The large helical device (LHD) is a superconducting toroidal facility having a mission of steady state operation of high temperature plasmas. The major and minor radii of the plasma, and the toroidal magnetic field strength are 3.9m and 0.65m, and 4T, respectively. While LHD is a plasma physics experiment device, it has a feature of a large-scale plant due to steady-state capability.

High power and long pulse heating systems for LHD are under development. The plasma heating systems consist of ECH (Electron Cyclotron Heating), NBI (Neutral Beam Heating) and ICH (Ion Cyclotron Heating). Almost of all systems are controlled by PLC (Programmable Logic Controller), VME (Versa Module Europe) and other computers. These systems are controlled by man-machine language of GUI (Graphical User Interface) system. Research and Development of fail and safe control system for heating system is being developed. Here, two unique methods of Exclusive and Synchronized operations have been tested. This system uses VME controller with monitor program and VME digital output module. The system writes some correct sequence programs on VME processor beforehand and the VME processor makes a data base from the programs. Then the VME processor reads a new sequence program and compares the data base of sequence programs. If the logical sequence is incorrect then the VME processor judges to select Exclusive operation or Syncronized operation. Exclusive mode is explained as follows. Usually VME processor executes a correct sequence command. When the processor reads an incorrect sequence command, VME processor outputs an error information, and the VME processor finds out a few next sequence commands from a date base and writes these sequence commands on a display. The operator can select a command from the menu table and execute step by step manually. On the other hand, Synchronized mode is as follows. When the VME processor reads an incorrect sequence command then the VME processor rearranges correct sequence commands. The above mentioned system is considered to be effective against a human error.

An easy operation system of LMS (LHD Man-machine System) is used for LHD, which is composed of communication programs, data base programs, GUI program and work stations. LMS can be connected to heating system by two-way communication on the LAN. If heating devices have key accounts, we can operate the heating system by GUI of LMS on LAN.