heating was held constant i.e., no-burn-control case. Above a certain value of the proportional gain, a runaway effect was triggered where excursive increases in the neutron yield rate and stored energy were observed. With burn control, where the stored energy was controlled at a constant value by a feedback control system using the external heating, the runaway was not triggered, and the neutron yield rate was kept at a constant value in the L-mode plasmas. Zero-dimensional calculation indicated that the runaway triggered by increasing the proportional gain well simulates the runaway triggered by improved confinement. The limitations came from differences between deuterium-tritium and D-D plasmas, such as the dominant reaction for the neutron yield and the temperature dependence of the fusion reaction rate, which were discussed together with improvement on the burning plasma simulation scheme.

Development of PC-Based Control System in JT-60SA

Abstract The JT-60 operations were stopped in 2008 in order to be upgraded to a superconducting tokamak device, JT-60 Super Advanced (JT-60SA). The design activity of JT-60SA is going on under the ITER-BA project, and the discussion on the operational scenarios of JT-60SA has begun. On the basis of these situations, we have been on a developmental work for JT-60SA control system. The JT-60 real time control system is composed of a workstation and a VME-based real time controller using a VxWorks. The VxWorks is one of the most commonly used real-time OSs in the embedded system markets. However, the introduction cost is higher than that of other RTOSs. From a cost-effectiveness and a long-term stable supply viewpoint, we have chosen INtime running on Windows OS-based Personal Computer. INtime is able to add a real-time performance to a PC on which Windows is installed. Therefore, in JT-60 real time control system, some of the subsystems running on VxWorks have been replaced with a PC-based control system. In future development activity, we plan to adopt the PC-based controller with INtime as the standard of JT-60SA control system. In this report, the developmental status of JT-60SA control system will be described.

Architecture Plan of the Real-Time Diagnostic Signals Acquisition System Toward JT-60SA Project

Abstract For a steady state operation of JT-60SA, a plasma feedback control using various diagnostic sensor signals plays an essential role. To realize this, Real-Time Diagnostic Signals acquisition System, RTDS, which utilizes PC-based real-time OS “INtime”, has been under consideration toward JT-60SA project. Real-Time Processor, RTP in JT-60 data processing system, which utilized a WS-based computer with real-time UNIX, was becoming increasingly difficult to maintain, manage, and improve due to the aging of the system and the limited capability of the CPU. To solve these problems and assess the feasibility of introducing clustered architecture, a prototype had been developed with the existing RTP and a VxWorks computer at hand. Its effectiveness as the architecture of the next RTDS was verified on JT-60U experiments, but the actual RTDS will employ PC-based “INtime” system, which consist of a general-purpose personal computer and a real-time operating system “INtime”. Moreover, long-pulse experiments of more than 400s will be planned in JT-60SA project. Therefore, real time monitoring will be required as an essential function that displays acquired diagnostic signals in real-time during long-pulse experiment. This function will also be realized by utilizing the RTDS.

Study on Plasma Shape Reproduction of Spherical

Cauchy-Condition Surface (CCS) method is a numerical approach to reproduce plasma shape which has good precision in conventional tokamak. In order to apply it in the plasma shape repro-duction of Compact PWI experimental Device (CPD) which is a new spherical tokamak in Kyushu University, the calculation results of CCS method on CPD is reported in the paper.